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post #121 of 130 Old 09-25-2013, 02:39 PM
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Originally Posted by noah katz View Post

Hi John,

Is that supposed to be a sine wave?

If so, why do both traces have glitches?

I can't recall where it's posted, but I believe those images were from a paper or presentation online. I believe it was a complex signal, not a sine wave, but John will have to confirm as it's a bit ambiguous beyond there clearly being a difference without the input signal for comparison.

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post #122 of 130 Old 09-25-2013, 03:43 PM
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"So this 300hz tone bein input creates a 5th order harmonic at 1500hz. In the case of a TD woofer where a lot has been done to reduce flux modulation and linearize inductance, this 5th order harmonic will be low to begin with. There is also no breakup of 10dB or so due to the dustcap in that region. In a driver where there is no inductance control, this harmonic distortion will be as much as 10dB higher to begin with. Then factor in a 10dB increase in frequency due to the breakup. Not only is this a 20dB increase in magnitude of that 5th harmonic, but the dustcap creates a resonance that does not decay quickly. The 5th harmonic tone will be very high in level and continue for a long period of time. This is highly audible."

highly audible is what i would question. with a 4th order low pass at 300hz, spl is down about 55db by the breakup. that is low enough to not be concerned with it.

"It's important to recognize what a graph does and does not show. In this case you are only looking at Le vs. VC position. The variance of Le vs. current vs VC position is another 3D variable which inductance control helps with to varying degrees for different methods. A great case to look at for this is near the Fb of a PR reflex design, a bandpass, or horn. I've measured more than a few cases where excessive Le modulation results unexpected distortion increase despite modest excursion vs. rated Xmax."

yep, but that isn't what was mentioned so i didn't address it. :-)~

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post #123 of 130 Old 09-25-2013, 04:03 PM
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Quote:
Originally Posted by noah katz View Post

Hi John,

Is that supposed to be a sine wave?

If so, why do both traces have glitches?

This would actually be multiple tones occurring at the same time. This wasn't a great example because the one with shorting ring also isn't highly accurate. I wish it had another trace of the actual input signal. The point is that the flux modulation affects both time and amplitude response.

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post #124 of 130 Old 09-25-2013, 04:07 PM
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Quote:
Originally Posted by LTD02 View Post

"So this 300hz tone bein input creates a 5th order harmonic at 1500hz. In the case of a TD woofer where a lot has been done to reduce flux modulation and linearize inductance, this 5th order harmonic will be low to begin with. There is also no breakup of 10dB or so due to the dustcap in that region. In a driver where there is no inductance control, this harmonic distortion will be as much as 10dB higher to begin with. Then factor in a 10dB increase in frequency due to the breakup. Not only is this a 20dB increase in magnitude of that 5th harmonic, but the dustcap creates a resonance that does not decay quickly. The 5th harmonic tone will be very high in level and continue for a long period of time. This is highly audible."

highly audible is what i would question. with a 4th order low pass at 300hz, spl is down about 55db by the breakup. that is low enough to not be concerned with it.

You're referring to frequency response, John was referring to distortion. The electronic low pass doesn't affect the 5th harmonic distortion product of a 300Hz input. Peaks in the response can amplify distortion products. Audibility becomes a tricky thing to figure as real use involves more than just one sine wave, but the case described would have different distortion behavior. So far as audibility, remember that the higher the harmonic, the more audible the same level of distortion is.

Quote:
"It's important to recognize what a graph does and does not show. In this case you are only looking at Le vs. VC position. The variance of Le vs. current vs VC position is another 3D variable which inductance control helps with to varying degrees for different methods. A great case to look at for this is near the Fb of a PR reflex design, a bandpass, or horn. I've measured more than a few cases where excessive Le modulation results unexpected distortion increase despite modest excursion vs. rated Xmax."

yep, but that isn't what was mentioned so i didn't address it. :-)~

You answered a comment about linearity of inductance of the B&C mentioned with Le vs. (x) graph. I only pointed out that this was but one variable, and not all inclusive.

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post #125 of 130 Old 09-25-2013, 04:10 PM
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Originally Posted by LTD02 View Post

highly audible is what i would question. with a 4th order low pass at 300hz, spl is down about 55db by the breakup. that is low enough to not be concerned with it.

Again, this is not at all what is in question here. The signal being input is about 55dB down because of the lowpass. The harmonics are not created by that signal that is 55dB down. They are created by the motor of the driver and are a direct result of the 300hz fundamental, not any input at 1500hz. Because they occur in the woofer after the crossover, they are not affected by it.

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post #126 of 130 Old 09-25-2013, 07:38 PM
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so you are saying the 5th harmonic is going to have whatever bump in frequency occurs at around 1500 hz or so in it?

gotcha.

so add 10db to the 5th harmonic, which tends to be down how much (20-30db below the 2nd harmonic distortion)? then add to that the masking effect in real music and you are saying that is audible?

no way. :-)

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post #127 of 130 Old 09-25-2013, 07:44 PM
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"So far as audibility, remember that the higher the harmonic, the more audible the same level of distortion is."

+1.

"I only pointed out that this was but one variable, and not all inclusive."

+1 again.

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post #128 of 130 Old 09-25-2013, 08:34 PM
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Quote:
Originally Posted by LTD02 View Post

so you are saying the 5th harmonic is going to have whatever bump in frequency occurs at around 1500 hz or so in it?

gotcha.

so add 10db to the 5th harmonic, which tends to be down how much (20-30db below the 2nd harmonic distortion)? then add to that the masking effect in real music and you are saying that is audible?

no way. :-)

Your guess as far as the level that a 5th order harmonic will be down is based on standard THD sweeps though. If you do a simple sweep you may measure -50db 5th harmonic at 1500hz. Not very significant. If you run the same sweep while playing a 30hz sine wave at high excursion the odd order distortions will be far higher. This is the best way to simulate a real world situation as we never just put in a sweep playing one frequency at a time. It is many frequencies at the same time. The result may be a 5th harmonic that is only -20dB from the fundamental. Factor in the 10dB breakup at that point. The motor induced distortion 5 octaves above the crossover may be creating distortion only 10dB less than than the level of the fundamental at 300hz. It is also in a frequency range where the decay time is very long meaning this tone lingers longer as well. Often longer than the fundamental. It is a reason that good speakers take into account these issues of high order distortions. The higher the order, the more audible it is with much lower distortion percentage. The percentages as measured by sweeps really don't mean much anyway as they don't apply to the real world. Factor in that the range of 1-3KHz is the most sensitive to the human ear as well.

AES had done a lot of testing on this back when I was in college. They digitally generated levels of distortion and added it to music. They added various levels of different harmonic distortions. H2 distortions could be as much as 100% and almost inaudible. H5 distortions could be audible with very small amounts. H20 distortion can be audible with as little as .1%. The farther away from the fundamental, the easier it is for our ears to recognize something isn't right. Adding in a dustcap breakup which will only increase higher order distortion in the 1-3KHz range is just not a good idea. Especially if the driver already has high levels because of the motor design. Removing both the dustcap resonance and lowering the cause of the distortion in the motor will have a significant benefit that will be audible.

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post #129 of 130 Old 09-26-2013, 06:04 AM
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all good points.

interesting ramification of this would be the use of frequency dependent absorption as some sort of speaker grill.

a relatively thin layer of most typical absorption allows 300hz and below to pass rather easily wile absorbing up to 60% or more of the sound by those higher frequencies. any thoughts on why something like that isn't more common?

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post #130 of 130 Old 09-26-2013, 06:44 AM
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Can someone explain what is the meaning of the fundemential with regards to odd and even order harmonic distortion?
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