Putting THD in the perspective

[Krunok]

I have a NTi MM2215, 154db at 3%.

That microphone was made for measurement of high sound levels, that is why distortion is stated at such high level.

 

[DS23MAN]

IF UMIK-1 would have distortion around 1-3% how is it even possible that is measures 0.07% distortion as it's own distortion would be much higher?

Your graph went missing, but what I remember you lowered the spl to get below 90db at 15cm. Remember mic's start to distort heavy above a certain spl. The cheap electrets start to do that above 95db.

 

[Krunok]

Your graph went missing, but what I remember you lowered the spl to get below 90db at 15cm. Remember mic's start to distort heavy above a certain spl. The cheap electrets start to do that above 95db.

I tested at 85db at LP (4 meters from speaker), and that produces more than 90dB at 15cm.

I also tested with 85db, 90db and 95db at 15cm and got practicaly identical results except for distortion LF peaks caused by cabinet resonance which increased slightly. This proves that UMIK-1 gives consistent measurements.

It is actually microphone like yours, which was designed for high SPL measurements, that may be problematic at lower SPLs.

 

[RayDunzl]

IF UMIK-1 would have distortion around 1-3% how is it even possible that is measures 0.07% distortion as it's own distortion would be much higher?

I would think that distortion measure is at or near its SPL limits, not in the normal use range.

https://www.minidsp.com/images/documents/Product Brief - Umik.pdf

Example:

https://www.invensense.com/wp-content/uploads/2015/02/AN-1112-v1.1.pdf

 

[Rja4000]

IF UMIK-1 would have distortion around 1-3% how is it even possible that is measures 0.07% distortion as it's own distortion would be much higher?

Well, first I guess distortion of the mic is higher at higher SPL.

That microphone was made for measurement of high sound levels, that is why distortion is stated at such high level.

It's rather that this is at high SPL that the distortion is really high.
So most manufacturer just provide the limit for SPL at which THD reaches 1%.
Just as Power amp have their power stated for 1% THD

You may want to read the DPA link I posted above.
Here it is again:
https://www.dpamicrophones.com/mic-university/the-basics-about-distortion-in-mics

 

[Krunok]

I would think that distortion measure is at or near its SPL limits, not in the normal use range.

View attachment 34109

https://www.minidsp.com/images/documents/Product Brief - Umik.pdf

Example:

View attachment 34110

That is what I believe as well. I believe UMIK-1 has much lower distortion at 90dB than this 1% at 133dB.

 

[Rja4000]

Another interesting reading about attempts to measure IMD on microphones
https://www.gearslutz.com/board/gea...41571-microphone-distortion-measurements.html

Note that they use 2 speakers with 2 DACs and 2 amps, to avoid the IMD to be produced by those.

I also found some measurements in Eartworks M50 review on Earthworks website (pdf)
https://earthworksaudio.com/wp-content/uploads/2017/07/EarthworksM50Review_AXJuly2017.pdf

Best performance is THD around 0.17% or -55dB

(Note: I copied those graphs from the freely-available-for-download document.
So I guess that's allowed by copyrights. If not, this should be removed.
This is extracted from an AudioXpress review)

 

[Krunok]

Well, first I guess distortion of the mic is higher at higher SPL.

It's rather that this is at high SPL that the distortion is really high.
So most manufacturer just provide the limit for SPL at which THD reaches 1%.
Just as Power amp have their power stated for 1% THD

That mic is a metal membrane mic specifically made for measurements at high SPLs. Such deivec may have various issues when emasuring at home SPLs (80-90dB), not only with distortion but with linearity as well. They were made for 120-160dB range, and that is where they operate in optimal fashion.

 

[Krunok]

Another interesting reading about attempts to measure IMD on microphones
https://www.gearslutz.com/board/gea...41571-microphone-distortion-measurements.html

Note that they use 2 speakers with 2 DACs and 2 amps, to avoid the IMD to be produced by those.

We already discussed that some time ago in a different thread.

