Is my new microphone defective?

[dkulmacz]

I've been playing around with REW software using equipment I had on hand, including a RØDE NT1 large diaphragm condenser mic. The mic isn't in any way calibrated, but the software seemed to produce decent results; at least they seemed to match what my ears were hearing. The NT1 was hooked to a Focusrite Scarlett 18i8 interface which supplies it with phantom power. My system consists of a pair of JBL LSR305s and a JBL LSR310s subwoofer, in a 10' x 12' room.

So I finally decided to spring for a calibrated microphone (at an affordable price), and purchased a Dayton Audio EMM-6 condenser mic. I used this to replace the NT1 in my measurement system. After swapping the microphone and recalibrating the inputs and output levels (EMM-6 mic required much more gain than the NT1), I took my first measurement and got drastically different results, particularly in the bass region. After confirming that the subwoofer was actually on and working, the measurements show bass SPL of around 20 dB lower than before; well below the level of the midrange and treble regions.

For a quick check, I disconnected the EMM-6 and re-connected the NT1 . . . after adjusting the input level lower, I took a quick sweep while holding the NT1 in my hand, and it reproduced my old measurements; bass was up about 20 dB, and consistent in level with the rest of the spectrum.

Note . . . by my ear the bass isn't lacking at all.

So is it possible that my new EMM-6 microphone is defective? Or am I doing something wrong with it? Both mics use phantom power so it's not a failure to enable that feature. Is it possible that the EMM-6 is correct, and the NT1 is vastly overdoing the bass frequencies?

Note I'm also using a miniDSP 2x4 HD to act as a crossover, but I've had it disabled for most of this testing; it was also present when I used the RØDE mic, so I don't think it's the issue. Also . . . when I measured with the subwoofer off (monitors only), I also measured poor bass response in comparison to earlier measurements (with the NT1) and just the monitors.

Is there any way I can test the microphone and see whether it's producing an accurate response?

Thanks all!!

 

[A J Womack]

Hi, the Rode NT1 is a pressure gradient mic not suited to acoustic messurement as it does not respond equally to sounds from all directions. The EMM6 is a a pressure ooerated mic which is what you want for acoustic testing, in fact theore are ragher s lot of them around these days, many I suspect from one or two factories in China with merely cosmetic differences between them and will very likely use the same capsule, Primo or Panasonic. I have used Behringer, t-bone (Thomann), Beyer and Earthworks test mics and at low frequencies they all pretty much performed the same way.
I have done acoustic tests on around 100 rooms measuring for bass response, and it takes a while before you can read the results with any accuracy, and being bass it also matters where the mic is positioned, one run only will rarely give any meaningful answers. So do at least 7 tests in one position, discount any freakish traces and the work out the average. Move the mic elsewhere and repeat. You will the get an idea of how the bottom end is performing in your room.
Alternatively put your room dimensions into a reliable room mode calculator e.g. REW and you will find out the lowest freqency your room will produce, around 40 to 45 Hz is a quick guess. If there is a cluster of modes around any specific freqency three or more over a range of plus or minus 5Hz or so you might need treatment.

Speaker systems can sound quite diffent from one room to another, do not chase very bass frequency response if your room is not big enough to reproduce it.
One room I had to test in a music college, was used for teaching double bass, the problem they expected to solve was not being able to hear the fundametals of all notes! They were there you just had to be two rooms away!
But the best judge is your ears, if it sounds right, it is right.
I hope this ramble has been helpful.
For more information on bass trapping look up Karl Brown on YouTube.