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Acoustic testplan and results from stone and timber circles

Please check the terminology section for some defined words. The authors of this web site have visited stone and timber circles some 15 days to make many acoustic observations.

Content

The circles under investigation

Three timber circles are investigated:

  1. Goseck, Germany
  2. Pömmelte-Zackmünde, Germany
  3. Heldenberg, Austria
Two stone circles:
  1. Dromagorteen stone circle, Kerry, Ireland
  2. Grange Circle B, Lough Gur, Ireland
One timber circle has not been investigated by ourselves, but is of interest:
  1. Mansfeld, Germany
A few reference measurements were performed:
  1. a Home garden
  2. a few open fields (semi-anechoic space) in Goseck, Berlin and Skerries

The dimensions of circles

Goseck, Germany

Reconstructed Goseck (from around 4800 BCE) has two tightly spaced (~4cm space between them) (timber) palisade rings with diameter of ~52m (1st palisade) and ~60m (2nd palisade). The posts have a diameter of 20cm and a height of 2.5 to 3m. The posts are quite straight and have no bark.

Weather conditions at Goseck are here.

Goseck map
Goseck timber circle [Bertemes, 2010]

Pömmelte-Zackmünde, Germany

Reconstructed Pömmelte-Zackmünde (from around 2300 BCE) has one tightly spaced (~4cm space between them) (timber) palisade rings, one medium spaced (~20cm space between palisade) and two widely spaced (~2m) (timber) palisade rings. The diameter of the tightly spaced palisade are resp. ~75m (1st palisade) and ~115m, while the two widely spaced palisade are ~45 m and ~55 m in diameter. The posts have a diameter of 20cm and a height of 2.5 to 3m. The posts are a little bit crooked and have no bark.

Weather conditions at Pömmelte-Zackmünde are here.

Pommelte-Zackmunde
Pömmelte-Zackmünde timber circle [Spatzier, 2012]

Grange Circle B, Ireland

The Grange Circle B at Lough Gur (from around 2900 BCE [Prendergast, 2016])  has an internal diameter of around 45.5m and its standing  stones are on average slightly higher than 1.5m (some are though higher). There is an earthen bank (~ 9m wide and ~1m high on the inside and ~2m on the outside) along the standing stones (on outside).

Weather conditions at Grange Circle B are here.

Grange stone circle plan
Grange Circle B [Ó Ríordáin, 1951  (adjusted to True North) and Google Earth]

Dromagorteen stone circle, Ireland

Dromagorteen stone circle (Early/Middle Bronze Age: 2000 to 1150 BCE), situated in the Bonane Heritage park, is of the type of Axial Stone Circle (ASC) with 13 stones. The circle has a diameter of around 10 m. This one might be too small to be compared with others.

Weather conditions at Dromagorteen are here.

Fig. 1 Dromagorteen stone circle
Dromagorteen stone circle [after Bonane Heritage park, 2010]

Mansfeld, Germany

Mansfeld at the former Am Archäopark, which is a reconstruction of Schalkenburg, Quenstedt (from around 4800 BCE),  has a 1st palisade with an short axis of 35m and a long axis of around 44m. Its 5th palisade is around 90m by 120m. The reconstruction though has deteriorated so much in the last years (at least from 2005 on) that it is not presentative anymore. The posts had a diameter of ~27cm and a height of 2 to 3m. The posts were quite crooked and many had (peeling) bark. Mansfeld is build on a sloping terrain: the north east of Mansfeld is some 2m lower than the south west corner of the 1st palisade (around 2.5deg). Quenstedt was build at the top of a hill [Kaufmann, 2011, page 109]. Quenstedt might have had tightly-spaced double palisade palisades (like Heldenberg) [Kaufmann, 2011, page 107].

Weather conditions at Mansfeld are here.

Mansfeld - Schalkenburg
Mansfeld reconstruction from Quenstedt [Google Earth, 2009; Wikipedia]

Heldenberg, Austria

Heldenberg, which is a reconstruction of Schletz timber circle, Austria (from around 4850 to 2550 BCE, so similar to some of the Central Germany circles; like Goseck),  has two tightly-spaced palisade circles one with an axis of ~24m and the other one somewhat larger (~24.3m); and one widely (~1.5m) spaced palisade (~30m diameter). The tightly-spaced double palisades have gaps between posts of ~10cm. Seen from the centre, there are no gaps; posts of 2nd palisade are shifted somewhat relative to the 1st palisade. The posts have a diameter of ~25cm and a height of 2.8 to 3.2m. The posts are straight. Bark is still on them (no peeling bark, at least in 2013). Heldenberg is on a terrain slope of around 4.5 deg (Google Earth showed 5 deg).
Scheltz looks also to be on a slight ridge and thus on a sloping terrain (around 6 deg).

Re-reconstructed Heldenberg

The circles was re-reconstructed (in 2016), after the posts had rotted after the initial construction (13 years ago). The height of the posts on the inside of the palisades were on average ~1.9m while the posts on the outer side of the palisade were on average ~2.3m. This is some 0.9m lower than the initial reconstruction. The posts are still barked, but were loosing their bark. There were at some places considerable gaps between the posts.

Heldenberg, reconstructed
                timber circle
Heldenberg reconstruction from Schletz [Google Earth, 2016]

Archaeoastronomy

Goseck

Likely winter solstice and summer solstice Sun rise/set, Beltane and Lughnasadh Sun rise/set.

Pömmelte-Zackmünde

Likely Imbolc and Samhain Sun rise.

Grange Circle B

Likely Beltane and Lughnasadh Sun rise.

Dromagorteen

Likely summer solstice Sun rise and major lunar standstill limit event rise.

Quenstedt

Likely summer solstice Sun rise/set and winter solstice Sun rise.

Schletz

A study on the archaoeastronomy of Austrian timber circles has been done as part of the ASTROSIM project [ASTROSIM]. The results are meager for the 32 Austrian KGAs investigate. No significant astronomical evident has been found for the positioning of entrances, it looks that entrances of the Austrian KGAs are positioned by looking at the lay of the land [Zotti, 2011].

Measurement methodologies

Room based acoustic measurements (see for instance [Ahnert]) might not be very effective in these large open space. Perhaps music-hall methodologies are more important. Perceptions of effects are just as important as measurements. There look to be three different measures:

The following type of measurements/observations could be done (bold measurements have been assessed at the circles):

Considerations for locations of the measurements:

Sound sources

The following sound sources were considered (bold means that they were used during the experiments):

Equipment list

The following equipment was used during the investigations:

Questionnaire

A questionnaire has been made for Goseck on SurveyMonkey. If you want to provide input, please do.

Dromagorteen stone circle (Nov. 2015)

Participant

Victor Reijs

Weather data

Date
Location
Wind Speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
14/11/2015
Dromagorteen ~10
WSW
high 2
~16
1009
~341
~82
15/11/2015
Dromagorteen ~10
SW
high 2
~13
1005
~339
~88

Equipment

The microphone (Zoom H1 recorder) was on top of the recumbent stone (Stone1) some 0.8 m high and the sources (balloon, paper banger) were at around 1.2 m high.

Measurements

In below figure is an example of the popping of a small balloon between the two portal stones (Stone 6 and Stone7). You can see power peaks around:

Fig. 2 Impulse responce from small
          balloon
Impulse response from small balloon

The above ETC graphs are made by the Aurora module for Audacity 2.0.0.

Binaural recording

One binaural recording (with paper banger impulse from near Stone 1) was made.
Sloping hill on the north-west sid eof
        the stone circle
Sloping hill on the north-west side of the stone circle

The below graph gives the power levels at Stone1. At ~0.7sec, around a distance of 145m from source, there is this rise in the terrain (in summer solstice sunrise direction).
Impulse response at Stone 1, by
          paper banger
Impulse response at Stone 1, by paper banger

Perceptions

Lessons learnt

Observations in Home garden

Participant

Victor Reijs

Binaural recording

A binaural microphone recording has been done by walking through the Home garden while recording a video and tracking the location. A composite video is available here (it is important to have a stereo headset to appreciate the binaural effects).