 

[Rja4000]

That mic is a metal membrane mic specifically made for measurements at high SPLs. Such deivec may have various issues when emasuring at home SPLs (80-90dB), not only with distortion but with linearity as well. They were made for 120-160dB range, and that is where they operate in optimal fashion.

Hi
As I understand it, our fellow @SIY is the author of this review.
He may have more input...

 

[Krunok]

Hi
As I understand it, our fellow @SIY is the author of this review.
He may have more input...

He can provide valuable inputs on various things, I'm sure this one is included.

 

[DS23MAN]

That mic is a metal membrane mic specifically made for measurements at high SPLs. Such deivec may have various issues when emasuring at home SPLs (80-90dB), not only with distortion but with linearity as well. They were made for 120-160dB range, and that is where they operate in optimal fashion.

That's not correct, a high spl mic has a higher noise floor. The M2215 has 25db(A) and the M2230 16 db(A).

https://www.nti-audio.com/Portals/0/data/en/Measurement-Microphones-Specifications.pdf

 

[Rja4000]

That mic is a metal membrane mic specifically made for measurements at high SPLs. Such deivec may have various issues when emasuring at home SPLs (80-90dB), not only with distortion but with linearity as well. They were made for 120-160dB range, and that is where they operate in optimal fashion.

May also be a limitation of the loudspeaker used for the measurement.
Same "the chicken and the egg" story (or, as Floyd Toole says "Circle of confusion")

 

[Krunok]

That's not correct, a high spl mic has a higher noise floor. The M2215 has 25db(A) and the M2230 16 db(A).

https://www.nti-audio.com/Portals/0/data/en/Measurement-Microphones-Specifications.pdf

Good. Than you can show us some of your measurements.

 

[Krunok]

May also be a limitation of the loudspeaker used for the measurement.
Same "the chicken and the egg" story (or, as Floyd Toole says "Circle of confusion")

My point was that both, loudspeakers that can produce such high SPL and microphones that can measure it, were not designed for home use and would operate optimally when put to that task. Do you really think a loudspeaker that can produce 154dB is optimal for home listening?

 

[SIY]

Just a couple of observations:

It's not trivial to measure mic distortion at lower SPLs without having a very, very quiet chamber. Generally speaking, even mics rated for high SPL will have low distortion at low SPLs (less mechanical movement of the diaphragm, smaller relative motion of the diaphragm and backplate, lower voltage swing in the preamp), but the noise (ambient and mic self-noise) will complicate quantification.

By and large, I see lowest distortion with mics having metal diaphragms. One notable exception is the DPA 4099, which showed remarkably good distortion performance, but has a polar pattern and frequency response which makes it great for performance use, but lousy for measurement.

 

[Rja4000]

Just a couple of observations:

It's not trivial to measure mic distortion at lower SPLs without having a very, very quiet chamber. Generally speaking, even mics rated for high SPL will have low distortion at low SPLs (less mechanical movement of the diaphragm, smaller relative motion of the diaphragm and backplate, lower voltage swing in the preamp), but the noise (ambient and mic self-noise) will complicate quantification.

By and large, I see lowest distortion with mics having metal diaphragms. One notable exception is the DPA 4099, which showed remarkably good distortion performance, but has a polar pattern and frequency response which makes it great for performance use, but lousy for measurement.

The 4099 and 4060 are using similar diaphragm, as far as I know.
The later being an omni.

(The 4099 and 4088 (headset version) are fantastic microphones !)

 

[DS23MAN]

My point was that both, loudspeakers that can produce such high SPL and microphones that can measure it, were not designed for home use and would operate optimally when put to that task. Do you really think a loudspeaker that can produce 154dB is optimal for home listening?

If a speaker is producing 110db at 1m and you put a mic at 25cm, what will the pressure be at the capsule?

 

[DS23MAN]

Good. Than you can show us some of your measurements.

A Seas W26FX001 with digital MFB and current drive with feedback gain exceding 30db, measured at 25cm. Mic level calibrated for spl at 1 meter.

 

[SIY]

(The 4099 and 4088 (headset version) are fantastic microphones !)

Here's a couple clips I recorded with the 4099.