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Old 5th March 2013, 10:54 AM   #1291
Elias is offline Elias  Finland
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Quote:
Originally Posted by soongsc View Post
Why would the modulation frequencies be in the subsonic region?
Because music is relatively slow process. In reference human speech has most energy in around 3 Hz modulation frequency.


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Old 5th March 2013, 11:24 AM   #1292
soongsc is offline soongsc  Taiwan
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So the modulation frequency is sort of simulating the human voice characteristic? What I don't understand is that since the audio speaker normally filters out the subsonic modulation, in effect, the resulting sound had very little modulation, thus MTF is going to be high, would it not? The only problem is that if the driver movement moves to the nonlinear region due to the subsonic signal, then you start creating more harmonics. So what is the true benefit of using the subsonic modulation to drive the test?
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Old 5th March 2013, 11:56 AM   #1293
soongsc is offline soongsc  Taiwan
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Originally Posted by Kindhornman View Post
Soongsc,
How can we leave the room out of the equation? If the test was in an anechoic chamber or outside I have not problem with doing that, but not if you are testing in a room unless you are using some gating function to only look at the first response without the room additions. Do you have any other ideas here?
If we are looking to evaluate the speakers themselves, I would use only the gated section. Now, I may be wrong, but it seems to me there are a few things that is going to effect the playback which should show up in an MTF depending on how it is tested.

1. Delayed release of stored energy of the system.
2. Nonlinear effects of the driver material and the motor.
3. Diffraction from the driver, and enclosure, and any part that is not moving in phase with the voil.

What we really want to do is to evaluate how the combination of these effects the transfer of music signals.

Now, if we look at the Orions and the Behringers, one uses waves from both sides of the driver, and the other has large ports close to the drivers, so it would really be interesting to see how these different design concepts show in the MTF. But I think we should use a gated part of the impulse, and see how a specific sound spectrum is effected by this part of the impulse. Not sure how it would be done mathematically though.
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Old 5th March 2013, 12:40 PM   #1294
Elias is offline Elias  Finland
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Quote:
Originally Posted by soongsc View Post
So the modulation frequency is sort of simulating the human voice characteristic? What I don't understand is that since the audio speaker normally filters out the subsonic modulation, in effect, the resulting sound had very little modulation, thus MTF is going to be high, would it not? The only problem is that if the driver movement moves to the nonlinear region due to the subsonic signal, then you start creating more harmonics. So what is the true benefit of using the subsonic modulation to drive the test?

In order to understand MTF it may be in order to review what is modulation
Amplitude modulation - Wikipedia, the free encyclopedia
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Old 5th March 2013, 02:52 PM   #1295
dewardh is offline dewardh  United States
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Originally Posted by soongsc View Post
What I don't understand is that since the audio speaker normally filters out the subsonic modulation,
No, that's not it. There are no subsonic "tones" to be filtered out . . . what is being looked for is amplitude modulation of higher frequencies (divided into numerous perceptual "bands"). The argument for "speech" is that that's where the actual "information" is . . . and the argument for music is that that's where we (might) find what (some) people call "dynamics".

If that is indeed the case for music then it's not a function of the speaker per se, it's a function of "modulation leveling" by reflected sound . . .

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Old 5th March 2013, 03:10 PM   #1296
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Hi All
Elias, music is slow or can be anyway, I think the things which tell you “there it is”, are fast, related to short events. While speech might be centered around 3 Hz (don’t recall) I do know they were measuring the modulation rates up to about 12 or 15 Hz and that like optics, the higher rates tended to suffer first /most. At the semianr, I had asked Sander van Wijngaarden how high a rate they investigated and he said about 30Hz.
I wonder how high a rate is audible though, for example, when you tune a 12 string guitar or piano, you DO NOT tune the groups of strings to the same note, they are ideally slightly different because that “beating” or fast amplitude modulation, sounds nicer than a pure tone.

Soongsc, you hit the nail on the head, the amplitude modulation of each of the frequency bands is a signal which emulates talking or rather how the information in the voice (what words) is transmitted or lost. If you examine a spectrogram (frequency, amplitude, time) of speech, you can see it is largely changes in pitch AND amplitude, we often measure amplitude and time(at one level) but rarely measure anything to do with changes in amplitude, so to me, it looked like an ignored dimension, ripe for investigation.
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Old 5th March 2013, 03:50 PM   #1297
gedlee is offline gedlee  United States
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I would like to note that based on the techniques in the links, the MTF will not be sensitive to nonlinearity at all. It would be somewhat sensitive to thermal effects. As defined, however, it will depend almost exclusively on the speakers directivity and the rooms reverberation. Horns will win this every time. But this metric could be a good correlate to "dynamics". However, it is just a single factor in that it ignores an awful lot of stuff that we know are factors, like frequency response.

What I do like about it is that it would show how the room and speaker work together in the specific room. But since it is so strongly dependent on RT, comparisons of speakers in two rooms with different RTs would be meaningless. The lower RT will have a significant advantage. This also makes clear that good MTF and good spaciousness would be counter to each other - which may also be very true, just as it is true for spaciousness and imaging being counter to each other.
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Old 5th March 2013, 03:56 PM   #1298
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Good observations Earl. Perhaps this also explains (part of) the ongoing directivity debate, if people have different priorities for their evaluation or design of a speaker?
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Old 5th March 2013, 04:04 PM   #1299
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by dewardh View Post
No, that's not it. There are no subsonic "tones" to be filtered out . . . what is being looked for is amplitude modulation of higher frequencies (divided into numerous perceptual "bands"). The argument for "speech" is that that's where the actual "information" is . . . and the argument for music is that that's where we (might) find what (some) people call "dynamics".

If that is indeed the case for music then it's not a function of the speaker per se, it's a function of "modulation leveling" by reflected sound . . .
Well, there are interactive waves in a room, I would not say those are modulating simply because the phenomena is different. What we are really trying to do is how accurately is the signal transferred to the receptor. This is also the intent of it's application in video.
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Old 5th March 2013, 04:08 PM   #1300
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Tom,

Toole reported that speech intelligibility is increased when certain reflections are present. Does STIPA show a better value under such conditions?
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