Thanks Dan, I agree and have no other comment.
But I could add:
Have you ever put a medium class directional microphone on a rotating plate=
in front of a 10kHz speaker and looked at the linear voltage output for
different degrees?? I guess not....
Cause if you do, you will find so many peaks and gaps - 40 db and more!! -=
when turning the mic only a few degrees one or the other direction!
And if you take another microphone of the same type, it will probably show=
a quite different "exact" polar pattern. I agree with what you say, but I
think we must accept that polar patterns are very approximative and that,
perhaps, the db scale is the most "readable".
If one manuf uses db, everyone else has to do the same. But in this case it=
is not fraud, just an approximation.
The same goes with frequency curves: If you make a slow voltage sweep,
instead of db, - you will see a very edgy curve, unless it is a very good
mic. B.t.w - I heard from one of the more prominent mic labs that they put=
a smoothening condensor on the printer input if the freq. measurment gets
too edgy.... They say that "nobody can read an edgy curve anyway....it
doesn't make sense." It's perhaps true, but also misleading.
Klas.
At 20:02 2005-05-12, you wrote:
>Klas, you wrote,
>
> >A simple way to learn the difference is to put an attenuator on the mic =
and
> >lower the mic self noise until you start to hear the MD / DAT /Edirol
> >/whatever mic amp noise. Then you can hear the difference.
>
>Excellent plan.
>
> >2/ When reading noise figures, consider that "A-weighted" noise or
> >"CCIR-weighted" noise means that one has compensated for the frequencies
> >which are most audible to the human ear.
>
>At low sound levels!
>
> >For naturesound recordists there should be another way to "weight" a noi=
se,
> >compensating for the noise which is most masked by nature atmosphere. A
> >high frequency noise can be audible "on top" of the atmosphere, while a =
low
> >frequency noise is masked by it and not possible to hear at all.
>
>A-weighting is suitable for that, it mostly rolls off the bass.
>
> >3/ When I send my postings on this list, I don't feel that I am understo=
od.
> >I do not succeed in finding the right words for my logic. Let me try
> this one:
> >
> >Suppose a microphone has a self noise of 16 db(A). Fine. That cannot be
> >changed by any pre-amp.
> >Then the question must be: "How sensitive (output =3D mv/Pa) must that
> >microphone be to "noise-dominate" over the MD/DAT/ Etc mic input noise?
> >That is the question which needs to be answered!
> >
> >I mean - the noise you hear should always come from the mic!!! The mic m=
ust
> >always be the weakest link in the chain!
>
>Yes.
>
> >4/ Sensitivity must be presented as mV/Pa, NOT -db, whatever - as there =
is
> >too much cheating on the market, using different reference levels for th=
e
> >db measuring.
>
>I'd prefer a dB rating to a common standard, but I agree entirely
>that mic sensitivity specifications are a morass of confusion. I use
>a Shure cardboard slide rule to convert from one reference to another.
>
> >I spent two hours on the web a few days ago (with broadband- finally!! h=
ere
> >in the woods!!) - to straighten out my questions about "sensitivity"
> >expressed as "db". I found myself in a total mess of different standards=
.
> >If you like to try - please visit
> >http://www.acoustics-noise.com/dBA-B-C-D-U-G-U-AU-tables.shtml for examp=
le.
>
>That's about -weighting-, not sensitivity standards. The weightings
>other than A and C are rarely encountered and we needen't worry about
>them.
>
> >When the data sheet says: "10 mv/Pa at 1000 Hz" - fine, that is a fact! =
One
> >can understand it. But when it says: "Sensitivity -64" db or something, =
I
> >don't care about it. I don't see any good reason why somebody should lea=
ve
> >an established and accurate expression (mV/Pa) in favor of a strange fig=
ure
> >(db), unless there is fraud going on.
>
>dB figures are easier to understand and translate to effects, -when-
>they are using the same reference.
>
> >We must all understand that: When one manufacturer starts manipulating w=
ith
> >data, even lying, all the others have to follow. Or die.
>
>Example: the use of dB scales for mic directivity polar plots. Makes
>no sense. A linear scale (0 to 1) shows the real shape of the pattern.
>
>-Dan Dugan
>
>
>
>"Microphones are not ears,
>Loudspeakers are not birds,
>A listening room is not nature."
>Klas Strandberg
>Yahoo! Groups Links
>
>
>
>
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
________________________________________________________________________
________________________________________________________________________
"Microphones are not ears,
Loudspeakers are not birds,
A listening room is not nature."
Klas Strandberg
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