Distortion in Measurement Microphones - actual measurements

[b_force]

Just look up the pressure difference between about 15 degrees C to something like 30 degrees C or so.

Anything lower is not good for anything else in the house, besides the fact that it's not comfortable to listen at those temps anyway. That also basically counts for temperatures above 30 C

If I look at the chart of the outside pressure here today, the difference was a whopping 0.44% !!!!
With a difference in 10-15 degrees C / Kelvin.

I think I did an entire calculation a long time ago somewhere.

 

[IamJF]

Now I keep on wondering how low the Behringer would go below 95dB ...

Noise kicks in there soon and will mask the THD of the mic. You can just use the calculations I showed here to get the estimated THD values, depending on your measurement signals you get a little more or less noise influence.

But when you are interested in THD ... these electret mics are comming to their limits quickly. It's a narrow band between self noise and mic THD.

 

[tktran303]

Anyone tested an Isemcon EMX-7150?

@vineethkumar01 recently purchased this microphone. It has a self same max SPL of 145 (3%) as the M50, but slightly higher self noise (30dB). Upside is that its a nicer price than the M50. Comes with frequency response compensation file too.

 

[kevinkr]

I own one, but have not used it to date, and some point I will along with the Motu M4 I bought to use with it.

 

[tktran303]

If that's the only thing you're disappointment about? lol

I can make a whole list.
But one of the biggest is only using one single sound pressure level to do these tests.
Which gives us absolute no idea at all how a certain distortion problem develops (and where it's coming from).

The second one is using absolutely totally silly and unusable graph ranges.
Good gull-range mid-woofers that only show distortion from 100Hz and up, subwoofers that only show 50Hz and up etc.

If we want to compare the low end we need to make sure the system response is identical between drivers.
As far as I know, absolutely no-one doing 3rd party measurements has been doing such thing in the last 30 years.

Since we use subwoofers so close to the drivers Fs, I find Klippel LSI saying a lot more than just distortion measurements.

Anything else can be extrapolated from there, especially in combination with those Klippel LSI measurements.

So the question again, why would you want to measure such insane numbers if there is not a single practical reason for it?

I’m not sure if this post was directed towards me, but I don’t have access to a Klippel LSI.
So I need a way of measuring things without it.
Some other readers might find it useful too.

I certainly agree with equalised low end responses. @TMM did exactly that some years ago-
http://feleppa.com.au/speakermeaswoofer.html


Also, sometimes applications come AFTER theory. Both are valuable in their own right, right?

 

[b_force]

I’m not sure if this post was directed towards me, but I don’t have access to a Klippel LSI.
So I need a way of measuring things without it.

I opted for a poor man's Klippel LSI already multiple times.

Which can be done by just looking at the impedance measurements at different and higher voltages.

Thanks btw, I forgot about that website. 👍

I don't really understand what you're trying to say with the last part? Sorry.

 

[IamJF]

@vineethkumar01 recently purchased this microphone. It has a self same max SPL of 145 (3%) as the M50, but slightly higher self noise (30dB). Upside is that its a nicer price than the M50. Comes with frequency response compensation file too.

Why are these mics specified at 3% THD? Earthworks also has already 2% at 140dBSpl (that's probably tolerance, mine is not very sensitive).
Standard for studio mics is 0,5% and for electronics and most other stuff 1%. Find it strange that your REFERENCE is specified with worse THD for maximum SPL.

 

[tktran303]

To be honest, the problem with standards is that everyone has their own standards.
AFAIK, Brüel & Kjær spec their capsules at 3% THD, and peak SPL at 10% THD.

Here's what I've gathered so far study on microphone capsules / phantom powered microphones:
In no particular order...

�

Brand​	Model​	Noise Floor​	Maximum SPL based on THD (%)​
​	​	dB​	Not listed​	10%​	3%​	2%​	1%​	0.5%​	0.3%​	0.1%​	0.03%​
Sonarworks​	SoundID Reference(2024)*​	​	124​	​	​	​	​	​	​	​	​
Merry Electronics​	MMA209-003*​	​	​	133​	​	130​	128​	​	120​	110​	94​
Sonarworks​	Xref20/SoundID​	24​	128​	​	​	​	​	​	​	​	​
miniDSP​	Umik-1​	​	​	​	​	​	133​	​	​	​	​
miniDSP​	Umik-2​	20​	125​	​	​	​	​	​	​	​	​
Line Audio​	Omni1​	18​	​	​	​	​	​	133​	​	​	​
iSEMcon​	EMX-7150​	30​	​	​	144​	​	136​	130​	​	​	​
​	CPX-1212​	​	​	​	155​	​	​	​	​	​	​
micW​	M215​	18​	​	​	​	​	135​	​	​	​	​
Earthworks(2022)​	M23​	20​	​	​	​	​	​	​	​	​	​
Earthworks​	M23R​	​	140​	​	​	​	​	​	​	​	​
Earthworks​	M30​	20​	140​	​	​	​	​	​	​	​	​
Earthworks​	M50​	20​	140​	​	​	​	​	​	​	​	​
Audix​	TM1/Plus​	28​	140​	​	​	​	130​	​	​	​	​
ACO Pacific​	7502PH​	18​	​	​	​	​	150​	​	​	​	​
PCB Piezotronics​	376A31​	40​	​	​	165​	​	156​	​	​	​	​
​	376A33​	22​	​	​	​	​	150​	​	​	​	​
​	376A32​	15​	​	​	​	​	137​	​	​	​	​
Dayton Audio​	EMM-6	24​	​	​	​	​	127​	​	​	​
Behringer​	ECM8000​	​	NL​	​	​	​	​	​	​	​	​
NTI Audio​	M2010​	24​	​	​	142​	​	​	​	​	​	​
​	M2215​	25​	​	​	153​	​	​	​	​	​	​

