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Author Topic: Measurement Microphones  (Read 77961 times)

Jens Brewer

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Re: Measurement Microphones
« Reply #10 on: December 17, 2008, 11:09:49 am »

+1 for the M30, but it does make me nervous carrying that on road, even as well protected as it is.  If you are just starting with measurements, and are primarily using it for system tuning rather than lab work/crossover setting, I would suggest something like the TR40.  Perfectly good for what we need it for and if something bad happens to it (like a lighting guy running over it with a genie lift, ahem), you won't go into seizure.  I know that the good folks at Rational Acoustics are having a X-mas sale on such items right now.   Razz
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Silas Pradetto

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Re: Measurement Microphones
« Reply #11 on: December 17, 2008, 11:16:43 am »

I use one of those cheapo DBX measurement mics that are sold for use with the Driverack 260. Are these any good? Who makes them?
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Tom Young

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Re: Measurement Microphones
« Reply #12 on: December 17, 2008, 11:45:10 am »

I forget the manufacturer's name but these are the same mic as supplied with the Audio Toolbox from Sencore (originally from Terrasonde). I have had a few of these but use my SF101 when doing critical measurements (mostly SPL). 1-2 of my 'expert' sources think these mic's are not very good. But if you can do a "mic compare" procedure against another known "good" mic you may find it is OK.

The problem with all of these cheap plastic diaphragm mic's is that (obviously) they are mass produced and are sold for dirt cheap prices. More conscientious microphone manufacturers will test them (when assembled) and group them according to quality (frequency response, primarily) and then sell the best ones for more money to the buyers who then brand them. When you see the same basic mic (as far as physical appearance) sell for well under $100. (Behringer, for example) versus over $100. (Audix, others) it may be safe to assume that the pricier ones use flatter response diaphragms. But who knows ?

One of the problems with all plastic diaphragms is when they are exposed to higher temeratures (such as storage in a car trunk on a hot summer day), they stretch and then may not return to their previous state when back at cooler temperatures. So the frequency response changes. Even those diaphragms that are (pre) stretched (and possibly heat stretched) by the manufacturer may not be immune to this high-temperature condition. So I wonder how hot the inside of a shipping container gets when exposed to direct sunlight on the container ship from China and/or waiting in either port ?
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Tom Young
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Mac Kerr

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Re: Measurement Microphones
« Reply #13 on: December 17, 2008, 11:55:24 am »

Tom Young wrote on Wed, 17 December 2008 11:45

One of the problems with all plastic diaphragms is when they are exposed to higher temeratures (such as storage in a car trunk on a hot summer day), they stretch and then may not return to their previous state when back at cooler temperatures. So the frequency response changes. Even those diaphragms that are (pre) stretched (and possibly heat stretched) by the manufacturer may not be immune to this high-temperature condition. So I wonder how hot the inside of a shipping container gets when exposed to direct sunlight on the container ship from China and/or waiting in either port ?

I just took the opportunity to check my rather old, well traveled TC30k against a fairly new well cared for M30, and an Audix T40. This was done at about 8' from an L'Acoustics 108. Relative to the M30 my mic had a falling response starting at about 1k that put it down about 2dB at 20k. All the little system response dips tracked perfectly between the two mics. The Audix had a rising response relative to the M30 that put it about 4dB high at 20k, with a sharp rise above about 8k. When I can, I will send my mic in for service, but I am still fairly confident in its performance. I pack it in a plastic tube with foam ends, then in my tool bag, which goes in my suitcase, which goes in the belly of the plane many times a year. So far so good.

