Putting THD in the perspective

[JohnYang1997]

Some pages for reference

https://clarityfidelity.blogspot.com/2016/05/audeze-lcd-2-fazor-over-ear-headphones.html

https://m.blog.naver.com/PostView.nhn?blogId=gre_nada&logNo=221293072936&navType=tl

https://clarityfidelity.blogspot.com/2016/06/stax-sr-404-signature-over-ear.html

https://clarityfidelity.blogspot.com/2016/12/stax-sr-202-basic-over-ear-headphones.html

https://m.blog.naver.com/PostView.nhn?blogId=gre_nada&logNo=221639412048&navType=tl

https://m.blog.naver.com/PostView.n...=221407076973&referrerCode=0&searchKeyword=ie

 

[JohnYang1997]

I suspect that amir used thd+n instead of thd? The back ground noise is of course way louder than the distortion you want to measure. It's especially true for open back headphones the creeped up (flat slope) distortion from midrange to bass is basically the ambient noise.(the hump below 200hz is just distortion due to low fundamental amplitude).

 

[Thomas_A]

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I’m unsure why they (NRC) didn’t measure below 50hz, since the salon2 is rated at -3db at 24hz. My guess is the distortion numbers at that number are close to double digit. Certainly audible! It would be better if speaker manufactures were more honest. But let’s be real, not much musical content below 30hz. Still. Good to be honest.

Their anechoic room is not good eonugh below 50 or 80 Hz

 

[Drone/doom]

I suspect that amir used thd+n instead of thd? The back ground noise is of course way louder than the distortion you want to measure. It's especially true for open back headphones the creeped up (flat slope) distortion from midrange to bass is basically the ambient noise.(the hump below 200hz is just distortion due to low fundamental amplitude).

Amir saying that the high THD the ER4XR or a SR225e i was talking about could be much lower in reality, like <0.2% and your examples are even lower. There lot's of issues i have beyond mic distortion like ambient noise, glitches and much more causing some to be higher that actually are. Even tyll's THD charts had glitches like some full size having 2 to 10% THD or channel imbalance.

I still doubt the 0.5 to 1% in the ER4's mid range is even audible since at 70db the ER4PT with 7db bass boost & 3.5db treble sounded fantastic yet still very clean. Sub 0.5% levels are what i would expect if constant 85 to 105db content is needed, Like filling a large venue with sound not at home at 55db listening to metal.

 

[Rja4000]

In headphone distortion tests I have done, all the distortion is from the measurement mic, and not much from the headphones! Measurement mics are rated up to 3% distortion. Indeed finding distortion specs even for high-end microphones is hard. It is said that woofers will distort more than the microphone and that may be so but I have not seen hard data for that either.

You may find one figure here
https://www.dpamicrophones.com/ddicate/4006-omnidirectional-microphone
This is a typical high-end (reference) omnidirectional microphone, used for critical recordings (cost >2000€).
They state
Total harmonic distortion (THD) < 1% up to 139 dB SPL peak
As I understand it, that includes the "High-end preamp".

(By the way, DPA is a daughter company of Brüel & Kjær)

 

[JohnYang1997]

Amir saying that the high THD the ER4XR or a SR225e i was talking about could be much lower in reality, like <0.2% and your examples are even lower. There lot's of issues i have beyond mic distortion like ambient noise, glitches and much more causing some to be higher that actually are. Even tyll's THD charts had glitches like some full size having 2 to 10% THD or channel imbalance.

I still doubt the 0.5 to 1% in the ER4's mid range is even audible since at 70db the ER4PT with 7db bass boost & 3.5db treble sounded fantastic yet still very clean. Sub 0.5% levels are what i would expect if constant 85 to 105db content is needed, Like filling a large venue with sound not at home at 55db listening to metal.

No. He's saying the distortion is coming from the MIC. How simple is that....
Also tyll's measurements are THD+N and he measures 100db too (which is very high).
Most importantly I wasn't talking about er4 or anything I was saying the proper measurement microphones can measure very low distortion harmonics. I have used gras ra0045 and bk 4157 ear simulators before so I know.

 

[Drone/doom]

No. He's saying the distortion is coming from the MIC. How simple is that....
Also tyll's measurements are THD+N and he measures 100db too (which is very high).
Most importantly I wasn't talking about er4 or anything I was saying the proper measurement microphones can measure very low distortion harmonics. I have used gras ra0045 and bk 4157 ear simulators before so I know.

No he saying the mics cause exaggerated/added distortion don't twist what is said, Even good mic was 1 - 3%?. Why are you being ignorant to the fact that any THD chart about any Grado are void also even 90 to 100db is a issue with some headphones dying from pushed to hard since all Grado headphones are 32ohm with high sensitivity.

There another blog I've read where some of his THD charts have had high numbers either from Ambient Noise, AC hum and stuff.

 

[JohnYang1997]

No he saying the mics cause exaggerated/added distortion don't twist what is said, Even good mic was 1 - 3%?. Why are you being ignorant to the fact that any THD chart about any Grado are void also even 90 to 100db is a issue with some headphones dying from pushed to hard since all Grado headphones are 32ohm with high sensitivity.

There another blog I've read where some of his THD charts have had high numbers either from Ambient Noise, AC hum and stuff.

Like I said tyll uses thd+n instead of thd. Thd+n means any signal apart from the fundamental is put into the thd+n where thd only counts the individual harmonics. If you can't understand this, it's a "you" problem not a "me" problem.
Also how am I ignorant when I wasn't even talking about it. Of course I know grados have high distortion and almost all BA iems have high distortion in the mids. That's irrelevant from what I argued.

