rogs

Measuring max SPL
« on: July 12, 2020, 07:51:03 AM »
I've built several DIY mics over the last few years, and have always found it relatively straightforward to get an idea on most performance parameters, by comparing the mic against a commercial device with a published  spec.
But to date, I've not been able to work out how to measure the maximum SPL level a mic can sensible receive, before it distorts unacceptably.
I'm sure there's probably a simple way to do it - I  just can't see it! ....

Any ideas on how to measure max SPL of a DIY capsule /circuit combination, without having access to a 'pro' test set up?
www.amx.jp137.com - A DIY RF condenser mic project


Re: Measuring max SPL
« Reply #1 on: July 12, 2020, 11:01:34 AM »
Just an idea. I'd buy (loan) a calibrated A weighted SPL meter, put both mic under test and the meter in front of a powerful PA speaker.

Plug the mic into a PC with REW software and measure THD at different SPL levels read by the meter.

You can actually calibrate your REW setup for accurate SPL readings using the SPL meter for the first time, and never use that meter again. Once you do the calibration, REW should also give you accurate SPL readings. 

You get THD readings through entire frequency range.

I haven't tried this, but i see no reason why it wouldn't work. I would also do it outdoors if possible, to avoid reflections.

Someone somewhere mentioned once physical distortion a capsule produces which can occur at lower SPL levels than circuit THD limits, and impact sound considerably. This might occur at specific frequency, might be a resonant thing as well. Never tested that, but i can see where it comes from, might be worth exploring.     
« Last Edit: July 12, 2020, 11:08:05 AM by kingkorg »

rogs

Re: Measuring max SPL
« Reply #2 on: July 12, 2020, 04:21:26 PM »
Thanks for your reply -- I shall endeavour to locate an SPL meter to  allow me to set a reference point. Excellent suggestion.
(I'm hoping my brother still has his -  that would be the cheapest option!  :-)  )

Sometimes the capsule specs include a max SPL level - although I think some of the 'Chinese' capsule specs  might just be marketing figures plucked out of the air...... Actual testing should prove interesting.

One aspect that sometimes gets discussed is the amount that DC bias can affect both max SPL and capsule distortion figures....
So, although a higher DC bias can improve sensitivity, it may also limit the max SPL --- or so I'm led to believe?

It will be interesting to see whether the low RF AC bias I apply to the capsules in my RF mics allows for  higher maximum SPL levels....

First - I need to locate an SPL meter....
www.amx.jp137.com - A DIY RF condenser mic project


 

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