[bjs]

I'm trying to ascertain what SPL levels will damage the little 6mm capsules that are used in the various measurement mics.

It seems most of these are rated to around 120dB. But I can't find any information on a damage limit.

Presumably there is a point when the diaphragm is physically damaged (either stop working or loose it's calibration due to permanent deformation ). I'm guessing it would be high (>160dB etc) but perhaps not.

I'm also assuming the electronics cannot be damaged by high SPL. Rather, it will just clip.

I note on Linkwitz site, he states the Panasonic WM60 capsule can swing 5Vpp at 141dB. Presumably he didn't damage it to find that out! SL also states that the WM61 capsule outputs a maximum of 5Vpp at 134dB. Overall he didn't seem too fussed about 140dB levels (other than the obvious distortion issues).

Anyone with input on this subject?

 

[tonyvdb]

I suspect that it will depend on the manufacturer of the SPL meter. The Galaxy CM140 can read measurements up to 140db so I highly doubt that 140db would damage it and that is extremely loud.
The radio shack meters may not handle that very well.

 

[dyohn]

I doubt the db SPL required to cause physical damage to the transducer of a measurement microphone could be attained by anything short of a Saturn V rocket launch.

 

[Ricci]

Damage to electronics would be dependant upon the amount of voltage sent into them. It'd take quite a bit to fry even modest components.

I doubt that the mic diaphragm will get damaged by anything short of a sustained 140db level of low freq's. Some drum microphones are rated for 155-160db, obviously that's a different anaimal but... The cheaper measurement mics do start to distort with low freq's at volumes past 110db.

 

[bjs]

The Galaxy CM-140 is a much larger capsule though. I'm specifically wondering about 6mm capsules which are all rated much lower.

But you raise a good question: does capsule size affect damage limits?

As for 140 dB being loud, yes it certainly is for far field measurements but not when doing nearfield driver measurements (which is what I'm currently doing and got me onto this train of thought).

 

[Ricci]

Very high volume close mic LF driver measurements are going to be rough on the mic and it will exhibit high distortion if you are up over 120db, which really isn't even driving the sub very hard at all when the mic is so close to the cone. It may affect the accuracy of the measurements adversely especially any distortions. I'd limit things to under 120db indicated by the mic. (Look for a test that Herb kindly did for me on the ECM8000 capsule). Some of the better Earthworks or AO Pacific mics would probably be fine, but not these.

 

[bjs]

I must be a slow typer...all these responses while I typed only three lines in response to Tonyvdb! lol

As for the general thought that they are hard to damage...I'm not certain. Diaphragms are extremely fine/delicate and I can easily see them being permanently deformed. At least to the point they loose their calibration.

Perhaps someone with direct knowledge/experience will weigh in.

 

[dyohn]

Measurement mics are generally not meant to be used for high SPL readings and yes, the distortion would be through the roof above a certain point. 110 or 120dbSPL seems like a reasonable estimate for that point. But actual physical damage to the diaphragm? I'd be shocked to see that happen at any attainable dbSPL.

As far as taking near-field measurements at 140db, please explain this. If you are trying to hit super high SPL levels then you need to use a proper SPL measurement system such as a Term Lab. Measuring loudspeaker FR or distortion should not be done with greater than 1 watt (or 2.83 volts) input, and I don't know of any system that is 140db/watt-meter efficient.

 

[bjs]

dyohn:

Yes, I'm talking damage not distortion. Separate thread coming up regarding distortion (but I can't keep up with you guys! lol).

As for why the high dB levels. It is easy to hit them during proper indoor nearfield subwoofer measurements. Backing off mic distances include too much of the room for artifact free results.

For example, at 1 watt the distortion of my subwoofer is barely measureable...point oh something...but at 20Hz and only 50% of Xmax it can be 5% or 15% by changing only the box size. One would never know that box size has such effect if they limited themselves to small signal testing such as you suggest.

 

[dyohn]

Yes, I see where you're coming from now. That being said I've measured sub 50-Hz tones @ 148db using my Earthworks mic and then taken small signal FR readings on a tweeter without any apparent loss of resolution. As long as you are only looking for an approximate db SPL level and are not trying to actually mearure FR at high levels (or looking for fractional db accuracy) it will work. Again, I won't go so far as to say I could prove it, but I do not believe you can actually damage a small capcule mic with high SPL that can be attained using any conventional loudspeaker technology. Damage to a large diaphragm ribbion mic, now that's a different thing...

 

[Anechoic]

You can damage mics, but like dyohn indicated, it's going to take an SPL far above what you're likely to encounter (or something like sticking a pin into the diaphragm, dropping it, etc). There is a slight risk of damage a mic if you stick it into an air-tight chamber (like an acoustical calibrator) too quickly, that's about the only scenario that I consider when I worry about damaging a mic through normal usage.

As others have noted, unacceptable distortion may occur at SPLs way below the damage threshold.