 

[b_force]

More information on Earthworks;
https://audioxpress.com/article/fresh-from-the-bench-earthworks-m23r-measurement-microphone

Unfortunately (as usual), the graph only goes up to 130dB.
So the rest we have to guess.

 

[b_force]

Btw, if we take 94dB reference at 1 meter.

The majority of these microphones should be able to measure at around 5cm distance from the source.
Which will be about 120dB or 114dB at 10cm.

@tktran303 I tink it's good to add that the majority (if not all) of those values is at 1kHz
Edit: maybe also handy to add a global price as well

 

[uriy-ch]

The majority of these microphones should be able to measure at around 5cm distance from the source.
Which will be about 120dB or 114dB at 10cm.

I apologize for being off topic. But I’m very interested - what formula can be used to calculate the increase in SPL with decreasing distance for measuring with a microphone less than 1m? Somehow I tried to find this formula, but could not.

 

[ernperkins]

Here' my favorite calculator (with formulas listed): https://sengpielaudio.com/calculator-distance.htm

 

[markbakk]

I apologize for being off topic. But I’m very interested - what formula can be used to calculate the increase in SPL with decreasing distance for measuring with a microphone less than 1m? Somehow I tried to find this formula, but could not.

There is none. Not a simple equation without regarding the cone dimensions anyway. Going under 1m means leaving point source approach, so 6dB doubling when halving the distance isn’t valid anymore. But one always can integrate the contribution from all imaginary sound sources forming a membrane of a loudspeaker driver.

 

[1audio]

Power supply voltage becomes a limitation at high levels. The B&K mikes need a 130v supply to meet the max output specs. I suspect electret mikes with internal JFets like the Primos will be more limited.
The 3% distortion limit goes back to the 1950s. Pistonphones can have a low as .3% thd at 124 dB.
Sound increasing as you get closer becomes nonlinear if the source is large so the double/halve spl with double/ halving distance should be used with caution.

 

[uriy-ch]

There is none. Not a simple equation without regarding the cone dimensions anyway. Going under 1m means leaving point source approach, so 6dB doubling when halving the distance isn’t valid anymore. But one always can integrate the contribution from all imaginary sound sources forming a membrane of a loudspeaker driver.

Agree. The problems of classical calculations begin when the sound source can no longer be represented as a point source, I thought there was a formula that takes into account the size of the diffuser, but I couldn’t find it....

I came across this problem when I wanted to measure the integrated noise of the amplifier using a microphone and speaker, and in order to get rid of the room noise, I placed the microphone near the speaker cone, and then I realized that recalculating the sensitivity of the speaker to the close distance of the microphone is not a trivial task . Therefore, I became interested in how people know what SPL will be created by the speaker in the near field....

 

[b_force]

Ever heard of just ballpark figures?

Btw, technically it's not true that there no equation.
The equation only works well for a perfect monopole in a space without any reflections.

 

[uriy-ch]

Ever heard of just ballpark figures?

Got it, you indicated the approximate range of the expected increase in SPL.

Btw, technically it's not true that there no equation.

Agree. There is an equation somewhere, but I couldn’t find this equation on the Internet. I got around this problem empirically, i.e. measured SPL in the near field at 1W and at a distance of 1m. Now the formula is no longer important to me, I just remain interested.

 

[b_force]

Here' my favorite calculator (with formulas listed): https://sengpielaudio.com/calculator-distance.htm

@uriy-ch formula is right on that page?

Or any other standard book about acoustics. So probably also on internet somewhere.

 

[bwaslo]

Power supply voltage becomes a limitation at high levels. The B&K mikes need a 130v supply to meet the max output specs. I suspect electret mikes with internal JFets like the Primos will be more limited.

Limited like in 2-wire configuration when they operate in common source configuration, with under a volt from gate-source cutoff?
Though in common drain config, bootstrapped or cascoded, the voltage swing can be dramatically boosted until the limit becomes distortion from the diaphragm.

 

[uriy-ch]

@uriy-ch formula is right on that page?

As I understand it, the formulas on this page are given for a point source of sound.