Draw away measurements (loudness)

The question is: Would a 50W amplifier provide enough power for sound level measurements in open space aka timber circles?
An amplifier (Panasonic SG-HM-10L) was put at the top of a Home garden (where the house is). The walled garden is rectangular (~8m wide and ~15m deep) and its walls are covered with trees/bushes. There is though a glass conservatory for the first 4m. Brown noise was played and the audio power was around 10W.
The sound level in dBSPL was measured while drawing away from the sound source, see below picture.

Sound level between 0 and 13m
Sound level of brown noise

The dip around 5m could be due to the shadow-reflections from the conservatory.
There is some 4 dB between the power at 20m and 31m (to be compared to Grange Circle B) and there is some 2dB between the power at 25m and 30m (to be compared to Goseck).

Lessons learnt

As the sound level of 'silence' was around 50dBSPL, one would need at least some 20 dB above that for kind of accurate results. If the inverse square law holds, that would only give a maximum distance of  ~30m at 10W. If we increase the amplifier output to 50W (aka 6 dB more than 10W), the sound would reach a distance of some 60m. This is comparable to the diameter of the timber circles. So 50W amplifier looks to be just good enough.

Pre-test in early April, 2016

Participants

Reinhard Mussik, Finn Hockauf and Elke Hockauf

Test plan for Goseck and Pömmelte-Zackmünde

Measurements done, to get a feel of the timber circles, are around:

The quality of the recording was not essential, but noting experiences/perceptions where possible effects can happen, helped us to direct our attention for our May visit.

Weather data

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
9/4/2016
Goseck ~12
NE
low 3
~12
1010
~338
~55
10/4/2016
Pömmelte-Zackmünde ~18
SE
high 3
~12
1014
~338
~60

Goseck

Equipment

Impulse sound source: balloons ~45 cm (when blown up)
Music sound source: 3W loudspeaker
The microphone (Samsung Galaxy S5, not in flight-mode) and the sound sources were at around 1.2 m high.
No wind muffler was used.

Measurements and results

Several measurements were done. One was with the impulse sound (balloon) at the centre (X) and the Observer (O) 1 m from the inner palisade (the inset of below picture gives idea where the X and O are). In the below picture also the impulse response (IR) at location O has be shown (the wiggly sound graph). Furthermore you can see several dots (blue, orange, red) near the time line, these are determined by using a computer model for predicting the IR. As can been seen the computer model maps well the actual peaks (as there is periodicy: flutter echoes) in the response (although multiple peaks from 5*A-O are not all predicted by the computer model).
An animation can also be seen here.

Simulation and actual peaks in impulse
        response of Goseck

Other measurements done can be predicted somewhat by the dimensions of the two palisades and the locations of X and O. It looks that Precedence, ASW and LEV effects can occur.
There is a timbre difference when O is being inside, between and outside the palisades.
Draw-off measurements did not work as the power of the music sound source (3W CD player) was not enough. This was known, as we did not have 240 VAC available for the pre-test.
No focal points were experienced by listening with the ears.
Due to overload of the microphone we could not measure the power difference just within the 1st palisades and just outside the 2nd palisade.
When X and O are around 1m from the inner palisade, a chirp echo has been observed.

Perceptions

Lessons learnt

Pömmelte-Zackmünde

Equipment

Impulse sound source: balloons ~45 cm (from top to month piece)
Music sound source: 3W loudspeaker
The microphone (Samsung Galaxy S5, in flight-mode) and the sound sources were at around 1.2 m high.
No wind muffler was used.

Measurements and results

Draw-off measurements did not work, as sound levels were not easy to measure from recordings.
Focal points were experienced by listening with the ears (and after that recognisable on recordings).
When X and O are around 1m from the inner palisade, no explicit chirp echo has been observed. There might be some though...

Perceptions

Lessons learnt

Pre-test at the Grange Circle B, Lough Gur (April, 2016)

Participant

Victor Reijs

Weather data

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
25/4/2016
Grange ~18
W
high 3
~7
1022
~335
~90
26/4/2016
Grange ~13
NW
low 3
~5
1018
~334
~70
27/4/2016
Grange ~12
NW
low 3
~1
1019
~332
~87

Equipment

Measurements

Results

Stone circle's bank as noise barrier

The sound level on top of the bank is around 2dB lower than on the edge of the circle (~20m), while several meters further (but 'behind' the bank at field level, ~31m) it is some 19dB lower than at edge of circle. Compare this with the 4dB decrease in open air. Open air sound is some 3 times (15dB) louder then just behind the bank of Grange Circle B. The bank is an effective barrier, see also this section.

Perceptions

The following perceptions where made:

We found that the dominant reflection is from the Rannach Crom Dubh. Subjectively, the most exciting thing we heard was when we had one person chanting from the center of the circle towards Rannach Crom Dubh. When standing on the bank, behind the chanting person, an interesting ‘overdub’ effect could be heard. We speculated that this could be used as a ‘voice of the gods’ effect.
This could be related to the on average some 2 dB difference between direct sound and reflection against Rannach Crom Dubh. Although measurements need to be taken at the bank to determine if the reflection is there still more powerful than the direct sound (form the source in the centre).

Lessons learnt

Test in May, 2016

Participants

Victor Reijs, Reinhard Mussik, Finn Hockauf and Elke Hockauf

Weather data

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
5/5/2016
Pömmelte-Zackmünde ~13
NE
low 3
~14
1027
~339
~51
6/5/2016
Goseck ~5
E
high 1
~12 to ~18
1021
~338 to ~342
~65
7/5/2016
Goseck ~9
SE
mid 2
~16
1017
~341
~50
8/5/2016
Pömmelte-Zackmünde ~20
E
low 4
~15.5
1019
~340
~70

Goseck

Draw-away measurements

In this picture the draw-away measurements at Goseck are shown (they start with the letter G and using Pink, Horn or Whisper sounds):

Shadow effects

Several of shadow effects were experienced (mostly in timbre changes) at Goseck:

The reason could be that the Summer area is wider than the Beltane area and thus the Summer area has less attenuation for lower frequencies. The higher frequencies might be attenuated more by the few posts within the Summer area than the open area of Beltane.

If we compare the spectral power of Summer area with the Palisade area's, we get the below picture. One can see that the Summer area has for most frequencies a higher spectral power (orangy) than the Palisade area's (purply).
Spectral power difference summer and Palisade areas

Whispering gallery effects

Although whispering galley effects were anecdotally mentioned [person at Goseck visitor centre, pers. comm 2016], such effects have not been experienced or recorded when using Babble, Whisper or Horn sounds. Whispering on one side of the 1st palisade was not heard on its opposite side. The whispering gallery effect would be most pronounced beside the circumsphere and almost non audibility in the centre of the circle); but sound level measurements did not show such a difference.

Chirp echoes

Chirp echoes were heard near the 1st and 2nd palisades by popping balloons and hand clapping. One though has to exert considerable energy to generate it (compared to Chichen Itza where one has hard, crisper and regular stair surface).

IRs from centre

The IRs made show comparable aspects as during the April visit: some bouncing due to the 1st and 2nd palisade and bouncing of the far side of the palisade(s): flutterechoes. Also such behavior is seen outside the circle: 10m in front of the entrance; near the ditch; and on the bank.

IRs between palisades

Several IRs between the 1st and 2nd palisades were generated: in the April pre-test and repeated in the May test sessions. The following results have been seen in the measurements when popping the balloon in radial direction (towards 2nd palisade):

Below is a graphical view of the number of occurrences of peaks for different sector lengths between source and microphone (several measurements per sector lengths were done).

Peaks-distances for different arc
        lengths

SketchUp was used to determine where the reflections might occur. Circles (red) were used (diameter; half of above mentioned distances), and ellipses (yellow) which shows any location that would provide reflections at the right time seen from the sector length (black line).

Determining echo location form circles
        or ellipses.


If the balloon is pop in a tangent direction (measured in May), the reflections from the middle or far 1st palisade are significantly reduced or non existent.
Chirp echoes were perceived at several microphone locations.

Word clarity

No word clarity test has been performed, as one could understand each other in all areas within the 1st palisade (and the background noise < 50dBSPL is much lower than the speech).

