Or I have the right stuff and we all have the right stuff! Of course the "r=
ight" stuff is whatever results in a pleasing, high resolution sonic image =
in whatever context the recording will be used.
It's interesting to me that the green foam I bought looks and feels just li=
ke the mattress foam I have at home. But the green foam is attenuating high=
frequencies at 1dB per inch and I cannot detect any attenuation at all wit=
h the same thickness of mattress foam. Something is going on in the cell st=
ructure of the foam that is invisible to my eye. Both are clearly open cell=
and of similar density. Mysterious.
I measured the attenuation by simply playing a 2000 Hz signal on my compute=
r and measuring the SPL with a sound level meter, with and without the foam=
covering the sensor (microphone) of the meter. The same could be done with=
a mic and recorder, measuring the dB difference in Audacity or whatever. T=
he SPL meter is just easier. I don't know if that is a legit method, but it=
did reveal the difference between the green foam and the mattress foam. I =
am going to search for another foam source, maybe even go to a junkyard and=
try to get some car seat foam. That looks denser to me, but will it be mor=
e acoustically dense? Only one way to find out at this point.
BTW, my green foam, at 1.5 lbs per cubic foot density, is similar to the fo=
am linked to on the diyboundarymic blog. So maybe it is the "right" stuff. =
Just not identical to what Crown is using, which may be proprietary.
best
John Crockett
Westminster, Vermont
The Overflight State
--- In Peter Shute <> wrote:
>
> So does this mean you've got the the wrong stuff, or that we've all got t=
he wrong stuff?
>
> How do I make this measurement? If I record a sound source with and witho=
ut it covered by the small piece I have, won't I pick up lots of reflected =
sound from other directions?
>
> Peter Shute
>
>
> --------------------------
> Sent using BlackBerry
>
> ________________________________
> From:
> To:
> Sent: Fri Jul 13 09:13:09 2012
> Subject: [Nature Recordists] Re: Foam for SASS
>
>
>
> Hmmm. By this test, my green foam fails. Using a SPL meter, I am measurin=
g about 1dB per inch attenuation of a 2 kHz signal. Maybe I need to keep lo=
oking for the right foam. I'm not confident this green stuff is going to ad=
equately separate the channels.
>
> John Crockett
> Westminster, Vermont
>
> --- In <naturerecordists%40yahoogr=
oups.com>, Paul Jacobson <pj@> wrote:
> >
> > The SASS patent indicates that the foam for the nose should attenuate f=
requencies above 1200hz by at least 3dB per inch. All you need to do is tes=
t for that property.
> >
> > cheers
> > Paul
> >
> > On 12/07/2012, at 5:42 AM, Peter Shute wrote:
> >
> > >
> > > It would be good if someone could come up with an objective test for =
identifying this stuff. I was told I should be able to blow through it, but=
with more difficulty than with medium density foam, which I wouldn't call =
an objective test unless I had several samples to compare.
> >
> >
> >
> >
>
>
>
>
>
>
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