(Recording) SPL operating range for mobile phone microphones


#1

Sorry in advance, this isn’t a JUCE question. However, it’s a question to which the JUCE community is more likely than anyone else to have the answer.

Does anyone have any idea what the maximum SPL a modern mobile device might be able to record before bad things happen?

And what like those bad things be? Distortion? Clipping? Both?

If 1000 people record a track at a music festival, what are their recordings likely to look like? I think these things reach 135dB, So I’m guessing its very likely an old-ish Android device near the speakers will clap out.


#2

Well, I don’t know any scientific measurements but I’ve recorded videos at gun ranges (~120-130 dB transients) with my iPhone (not exactly the low end Android you’re concerned about) and the audio turns out crystal clear. Looking at most concert videos on YouTube nowadays will show you the audio generally turns out pretty well.

Unfortunately, SPL limits aren’t something your average user is even aware of or cares about, so I don’t think any phone manufacturer gives them out. I would figure out which phone models you want to target are and see if you can go on iFixit or a similar site and find out what microphone components they use, from which you should be able to find SPL limits from manufacturer white papers.

That said, I’m pretty positive all phone microphones are a straightforward dynamic design, which are known for holding up well even at high SPLs…


#3

Hope I‘m not getting you wrong because of language based irritations, but if I understood you right you meant that phone microphones are dynamic capsules? That’s definitely not true, as dynamic microphones have a lot bigger size compared to condenser microphones. Most phone microphones should be mems condenser microphones. Those might be all-in-one-chips with the microphone itself and the AD converter built in, in which case you might find some dataseets which might or might not contain those specifications. However if the manufacturer decided to chose a separate analog microphone combined with some preamp and an AD converter, the microphone itself wouldn’t be the only limiting factor, there might be analog clipping in the preamp stage or digital clipping at the ADC stage with the microphone itself working in a totally specified range.
So I wouldn’t go the theoretical route but take some cheap phones and measure them. As your description doesn’t sound like an application with high end demands, maybe this will help you getting a rough idea of what you should expect.

By the way:

Isn’t Clipping some kind of ultra hard distortion? So what do you think of when you write „both“?


#4

IIRC most phones have AGC built into the analog front end or some kind of dynamics processing to prevent clipping the ADC. It’s not perfect.

Cell phones use MEMS capsules, and those are spec’d to handle around 120-130 dB SPL. But keep in mind that’s below what will kill most of them and the measurement can vary.

The actual failure mode of a MEMS capsule is pretty varied across manufacturers. You have to read the documentation and/or break a few capsules to figure out what will happen. It’s not like condenser mics where the diaphragm will tear, or a dynamic mic where the voice coil assembly will be torn from the surround. In both those cases the mic will usually continue to make a weak, distorted sound. But much like your ear, most capsules won’t be destroyed when you pass their rating for short impulses like say a gunshot. It’s sustained pressure changes past normal operation that weakens and breaks things.

And no concert is reaching 135dB SPL. That’s “rip your eardrums” loud. They’re going to be chilling around 115-120 dB SPL, depending on how far you are from the speakers of course.


#5

I’m probably totally wrong, good points on all accounts.