Perceptions

Press coverage

The Mitteldeutsche Zeitung, 'Das große Rauschen' (9/5/2016) published an article (with pictures) around the above acoustic research. Others were also published: Mitteldeutsche Zeitung, 'Erbauer von Goseck nutzten Klangeffekte' (11/5/2016); Magdeburger Volkstimme, 'Forscher finden steinzeitliches Tonstudio' (11/5/2016); ; Leipziger Volkszeitung, 'Goseck-Erbauer nutzten Klangeffekte (11/5/2016); Dresdner Neueste Nachrichte, 'Goseck-Erbauer nutzten Klangeffekte' (11/5/2016); Bild Halle, 'Schall-Geheimnis in Goseck entdeckt' (12/5/2016); and Altmark Zeitung, 'Goseck-Erbauer nutzten Klangeffecte' (12/5/2016).
These news paper articles reached a readers' pool of around 1.25 million.

Further articles on the Internet: Die Welt, 'Erbauer von Goseck nutzten Klangeffekte für Rituale' (10/5/2016); Die Welt, 'So ausgefeilt war die Klangtechnik der Steinzeit' (10/5/2016); and FOCUS Online, 'Erbauer von Goseck nutzten Klangeffekte für Rituale' (10/5/2016).

Pömmelte-Zackmünde

Draw-away measurements

In this picture the draw-away measurements at Pömmelte-Zackmünde are shown (they start with the letter P and using Pink sound). No specific observation from these measurements. We first had equipment problems and then there was considerable wind (low force 4), so further measurements were not possible.

Comb effect

Brown noise draw-away measurements were done from the centre of Pömmelte-Zackmünd upto 7 steps away (1 step is approximately 1m). In the below spectrogram one can see; that when walking from 7 seven steps towards the centre (0 step) and then again 7 steps away, equally spaced bands of frequencies are attenuated and the bands move up in frequency when going further away from the centre. This is related to the comb effect: the interaction between the direct sound and the reflection against the ground plane.
Draw away spectrogram using brown noise in centre
        Pommelte

Similar draw-away was done when using Shamanic drum (now up to 10 steps from centre). The sound changed considerable in timbre when closer than 7 steps from the centre; more high pitches were heard which can be seen to emerge in the spectrogram.
Shamanic Drim from centre of Pommelte

Chirp echoes and whispering gallery effects

Chirp echoes were very faint and no whispering gallery effects were experienced. Possibly due to more rough positioning of the posts.

IRs from centre

In general we see reflections due to a ballon pop: from the near palisade; one that has gone to the far side of the palisade (~0.22 sec = ~74m); and one that went between the near and far sides of the palisade (~0.42 sec = ~149m).
Depending on the distance from the near palisade, the reflections from the near palisade arrive faster after the direct sound; reflections from the far palisade keep the same timing from the direct sound (flutter echoes).
 
Most of the energy of the reflections are in the range between 150 and 400Hz, the later the less higher frequencies with every wave (which ends with another reflection against the far palisade reaching the observer). See below spectrogram.
Spectrogram at 10m from centre balloon burst, Pommelte
A balloon pop has enough powerful frequencies between 150 and 2,000Hz, so the circle's acoustic properties have changed the original spectrum of the balloon pop during each wave.
See also section Reflections in circle for an evaluation of the results.

Word clarity

No word clarity test has been performed, as one could understand each other in all areas within the 1st palisade (and the background noise < 50 dBSPL is lower than the speech).

Observations at Heldenberg (Sept. 2013)

There have been done acoustical measurements Heldenberg on Sept. 2nd, 2013 [Pomberger & Mühlhans, 2015].

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
2/9/2013
Heldenberg ~37
WSW high 5
~20
~1022
~343
~52

In the below paragraphs some of their findings are summaries, so that they can be compared to our own measurements.

Source source

Balloon pop (~25cm diameter) positioned in the centre. And pricked at the tip of the balloon (directed to the sky).
Source height at ~1.3m and receiver height at ~1.7m

Chirp echoes

One could detect a chirp echo when the observer is near the palisade and the balloon pop at the centre. It is expected that the chirp echo will be more pronounced with the balloon pop is near the palisade.

IRs from centre

The setup used:

Setup used by
        Muhlhaus

In the centre the IR shows a flutter echo with a periodicy of ~70ms, which is equivalent to the diameter of the circle. The reasoning in the article is that the centre is a kind of focal point (Brennpunkt), but perhaps better to call it a focus point. The flutter echo is also pronounced in the centre as there is a perpendicular (white path) direction of the terrain slope and thus lowest loss for a flutter echo.
If the observation point is further from the centre, the perceived flutter echo is reduced according [Pomberger & Mühlhans, 2015, page 25]:

Auf halbem Radius des Kreises treffen die Echos jeweils zeitversetzt im Abstand von etwa 35ms ein, wodurch der Impuls in der Hörwahrnehming zu einem Schallereignis verschmilzt [precedence], das Flatter echo ist dort nur messtechnisch erfassbar.

The measurement was perpendicular to the terrain slope (white path), and it looks the terrain slope has not introduced additional losses.

Heldenberg balloon in centre, mic
          at 6m
Heldenberg IRs, balloon in centre and mic at 6m [IR from Mühlhans, 2015]

They also did measurements of  tangent (purple path) to the terrain slope, when the mic was 6 and 12m from centre (near the palisade/entrance). In the 12m case, there is no palisade but an entrance, so no near palisade reflections/diffractions. Looking at the energy there does not seem to be a significant different between the two directions for both 6 and 12m. The 12m ones sound slightly differently, perhaps due to timbre or low preference effects the near palisade.

6m from centre, Perpendicurlar and
        tangent
Heldenberg IRs, balloon in centre and mic at 6m: tangent and perpendicular to terrain slope [IRs from Mühlhans, 2015]


In direction and tangent of slope at
        Heldenberg
Heldenberg IRs, balloon in centre and mic at 12m: perpendicular and tangent to terrain slope [IRs from Mühlhans, 2015]

The T20 for the perpendicular (white) and the tangent (purple) path are respectively: 0.43sec and 0.42sec.

Tightly-spaced double palisades as noise barrier

The noise level difference between inside and outside the tightly-spaced double palisades is around 12 dB. This is considerable higher than at Goseck (a few dBs), which has no tightly-spaced double palisades. But lower than behind the bank of Grange Circle B (19 dB). See also this section.

Lesson learnt

The following ideas and lessons learnt are perceived:

Performance test at the Grange Circle B (April 2017)

Participants

Victor Reijs, Noirin Ni Riain, Moley Ó Súilleabháin.

Weather data

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
25/4/2017
Grange ~19
W
high 3
~8
1024
~336
~40
26/4/2017
Grange ~3
N
1
~3
1025
~333
~93

Equipment

Experience performance of different sound sources

Observations at re-reconstructed Heldenberg (June 2017)

Participants

Victor Reijs, Reinhard Mussik, Finn Hockauf and Elke Hockauf

Dates

There have been done acoustical measurements at the re-reconstructed Heldenberg on June 2nd to June 4th, 2017.

Date
Location
Wind speed [km/h]
Wind direction
Beaufort
Temp [oC]
Air pressure
[mbar]
Sound speed
[m/sec]

Humidity [%]
2/6/2017
Heldenberg ~6
E low 2
~21
~986
~343
~60
3/6/2017 Heldenberg ~5
W
1
~26
~983 ~347
~52
4/6/2017 Heldenberg ~16
S
3
~25
~976
~346
~65

In the below paragraphs some of the findings are summarised.

Sources

Balloon pops
Exponential Sine Sweep (ESS: 50 - 4000 Hz in 10 sec) using 2*8W RMS loudspeaker (height ~1m above ground)
Zoom H1 plus wind muffler on microphone boom (height ~1.25m above ground)

Influence on response due to terrain slope of Heldenberg

The microphone was place on a boom in the centre of Heldenberg (see below picture).

Position
        of the speaker. Microphone in middle

The loudspeaker was moved in intervals of ~2.2m from the centre over three paths (see the open dots in above picture). The three paths being:

A Sine Sweep (50 to 4000 Hz) was produced at each interval (at 0, ~2.2m, ~4.4m and ~6.6m from centre) and the resulting Impulse Response (IR) was derived using Audacity with Aurora Plug-in. Two times four IRs for each path can be seen at the top of below each three rows in the below graph.

