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Audibility of speaker nonlinear distortion - test
Audibility of speaker nonlinear distortion - test
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Old 13th November 2017, 12:53 PM   #1
PMA is offline PMA  Europe
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Default Audibility of speaker nonlinear distortion - test

Though I agree that linear issues are most audible for speakers, I am not sure that we may say that nonlinear distortion of speakers is not audible or is negligible. I also doubt the opinion that speaker nonlinear distortion has only low order components, as suggested e.g. by Geddes in [1]. The distortion profile of a speaker IME depends on speaker design, signal amplitude and signal frequency. A loudspeaker is a non-linear transducer.

I do not think it makes much sense to argue without proof, so I decided to prepare some test signals to check audibility of speaker nonlinear distortion. With my setup, I am able to remove quite effectively the ambient noise of the room and also microphone path noise, so I am able to get high dynamic range even from the recorded signal. You will see it in attached plots. Distortion of the amplifier that feeds the speaker under test is very very low, as you can see from the attachment as well.

It is very difficult or rather impossible to prepare a valid test with music samples, this way, it means by recording at acoustical side. So I have prepared 3 sets of test files with sine frequencies. Every set contains a source digital file and a recorded file with ambient noise and microphone noise removed.

1kHz sine at 4Vrms
http://pmacura.cz/speaker1k.zip

10kHz+12kHz twin tone IMD at 5.66Vpeak
http://pmacura.cz/speaker10+12k.zip
This is a test on intermodulation, be careful not to use very high gain, because the test signals are in the top octave of human audibility range.

2kHz sine
http://pmacura.cz/speaker2k.zip
This was recorded 2 years ago and I believe that at 2.8Vrms, but I am not absolutely sure. However, the speaker under test has the highest level of distortion at about 2kHz, though distortion profile is different. That is the reason why this test was posted as well.

100Hz sine (added Nov 16)
http://pmacura.cz/speaker100.zip

In case you are interested to participate in the test, please download the files and make Foobar ABX test. In case of a positive test result, please post a valid ABX protocol here. I suggest to make 12 or more trials during one test. That means 12/12 should be a great result.

I was able to get a positive and repeatable result for the 1kHz and 10+12kHz tests. I have troubles with the 2kHz test. And how about you?

Attached are the spectra of the recorded files and amplifier THD vs. frequency plot.

--------------------------------------------------------------------------
Literature:
[1] Geddes, E.R.: The Perception of Distortion. Audio Intelligence, Bangkok, Thailand, p. 26

================================================== ===========
Music sample with flute concert added on Nov 14
http://pmacura.cz/flute.zip

more in this post:
Audibility of speaker nonlinear distortion - test

================================================== ===============

Intermodulation test 60+300Hz added on Nov 18

http://pmacura.cz/60+300_speaker.zip

original file + recording through 7" woofer at 4Vrms
Attached Images
File Type: png 1000Hz_rec.PNG (117.4 KB, 519 views)
File Type: png 10+12khz_rec.PNG (108.9 KB, 515 views)
File Type: png speaker_dist_2k_extracted.PNG (116.7 KB, 509 views)
File Type: png measuring_amp.PNG (45.1 KB, 505 views)

Last edited by PMA; 18th November 2017 at 08:18 AM.
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Old 13th November 2017, 01:48 PM   #2
Mooly is offline Mooly  United Kingdom
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Audibility of speaker nonlinear distortion - test
Interesting. OK, let me start the ball rolling, I had just one attempt at each file:

(Edit... if you look at the second image you will see there are 22 samples with 15 and 16 appearing twice. That is Foobar, not me )
Attached Images
File Type: jpg 1 kHz.JPG (102.0 KB, 497 views)
File Type: jpg 2 kHz.JPG (105.1 KB, 91 views)
File Type: jpg 11 plus 12 kHz.JPG (106.9 KB, 76 views)
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Old 13th November 2017, 01:58 PM   #3
PMA is offline PMA  Europe
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Great result Karl, I think no need for you to torture your ears with further trials .

