Hi,
The trouble with Angelo's kit is that it's not really "hi-fi".
Works well for what it was designed for (noise pollution research) but
not really good enough for serious audio. Because it's based on
differencing omni's to generate directional responses it has a
relatively limited bandwidth and because of the difficulty of
calibrating it it is not necessarily very accurate. As Fons says, the
cost of a good, flat frequency response, underwater speaker is
prohibitive (not to say humungous!) but, even worse, underwater
anechoic chambers are not exactly common so you'd need to do the
calibration in deep water, well away from the shore, sea bottom etc.
Don't forget that the speed of sound in water is 5 times that in air
so everything has to be 5 times bigger (hence the large size of his
hydrophone). You CAN get figure 8 hydrophones but only if you have
military sized budgets - they have been used in aoustic torpedoes and
DIFAR buoys (google them) but it looks like using Blumlein
differencing techniques, with two different separations to cover low
and high frequencies separately might be the best approach for audio
purposes. Good hydrophones are several hundred (or more) Euros each
(for instance the Reson ones from
http://www.ambient.de/en/products/ambient-recording/underwater.html),
so this can get expensive and if you want to work in anything other
than the top waters, the cost of connectors and cable is frightening.
There are cheaper alternatives like the Dolphinear ones
(http://www.dolphinear.com/) which are pretty good or the JrF ones
(http://hydrophones.blogspot.co.uk/) or you can even make your own
(http://www.dosits.org/resources/all/classroom/buildhydrophone/ or
http://leafcutterjohn.com/?p=915).
As you can tell, I have been looking at this a lot, in the context of
the TBA-21 Academy project (http://tba21academy.org/), though since my
retirement I am no longer directly connected to them (at present)
Dave
http://www.dezeen.com/2011/09/14/sonic-seascape-terrace-by-decoster-taivalkoski-haaslahti-and-montes-de-oca/
On 19 February 2013 04:03, Marc Lavallée <m...@hacklava.net> wrote:
> umashankar manthravadi <umasha...@hotmail.com> a écrit :
>> angelo farina has exactly the beast you are looking for. he had a
>> power point presentation describing its use here is the link
>> http://www.angelofarina.it/Public/Presentations/UAM2011_Underwater_Ambisonics_files/frame.htmumashankar
>
> Fons Adriaensen <f...@linuxaudio.org> a écrit :
>> Most hydrophones (and certainly any low-cost ones) will be
>> omnis, so the A/B processing will be very different from
>> what is required for a normal tetra mic using directional
>> capsules.
>
> Hydrophones are omnidirectional, and the underwater probe for the
> Brahma is tetrahedral... Are omnidirectional "sensors" appropriate to
> build tetrahedral ambisonic microphones?
>
> --
> Marc
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--
As of 1st October 2012, I have retired from the University, so this
disclaimer is redundant....
These are my own views and may or may not be shared by my employer
Dave Malham
Ex-Music Research Centre
Department of Music
The University of York
Heslington
York YO10 5DD
UK
'Ambisonics - Component Imaging for Audio'
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