The
        impulse responses derteived from ESS

The three rows of graphs relate to:
Each IR is presented as a frequency spectrum graph over the first 300msec: yellow, highest power; red, intermediate power; blue, low power; and light grey, no power. A flutter echo of ~70msec can be seen in the IR graphs.

Comparing the different paths (with different terrain slopes), there is no real difference in the IRs, except that the W(hite)R(ight) IRs seem to persist a little longer. The red path's UP and DW might be slightly lower in power.
But overall the IRs look to have the same behavior in distance from centre of the circle and in time.
This is not really expected as the height of the palisade (1.9m) is just a little lower than the threshold height (~1.95m) for Heldenberg's terrain slope. That the reflections are still pronounced can be due to two things: a) the second row of posts (~2.3m) has influence or b) the effective acoustical height is larger than the actual height.

Producing clave sounds at different heights

The claves have been used at the UP and DoWn locations (on the red path) and then at different heights from the ground level: ~1m, ~1.6m, ~1.75m and ~2m. The microphone is at a height of around 2m
At the UP location, a flutter echo is seen for most heights, although when the claves are at 2,m height the flutter echo is barely noticeable. Have not been able to explain this on a theoretical level, as the microphone is for any clave height level at a lower, so even the reflection from the opposite palisade (which is some 1m lower again) is not really possible, let alone a flutter echo! So scattering of sound must be happening within the circle.

For the claves at the DoWn location, beside the direct sound only the echo of the far (UP) palisade is registered at the microphone. After that no flutter echo. This is also following the theoretical path of the sound due to reflections.

This behavior is not fully understood yet.

Comparing Heldenberg of 2013 and 2017

A balloon burst has been used to compare the T20 properties (remember that T20 is not really defined in a non diffusing environment) in 2013 (distance 6m by Mühlhans) and 2017 (distance ~4.4m  by Reijs):

Comparing Reijs and Muhlhans

There is some difference seen between the two authors in the tangent and perpendicular paths.
For the tangent paths (see above picture): T20 of Mühlhans' purple path is around 0.42sec and of Reijs' red path is 0.46sec. A similar difference is present for the perpendicular paths: Mühlhans' white path is around 0.43sec and Reijs' yellow path is around 0.47sec. 
The JDN for the T20 is around 4%, so the difference between the decay times measured by Mühlhans and Reijs is perceptible.
The reason could be that Mühlhans' tangent measurements are from entrance to entrance, while Reijs measured (slightly more anti-clock wise) between the lowest and highest points which have palisade behind them. Another reason for the difference seen in  both paths could be that Mühlhans measured 6m from the centre, while Reijs measured ~4.4m from the centre.

The perpendicular path results are though also somewhat unexpected as the 2017 palisade is less well spaced (4%) than the 2013 palisade (<1%), see for instance on the right side of below picture where the gaps are much larger:

The gap sin
        the palisade are visible

Lessons implemented

The following ideas and lessons have been implemented:

Evaluation

Flutter echoes in a circle

If we have a circle and the impulse sound is in the centre, the resulting peaks in the sound level change with the distance of the observer from the centre:

In the below stylised and animated graph we see these peaks changing while the observer distance is increased in a single palisade ring. For comparison: A impulse sound at 27m from 1st palisade with the observer at distance of 10m from impulse response: the measured impulse response at 10m at Goseck has been overlayed. This are clear examples of flutter echoes.
One sees more flutter echo peaks in the Goseck impulse response due to the 2nd palisade reflections (8m or 23msec later).

Animation of sound levels in a circle
Goseck IR, balloon in centre and mic at a several distance (diameter 52m)

The direct sound (per definition at 0msec) and the reflections (2nd and 4th) returning from the furthest palisade side are fixed in time (independent of the distance of the observer from the centre) [red lines]. The reflections (1st and 3rd) due to the nearest palisade side change in time (dependent of the distance of the observer from the centre) [purple lines].
The height of the lines depends on the total length of the sound path (and the number of reflections against furthest or nearest palisade).

When the reflections come into the 10 to 40msec range, timbre changes can happen. Below10msec preference can be lowered (see section on Discrete reflections).

This also maps well on theoretical flutter echoes in Heldenberg (mic at 6m):

Flutter echoes at Heldenberg
Heldenberg IR, balloon in centre and mic at 6m (diameter 24m) [IR from Mühlhans, 2015]

So it looks that Goseck and Heldenberg (in tangent direction of terrain slope) behave similarly (even the loss due to a reflection against a palisade, is in both cases ~8dB).

A flutter echo can give an impression of a larger room then one expects, see this perception when flutter echo happens in a room. This is perhaps also the reason why in open air moment one gets the impression of a larger enclosed space when a flutter echoes happens.

Transparency of the palisades

The palisades of the circles have different area of gaps between the timber posts. Below are pictures of front view (and almost the full height of posts is included) of the 1st palisades.

Site
[picture taker]
Palisade picture
Straightness
&bark
Terrain
slope
(deg)
Gap area [%]
Goseck
[Reijs, 2016]
Gaps in Goseck's
              palisade
straight &
no bark
~0
16
Pömmelte-Zackmünde
[Reijs, 2016]
Gaps in Pommelte's
              palisade
straight-ish &
no bark
~0
15
Mansfeld
[Meinike, 2005]
Gaps in Manfeld's
              palisade
crooked &
  many
(peeling)
bark
~2.5
11
Quenstedt
(original of Mansfeld)
NA
NA
~0
NA
Heldenberg 2013
[J. Mühlhans, 2015]
fully black
straight &
mainly bark
~4.5
~1
(as seen
from centre)
Heldenberg 2017
[Reijs, 2017]
Der Heldenberg
              gaps
straight &
mainly bark
~4.5
4
Schletz
(original of Heldenberg)
NA
NA
~6
NA

The reflection energy of these palisades does not differ that much (max difference 0.4 dB for middle [(353 - 1414Hz] and low [88 - 353Hz] frequencies [Ahnert, page 37], which would not really be audible, as it is below the JND of 1dB). Diffraction might be different due to large variation of straightness of the posts.
Transparency of the palisades also will have an influence on the transmission of sound behind the palisade, the more dense the less energy.

Perceptions and stories

Inside of Pömmelte-Zackmünde [Reijs, 2016]
A video with sound made at the former site might help also, if available please inform us.

Influence of a terrain slope

In case we look at horizontal wave fronts when there is a terrain slope, sound energy can be lost depending on: the diameter of the timber circle; height of the palisade; the terrain slope; height of the source, and height of receiver. The threshold terrain slope not to loose energy is depending on the height of the source, as can be seen in the below picture (timber circle diameter 52m, palisade height 2.5m, source in centre, receiver at same absolute height as the source).
mAximum slope of terrian depedning
            on palisade heigth

If the timber circle is smaller (like Heldenberg: 24m) the threshold terrain slope not to lose energy is around 7deg. Heldenberg (2013 situation) is on a terrain slope of around 4.5deg, so that is why there is low loss perceived.

Furthermore, when having a sound source perpendicular to the terrain slope, the losses will also low; as the palisade sides are at the same  height (like there is no terrain slope;-). So the IR perpendicular to a terrain slope would be very similar to the IR of a site on flat terrain.

It is interesting to see that Austrian timber circle entrance pairs have a tendency to be more or less tangent or more or less perpendicular to the terrain slope [Zotti, 2011; ASTROSIM]. This is indeed quite evident for the Austrian KGAs, see below:

Entrance pairs aligned tangent or
        perpendicular to slope

Would this have a relation with the acoustic aspects of tangent and perpendicular to the terrain slope? And would the same yield for German circles (which are from a different region/culture)? No real answer available(yet), but there might be a thesis in 2017/2018 that could provide the basic data for this evaluation (Michel, possibly 2017).
An initial comparison (based on tentative data gotten from Michel on position of the German circles) between the cumulative distributions of the terrain slope seen (dashed line) in Austrian and German circle can be see below (the continuous line would happen if both cumulative distributions would be the same):

Comparing the dsitirbution of terrain slope sin German
            and Austria
There might indeed be a difference in terrain slope distribution (although it still needs to be investigated if the general distribution of terrain slope for the larger region in Austrian and German are different). It looks that more German circles than Austrian circle are build on flat terrain. The spread of the terrain slope is for both regions similar (maximum 7.5 deg).

