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This
is a proposal to experiment with the acoustics of the Beckhampton
Cove by building three moveable plywood panels to the approximate
size of the missing stones, and placing them on site to replicate
the original setting.
Of
the western avenue leading from the Avebury henge only two
stones remain. Known as 'The Longstones' the two have also
been named 'Adam & Eve'. The avenue was a long, curving
double row of stones, of which Eve is the only survivor; Adam
is the only remaining stone of the Beckhampton Cove. Coves
are a little-understood feature of some Neolithic henge monuments.
Roughly rectilinear, some coves appear to have been made up
of three stones, with one open side; the Beckhampton Cove
had four. It is particularly unusual in that the two side
stones were splayed.
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Aubrey Burl has suggested (WAM, 1988) that coves may be representations
of the stone chambers found inside some long barrows. If ancestor
or initiation rituals were once performed inside the barrows
then few people could be present, due to the lack of space.
Perhaps using a cove instead allowed a bigger audience to witness
or participate in the the ritual?
Such
an arrangement of stones may also have had acoustic effects,
with resonances or flutter echo. The splayed sides of the
Beckhampton Cove may even have projected sound out from the
cove.
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| Recent
excavation as part of the Longstones Project has revealed the
original position of the cove stones: |
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ADAM
N 51
deg 25' 21.6"
W 1 deg 52' 24.4"
OS
grid ref: SU 08897 69309
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Weighing
some 62 tons, Adam is a huge slab of sarsen stone 1m thick.
It has been set with its smoothest face to the inside of the
cove, suggesting that sound reflection may have been part
of its original purpose.
Although the face is far from being flat, with many depressions
up to 10 cm deep, it reflects sound extremely well. Standing
20m in front of the stone and clicking a pair of claves produces
a loud and clear echo.
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The
Longstones are sited in an open meadow that can be very windy and
securing the panels is important. The area is a World Heritage Site
and there is no possibility of disturbing the ground by driving
in pegs etc, so it is proposed that the replica cove stones be made
of ¾" (19mm) exterior plywood, braced firmly onto horizontal
timber runners strong enough to resist wind. The panels could easily
be pre-built for quick final assembly on site. Each would made up
of two standard sized plywood panels measuring 8' x 4' (2440 x 1220
mm). Although very heavy, it would still be possible to move them
around, and the site is reasonably flat. It is possible that a local
supplier might provide the timber free of charge.
Note that permission from both English Heritage and the landowner
would be required - at present this is only a proposal for discussion.
The
table below shows absorption coefficients for different materials,
where 1 is total absorption and 0 is total reflection. It demonstrates
that ¾" plywood reflects sound well over a wide frequency
range. It is assumed that sarsen stone will behave similarly to
poured rough concrete.
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UPDATE:
THE ACTUAL EXPERIMENT
This
page was first put up on 24/6/09 and posted to the Yahoo Archaeoacoustics
Group.
After
some discussion and computer modelling, a physical model was built
- with exciting results!
READ
ON
Text
& photographs copyright Steve Marshall 2009. All rights reserved.
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