Code:
foo_abx 2.0.2 report
foobar2000 v1.3.7
2017-11-13 15:25:10

File A: 1000Hz_gen.wav
SHA1: b303226639a6f0633023c06bccc5dcc3711f2742
File B: 1000Hz_rec.wav
SHA1: 774114f7416ddbdc290faece1c8b02d9ec2f676c

Output:
WASAPI (event) : Speaker (USB Sound Blaster HD), 24-bit
Crossfading: NO

15:25:10 : Test started.
15:26:17 : 01/01
15:26:23 : 02/02
15:26:28 : 03/03
15:26:33 : 04/04
15:26:40 : 05/05
15:26:46 : 06/06
15:26:51 : 07/07
15:26:56 : 08/08
15:27:04 : 09/09
15:27:09 : 10/10
15:27:14 : 11/11
15:27:20 : 12/12
15:27:20 : Test finished.

 ---------- 
Total: 12/12
Probability that you were guessing: 0.0%

 -- signature -- 
66457f88b6d14c3ab2a65c0d976cef97242e4603
Code:
foo_abx 2.0.2 report
foobar2000 v1.3.7
2017-11-13 15:22:38

File A: 10+12khz_gen.wav
SHA1: 821894330fe457aa2c82286c7f323c34d0dab4ac
File B: 10+12khz_rec.wav
SHA1: 271b9efc65be91ca113cfc1248032534c9f88463

Output:
WASAPI (event) : Speaker (USB Sound Blaster HD), 24-bit
Crossfading: NO

15:22:38 : Test started.
15:22:52 : 01/01
15:22:59 : 02/02
15:23:03 : 03/03
15:23:07 : 04/04
15:23:11 : 05/05
15:23:15 : 06/06
15:23:20 : 07/07
15:23:24 : 08/08
15:23:28 : 09/09
15:23:32 : 10/10
15:23:37 : 11/11
15:23:43 : 12/12
15:23:43 : Test finished.

 ---------- 
Total: 12/12
Probability that you were guessing: 0.0%

 -- signature -- 
0e837b325355134d998e16492b65fe0fa979c212
I am not good in the 2kHz profile.
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Old 13th November 2017, 02:04 PM   #4
Mooly is offline Mooly  United Kingdom
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Audibility of speaker nonlinear distortion - test
Thanks Pavel. I'm surprised you have trouble with the 2k one.

I don't know if this means much but the last time I tried listening (with headphones) to a function generator with switchable sine and square output, I found that at moderate volume and switching between sine and square I could differentiate the two up to around 4.8kHz. Above that frequency and both sounded the same.
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Old 13th November 2017, 02:10 PM   #5
PMA is offline PMA  Europe
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Perfect square has only odd harmonics, so the 4.8kHz sq wave has first audible artifact at 14.4kHz. That's the reply, decreasing ear sensitivity at very high audio frequencies.
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Old 13th November 2017, 02:16 PM   #6
Mooly is offline Mooly  United Kingdom
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Audibility of speaker nonlinear distortion - test
I guess so. Thanks Pavel.
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Old 13th November 2017, 02:50 PM   #7
TNT is offline TNT  Sweden
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Isn't sine a really bad signal for listening tests? I mean, it is transients that make up for the possibility to differentiate between instruments. Music is about transients. In tests with sine, these is only two and thats the beginning and end of the signal. In the simplests piece of music there are a lot.

My guess is that you will not find insufficiencies in the DUT by using sine in listening tests.

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Old 13th November 2017, 02:59 PM   #8
TNT is offline TNT  Sweden
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IM was OK... was really fast/sloppy so missed one

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File Type: png lacinato 10_12 IM.png (81.8 KB, 88 views)
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Old 13th November 2017, 03:02 PM   #9
TNT is offline TNT  Sweden
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But failed the 1k test.

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Old 13th November 2017, 03:09 PM   #10
Pano is online now Pano  United States
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Audibility of speaker nonlinear distortion - test
Well you have to start the tests somewhere, right?

Thanks Pavel - I'll have a listen later today. And I'll have a couple of requests, if you don't mind.
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