Looking at the 32 timber circles in Austria (KGA: Keisgrabenanlage) [pers. comm. Georg Zotti, 2015; ASTROSIM], it has been determined how many circles would have large losses for sounds tangent to the terrain slope (assuming palisade height 2.5m and source height 1.25m). 19 would have large losses, while13 timber circle would have low losses; this looks to be a random behavior (χ2-test; p=0.05). And also the relation between entrances direction, terrain slope and timber circle diameter looks to be random.

Austrian timber circles and then max.
        slope

Noise barriers

Noise barriers cause the receiver to experience a shadow effect, and sound reaches the receiver through diffraction.
There are two types of noise barriers that can be present at timber circles:


Timber palisades will only be effective sound barriers if the gap area is below the 2% (if more then 10% one can't perceive the difference) [BC Ministry of Transportation and Highways, 1997, page 2]. The investigated timber circles (except Heldenberg) all have a gap area of more than 11%. The tightly spaced palisades (like the tightly-spaced double palisades of Heldenberg) and banks (like at Grange Circle B) are more effective noise barriers.

The attenuation due to the barrier (compared to the situation with no barrier) is depending on the path length difference with and without barrier. If the source or observer is closer to the barrier, the larger the path length difference is. Other background information (and worksheets) can be found in [US Department of Housing & Urban Development, 2009, page 9-13, 23-25].
The attenuation looks something like below graph [BC Ministry of Transportation and Highways, 1997, page 2]:

Noise barrier attentuation depending
        of path length difference
For illustration purposes only

Here is a handy 2D interactive tool and a 1D from tool: source at 0m, barrier at 12m and receiver at 15m (more or less Heldenberg). One can derive at Heldenberg that the sound level before the barrier and after the barrier has a difference of around 15 dB (measured is 12 dB). For Grange Circle B, with its 9m wide bank (and stone circle at 1.5m) the tool gives around 10 dB, while measured is was around 19 dB.

The above information is for a noise barrier wall (a tightly spaced palisade), a bank's attenuation would be a few dB lower [BC Ministry of Transportation and Highways, 1997, page S-1, S-2].

Draw away measurements (loudness)

Equipment

An SPL meter was used at A-Weighting and Slow response.
The SPL meter was held at around 1m height and against the body of the measurer. The microphone directed to the speaker. The speakers were at around 75cm high. Everywhere the ground was covered with (mowed) grass, although at Pömmelte there was some wild plant growth (upto some 30cm).

Measurements

Naming convention of the measurements:

Draw-away sound power in Goseck, Pommelte, Garden and Open
        Field

The differences between the draw-away curves are not that large. The following evaluations can be made:

Lessens leanrt

Reverberation time

In most cases, with the sound source in the centre and the mic at 10m from the centre: the reverberation time (T30; derived through the Open AIR web page [Murphy]) and ¿Volume? (defined by the height of the palisade/stones, by assuming the circle is closed with a [absorbent] plane) of the circles were derived:

An overview of the optimum reverberation time (T60) depending on the Volume can be seen in the below graph:
Optimum RT60 depending on volume
The optimum reverberation time [Chan; fesi, 2007, page 57; Everest, page 154; line graphs: Reijs, 2016]

The line graphs are based on [Stephens, 1950]:
K = T60/( 0.0118*Volume1/3 + 0.1070)
with:    Volume in m3
            T60 = optimum 60dB reverberation time [sec] at 500 Hz
            K = (optimum) suitability: 4 for speech, 5 for orchestra, 6 for chorus

It is important to realise that the T30's (estimator of RT60) relation with ¿Volume? might not be really applicable for this type of open air monuments, which does not really have a real Volume (see also [Pomberger & Mühlhans, 2015, page 25]):
If the above optimum reverberation time-¿Volume? relation is though relevant in some way; studio (speech); cinemas; television studios; openplan offices; and pop and rock concerts are 'applicable' for the measured T30.

But there were forests in the past and these can have reverberation times between 1sec and 2sec [Shelly, 2013; Grzinich, 2015], so larger then perceived in timber circles (T30 of up to 0.7sec). Is the timber circle a symbolic version of the forest, to replicate the natural reflections and/or supernatural voices?
Also interesting that Spengler says that 'The character of the Faustian cathedrals is that of a forest' and that the 'Cathedral and organ form a symbolic unity like temple and statue'. Of course organs meld very with a cathedral due to the long reverberation times: 'the organ, which roars deep and high through our churches in tones that, [...] seem to know neither limit nor restraint' [Spengler, page 199-200; Schafer, 1977, page 23].

But caution is warranted in interpreting the optimum reverberation time!
Clarity might be a much better measure for open air monuments.

Early Decay Time

It is interesting to note that not T30, but the EDT (Early Decay Time of the first 10 dB) is better related to the perceived reverberance [Bradley, 2011, page 714]. The EDT for the timbre/stone circles is broadly around 0.15sec, while the T30 is broadly around 0.6sec. An EDT shorter than the T30 would indicate an improved speech and music clarity [Brown, 2010]. The EDT of Grange Circle B is higher (0.5sec) due to the large reflection from Rannach Crom Dubh, here the C50 is indeed low (-3dB). Clarity can of course also be measured with C50 and C80.

Thus the reverberations times (T30~0.6sec) are close to a present day living rooms [Evert, 2001, Figure 7-17], while the EDT (~0.15sec)  is close to a semi-anechoic space. Are timber circle perceive as larger enclosed space, because there is a disconnect between the perceived visible size of the open space circle [Bregman, 1994, page 307,312] and the perceived reverberation (the EDT or T30) of a dead room? Could this be similar to the Moon illusion effect [Ross, 2002]?
Are the multiple flutter echoes generating envelopment and thus causing this large spacial impression?  

C50 and C80

In most cases, with the sound source in the centre and the mic at 10m from the centre: the C50 [weighted over 500, 1000, 2000 and 4000 Hz] and C80 [averaged over 500, 1000 and 2000 Hz] are derived through the Open AIR web page. Here they are for the circles:

Below gives an overview of the calculated values for C50 and C80 [Marshall, 1996, page 375; Smaart, 2015, page 24-25]:

Ranges for C50 and C80

That the measurement of 10m from centre towards Grange Rannach Crom Dubh stone has a rating of Poor for C50 (speech clarity), is obvious due to the fact that the 1st reflection has more sound power than the direct sound. All other measurements show that indeed speech is well treated by the monuments, as was also perceived by visitors at Goseck and Pömmelte-Zackmünde.
It seems all measurements show a high C80 (music clarity), aka good for electronic instruments. Perhaps percussion instruments, with their well defined beats, also fit into that category.

Discrete reflections

The reflections can perhaps be evaluated using below graph that looks at a single reflection that has a certain delay after the first (in)direct sound (the provided lines are based on Figure 6.6, 6.14 and 6.15 of Toole, which relates to an anechoic space). The measurements at Goseck and Pömmelte-Zackmünde are of course not in an anechoic space, but in an semi-anechoic space, but it is expected that the behavior is not that far off. Furthermore the comparison is using castanet sounds, as Toole does not have other sound sources closer to Balloons (he investigated: clicks without any reverberation, Mozart music and speech).

Delay of a single reflection

If there is a question mark before a label in the legend of the above picture, the line has been derived by the web-author through analogy of other acoustic. If the first reflection is above the dotted line, that reflection would be perceived as a second image by the listener (e.g. the red squares). If the first reflection is between the dashed and dotted line, then the location of the direct sound will be spread (ASW; e.g. yellow squares with red X). Between continuous line and dashed line Precedence (Haas effect) occurs for the direct sound location (e.g. yellow squares with blue *). And if the first reflection is below the continuous line, the reflection is not detected. Low Preference happens when the first reflections is earlier than ~0.01sec, while for first reflections between ~0.01 and ~0.04sec timbre changes (comb effect) can occur.

