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Re: Re: CVX tests

Subject: Re: Re: CVX tests
From: Walter Knapp <>
Date: Sat, 27 Apr 2002 21:40:08 -0400
Simon Squire wrote:
> >
> > The location in the housing may be providing some form of pressure
> > "preloading" to the capsule diaphragm.
> You agree with our designer...

It should be noted that this would not change the electronic noise,
which if primarily from the transistor built into the capsule.

There may be some use for this pressure loading when working on designs.
Something to think about.

> > 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
> mic.
> >
> This is only true if they are designed for the same purpose.

The MKH-20 is a omni, and would therefore be suitable for the same
things. Like all mics (except the Telinga) it was not designed for
nature recording. We borrow mics designed for other things.

I view the CVX as designed primarily as a froglogger (or birdlogger).
I'm not sure if it would stand up to use for quality recordings to be
sold to the public for listening. That's probably something yet to be
found out. I'm coming from the world of survey recording pushing into
the "quality recording" direction, so am kind of focused on that right
now. Though I'm also continuing survey work.

For a awful lot of my use a 360 degree coverage is a disadvantage. I
normally cannot get into a area of calling frogs but must record from
the side. So the extra coverage is just going to be sucking in more
unwanted noise. There are times when it would be nice, however. Right
now I'm primarily working on more variety in stereo fields of a
directional nature. I've used the Telinga stereo for some time. For
stereo I'm adding a modified SASS setup, a pair of MKH-816's, and a
variable field M/S setup. That many mostly because I had a good streak
of buys on ebay. I prefer to add one mic setup at a time. By the time I
get each of these suspended and wind protected I may spread them out a
bit anyway.

> When rain drops hit the CVX it definitely bangs!! Therefore the previous
> discussions about "hogs hair" and other such covers is also true for the
> CVX. I found a simple "hat" of loose polyester padding worked perfectly. No
> bangs in heavy rain, and the water would simply run off the edge.

You have the advantage that it starts out waterproof, you only need to
fix the noise. With most mics you are doing that and trying to keep the
mic from getting wet.

> > 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.
> >
> > Walt
> > 
> The CVX also benefits from the PZM effect, but the housing gives far more
> gain than just the 6dB. We usually quote around 14dB but this (like all
> measurements) can be debated till eternity. Also the CVX provides more gain
> as the frequency increases, which is great for birds, and making speach
> understandable. From my perspective your numbers look ok, except several
> assumptions. The only thing is that your conclusion about the frog not being
> heard beyond 1/2 mile does not match what we actuall hear!!

Yes, I knew I was making several assumptions. Seems like the only way to
get anywhere anymore.

I remembered seeing figures up to 9dB being quoted, don't remember the
14 dB. That's why I picked 10 for the gain from the housing.

If you get a gain of 14 dB instead of the 10 I assumed that would get
you a lot closer to a mile using the same attenuation rate. And about
dead even with the MKH-20 plus pre. On paper for noise floor, anyway.

How far out would you estimate you can pick up a frog calling at a level
equivalent to 90 dB at 1' from the frog? Before it drops into the noise
floor, ie it's volume on the recording is no louder than the noise
floor? That's not the end of being able to find the call on the
recording, with sonograms and so on it's possible to find much fainter
calls and identify them. But it's approaching what you will hear in the 

Have you done checks on frequency vs gain at different gap sizes?

> Thank you for your examination. The CVX design definitely needs more
> examination by knowledgable individuals, and field comparisons to mics like
> the MKH-20. If you had one of these to spare for a little while, we would be
> happy use it to challenge the CVX in the field.

I don't have a MKH-20 at all, though I have several of the older
MKH-110's. Lang would be the one to talk to about MKH-20's, which he
uses. I'm using a pair of the MKH-110's in the modified SASS I'm
building. They require a custom 8 volt power supply, so can't just be
plugged into anything.

I have a MKH-80, which is the older multi-pattern version (the newer
MKH-800 has a much higher frequency response). But could not spare it.
In fact it's new enough to me that I don't know it's capabilities yet.
I'll be using it mostly in a M/S pair with my MKH-30. Once I manage to
build a proper suspension and windscreen system for the pair.

Any measurements and theory are only a starting point. It takes actual
field use to really know. Most of the time when I buy mics it's with a
certain feeling of risk as I don't know how they will handle for me. I
use specs, asking others and so on to try and keep the risk down. It's
lovely, of course if you can borrow and try, or even go out with someone
who has the mic of interest and get to listen to it out there. It helps
a lot the get recorded samples or compare notes in groups like this, but
there is nothing like comparing to the actual original calls on the spot.



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