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Does a speaker in an anechoic chamber has minimum phase behavior?

abdo123

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A lot of people here including Amir are using minimum phase filters to correct the amplitude response of a speaker. And I understand that the audibility of phase distortion (if any) introduced by these filters is a very dubious thing to discuss to begin with, so please consider this discussion academic in nature.

How does a speaker resonance manifest itself in the (acoustic) phase response? Is a speaker in an anechoic chamber considered a minimum phase system for its entire range? (lets consider a system without an electrical crossover for now).

Should people use minimum phase filters or linear phase filters when it comes to manipulating a speaker's anechoic response? considering both options are available.
 

Frgirard

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Your question is surreal. the phase is an audiophile and only audiophile concern regarding the speakers .
 

sarumbear

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A lot of people here including Amir are using minimum phase filters to correct the amplitude response of a speaker. And I understand that the audibility of phase distortion (if any) introduced by these filters is a very dubious thing to discuss to begin with, so please consider this discussion academic in nature.

How does a speaker resonance manifest itself in the (acoustic) phase response? Is a speaker in an anechoic chamber considered a minimum phase system for its entire range? (lets consider a system without an electrical crossover for now).

Should people use minimum phase filters or linear phase filters when it comes to manipulating a speaker's anechoic response? considering both options are available.
As an electromagnetic driver converts energy as a band pass filter I don’t think it can be considered as minimum phase irrespective of any external reflections.
 

thewas

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A loudspeaker driver itself is mainly acting as minimum phase device but as soon as you add a crossover and other drivers it isn't anymore. Also effects like cabinet diffraction aren't minimum phase and these cannot be corrected by EQ. A good overview of which regions can be corrected by minimum phase filters is to generate the excess group delay as it shows which regions have a deviation from minimum phase behaviour.

Below also some quotes of Toole on the topic:

As the "creator" of the "new Harman target curve" I can clear up some misunderstandings. Those who have the 3rd edition of my book can see where the curve came from - Figure 12.4. It is nothing more than the steady-state room curve that results from measuring any of several forward-firing loudspeakers that have been awarded very high ratings in double-blind listening tests. These steady-state room curves are substantially predictable from the "early reflections" curve in the spinoramas, as is illustrated.
Now, if you measure such a curve or something very close to it, and your speakers are conventional forward firing designs, it means that you probably have chosen well. Small tilt-like deviations may be seen and broadband tone-control-like adjustments can be made to achieve a satisfactory overall spectral balance. No small detail adjustments should be made because it is highly likely that they are acoustical interference (non-minimum-phase) phenomena that two ears and a brain interpret as innocent spaciousness - room sound. "Correcting" these is likely to degrade the audible performance of truly good loudspeakers - unfortunately this behavior is not uncommon in auto-EQ algorithms created by companies that do not make loudspeakers.




To Resonate or not to Resonate, That is the Question?
Apologies to Shakespeare . . .

This discussion has drifted into an area of literal interpretations of classical definitions with some semantics thrown in. If there is a shallow hump in a frequency response, in literal terms it is a very low-Q resonance, implying a mechanical, electrical or acoustical system with a "favored" frequency range. In a physical system as complex as a loudspeaker it may sometimes be difficult to decide what is happening. Crossovers are equalizers, by any other name, that interact with transducers having inherently non-flat tendencies - the result is a combination of both electrical and mechanical elements. Equalizers can be resonators just as surely as acoustical cavities, enclosure panels and cone breakup. So a frequency response feature may be partly mechanical and partly electrical , but the end result can be that of a resonance having Q. Achieving a desirable flat on-axis sound using passive or active networks can result in non-flat off-axis behavior because transducers have frequency-dependent directivity. In a room the result is that even with flat direct sound, the early reflected and later reflected sounds may exhibit emphasis over a range of frequencies that could forgivably be interpreted as a low-Q resonance.

As discussed many times in this thread, transducers are inherently minimum-phase devices, so electrical EQ can modify the performance of mechanical resonances - a huge advantage for active loudspeakers or those for which accurate anechoic data are available.

