THE BECKHAMPTON COVE, AVEBURY - an archaeoacoustics experiment
www.stevemarshall.org.uk

 
Beckhampton Cove Experiment - Recordings & diagrams made by Stephen Allan 12/7/09

These files are the edited recordings from the Beckhampton Cove Archeoacoustics Experiment.

The audio files are 24 bit, 44.1 KHz WAV files except for Ex12 and Ex13 which are quite long, so these are in 192kbps mp3 format. (WAV available on request).

Each file and its associated graphic is a separate source and recorder set up.
These are termed Experiment 1 to Experiment 14.

For each audio file there is an explanatory graphic file in JPEG format showing the positions of the sound source and the recorder in relation to the cove.

All files except Ex12 and Ex13 are recordings of a balloon burst impulse. This tends to have a total duration of approximately 6ms but with a clearly distinguishable waveform.

The Files
Ex1 is a recording of the balloon burst with just a single chipboard 'stone' in place and shows the reflectivity of the chipboard sheets used. This may be compared directly with the file AdamW1 which was recorded using exactly the same set up and distances as for Ex1 but was carried out on the real stone in situ.

Download: EX1 WAV EX1 GRAPHIC

Ex1 shows that the chipboard sheets have a similar reflectivity to the real stone known as Adam. However at just 12mm thickness there will be far less reflection of the low frequencies. Also of note is how the reflection (55ms after the original impulse) is not only at a high level (-15dB from the original) but is also well preserved in both shape (harmonic content) and length.

Ex2 to Ex6 are a series of recordings made whilst searching for resonances and reflections within the cove. There is generally a lack of discernible reflective or resonant effects. This may be to do with the size of the chipboard sheets which, at three square metres are less than half the reflective area of the real stones.

Download: EX2 WAV EX2 GRAPHIC

Download: EX3 WAV EX3 GRAPHIC

Download: EX4 WAV EX4 GRAPHIC

Download: EX5 WAV EX5 GRAPHIC

Download: EX6 WAV EX6 GRAPHIC

Ex7 (not included) was a singer walking around within the cove whilst the experimenters moved around listening for any acoustic effects from in and around the cove. It was during this experiment that the experimenters noticed the megaphone effect from beyond the southern end of the cove.

Ex8 demonstrates this megaphone effect very clearly. The recorder is shielded from the source by the sheet of chipboard representing stone S. The first impulse is the direct sound, the second impulse 7ms later is the sound as reflected by the E and W stones. The reflection is surprisingly high in level being almost the same level as the original impulse. There is some smearing of the reflected impulse probably caused by a slight inequality in the length of the paths travelled by the reflected sounds. The initial impulse has either travelled through the chipboard representing stone S or has been refracted around it. (An annotated picture of the Ex8 waveform is included as Ex8anno.jpg)

Download: EX8 WAV EX8 GRAPHIC EX8 GRAPHIC ANNOTATED

Ex8 should also be compared with Ex10 which was recorded in exactly the same way but from the northern end of the cove. In this recording there is no discernible reflected sound from anywhere within the cove. There are some late reflections coming from trees to the north of the cove which, at the time of setting up the experiment were considered to be far enough away from the cove to not interfere with the sounds within the cove.

Download: EX9 WAV EX9 GRAPHIC

Download: EX10 WAV EX10 GRAPHIC

Download: EX11 WAV EX11 GRAPHIC

Ex12 and Ex13 are recordings of a djembe drum being played within the cove.
The change in sound of the drum is clearly audible as the recorder is moved into line with the cove. At the southern end, as the recorder is moved along a line parallel with the line of the Beckhampton Avenue and into line with the North/South axis of the cove the sound level increases and gets 'harder' in quality whilst at the northern end the sound gets quieter and softer as the recorder is moved onto the North/South axis and behind the chipboard sheet.

Download: EX12 WAV EX12 GRAPHIC

Download: EX13 WAV EX13 GRAPHIC

Ex12 was recorded at the northern end of the cove. The djembe is being played in the middle of the cove towards the southern end. The recorder is 10m north of the northern 'stone' and is moved westward along a line parallel with the line of the Beckhampton Avenue - the movement is announced during the recording. Extra echoes can be heard coming from trees and other reflectors to the north which, at the time of constructing the imitation cove, were thought to be far enough away to be discounted.

Ex13 was recorded at the southern end of the cove. The djembe is being played in the middle of the cove and towards the northern end. The recorder is 10m south of the southern 'stone' and is moved eastwards along a line parallel with the line of the Beckhampton Avenue - the movement is announced during the recording. It can be heard clearly that as the recorder is moved the sound level increases and takes on a 'harder' quality.

As a control, a further recording (not included) was made from the same position as Ex13, but with all four panels laid flat on the ground.


Environmental Conditions:

Experiment times
Ex1 - 10.28
Ex2 - 11.40
Ex3 - 11.50
Ex4 - 11.54
Ex5 - 11.57
Ex6 - 12.08
Ex7 - 12.15
Ex8 - 12.32
Ex9 - 12.33
Ex10 - 12.40
Ex11 - 12.42
Ex12 - 13.02
Ex13 - 13.03

Associated weather
time - temp - humidity
10:20 17.0 °C 88%
10:50 17.0 °C 77%
11:20 17.0 °C 82%
12:20 19.0 °C 64%
12:50 19.0 °C 60%
12:50 19.0 °C 68%
13:20 20.0 °C 64%


Recordings & Text Copyright Stephen Allan 2009. All rights reserved.
Contact Email: stephen (dot) allan (at) uwe (dot) ac (dot) uk