Inexpensive Measurement mic

Andrew Broughton

Andrew Broughton

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Feb 2, 2011
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Lots of people said that the Behringer works fine as a measurement mic. I bought 4 of them, figuring one might be in the ballpark. None of them were the same as each other and none of them were close to the 4007 I was using as a reference, so I returned them.

Is there a reasonably-priced alternative, perhaps in the <$500 range?
 
Re: Inexpensive Measurement mic

There are several out there that will work. I have one earthworks m30 that is over the price range and it was used all the time until Smaart 7 came on the scene. Knowing that I couldn't afford a large selection of M30's I decided to somewhat put it away for the near field analysis of speaker systems. I ended up going to a store near by and they let me open up a few of the RTA420 mics, you might know them as the mic that comes with the DriveRack. I did a mic compare of three RTA420 to see how they compared to the M30 and how they compared to themselves. There was a slight hump in the 10k area that the M30 didn't have, but they were all generally close in their frequency and phase response. It should be noted that the 420 is pin 3 hot so the phase was out- no a big deal as long as you know that it is going into a tuning. You can buy these mics for less than $80 a piece and they are mics that you don't have to worry about getting damaged, lost or stolen like you would a more expensive mic.

I also did a test against a Behringer mic and it compared well to the M30 in it's responses.

When it comes down to it and you are measuring a speaker system in the field these small inconsistencies are going to be a huge difference if we are talking about a dB or so at some given frequency. You can move the mic around the free field and create that effect based on comb filtering and patterns. It's my belief that once you get into the rear of the room that our coherence is going to be so polluted that we have to really look for the big issues, i.e. things that are greater than your single dB inconsistency.

I still carry the M30 in the measurement rig, but it doesn't come out that much since I know how these other mics compare.

Check out http://www.tigeraudioinc.com/sales.html for the RTA420 or http://www.rationalacoustics.com/store/microphones.html for a few more...
 
Re: Inexpensive Measurement mic

Andrew,

You compared a $100 mic to a $2,000 mic and found they differed? :D The only good way to do that would be to buy 8, measure them all, and return the 4 that are furthest apart. Regardless, in my experience cheap mics are going to be off by 2-3dB at 16kHz. Just know in which direction. You want a real flat mic, you need to buy a real mic. What is your standard for "close"?

The cheap mic I use is no longer made.
While I love Earthworks, I don't use any of their mics for measurement because I avoid plastic diaphragms... my mic needs to be flat today, but also tomorrow.
The Rational Acoustics Store has a wide selection of excellent mics at reasonable prices, the mics available from them were chosen for a reason. I am considering a pair of the Audix TM1 myself.
If you want a great mic at half the cost of your 4007 check out Ray Rayburn's stuff. Very pro mic for a reasonable price.
 
Re: Inexpensive Measurement mic

Hi,

the guy, who introduced me to Systune, carried four Beyerdynamic MM1 and told me, these are close enough for system tuning.
MM1 are 1/4 inch, so you would need an adapter for off-the-shelf calibrators,which afaik is not included.
I never used these,but I trust this guy

As Bennet said, the main deviation of measurement microphones will occure in the HF region and I always found it better to judge the amount of high shelve, when needed, by ear

Uwe
 
Re: Inexpensive Measurement mic

Well, $80, but still crazy cheap.

The great thing about a cheap mic is that you can buy several and use them with a multi-channel measurement rig to hunt down LF and MF problems.

One should also have a fairly decent mic to use for one channel at a time measurements, but I think the Audix will probably fill that role.

My little secret is the same as Uwe's... I do 90% of my system work with a $100 microphone and adjust the HF by ear... my measurements at frequencies above 6kHz or so only need to be accurate relative to each other. I will definitely be setting levels up there by ear.
 
Re: Inexpensive Measurement mic

Find someone that has one of the microphones made of gold and then compare what you buy to it at some point. Microphones that don't come with a serial numbered frequency response chart are a lot like the human ear. We all hear it a little a different. If you know how your mics are responding to the same stimulus you can get away with a lot. I know that I like the results I get with the M30 and I know that they RTA420 read hot in the upper 10-12kHz area so if I'm not careful I might pull something out that I don't want to. If it's a job that requires documentation (screen shots) having a calibrated mic with a copy of it's frequency response is great and fool the heck out of the client because it looks so fancy. No really, it's a great item to put in for the next guy so he or she can help figure out why you made some of the decisions that you made.

You'll get quality results with the Audix.
 
Re: Inexpensive Measurement mic

i have a first gen superlux ecm 999 that i use for a lot of stuff,,i have 2 superlux ecm 888? i think they call them now,,which are a small condensor format and battery powered, and i have a audix tr40.
i have compared them all against eachother, and found very little difference between the 999 and the tr 40,,about 2db @160. the 888's are a little off to eachother and the other 2 between 6k to out,,and patchy below 80ish hz.
the 999 and the tr40 physically look exactly the same,,as well as the behringer and dbx budget models. ill leave u to ponder that.
i know the 999's have changed response averages for all runs after the first gen series, (and most reports of them i have heard arent so flattering as the first gen),about the same time as the dbx and beh became available.
 