In the crossover between a 6- to 8-inch woofer and a 1-inch tweeter, a directivity mismatch at crossover is unavoidable. Above crossover, the tweeter has much wider dispersion than the woofer, so there is an energy rise over a wide frequency range. Is this a resonance? Technically not, in the dictionary definition sense. However, there is a broad hump in radiated energy, so perceptually it may appear to be so. Figure 4.13 shows such an example where even crude room curves were adequate to recognize the energy excess in an above-crossover energy excess and attenuate it. Because wide bandwidth (low-Q) phenomena are detected at very small deviations there was a clear improvement in perceived sound quality even though medium and higher-Q "real" resonances were essentially unchanged. Addressing all of the "resonances" was not surprisingly the best.

So, don't get hung up on semantics. Deviations from a linear frequency response are all describable as "resonances" if one chooses to. Broadband trends are very low-Q, narrower trends, medium Q, and so on. Even a bass tone control is an opportunity to manipulate a "resonance" - in this case the hump that develops above the low cutoff frequency which, depending on the system design will have a Q.

Narrow dips are usually the result of destructive acoustical interference and are usually audibly innocuous because they change with direction/position. Broader dips can be interpreted as anti-resonances if one chooses to, whether there is an associated frequency selective absorption process or not. Mostly not.




As I said, because loudspeaker transducers are minimum-phase devices one can use electrical parametric EQ to attenuate the mechanical resonances in transducers - using anechoic data of course. So, if you add a hump to an otherwise neutral/resonance free speaker you have added a resonance. This is why it is crucial to pay attention to what "room equalizers" are doing. If they "see" a ripple in a measured curve caused by acoustical interference of direct and reflected sound, and try to flatten it, they may be adding a resonance and degrading a good loudspeaker.


Source and more: https://www.audiosciencereview.com/...ut-room-curve-targets-room-eq-and-more.10950/
 
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mdsimon2

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As an electromagnetic driver converts energy as a band pass filter I don’t think it can be considered as minimum phase irrespective of any external reflections.

Would you not expect the phase response of a single driver to follow the band pass magnitude response? Isn't that minimum phase behavior?

In general I would expect single drivers to behave as minimum phase. This is why when designing a crossover if you use minimum phase filters to flatten the frequency response of each driver you also get phase alignment.

Michael
 

HarmonicTHD

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A loudspeaker driver itself is mainly acting as minimum phase device but as soon as you add a crossover and other drivers it isn't anymore. Also effects like cabinet diffraction aren't minimum phase and these cannot be corrected by EQ. A good overview of which regions can be corrected by minimum phase filters is to generate the excess group delay as it shows which regions have a deviation from minimum phase behaviour.

Below also some quotes of Toole on the topic:

As the "creator" of the "new Harman target curve" I can clear up some misunderstandings. Those who have the 3rd edition of my book can see where the curve came from - Figure 12.4. It is nothing more than the steady-state room curve that results from measuring any of several forward-firing loudspeakers that have been awarded very high ratings in double-blind listening tests. These steady-state room curves are substantially predictable from the "early reflections" curve in the spinoramas, as is illustrated.
Now, if you measure such a curve or something very close to it, and your speakers are conventional forward firing designs, it means that you probably have chosen well. Small tilt-like deviations may be seen and broadband tone-control-like adjustments can be made to achieve a satisfactory overall spectral balance. No small detail adjustments should be made because it is highly likely that they are acoustical interference (non-minimum-phase) phenomena that two ears and a brain interpret as innocent spaciousness - room sound. "Correcting" these is likely to degrade the audible performance of truly good loudspeakers - unfortunately this behavior is not uncommon in auto-EQ algorithms created by companies that do not make loudspeakers.




To Resonate or not to Resonate, That is the Question?
Apologies to Shakespeare . . .