If more than one reflection happens after the direct sound, it looks that the latest reflection determines if one experiences a second image.
For instance in Shamanic drum recordings, the experiences anywhere in the circle is of a second image, because the reflection against the far side of 1st palisade at Pömmelte-Zackmünde is always ~0.22 sec after the direct sound (blue diamonds). If one removes the reflection due to this far side 1st palisade reflection, the remaining reflection (e.g. some of the red diamonds in above picture) determines more or less if there is a second (third?) image or not.
For music (red dotted line) any reflection would not really provide a second image. For speech (green dotted line), these remaining reflections would  perhaps provide some second imagine might when one is near the sound source, but in that case the second image sound level might be quite small compared to direct sound.
This can be seen also in the below picture, where one can see from 0.08sec the extrapolated echo (dotted) lines for different sound types (somewhat following the theory of section 'Large spaces' of Everest, 2001, page 359). The diamond symbols are the reflection sound levels as measured from Shamanic drum sounds in Pömmelte-Zackmünde, while the delay is related to the receiver distance from the 1st palisade.

Reverberation and long delay

So percussion instruments (diamond symbols well above black dotted line) have an advantage in Goseck and  Pömmelte-Zackmünde. This can be linked perhaps to the following quote of HaYa RomanowSky on Goseck:

Wonderfull place in the world, my best place for drumming and shamanic circle for freedom and peace with hayayoga.

Simulating a timber circle on sloping terrain

To determine the effect of sloping terrain, a model of a timber circle has been build in SketchUp Make (radius ~52m, sound source 1m meter from centre and observer 10m from sound source). Here is a picture of such a timber circle on slopping terrain:

Slooping terrain (1.7 deg, 47m in
        diameter)

An Excel spreadsheet has been made to automate the parametrised generation of a model of a timber circle looking at: circle diameter, terrain slope, palisade height, gap between posts, individual straight or randomly 'crooked' palisade posts. This can be used to make a 3D model or an acoustic simulation of the site. Several models have been made:

Type of circle
Terrain
slope
[deg]
Gap
area
[%]

Acoustic Absorption
Coefficient compared
to hardwood

Roughness
(peak-amplitude)
[m]
Closed circle
0
0
0
0.05
Closed circle 4
0
0
0.05
Straight posts
0
16
-16%
0.01
Straight posts 4
16
-16% 0.01
Randomly 'crooked' posts
0
16
-16% 0.007
Randomly 'crooked' posts 1.5
16
-16%
0.007
Randomly 'crooked' posts 4
16
-16% 0.007

Auralisations of the closed circle models in the licensed CATT-Acoustic v9.1 shows that the expected behavior with regard to the reflections/flutter echoes can recreated: in case of a terrain slope of 4deg much fewer flutter echoes are present in the simulation.
Hopefully in the future a grant will be available, so more thorough analysis can be done using acoustic simulation software.
<the demo version of CATT-A does not provide enough rays/cones to achieve good results>

Auralisation

Some auralisations have been made of a drum sound (recorded in anechoic room; available on Open AIR library [Murphy]), which has been convolved (using Aurora Plug-in for Audacity 2.0.0) with the IRs derived from our measurements:
<below auralisations are somewhat harsh [used too short IRs and sometimes there was even overload of mic]; new auralisations will be included soon>

Some of above auralisations (and IRs for different locations inside a site) are available at Open AIR library.

Summary

Some aspects to be reconsidered in the future for future acoustic measurements at timber/stone circles:

Lessons learned

Speculative workflow how aural aspects emerge in buildings

Blesser provides a workflow how architecture could have been developed in which acoustic/aural aspects played a role:
  1. Social needs determines size of audience
  2. Building technology limits size & geometry
  3. Size, materials, & shape determine acoustics
  4. Once constructed, listeners adapt to space
  5. Experience enhances subjective quality
  6. Future spaces replicate earlier spaces
  7. Incremental evolution by trial and error [Blesser, 2011, slide 23]
How to determine if there is intend in former construction, can only be done by using triangulation; through investigating multiple sources, options or plausible explanations. This maps very well on the methodology which Schaefer [2004] proposed; a slightly amended version is here.

Opportunities for the future

How could the circles be used in the past and how could they be used for present day musical performances? Both parts of this question could help with regard to understanding the aural interests of modern and past people.

According to Trochimcyk (2001, 42), the circle has a semiotic and symbolic association in music. Several compositions have been made in the last century around a circular setup of the musicians and audience. The circle provides a focus (its centre) and a hierarchical ordering (inside and outside the palisade/bank).  Trochimcyk (2001, 45) thinks that composer Karlheinz Stockhausen related his composition Carré to megalithic circles and/or medicine wheels. Another music piece is based on the circlar setup of Stonehenge: Trombonehenge by Charles Hoag. While Iannis Xenakis created the composition Terretektorh, where the audience and musicians inter mingle within a circular setup (Trochimczyk 2001, 47-8). One should also look at the tradition performances at the heart of the African village, where audience and musicians are dynamic dispersed and moving around this central area.

So could a Neolithic circle be used to make (modern) performances, by utilising the circle‘s specific acoustic properties?
Percussion and speech  (or music with a similar rhythm) look to be mostly effected by the observed reflections and (flutter) echoes. HaYa RomanowSky (2015) finds Goseck the best place for drumming. And Noirín Ní Riain had an excursion with her student to the Grange Circle B to determine where traditional folk songs and ancient hymns could be performed best (Cassidy/Dormer/u. a. 2016, 120). She further comments that the construction of such ancient sites and genius loci (spirit of lace) was directly influenced by acoustic considerations; the prime purpose of these communal sites was to allow people to communicate through sound. And certainly, the energies in the Grange Circle B alter radically in response to sounds, particularly vocal sounds (Riain 2011). Another investigation was by Beate Pomberger who performed with her colleagues different Neolithic instruments at Heldenberg (Let/Luksan 2014; Pomberger/Mühlhans 2015).

So there are opportunities to determine how to use the specific acoustic properties and to include them in present day aural experiences. This by utilising: (flutter) echoes, clarity, timbre, spatial impression and other acoustical measures. Furthermore different/varying locations of the instruments, performers and audience need to be explored; to determine how an Apollonian or Dionysian type of performance (Schafer, 1977, 5-6) could yield interesting results in present times. And this might give insight in the aural/cultural background of the past.

So lets take Grange Circle B and listen to several auralised sounds:
Anechoic
 originals

Grange Circle B, source in centre,
microphone 5m from

Grange Circle B, source in centre,
microphone 10m from

Grange Circle B, source in centre,
microphone 15m from

Stones shaping a V
Rannach Crom Dubh Stones shaping a V
Rannach Crom Dubh Stones shaping a V Rannach Crom Dubh
synthesised drums
synthesised drums synthesised drums synthesised drums synthesised drums synthesised drums synthesised drums
female speech
female speech female speech female speech female speech female speech female speech
music (Mozart)*
music (Mozart) music (Mozart) music (Mozart) music (Mozart) music (Mozart) music (Mozart)
operatic voice
operatic voice operatic voice operatic voice operatic voice operatic voice operatic voice
*this row will be replaced with an anechoic recording.

The yellow highlighted sounds are significantly different from the original. The blue highlighted sound close to the originals, but there are certainly timbre changes. So how could this be used during a performance? Ideas are very welcome.
Soon other auralisations will be shown here (of Goseck, Pömmelte-Zackmünde and Heldenberg).

So we might even learn how the circles were used in the past. Let the spaces speak! Are you listening?

