Volker, some years ago while recording bats in Utah, we picked up an odd bu=
t constant ultrasound freq around 70kHz with our trusty bat detector. We kn=
ew it wasn=92t bat echolocation. As we got closer to the cottonwood tree we=
thought might be the source, the signal became louder. We drilled a small =
hole in the trunk of the tree about the diameter of a pencil eraser and abo=
ut 10 - 12cm deep, inserted a B&K 8103 hydrophone, and recorded the signal =
to a very cumbersome HP instrumentation device with a tape speed of 120ips.=
Back at the studio, I slowed up the speed by a factor of 7 and got the fol=
lowing: https://www.youtube.com/watch?v=3DuWkMWDSVZuQ
Most current explanation: after a period of drought, the cells in the xylem=
and phloem suck in air to maintain osmotic pressure. When the cell walls d=
ry and split, they emit a tiny signal that, when enough cells pop at the sa=
me time, they will generate a constant signal. As they die, they form tree =
rings. Admission of guilt: most of what we recorded sounds like static and =
that is generally the signal one should expect. But one section was quite r=
hythmic, hence the segment that I sampled for presentations.
I haven=92t experimented with that model since. But I suspect that with cer=
tain species of trees (and smaller vegetation) you would find a wonderful s=
ymphony of signals all waiting to be discovered and explained.
Bernie
>
>> On Mar 27, 2019, at 4:41 AM, 'Volker Widmann' <volw=
> [naturerecordists] < <nat=
>> wrote:
>>
>>
>>
>> Hello fellow recordists!
>>
>> Which microphones would you recommend for recording the sap flow in tree=
s and the gnawing of beetles underneath the bark?
>>
>> Thanks
>>
>> Volker
>> --
>> Diese Nachricht wurde von meinem Android Mobiltelefon mit GMX Mail gesen=
det.
>>
>
>
>
>
"While a picture is worth a thousand words, a
sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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