This discussion has drifted into an area of literal interpretations of classical definitions with some semantics thrown in. If there is a shallow hump in a frequency response, in literal terms it is a very low-Q resonance, implying a mechanical, electrical or acoustical system with a "favored" frequency range. In a physical system as complex as a loudspeaker it may sometimes be difficult to decide what is happening. Crossovers are equalizers, by any other name, that interact with transducers having inherently non-flat tendencies - the result is a combination of both electrical and mechanical elements. Equalizers can be resonators just as surely as acoustical cavities, enclosure panels and cone breakup. So a frequency response feature may be partly mechanical and partly electrical , but the end result can be that of a resonance having Q. Achieving a desirable flat on-axis sound using passive or active networks can result in non-flat off-axis behavior because transducers have frequency-dependent directivity. In a room the result is that even with flat direct sound, the early reflected and later reflected sounds may exhibit emphasis over a range of frequencies that could forgivably be interpreted as a low-Q resonance.

As discussed many times in this thread, transducers are inherently minimum-phase devices, so electrical EQ can modify the performance of mechanical resonances - a huge advantage for active loudspeakers or those for which accurate anechoic data are available.

In the crossover between a 6- to 8-inch woofer and a 1-inch tweeter, a directivity mismatch at crossover is unavoidable. Above crossover, the tweeter has much wider dispersion than the woofer, so there is an energy rise over a wide frequency range. Is this a resonance? Technically not, in the dictionary definition sense. However, there is a broad hump in radiated energy, so perceptually it may appear to be so. Figure 4.13 shows such an example where even crude room curves were adequate to recognize the energy excess in an above-crossover energy excess and attenuate it. Because wide bandwidth (low-Q) phenomena are detected at very small deviations there was a clear improvement in perceived sound quality even though medium and higher-Q "real" resonances were essentially unchanged. Addressing all of the "resonances" was not surprisingly the best.

So, don't get hung up on semantics. Deviations from a linear frequency response are all describable as "resonances" if one chooses to. Broadband trends are very low-Q, narrower trends, medium Q, and so on. Even a bass tone control is an opportunity to manipulate a "resonance" - in this case the hump that develops above the low cutoff frequency which, depending on the system design will have a Q.

Narrow dips are usually the result of destructive acoustical interference and are usually audibly innocuous because they change with direction/position. Broader dips can be interpreted as anti-resonances if one chooses to, whether there is an associated frequency selective absorption process or not. Mostly not.




As I said, because loudspeaker transducers are minimum-phase devices one can use electrical parametric EQ to attenuate the mechanical resonances in transducers - using anechoic data of course. So, if you add a hump to an otherwise neutral/resonance free speaker you have added a resonance. This is why it is crucial to pay attention to what "room equalizers" are doing. If they "see" a ripple in a measured curve caused by acoustical interference of direct and reflected sound, and try to flatten it, they may be adding a resonance and degrading a good loudspeaker.


Source and more: https://www.audiosciencereview.com/...ut-room-curve-targets-room-eq-and-more.10950/
Thanks. Interesting.

So do I understand that correctly (you even quoted Toole), that EQing based on anechoic (eg Klippel) data the small deficiencies of speakers is not such a good idea afterall (even if these speakers exhibit “benign” directivity)?

Thanks.
 

thewas

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Thanks. Interesting.

So do I understand that correctly (you even quoted Toole), that EQing based on anechoic (eg Klippel) data the small deficiencies of speakers is not such a good idea afterall (even if these speakers exhibit “benign” directivity)?

Thanks.
As Toole says there is no black and white answer, generally high Q positive filters should be avoided and in the end listening tests should decide.
 

Frgirard

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Thanks. Interesting.

So do I understand that correctly (you even quoted Toole), that EQing based on anechoic (eg Klippel) data the small deficiencies of speakers is not such a good idea afterall (even if these speakers exhibit “benign” directivity)?

Thanks.
the kh420 demonstrate you are wrong .
 

gnarly

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Hi,
first, i think thewas' post #4 has a lot of great info....