References

Ahnert, Wolfgang, and Wolfgang Schmidt. "Appendix: Fundamentals to perform acoustical measurements." in EASERA users manual. Berlin: Software Design Ahnert. in http://renkusheinz-sound.ru/easera/EASERAAppendixUSPV.pdf [accessed 23 July 2016].
Albert, Donald G. 2004. "Past research and sound propagation through forests." US army coprs of engineers. in http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA427598.
Bate, A.E, 1938, 'Note on the whispering gallery of St Paul's Cathedral, London', Phys. Soc, Vol 20: pp 293-7
BC Ministry of Transportation and Highways. 1997. Noise control earth berms: Guidelines for the use of earth berms to control highway noise (Victoria, British Columbia). in https://www.th.gov.bc.ca/publications/eng_publications/environment/references/Guidelines-Noise_Control_Earth_Berms.pdf [accessed 18 July 2016].
Bertemes, Francois, and Andreas Northe. 2010. 'Die Kreisgrabenanlage von Goseck', Archäologie in Sachsen-Anhalt, Vol 5: pp. 9-32.
Blesser, Barry, and Linda-Ruth Salter. 2007. Spaces speak, are you listening? (London: The MIT Press).
Blesser, Barry. 18 Sept. 2011. "Beyond measurements: A framework for aural experience of ancient spaces." in Acoustics of ancient theatres. Patras. in http://www.blesser.net/SP_downloads.html [accessed 30 July 2016].
Bradley, J.S. 2011. 'Review of objective room acoustics measures and future needs', Applied acoustics, Vol 72: pp. 713-20.
Bregman, Albert S. 1994. Auditory scene analysis: The perceptual organization of sound (Bradford Books).
Brown, Pat, and Peter Mapp. 2010.'Early Decay Time as a system performance benchmark', SynAudCon, in http://www.prosoundtraining.com/site/synaudcon-library/early-decay-time-as-a-system-performance-benchmark/ [accessed 29 July 2016].
Brown, Timothy J., and Paul Handford. 2003. 'Why birds sing at dawn: the role of consistent song transmission', Ibis, Vol 145: pp. 120-29.
Bonane Heritage Park. 2010.'Tours', in http://www.bonaneheritagepark.com/tours.htm [accessed 24 November 2015].
Campanini, Simone, and Angelo Farina. 2009. "A new Audacity feature: room objective acoustical parameters calculation module." in Linux audio conference: pp. 1-6. Parma.
Cassidy, Tom, Alan Dormer, and Mikael Fernström. 2016. 'If only those stones could speak - Acoustic experiments at Grange stone circle', Lough Gur & district Historical Society Journal 2015-2016, Vol 18: pp. 115-21.
Chan, Lok Shun Apple.'Requirements for Good Room Acoustics', in http://moscow.cityu.edu.hk/~bsapplec/newpage15.htm [accessed 3 June 2016].
Crocker, Malcom J. 1998. Handbook of Acoustics (Wiley).
Cross, Ian, and Aaron Watson. 2006. 'Acoustics and the human experience of socially-organized sound.' in Chris Scarre and Graeme Lawson (eds.), Archaeoacoustics. (Cambridge: McDonald institute for archaeological research).
Declercq, Nico F., and Joris Degrieck. 2004. 'A theoretical study of special acoustic effects caused by the staircase of the El Castillo pyramid at the Maya ruins of Chichen-Itza in Mexico', Journal Acoustical Society of America, Vol 116: pp. 3328-35.
Deihl, David, T., and Carlson F. Roy. 1968. 'N Waves from bursting balloons', AMerican Journal of Physics, Vol 36: pp. 441-44.
Everest, F. Alton. 2001. Master handbook of acoustics (New York: McGraw-Hill).
Farina, Angelo. 2012. "Aurora for Audacity 2.0.0." in http://pcfarina.eng.unipr.it/Public/Aurora-for-Audacity/2.0.0/.
Fernström, Mikael. 2016, 'Re: Grange stone circle and its acoustics', Pers. comm. 4 May, 2016.
fesi. 2007. Acoustics in rooms (Darlington: Thermal Insulation Contractors Association). in https://www.arauacustica.com/files/publicaciones_relacionados/pdf_esp_350.pdf [accessed 4 June 2017].
Graves, Tom, and Liz Poraj-Wilczynska. 2009. 'Spirit of Place as process: Archaeography, dowsing and perceptual mapping at Belas Knap', Time and Mind, Vol 2: pp. 167-94.
Goseck museum. 2016. "Whispering gallery effect." ed. by Victor Reijs. Goseck.
Grzinich, John. 2015.'Forest reverb - impulse response', Soundcloud, in https://soundcloud.com/maaheli/forest-reverb-impulse-response [accessed 1 August 2016].
Harley, Maria Anna. 1993. 'From point to sphere: Spatial organization of sound in contemparary music (after 1950)', Canadian university music review: pp. 123-44.
Harley, Maria Anna 1998. 'Spatiality of sound and stream segregation in twentieth century instrumental music', Oraganized Sound, Vol 3: pp. 147-66.
Hasenhündl, Gerhard, Wolfgang Neubauer, and Gerhard Trnka. 2005. Kreisgräben – eine runde Sache: Sechs Wege zu ausgewählten Kreisgräbenanlagen im Weinviertel. (Horn/Wien: Druck Berger).
Hendy, David. 2013. Noise: A human history of sound and listening (HaperCollins).
Kaufmann, Dieter, and Rosemarie Leineweber. 2011. 'Die spatstichbandkeramische Palisadenringanlage von Quenstedt: Archaologischer Befund und Nachbau', Tagungen des Landesmuseum für Vorgeschichte Halle, Vol 8: pp. 105-20.
Let, Petrus van der, and Martin Luksan. 2014. "Klange der Steinzeit." Aschaffenburg: Alibri.
Londhe, Niranjan, Mohan D. Rao, and Jason R. Blough. 2009. "Application of the ISO 13472-1 in situ technique for measuring the acoustic absorption coefficient of grass and artificial turf surfaces." in Applied acoustics, Vol 70: pp. 129-41. in http://www.sciencedirect.com/science/article/pii/S0003682X07002009.
Lubman, David. 1998. "Archaeological acoustic study of chirped echo from the Mayan pyramid at Chichen Itza, in the Yucatan Region of Mexico ... Is this the world's oldest known sound recording? ." in 136th meeting Acoustical Society of America. Norfolk, Virginia.
Lubman, David. 2008. "Convolution-scattering model for staircase echoes at the temple of Kukulkan." in Acoustics 08: pp. 4161-66. Paris.
Mallinger, Eva. 2011. "Trainingseffekte und Listenäquivalenz des Freiburger Einsilbertests im Störschall." p 6 July. Erlangen-Nürnberg: Friedrich-Alexander-Universität.
Marshall, Gerald. 1996. 'An analysis procedure for room acoustics and sound amplification systems based on the early-to-late sound energy ratio', Journal Audio Engineering Society, Vol 44: pp. 373-81.
Michel, Christina. "Constructed Knowledge? New insight on spatial pattern and viewsheds of Middle Neolithic circular enclosures." Freien Universität Berlin, possibly 2017.
Murphy, Damian, and Simon Shelley.'The Open Acoustic Impulse Response Library', Audiolab, Department of Electronics, University of York, in http://www.openairlib.net/ [accessed 1 June 2016].
Mussik, Reinhard, and Victor M. M. Reijs. 2017 forthcoming. 'Akustische Messungen in den rekonstruierten Kreisgrabenanlagen Goseck und Pömmelte-Zackmünde', Archäologie in Sachsen-Anhalt, Vol 9.
Ó Ríordáin, Seán P., 1951. 'Lough Gur excavations: the great stone circle (B) in Grange townland', Proceedings of the Royal Irish Academy, Vol LV: pp. 37-74.
Open Source. 2012. "Audacity: A free digital audio editor." SourceForge.net. in http://audacity.sourceforge.net/.
Parker, Rupert. 2013. "Das Stonehenge Experiment - Die ultimative Doku." YouTube. in https://www.youtube.com/watch?v=3jXpempXiro&feature=youtu.be.
Pomberger, Beate Maria, Jörg Helmut Mühlhans, and Christoph Reuter. 2013-2014. 'Forschungen zur Akustik der Prähistorie. Versuch einer raum- und instrumenten akustischen Analyse prähistorischer Bauten und Instrumente.', Archaeologia Austriaca, Vol 97-98: pp. 97-114.
Pomberger, Beate Maria, and Jörg Helmut Mühlhans. 2015. 'Der Kreisgraben - ein neolithischer Konzertsaal? Musikalisch-akustische Experimente im rekonstruierten Kreisgraben von Schletz', Archaologie Osterreichs, Vol 26: pp. 18-28.
Pompoli, Roberto, and Nicola Ordi. 2000. 'Guidelines for acoustical measurements inside historical opera houses: procedures and validation', Journal of sound and vibration, Vol 232: pp. 281-301.
Prendergast, Frank. 2016. 'Grange stone circle (B) - New thoughts on an old monument', Lough Gur & district Historical Society Journal 2015-2016, Vol 18: pp. 66-77.
Reijs, Victor. 2016.'Acoustic testplan and results from stone and timber circles', inhttp://www.archaeocosmology.org/eng/woodcircleaoucistictestplan.htm [accessed 1 August 2016].
Riain, Noirin Ni. 2011. Theosony: Towards a theology of listening (Columba Press).
Richter, Andreas. 2016. 'Das große Rauschen', Mitteldeutsche Zeitung, 9 May, p 9.
Ross, Helen E., and Cornelis Plug. 2002. The mystery of the moon illusion (Oxford, New York: Oxford University Press).
Sacher, Reinhard Josef. 1985. 'Musik als Theater: Zur entstehungsgeschichte des instrumentale theaters'.
Schaefer, Brad E. 2004. "Case studies of three of the most famous claimed archaeoastronomical alignments in North America." in Oxford VII. Flagstaff Az.
Schafer, R. Murray. 1977. The soundscape: Our sonic environment and the turning of the world (Rochester: Destiny).
Schier, Wolfram. 2014. "Die Kreisgrabenanlage von Ippesheim." in Neolithische Kreisgrabenanlagen in Europa, Internationale Arbeitstagung: pp. 181-96. Goseck.
Shelley, Simon, Damian Murphy, and Andrew Chadwick. 2013. "B-format acoustic impulse response measurement and analysis in the forest at Koli National Park, Finland." in 16th Int. Conference on Digital Audio Effects (DAFx-13): pp. 1-5. Maynooth.
Smaart. 2015. Smaart 7: Impulse response measurement and analysis guide (rational acoustics). in http://www.rationalacoustics.com/wp-content/uploads/2015/04/Smaart-v7-IR-Guide.pdf [accessed 5 June 2016].
Spatzier, Andre. 2012, 'Systematische Untersuchungen der Kreisgrabenanlage von Pömmelte-Zackmünde, Salzlandkreis. Zum Abschluss der Grabungen an mitteldeutschen Rondellen im Rahmen der Forschergruppe FOR 550', Archäologie in Sachsen-Anhalt, Vol 13: pp. 89-98.
Spatzier, Andre. 2016. "Re: location of Pömmelte-Zackmünde circle."
Spengler, Oswald. 1991. The decline of the west (Oxford University Press).
Stephens, R.W., and A.E. Date. 1950. Wave motion and sound (London: Edward Arnold).
Sosnowski, Sandra. 2012. 'Neue Erkenntnisse zu Aufbau und Rekonstruktion der Kreispalisadenanlage auf der Schalkenburg bei Quenstedt, Lkr. Mansfeld-Südharz.' in Harald Meller and François Bertemes (eds.), Neolithische Kreisgrabenanlagen in Europa: pp. 121-34. (Halle (Saale)).
Toole, Floyd E. 2013. Sound reproduction: Loudspeakers and rooms (New York: Focal Press).
Trochimczyk, Maja. 2001. 'From circles to nets: On the signification of spatial sound imagery in new music', Computer music journal, Vol 25: pp. 39-56.
US Department of Housing & Urban Development. 2009. "Chapter 5: Noise assessment guidelines." in HUD noise guidelines. US Department of Housing & Urban Development. in https://www.hudexchange.info/onecpd/assets/File/Noise-Guidebook-Chapter-5.pdf [accessed 19 July 2016].
Wiermann, Roland R. 2014. 'Rhythm is it - Ein trichterformiges Tonobjekt aus Halle-Radewell', Archäologie in Sachsen-Anhalt, Vol 7: pp. 33-35.
White, Glenn., and Gary J. Louie. 2005. The audio dictionary (University of Washington Press).
Zotti, Georg, and Wolfgang Neubauer. 2011. "Astronomical and Topographical Orientation of Kreisgrabenanlagen in Lower Austria." in SEAC2011, ed. by Fernando Pimeta, N. Ribeiro, Fabio Silva, Nick Campion, A. Joaquinito and L. Tirapicos. Evora, Portugal.