 

[Rja4000]

By the way, speaking about THD and how much you can hear the difference:
I own a pair of 4-Channels Microphone Preamps from Focusrite.
They name it "Focusrite Liquid 4pre" and as Sound on sound described:
"preamps can be individually configured to behave like pretty much any classic or vintage preamp you care to think of "
This is done by using convolution and also some analog-level tricks.

Interestingly, they also allow to set an additional level of Harmonic distortion

The idea is similar to the Project Polaris HP Amp

I measured one channel
One channel (in RED), SINAD compared to RME ADi-2 Pro fs (in BLUE)

Then the same channel with "Harmonics" set to level "1" (out of 15)

Up to level 8, you add mainly 2nd harmonic, around 0.67% per "level"
Here is level 8

Above that, you add odd harmonics too (3rd and 5th order)
(Note that this is explained in the manual)
Here is the maximum level of Harmonics (Level "15")

I can tell you, because I used it regularly:
One can for sure hear the difference between "0" and level "8" or "15".
You can't always say exactly what's added, but you hear a difference.

I find actually that more usefull for music production than the "world famoust Pre-Amps" simulation (convolution) that this Pre-amp offers.
(Except, maybe, some "valve" preamp settings)

Other than that, in "FLAT" mode, the preamp is really good.

 

[Krunok]

Did you measure this in front of the woofer?

That is a tricky question when measuring transmission line speaker which has one woofer firing front, another firing up and transmission line opening at the bottom of the speaker. I measured it 15 cm on-axis with tweeter as that is suggested in REW's help (thank you @NTK !).

 

[DS23MAN]

So this measurement is not valid. You wil need to do this freefield at a distance.

 

[Krunok]

No he saying the mics cause exaggerated/added distortion don't twist what is said, Even good mic was 1 - 3%?. Why are you being ignorant to the fact that any THD chart about any Grado are void also even 90 to 100db is a issue with some headphones dying from pushed to hard since all Grado headphones are 32ohm with high sensitivity.

There another blog I've read where some of his THD charts have had high numbers either from Ambient Noise, AC hum and stuff.

Guys, I don't really want this thread to turn into how to measure headphones distortion. If you would like to discuss that I kindly ask you to open another thread.

 

[Krunok]

So this measurement is not valid. You wil need to do this freefield at a distance.

Results would be pretty much the same. You can tell from the impulse response that reflections didn't play significant role in this measurement.

Btw, if speaker doesn't generate much additonal harmonics when playing single tone I don't see where the difference would be.

 

[DS23MAN]

The main output at 42Hz wil be the port, not your woofer. Close range distortion can only be done with a closed box.

 

[Rja4000]

You may find one figure here
https://www.dpamicrophones.com/ddicate/4006-omnidirectional-microphone
This is a typical high-end (reference) omnidirectional microphone, used for critical recordings (cost >2000€).
They state
Total harmonic distortion (THD) < 1% up to 139 dB SPL peak
As I understand it, that includes the "High-end preamp".

(By the way, DPA is a daughter company of Brüel & Kjær)

On may also want to read this, about Microphone distortion.
And about audibility of distortion in general.
Very interesting

 

[Krunok]

The main output at 42Hz wil be the port, not your woofer. Close range distortion can only be done with a closed box.

That is true, but harmonics would come from woofers, not the port. And microphone didn't pick them, hence low distortion figure. At 76Hz, where cabinet resonates I'm getting app 1%.

Btw, transmission line is not same as bass reflex.

 

[MZKM]

With single sine waves I noticed I can spot 1% at pretty much all frequencies, 0.5% only with higher frequencies (1kHz+) and 0.2% sounded clean to me at the entire range. Obviously it gets much harder to spot distrotion with music due to masking.

Tones that measured 1% came out "muddied", not clean. My guess is that all those distortion spikes are because of resonances - either of the enclosure or within driver itself. With lower freqeuncies I was able to verify that by putting my hand on the side of the speaker.

The graph is for audible distortion for music (they played a handful of genres), playing sine waves will indeed be less forgiving.

 

[Rja4000]

You may find one figure here
https://www.dpamicrophones.com/ddicate/4006-omnidirectional-microphone
This is a typical high-end (reference) omnidirectional microphone, used for critical recordings (cost >2000€).
They state
Total harmonic distortion (THD) < 1% up to 139 dB SPL peak
As I understand it, that includes the "High-end preamp".

(By the way, DPA is a daughter company of Brüel & Kjær)

I personnaly own a few DPA 4060/4061, which are much less expensive miniature electret microphones.
Those are like a swiss army knife of microphones.

They are also specs with a level for THD <1%
Total harmonic distortion (THD) - Legacy < 1% THD up to 123 dB SPL peak; < 1% THD up to 120 dB SPL RMS sine
Total harmonic distortion (THD) - CORE (newer electronic for impedance adapter) < 1% THD up to 129 dB SPL peak

 

[Krunok]

I personnaly own a few DPA 4060/4061, which are much less expensive miniature electret microphones.
Those are like a swiss army knife of microphones.

They are also specs with a level for THD <1%
Total harmonic distortion (THD) - Legacy < 1% THD up to 123 dB SPL peak; < 1% THD up to 120 dB SPL RMS sine
Total harmonic distortion (THD) - CORE (new model) < 1% THD up to 129 dB SPL peak

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?

 

[DS23MAN]

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