Re: Inexpensive Measurement mic

Brandon G Romanowski said:
Are the RTA 420, the DBX RTA-M , and the APEX 220 all the same mic ?
Click to expand...

Bingo!

Here's my short bang for the buck list of reference mics in order of quality.

Apex 220 - $60 or so
Beyer MM1 - $199 or so. Comparable to TM1 in my book. Drill out a rubber cork for use with a calibrator.
Josephson C550H - $445. preshrunk "polyester diaphragm, metalized with a rugged nickel-chromium alloy"
DPA 4090 - $620. Nickel Foil diaphragm
SF101a - $920. Titanium diaphragm.

The MicW N241 ($855, "all metal" diaphragm) has caught my eye as well, but I don't know much about it.

In my opinion, the law of diminishing returns operates pretty heavily above the SF101a level for 99% of pro audio work.

I was on quite the reference mic kick a while back. If there's interest I'll post the links I found most helpful, which, incidently include more of my commentary and findings.

Grant
 
Re: Inexpensive Measurement mic

I have six RTA-420's, along with my trusty Earthworks M30. Two of the RTA 420's compare rather favourably with the M30, the other 420's have about 2-3 dB of variance between them primarily in the frequency range above 8K, but otherwise they are for the most part flat in the frequency range of interest for most sound reinforcement system optimization. If you're doing high end studio monitors, well that's another story...

If you're using Smaart 7, then I highly recommend any mic purchases be made *with* a calibration file for an upcoming new "feature." Oooops, did I say that??? ;) The set of four Audix TM-1's with a usb key of data is a rather good value.
 
Re: Inexpensive Measurement mic

One thing to note, particularly with the RTA-420 and similar (Apex, DBX, etc) cheapie test mic...if you see a HF bump in the microphone's response that is troubling you, try angling the mic at 90 degrees from the source (eg. pointing straight up). You may find that using the mic in this orientation gives you a "flatter" response in the very high frequencies! This leads me to believe that this particular test mic is more appropriate for 90 degree off axis pickup.
 
Re: Inexpensive Measurement mic

Arthur Skudra said:
If you're using Smaart 7, then I highly recommend any mic purchases be made *with* a calibration file for an upcoming new "feature." Oooops, did I say that??? ;) .
Click to expand...
Cool, about time someone will incorporate what Hall Engineering was doing in 1981 with their SLM-201.
Thirty years later, still miss their test system.

Of course, the accuracy of the calibration file comes into play, do we trust a manufacturer of a cheap microphone to have been tested with a perfectly calibrated system by someone who makes no mistakes in the process?
 
Re: Inexpensive Measurement mic

Art Welter said:
Cool, about time someone will incorporate what Hall Engineering was doing in 1981 with their SLM-201.
Thirty years later, still miss their test system.

Of course, the accuracy of the calibration file comes into play, do we trust a manufacturer of a cheap microphone to have been tested with a perfectly calibrated system by someone who makes no mistakes in the process?
Click to expand...

Anyone buying a cheap mic expecting it to do what an expensive one can is probably compromising gear in other places you don't want to know about. Any old uncalibrated mic will be fine for phase alignments (which are relative), and anyone doing nearfield box tuning is probably already using a premium calibrated mic.

Not to say that a whole pile of cheap calibrated mics wouldn't be useful in some situations, like looking at a room from many points simultaneously. In any case, comparing multiple 'calibrated' mics against each other is fairly easy and any miscalibrations would be obvious.

On another note, I'm enjoying my pair of Audix TM1s quite a bit.
 
Re: Inexpensive Measurement mic

Silas Pradetto said:
Anyone buying a cheap mic expecting it to do what an expensive one can is probably compromising gear in other places you don't want to know about. Any old uncalibrated mic will be fine for phase alignments (which are relative), and anyone doing nearfield box tuning is probably already using a premium calibrated mic.
Click to expand...
Hey Silas,

What the fuck are you talking about? Phase is as relative as amplitude, by your definition. The calibration of the mic is strictly for SPL level measurement. How flat it is (on and off axis), and how stable it is, depends on the quality and size of the capsule. It doesn't matter if you're in the near field or the far field.

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Re: Inexpensive Measurement mic

LOL! Bennett, I know, sometimes I'm terrible at explaining myself. :blush:

I was trying to say that many of the things a reference mic is used for in the field are relative, like phase alignments, or comparison of off-axis sound to the on-axis sound. I'm also implying that an absolutely-calibrated reference mic isn't nearly as critical at a gig versus in a lab where someone is developing DSP tunings for a new speaker model.

And my line about buying cheap and expecting premium performance is self explanatory, I hope.

Maybe that made sense. But probably not; I need to go to sleep. I'm going to wake up tomorrow and punch myself when I read this thread, aren't I...
 
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