Need help with microphone; should I return a new purchase?

dkulmacz

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Sorry for spamming multiple forums, but I noticed the "Calibration Equipment" forum had much less activity and I'm hoping for a quick answer if possible . . .

I have been using REW software to measure my room, using a RODE NT1 condenser microphone. Results looked as expected. Last week I bought a Dayton Audio EMM-6 calibrated measurement mic, which I've inserted into the system in lieu of the NT1. After recalibrating my levels and taking new measurements (NOTE: EMM-6 required a lot more gain), I've found the results from the EMM-6 to be completely different from the NT1; particularly, the bass response is about 20 dB lower across the range. The midrange and upper frequencies seem to be roughly in line with the old measurements. I'm no expert on distortion, but it appears that the EMM-6 also has much more distortion, across the range.

As a check, I quickly hooked up my NT1 again, reset the level, and took a quick sweep while simply holding the mic in place. It appears that the NT1 reproduces the original curve, or at least is a lot closer than what I get from the EMM-6.

Is it possible that my new EMM-6 is defective and producing a low, noisy, bass-lite signal and needs to be exchanged? Or is it more likely that my RODE NT1 is producing a bass-heavy signal? Or . . . am I using the EMM-6 wrong? Note that both mics use phantom power, and it was enabled for both.

My plans today are to 1) use the EMM-6 to record some actual audio and listen to the result . . . I'm assuming it should be a relatively normal recording, and should not sound tinny or noisy; 2) re-take data measurements a bit more accurately with both the EMM-6 and the NT1, and then also with a Shure SM57 I have sitting around for comparison; and 3) do a "Real Time Analysis" using stepped sine waves with all the mics, for comparison.

I purchased the EMM-6 last week and if it's defective I need to start the return or exchange process soon, so I'm hoping for any advice anyone here might have. Thanks!!!
 

dkulmacz

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Yes, I did. No calibration file available for the NT1.

Here is a graph showing SPL from the two mics that I took today . . . mics are both set up on different stands, right next to each other, at the listening position, and plugged into different inputs on my interface. I initially set both mics to -18 dBFS using "Main speaker test signal", but had to turn the gain down on the EMM-6 during testing because it overloaded in the upper frequencies. It's closer to -21 dBFS now.



Here are two plots showing SPL and Phase, along with the mic cal file. Note all these files have 1/6 Smoothing




I just can't believe that there's not something wrong with the EMM-6 mic . . . looks terrible.
 

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dkulmacz

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OK, here are two graphs of the distortion for both mics . . . the EMM-6 looks pretty bad. I also listened to both mics via headphones while taking data; the big difference is that the EMM-6 is NOISY. It has a noise floor very, very high, while the NT1 is virtually silent before the signal starts. I think I need to return this mic . . .

31446
31447
 

John Mulcahy

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Pretty odd response from the EMM-6. Looks as if it may not be getting phantom power, but you said phantom was enabled for it.
 

dkulmacz

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Pretty odd response from the EMM-6. Looks as if it may not be getting phantom power, but you said phantom was enabled for it.
Yes, absolutely. I just switched the power off on the EMM-6 and it went silent. Power back on; noise back up. I also switched the cables between the mics, problem stayed with the EMM-6.
 

dkulmacz

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Well, after listening to the high level of noise from the mic, I've initiated a return. Hopefully I can find another one at a similar price . . .

Unless anyone has a suggestion for a better alternative in this price range (I paid $54 for the EMM-6 new).
 

dkulmacz

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Pretty odd response from the EMM-6. Looks as if it may not be getting phantom power, but you said phantom was enabled for it.
OK, so I returned the EMM-6 and purchased another one . . . . and the new one looks nearly the same as the old one. Same shape curve, within the limits of positioning. As a check, I took data one more time with a Shure SM57 that I had available, and it looks much closer to the RODE results than to the EMM-6. I also routed the EMM-6 through my mixer instead of direct into the interface, to check for issues with the mic preamp or phantom power . . . results were identical.

Two mics couldn't both be bad, and I can't believe that the difference in the two types of mic would make this huge of a difference in the response. What the heck am I doing wrong?

EDIT: The new mic has a different serial number from the old and the calibration file looks different, so I'm assuming I didn't get the same mic back that I returned . . .
 

John Mulcahy

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The SM57 probably isn't the best comparison, being cardioid and not the most even response.

