Cove Experiment - Recordings & diagrams made by Stephen Allan
files are the edited recordings from the Beckhampton Cove Archeoacoustics
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
file and its associated graphic is a separate source and recorder
These are termed Experiment 1 to Experiment 14.
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.
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.
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.
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.
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.
(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.
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)
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.
and Ex13 are recordings of a djembe drum being played within
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.
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.
a control, a further recording (not included) was made from the
same position as Ex13, but with all four panels laid flat on the