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Re: Re: CVX tests

Subject: Re: Re: CVX tests
From: Walter Knapp <>
Date: Fri, 26 Apr 2002 22:52:37 -0400
Simon Squire wrote:

> Noise measurements in the anacroic chamber showed the Panasonic element h=
> 1% THD when it was out of the CVX. As soon as we put the same element in =
> CVX housing the THD dropped to 0.1%. Why this happens has not been
> investigated yet, due to limited chamber time, and money etc.

The location in the housing may be providing some form of pressure
"preloading" to the capsule diaphragm.

I suppose it's tradition to use a different mic noise criteria for every
brand of mic, but lets try and stick with the ones common for mics used
in nature recording. I don't believe I've seen THD being used for
discussing noise floor on a mic in the group before.

I may be all fuzzy in my thinking tonight, but here goes:

Panasonic's reporting for their capsule:
S/N ratio More than 62 dB
Sennheiser's reporting for the MKH-20:
Equivalent noise level
A-weighted (DIN IEC 651) 10 dB

Panasonic reports more than 62 dBA. Though not stated, this is usually
against 96dBA, making the equivalent to the MKH-20 of 34 dB A-weighted I
think. Now assuming the housing on the CVX adds some gain before the
mic. To be generous, say 10 dB. That would lower the noise of the combo
to 24 dBA. Adding 10 dB gain to the MKH-20 by using a very low noise
preamp would raise it's noise floor as it occurs after the mic. Which
would make it 20 dB at the extra gain.

In any case, the noise will place the upper limit on how far away
something can be recorded. I've carted my sound meter around measuring
frogs some. Highest I've measured, at about 1' distance is about 90 dB.
Working on sound falling off by about 6dB per each doubling of distance
that works out your mic might pick up that frog (barely) at a half mile
or so before it would fall into the noise floor. The MKH-20 plus pre
would do better by 4 dBA or more depending on the actual gain from the
CVX housing. Which should translate into greater reach.

I don't have the noise specs for the Telinga, so can't do the same
comparison there. I think it has about 10 dB gain before the mic. There
is also a reporting of the relative shortening of the "distance"
compared to a bare mic to 1/10 of actual. That all indicates that unless
the Telinga capsules are noisier than the CVX capsule that the Telinga
is likely to have greater maximum reach.

It should also be noted that the Telinga stereo mic element is a PZM
system. I don't know if this provides any of the gain associated with
PZM or not.

I'm not sure how the relationship of sensitivity would be resolved.
Panasonic reports:
Sensitivity =9635=B14dB (0db =3D 1V/pa, 1kHz)
Sennheiser MKH-20 reports:
(free field, no load) (1 kHz) 25 mV/Pa =B1 1 dB

One could say that the MKH-20 plus a low noise pre is going to be more
costly than the CVX, but the mics themselves are in a fairly similar
price group. MKH like prices create that kind of expectation. The
Telinga is also of the same sort of price, though it's not at all a omni mi=

> You will be interested in our stereo version which is currently in
> development. The first prototype is working very well, with less noise an=
> very good stereo separation. No numbers yet though. This will not be as
> rugged as the original CVX, but will be very light, and stereo, with simi=
> performance. Also we have been in contact with Cornell, because they want=
> compare the CVX with current mics. They do not have one yet though, so Do=
> can be the "comparator" for now if he wants.

I'll be interested in following the saga. I do particularly like the
weather resistance of the design. This, of course, makes it fairly ideal
for a froglogger.

Speaking of which, what are raindrops hitting it like for sound? Lets'
say one of our typical summer thunderstorms. I'd kind of expect the
housing may act as a drum.

> I will guarantee you have never heard anything like the CVX, or your mone=
> back. ( I'm starting to sound like a salesman, yuk, I'm a tech, give me m=
> soldering iron...)

So far it sounds ok. What appears to be the mic's noise floor is clearly
noticeable in the recordings I've listened to. Though I certainly don't
know if it's that or some other part of the process. I'm not surprised
at this in view of the capsule used. Kind of like the things with the
SASS mic, it would be nice to see some comparisons between the CVX as
designed and say a "MKH-20" modification.

Do you know if any frequency response graphs are available? Seems to me
like the design may partially act to favor some frequencies over others.



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