Jason, I think that you are essentially correct in your calculations.
Imaging underwater will always be different than outdoors in air because
of reflections at boundary layers (the surface + any water
stratification below). But that it the best you can do in most cases
for direction finding. But we don't really have a perception of what
"real" sound imaging is underwater. Or if you want to chase that
argument a little further, what is a faithful replication to our senses
(if we put our heads underwater) would be pretty much directionless. So
any attempt at mic spacing and placement is sort of done to replicate
whatever we expect that image to sound like. This gets even more
confusing seeing as how the hydrophones were not in liquid. I don't
know what the speed of sound in ice would be. And if it is
substantially different than that of the speed in water, what is the
phase distortion when sound from the same source arrives at the
hydrophone at different times though the different mediums?
As a guy who sells hydrophones, I certainly don't want to discourage
anyone from recording in stereo. The recordings are certainly way more
fun. But trying to figure out what is a faithful reproduction four our
senses is pretty open to interpretation.
Kind regards, Robb
On 1/26/2012 1:30 PM, jasonpudd wrote:
>
>
> Dan,
>
> This is wonderful!
>
> I want to understand the physics of the delay issue with the
> hydrophones. I assume that the delay would be best for the
> seperatation of the mics to mimic the delay time in air. So, if the
> speed in air is 343 m/s and the speed in fresh water is 1497 m/s then
> the correct seperation would be 4.36x the correct spacing in air? That
> would be about 74cm for the hydrophones? Have I got this right and
> will you get closer to the sound imaging we are used to?
>
> Cheers,
>
> Jason
>
|