31917


Although the NT1 is also cardioid it has a very flat response. The EMM-6 result is so far from what would be expected it does seem something must be wrong in the overall setup. Does it look any better if you make a nearfield measurement close to the speaker?
 

dkulmacz

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I figured the SM57 wasn't the best, but I wanted to see if it was closer to the NT1 or to the EMM-6, and it was much closer to the NT1.

My plan today was in fact to take some nearfield samples from both the monitors and the subwoofer, using all three mics for comparison. I'll post results when I have them.

Appreciate your reply!
 

dkulmacz

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I re-took data with the SM57 and EMM-6 at the listening position, and also recorded responses of both mics in Ableton. As before, listening to the signal was the key... the EMM-6 is so terribly noisy that I can't even pic out any of the frequency sweep signal until about halfway through the audio file. This mic has *got* to be defective, or else I'm breaking them somehow.

Here are some spectrograms showing the original REW data signal, the recording made by the SM57, and the recording made by the EMM-6. You can barely see the signal on the last one...

I don't think I need to mess with any near field measurements. I was expecting the frequency response to be different; I wasn't expecting to see (and hear) noise at this level. It's no wonder REW had trouble picking out any data.

31995

31996

31997
 

EarlK

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dk,

Send your mic back and get a full refund ( I'm assuming that you're dealing with Parts Express ).

Don't get another replacement from them unless you're convinced it's brand new ( and not from their " parts returns" bin ).

I'll also suggest that it's worth waiting to buy a properly calibrated EMM-6 from CSL ( Cross Spectrum Labs ) . CSL won't ship a defective mic.

:)
 

dkulmacz

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Send your mic back and get a full refund ( I'm assuming that you're dealing with Parts Express ).

Don't get another replacement from them unless you're convinced it's brand new ( and not from their " parts returns" bin ).
Funny, I don't want to be a conspiracy theorist, but... this is my second mic; I bought the first from P.E. via eBay. I was noisy just like this one, so I returned it. Immediately after shipping it back, I bought a second from the P.E. website. The site, however, was out of stock, and I was told it would be June until delivery. A few days later, I get my notification from eBay that my return has been accepted and refund processed... then within a week I have another mic at my door from P.E. Which -- while it has a different serial number taped on it -- behaves just like the first one. And the P.E. website still shows "out of stock" for the mics.

Do you have info on P.E.? I'm in contact with a couple engineers at Dayton Audio and I've sent them my data... hopefully they'll help me out.
 

EarlK

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Do you have info on P.E.? I'm in contact with a couple engineers at Dayton Audio and I've sent them my data... hopefully they'll help me out.
I have no inside info about what P.E. are sending you ( or how they are currently dealing with returned merchandise ).

I'd just call this my opinion or "informed conjecture" .

I suppose ( as long as your patience holds out and you're not paying for freight ) you can simply allow them to send you mics until you/they find one that doesn't have an issue ( I'm confident that there's at least one mic there that was only sent back due to " Operator Error" ) .

:)
 

dkulmacz

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as long as your patience holds out and you're not paying for freight
Well, so far my patience is holding and freight has been free. So I'll probably go at least one more round. I'm hoping the folks at Dayton Audio will come through for me.
 

dkulmacz

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Well, after some back-and-forth with the engineers at Dayton Audio, we've confirmed that the mic(s) I had been using were defective, so they sent me a new one (after re-testing it to insure it was working properly).

This one I listened to first, and it sounded fine. No discernible noise, and plenty clear and sensitive. After a quick calibration, my initial REW data showed great results; night and day versus the previous EMM-6 mics, and much more like the RODE and Shure mics I had been comparing them to. I'm now looking forward to doing some serious data collection and interpretation with good equipment.

I'm currently building up a 'cloud' ceiling absorber for my studio, a 39" by 47" panel of 3 1/2" thick rock wool, with a thin wood frame and covered in (white) felt. I plan on hanging it an inch or two below the ceiling so it catches first reflections from my monitors. I'm also making a few corner 'bolsters' made from rock wool... basically two 36" stacks of rock wool right triangles (15" on the short side), in a felt covering. I plan to use them to fill up a couple of available corners in the room (I already have two floor-to-ceiling bass traps installed up front, made from the same method, only bigger [18" on the side and 7 1/2' long] and in bedsheet covers, not felt).

Thanks to everybody who helped with ideas on what might be going on here...
 
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