At 9:06 PM -0500 2/14/04, Walter Knapp wrote:
>Disclaimer: I don't have official testing equipment here, I just use
>what I have and some common sense. Haggle with somebody else over
>exactly what the numbers are, I have some closer idea, but avoided
>giving numbers as the informal soundproofing is probably not absolute.
>I'm satisfied in the opinions I'm giving.
>
>Take a MKH-80, I have a pair in excellent shape, and tried this with
>both, singly and as a pair. I did not run the MKH-20's because I was too
>lazy to take them out of the SASS, I already had the MKH-80 M/S apart
>for something else I was doing.
>
>Get it in as soundproof a situation as you can. In my case this was
>wrapping in layers of closed cell foam and sandwiching it between
>mattresses and blankets in the quietest room in our house. No
>identifiable sound from the environment was heard during the testing
>below, it would be better to use a soundproof room but I'm fresh out of
>those. I repeated the test several times today with the exact same results=
.
>
>Turn on the Sound Devices MP2 with nothing connected to it and phantom
>power and so on switched off. Crank the gain to it's top setting and
>listen via good headphones using it's headphone connection. No led's are
>lighting, but yep there is the self noise. Set that fairly quiet in the
>headphones using the headphone amp setting.
>
>Check switching on the phantom power, little, if any difference.
>
>Now, connect the MKH-80's to the inputs, but don't turn on phantom
>power. Try the same test. Self noise is less than half as loud as the
>unconnected test. The drop is very dramatic. (note with no phantom power
>the MKH-80's are not running)
>
>Now turn the gain all the way down and turn on phantom power. Give the
>MKH-80's a few minutes powered just in case there is a change with
>"warmup". (I've never detected one) Now crank the gain to the peg. The
>led's -30 & -15 are on steady, 0 occasionally flickers. You have not
>changed the volume settings on the headphone through all this, so you
>get your ears blasted.
>
>Now, just why should we care about the MP2's self noise in this setup?
>It's obviously a huge amount lower than the MKH-80 used with it, which
>has a self noise spec of 10dBA. That's true for both my MKH-80's. It
>would not matter with the lowest self noise mics spec'd around 5dBA,
>like my MKH-70, I expect the results would be the same. As Klas said,
>the mic self noise is far and away the big component it seems from this
>informal test.
Thanks Walt. This seems consistent with Bob Cain's computation for
MP-2 as having around 4-5 dB(A) self noise. Would be interesting to
try this test with the Portadisk pre.
>
>In actual practice I would not use the pre cranked this high. I don't
>have to to get all that the sites in Georgia offer. At most maybe 3/4 up
>on the MP2 would be the limit. Even there I'm likely going to hear the
>mic's self noise. Which in MKH mics is a nice smooth hiss.
>
>The idea that the self noise level of a fully cranked pre means much by
>itself appears wrong. It's certainly not a standard of comparison
>without a lot of standardization as to mic and so on. It looks like
>from my test that you have to test the pre with the intended mic
>connected to be at all meaningful. The numbers quoted for cranked pre's
>need to have full specifics with them. Even then they are not reality of
>nature recording. At least as I find it in the state of Georgia with the
>high output mics I use.
>
>Recorded with a SASS/MKH-20 on a high tripod, input direct into the
>Portadisc, and not using near all the available clean gain:
>http://wwknapp.home.mindspring.com/SASS_MKH20_tall.mp3
>Note most folks play this louder than the original site which was
>actually pretty quiet. Think a site where a whispered conversation would
>be easy to carry on even if not very close together.
>
>I don't push mics to do things they were not designed for, like trying
>to get mics designed for local subjects to record distant ones. I try to
>use mics designed for the job or get closer. Which may also be why I'm
>not running around setting my gain on the top peg.
Nor does anyone if they can get adequate saturation ottherwise. The
fact that the lowest noise mics and pres are being pushed when trying
to record rural night ambience shows how easy it is to get very
noticeable amounts of noise recording natural ambience if one is
using gear with self-noise rof 10-15 dB(A) more-- like that consumer
MD mic pres.
>
>Maybe with low output mics it might be different, that's one of the
>variables you need to account for in such tests. As well as the gain at
>full of the pre before even thinking about comparisons. There are
>multiple differences in this that apply to comparisons.
>
>Walt
>
>
--
Rob Danielson
Film Department
University of Wisconsin-Milwaukee
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