Terminology

Terminology that is in bold is used on this web page (and underscored is terminology good to know/explain in general). It is important to state that no good or bad should be linked to the below terminology. Good and bad are quite cultural depending [Blesser, 2007], and as we don't know the behavior of the culture involved, no value statement is linked to any of the below terms.

apparent source width
A measure of perceived broadening of a sound image whose location is defined by direct sound [Tool, 2013, page 34] (ASW).
chirp echo
A distinctive chirp/bird-like sound caused by convolution-scattering due to a stair- or concave stepped surface [Lubman, 2008]. This is slightly different than flutter echo.
clarity
Characterising the degree to which discrete sounds stand apart from each other (related to C50 and C80).
coloration
timbre changes of the sound due to resonance or comb effect.
comb effect
Comb effect happen due to the interference of reflections which have a small delay to each other.
diffraction
The propagation of waves around small obstacles and the spreading out of waves beyond small openings.
echo
if reflection is experienced by listener as a standalone sound it is called echo (equivalent with second image).
flutter echo
Flutter echo is a distinctive ringing sound caused by echoes bouncing back and forth between hard, parallel surfaces following a percussive sound such as a hand clap. So a periodic reflection is seen (longer than 20 msec [White, 2005, page 156]). Sometimes flutter echo is also referred to as reflection.
Haas effect
similar to precedence.
listener envelope
A sense of being in a large space, of being surrounded by a diffuse array of sounds not associated with any localisable sound image. [Tool, 2013, page 34] (LEV).
precedence
When a sound is followed by another sound separated by a sufficiently short time delay (below the listener's second image threshold), listeners perceive a single fused auditory image; its perceived spatial location is dominated by the location of the first-arriving sound (the first wave front).
preference
is related to a (strong) spatial impression.
T20 Reverberation Time for 60 dB (RT60), but based on -5 and -25dB points on Schroeder curve.
T30
Reverberation Time for 60 dB (RT60), but based on -5 and -35dB points on Schroeder curve.
reflection
sound that is bounced (reflected, refracted, etc.) back to the listener. If it is heard as a standalone sound from the direct sound, it is an echo or second image.
refraction
Refraction changes the direction of travel of the sound by differences in the velocity of propagation (for instance encountering different atmospheric layers that have different temperatures).
second image
if reflection is experienced by listener as a standalone sound it is called echo (so second image is equivalent with echo).
slope
This is the steepness of a terrain (other words: gradient, pitch), and it is perpendicular to the contour lines. http://geokov.com/education/slope-gradient-topographic.aspx
scattering
scattering of sound waves against a rough surface in other directions than the reflected incoming wave goes.
shadow effect
An acoustic shadow is an area that gets less sound waves (diffracted sound), due to obstructions (posts) or disruption (wind).
timbre
the perception of the tonal distribution of an instrument or sound scape. The distribution can be determine by resonance, comb effect, etc. It is a subjective term, while an objective measure is spectrum.

Abbreviations

ASC
Axial Stone Circle
ASW
Apparent Source Width
C50 speech Clarity (50msec) [dB]
C80 music Clarity (80msec) [dB]
dd
Double Distance
EDT
Early Decay Time for 60 dB, based on 0 and -10 dB  points on Schroeder curve [ms]
ESS
Exponential Sine Sweep
ETC
Energy Time Curve
IACC
InterAural Cross-Correlation [%]
IAF Irregular Amplitude Fluctuations
IR
Impulse Response
JND
Just Noticeable Difference
KGA
KreisGrabenAnlage
LEV
Listener Envelopment
MLS
Maximum Length Sequence
RMS
Root Mean Square
RT
Reverberation Time [sec]
T20
reverberation Time for 60 dB, based on -5 and -25dB points on Schroeder curve [sec]
T30
reverberation Time for 60 dB, based on -5 and -35dB points on Schroeder curve [sec]
T60 optimum Reverberation Time for 60 dB [sec]
RTT
Round Trip Time [sec]
SPL
Sound Pressure Level

Acknowledgments

I would like to thank the following people for their help and constructive feedback: Mikael Fernström, Elke Hockauf, Finn Hockauf, Norma Literski-Henkel, Steve Marshall, Mechthild Meinike, Jörg Mühlhans, Damian Murphy, Reinhard Mussik, Uta Oelke, Frank Prendergast, André Spatzier, Auguste Storkan, Maja Trochimczyk, Georg Zotti and all other unmentioned people. Any remaining errors in methodology or results are my responsibility of course!!! If you want to provide constructive feedback, let me know.

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Major content related changes: January 22, 2016