Mac
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Ian M Barfoot

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Re: Measurement Microphones
« Reply #14 on: December 17, 2008, 11:59:58 am »

I to have an M30 which seems to be very good, not sure I would say they were too expensive for the road unless I have a slightly higher tolerance to cost. I have a number of DPA 4090's which could be used though I like those on Timpani or percussion so not always available. If it is critical I assume that Bruel & Kjar (Parents of DPA I believe) still make exceptional measurement microphones?
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Art Welter

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Re: Measurement Microphones
« Reply #15 on: December 17, 2008, 01:41:00 pm »

Tom,

Last winter, after getting lousy results from some subs I was building, used one of my B & K 4004 mics (+/- 2dB 10HZ to 40KHZ) in place of the mic as supplied with the Audio Toolbox  from Terrasonde.

This is how far off I found it to be:

-10 at 20HZ, -9 at 25, -8 at 30, -6 at 40, OK at 45 & 50, -3 at 55, -2 at 60, -1 at 70.

Turned out the sub's response was fine, but the mic was not.

The Terrasonde mic also read +2dB at 200 and 250, which was as far up as I was testing, but made the subs response look even more anemic, a full 12 dB loss over a decade of frequency!

The mic that came with a DOD RTA (the RTA & mic costing only about $250) that I have had for about ten years was within a few dB of flat in the same range- go figure.

Like you and Ivan say, best to compare your test mics frequently to a known quantity.

Art Welter
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Tom Young

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Re: Measurement Microphones
« Reply #16 on: December 17, 2008, 02:55:44 pm »

"If it is critical I assume that Bruel & Kjar (Parents of DPA I believe) still make exceptional measurement microphones?"

Hmmmm. Perhaps. And this partly depends on your definition of "critical".

Bruel and Kjaer 4007 (and other members of the 4000 family) are all very good and maintain their quality very well. I am not sure how robust they are. I have used a few SIM systems that had damaged 4007's but I don't know what they went through to get trashed like that. When I owned a 4007 I treated it very well because of its cost and my need for certainty. B&K introduced a cheaper model perhaps 2 years ago that is in the $700-800.00 range. I have not used these and don't know how they compare including how robust they may be.

Other measurement mic's used by acousticans and the like are available from ACO Pacific, GRAS and perhasp 1-2 others. I don't know how these compare to B&K's offerings.

I am very confident in my SF101 (enough to use it in *my* critical work) and will be able to tell in a few years if it remains 'good' as long as we would expect from a B&K.

Sorry if this is a bit vague. I guess that a simpler answer could have been that if you show up with a B&K 4007 many folks will take you very seriously.
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Tom Young
Electroacoustic Design Services
Oxford CT
Tel: 203.888.6217
Email: dbspl@earthlink.net
www.dbspl.com

Tom Young

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Re: Measurement Microphones
« Reply #17 on: December 17, 2008, 04:13:00 pm »

Yikes.

Guess I'll wait a few weeks and then put my ATB mic up for sale Wink

Not really surprised, though.

Thanks !
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Tom Young
Electroacoustic Design Services
Oxford CT
Tel: 203.888.6217
Email: dbspl@earthlink.net
www.dbspl.com

Bennett Prescott

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Re: Measurement Microphones
« Reply #18 on: December 17, 2008, 05:59:17 pm »

Ray Rayburn's site for measurement microphones is http://testmic.com/.

I have an ECM-999 from when they were good (he doesn't sell them anymore, due to aforementioned quality control issues) for my "beat it up, I don't care mic".
My "serious measurement" mic is one of his SF-101s, which has been really excellent. I haven't ever tried to measure in a snowstorm with it, but supposedly it'll do that... all I know is the thing is flatter than +/- 1dB for the entire reasonable measurement range (I don't need to measure below 20Hz or above 18kHz).

I see he now offers the SF-111, which is even better for less than twice the money!
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Art Welter

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Re: Measurement Microphones
« Reply #19 on: December 17, 2008, 07:30:35 pm »

Since I only have, and only tested one of these mics, I would not want to say they all are that bad, but I bet they are not particularly consistent unit to unit..
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Re: Measurement Microphones
« Reply #19 on: December 17, 2008, 07:30:35 pm »


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