I would like to share my latest blog where I test microphone distortion between four different mics.
https://josephcrowe.com/blogs/news/microphone-distortion-comparison
https://josephcrowe.com/blogs/news/microphone-distortion-comparison
Joseph,
In your blog you wrote:
"To interpret the results I compare the peak of the test signal against the black "grass" in the noise floor. The grass represents the intermodulation side band products. Normally this would be generated by the loudspeaker, however as we shall see, it is actually the microphone."
I can see a higher black noise floor on the two Dayton mics compared to the AKO Pacific 7052 and SM58, as well as their higher "grass" level relative to the lower grass level above 1kHz.
Having read through to your concluding remarks, I don't "see" how the microphone IM side band products been actually isolated from those generated by the loudspeaker.
Could you explain?
Thanks,
Art
In your blog you wrote:
"To interpret the results I compare the peak of the test signal against the black "grass" in the noise floor. The grass represents the intermodulation side band products. Normally this would be generated by the loudspeaker, however as we shall see, it is actually the microphone."
I can see a higher black noise floor on the two Dayton mics compared to the AKO Pacific 7052 and SM58, as well as their higher "grass" level relative to the lower grass level above 1kHz.
Having read through to your concluding remarks, I don't "see" how the microphone IM side band products been actually isolated from those generated by the loudspeaker.
Could you explain?
Thanks,
Art
yes where is driver distortion and where is mic? For AKO pacific case it’s unclear. To see which part distortions dominate you could by changing mic distance to driver
The test involved simply swapping out the various mics while all other test parameters remained the same including the test signal. Any change in the IMD is a result of the mic quality. I did a lot of testing with various tweeters and levels to come up with a test setup that provided a low distortion loudspeaker as a source which allowed me to do a test like this. Otherwise loudspeaker distortion would dominate and I would not see a difference in the microphone's performance. There are other ways of testing microphones but this seemed to do the job well that was easy to display and demonstrate.
Very insightful.
So can the SM58 be be used as a loudspeaker measurement mic ?
Are you planning to test other common mics?
Eg. Audix TM1, Sonarworks Xref20, Earthworks M30R?
How can viewers contribute or support you in these test?
So can the SM58 be be used as a loudspeaker measurement mic ?
Are you planning to test other common mics?
Eg. Audix TM1, Sonarworks Xref20, Earthworks M30R?
How can viewers contribute or support you in these test?
Understand , for higher distortion mics its ok.but for the mic with lowest distortions you still don’t know is this drivers or mics distortions you see
If you increase the distance, and the distortion is unchanged, it must be the source. If the distortion falls with distance and reduced level, it is the microphone
I had speakers with AMTPRO-4 and in my measurements it is not speaker with lowest distortion.
Had you made measurements with less frequencies per octave? Now it seems test signal can mask actual distortions and result is mainly mic noise levels comparison.
AMTPRO-4 had significant THD but it is not visible on your measurements.
Had you made measurements with less frequencies per octave? Now it seems test signal can mask actual distortions and result is mainly mic noise levels comparison.
AMTPRO-4 had significant THD but it is not visible on your measurements.
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I tested a variety of tweeters for IMD before settling on the AMTPRO4 because of its performance. I did not however look at harmonic. I will be doing a full test on the AMTPRO4 in the near future so I will look at harmonic. It’s possible that H2 rises quickly at higher SPL with H3 and H4 remaining low, that’s what I’ve seen from other tests. I’m not sure about the subjective offensiveness of this.
Electret preamp noise does not seem to be affected by input level. It’s just this consistent fixed noise at, for example, -65dB against the test signal level input. So moving the mic away is not a valid test. This is something I discovered in the last year. Keeping the mic close, however, does help improve S/N against environmental noise.
Dynamic cardioid mics such as the Shure SM-58 have a proximity effect that varies the amount of low frequency with distance, as well as "presence peaks", an rolled-off low frequency response.
Those features make the SM-58 a popular vocal mic, but a poor measurement mic regarding frequency response.
Art
Although placing a mic closer to the source improves S/N relative to external noise, the increased SPL also results in increased harmonic and intermodulation distortion in the microphone response.
That said, the Dayton Audio EMM-6 maximum SPL for 1% THD @ 1000Hz is 127 dB, the Dayton Audio UMM-6 maximum SPL for 1% THD @ 1000Hz is 135 dB while the 7052PH can take 150 dB SPL @1% THD, so no surprise to see the inexpensive electret condenser mics exhibiting more distortion, even at the relatively low (around 110+dB SPL at 5 cm) test levels.
Hard to find any distortion specs on cardiod dynamic microphones, but generally speaking they don't show "hard clipping" at high SPL as do condenser or electret condenser mics.
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What can cause 50 Hz peak Q variation on measurement images? Have they different FTT window size, averaging or sample frequency?
According to the blog, "The 4048 provides <14 dBA noise floor, the lowest in the industry." Maybe that means the lowest noise floor for a measuring microphone? Large diaphragm studio condenser microphones often have noise levels below 14 dB(A), four random examples:
http://studioprojects.com/b1_tech.html
http://studioprojects.com/cs1_tech.html
https://www.neumann.com/homestudio/en/tlm-102
https://www.neumann.com/homestudio/en/tlm-103
The last one in the list has the lowest noise level of these examples, 7 dB(A).
http://studioprojects.com/b1_tech.html
http://studioprojects.com/cs1_tech.html
https://www.neumann.com/homestudio/en/tlm-102
https://www.neumann.com/homestudio/en/tlm-103
The last one in the list has the lowest noise level of these examples, 7 dB(A).
Indeed they have. In fact any microphone that is not omnidirectional has proximity effect.
-yes there are many mic capsules with lower noise floors; several from ACO. In fact their lowest (7020) is spec'ed at less than 2db (though its dynamic range and bandwidth are poor relatively speaking).
The ACO that seems most relevant to speaker testing enthusiasts is the 1/2" 7012 even though it doesn't have quite as low a noise floor (it has a really high dynamic range and a very wide bandwidth). Within the ACO line for distortion testing I would have looked most closely at the 1" 7022.
Still, the 7052e is an excellent mic. capsule and stability is rated for longer than we will be alive.
(..and I still think the Rode NT1A, *calibrated for freq. response vs. position, would be an excellent auxiliary mic for distortion testing. Its noise floor is around 4-5 db.)
*with a cross-spectrum calibrated UMIK-1.
To say the SM58 in the real world is a low distortion mic is a bit far fetched. The transformer in this mic is a major contributor to its sound signature and adds alot of the "character" (much of it not so good) to the pot. For one thing its a passive dynamic mic without any preamp. The other big variable is how the output is being loaded ie. cabling and preamp. Try terminating this mic and the others you tested with 600 ohms and report back with the findings... i doubt the results will be close to the same you originally made.
Does it matter? if the results are from actual test setup, some mics measure lower distortion than others in a distortion measurement setup, why change the setup?