Two UMIK mics with very different low-dB spectrums. Have you seen this behavior?

[skid00]

I am aware that Mini-DSP has modified newer UMIK-1 mics, to 'alleviate' the USB noise spikes (and that this isn't a problem when analyzing a speaker).

I -didn't- know this until I purchased a newer mic... and measured these two very different noise levels. I have ordered an SPL meter, to verify that the real-time dB measurements are within reasonable levels, and I'll run a frequency sweep to see what differences show up under that situation.

The under-100 Hz noise is traffic, but does anyone know where that 8 kHz rise comes from? I am using the latest calibration files, specific to each mic (and the new mic was purchased directly from Mini-DSP (with *incredibly* fast delivery-thank you Mini-DSP!) and has a unique calibration file. There was no equipment running in the house, and the rise shows up in all the rooms.

 

[DanDan]

Very interesting. As a Consultant I frequently recommend or load UMIKs to clients. Several have tested exactly 1.8dB different to my B&K Sound Level Meter. One can write a correction into the Cal file. First line is sensitivity, just add or subtract your correction. The UMIK used to have a DIP switch inside to alter gain in 6dB increments. Is that what we see here?

 

[skid00]

I don't see an external DIP switch, and am leery of disassembly...

I'll consider cal file corrections when I get my dB meter.

Thanks for your input!

 

[DanDan]

You are welcome. From memory, REW reports the DIP switch setting..... Opening up requires bending a paper clip into a U shape. That new mic looks louder and quieter so all good then.

 

[MediumRare]

How old is the older one? The 1k + 8 levels of harmonics would drive me nuts, even if it didn’t matter for room correction. Would UMIK exchange it for you?

 

[Sam6string]

Dust? Aging? Temporal distortions?

 

[BenToronto]

I can't think of any reason why I would care about the noise level in the mic or profile in any measurement I can recall doing, just plain fooling around aside. If the absolute loudness calibration is OK, can anybody tell us why it matters?

While there seems to be widespread preference for the USB version, I find the traditional mic with phantom power from a second-hand mic mixer (a million of 'em around) give me flexibility, control, and more LEDs to keep an eye on.

I use REW straight electrically (not acoustically) sometimes and rarely bother (or remember) to switch in the mic individual calibration. The deviations are tiny. And very very tiny compared to the whopping big variations from moving the mic an inch.

B.

 

[skid00]

The older mic is ~3 years old. I don't believe it is malfunctioning.

I'm *still* waiting for a separate dB meter (a BAFX ‎BAFX3608 ). It should be arriving in a few hours...

Once I calibrate each UMIK's dB level, I'll re-run frequency sweeps with each mic. I expect them to be very similar. I'll post when I have those measurements.

I also don't think the self-noise is a problem, although it may explain why my REW graph's show harmonic distortion below 'ambient noise' so much!

 

[TimoJ]

Those 1KHz, 2KHz etc. peaks seem to be a hardware problem of some older UMIK-1 mics. I managed to fix it, posted about it to MiniDSP forums but can't yet post links here. So I'll paste the message here. And yes, the mic still works as good as before. Verified with another UMIK-1 and UMIK-2.

I think it's a grounding problem of the microphone's top cap. Looks like it's a manufacturing error.

Try this: hold the mic inside your hand and put your thumb on the top piece that houses the microphone capsule, with my UMIK-1 the 1KHz tone completely disappears.

And then I "fixed" the problem by putting a sharp knife into the top cap/main body seam and rolled the mic so that that the top cap moved little (less than 1mm) upwards. I think this caused top cap-main body grounding to make better contact. No more 1KHz tones after that. I put a piece of kapton tape over the seam.

 

[skid00]

Wow, TimoJ, thanks a bunch! I'll try this.