How does a speaker resonance manifest itself in the (acoustic) phase response? Is a speaker in an anechoic chamber considered a minimum phase system for its entire range? (lets consider a system without an electrical crossover for now).
When there's an anomaly in frequency response, it will cause phase to wonk out too, if for no other reason than the math behind the measurement ties the two together.
If the frequency response anomaly is within a single driver's operating range, it may or may not be a good candidate for minimum phase EQ, which would correct both freq response (more properly termed magnitude) and phase response.
The best way I know to determine whether the anomaly is a good candidate for EQ, is correct it on-axis, and then see how well the correction holds up off-axis. If it hold up well, I consider the anomaly minimum phase and suitable for correction, whether the anomaly is broad or narrow. Key for me, is simply does the correction work everywhere.

Yes, speaker is predominantly minimum phase for its entire range if it is a true full-ranger.
Sane for the pass bands of individual drivers.

IIR crossovers and their frequency ranges that have two or more drivers summing together, bust up minimum phase.

Also, in a broader perspective, I like to think minimum phase pragmatically ends, whenever multiple sources contribute to a frequency......like diffractions etc.

I think multiple sources breaks up minimum phase even when drivers are completely "in-phase" with each other on-axis .
Because, multiple sources entails multiple physical locations, which means "in-phase" only occurs a particular axis/distance/ spot of focus.

Should people use minimum phase filters or linear phase filters when it comes to manipulating a speaker's anechoic response? considering both options are available.
Well, I don't think linear phase filters should ever be used to manipulate a speaker's anechoic response,
because I think the only valid speaker EQs are minimum phase where when you fix magnitude and you also fix phase.
AND even then, those EQ's need to hold up both on-axis, and reasonably well off-axis.

Now, if by filters you include crossovers too, then I think complementary linear phase crossovers are an incredible (mostly unrecognized) blessing in speaker design.
But they don't really manipulate anything, they just help get the acoustic design to work as intended. So I'm not sure if this is part of the question.
 

René - Acculution.com

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A lot of people here including Amir are using minimum phase filters to correct the amplitude response of a speaker. And I understand that the audibility of phase distortion (if any) introduced by these filters is a very dubious thing to discuss to begin with, so please consider this discussion academic in nature.

How does a speaker resonance manifest itself in the (acoustic) phase response? Is a speaker in an anechoic chamber considered a minimum phase system for its entire range? (lets consider a system without an electrical crossover for now).

Should people use minimum phase filters or linear phase filters when it comes to manipulating a speaker's anechoic response? considering both options are available.
You may find my video on the topic interesting
 

Hasan Aydin

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You may find my video on the topic interesting
at 3:45:45 you said " if it deviates from the minimum phase step response, then it is not minimum phase" but I measured such a step response with a single driver speaker, without a crossover. Is it because of the room or that the driver is bass limited? and is it then a non minimum phase system at the listening position, although it has no crossovers or additional drivers?
 
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René - Acculution.com

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at 3:45:45 you said " if it deviates from the minimum phase step response, then it is not minimum phase" but I measured such a step response with a single driver speaker, without a crossover. Is it because of the room or that the driver is bass limited? and is it then a non minimum phase system at the listening position, although it has no crossovers or additional drivers?
Could be modes, diffraction, the measurement setup, ... Difficult to say. Remember that the term minimum phase is for a transfer function, and transfer function are really intended in some sense for 0D applications such as electrical circuits. When measuring or simulating 3D objects, we have to be careful about our interpretation of the data, as there are details such a the driver surfaces really being a continous 'array' of small 0D point sources and so when adding them up at high frequencies, or if you have diffration, you might be seing more than just a point source driver.
 

ctrl

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but I measured such a step response with a single driver speaker, without a crossover. Is it because of the room or that the driver is bass limited? and is it then a non minimum phase system at the listening position, although it has no crossovers or additional drivers?
In addition to what @René - Acculution.com stated, only a CB single driver speaker behaves almost (driver behaves never "ideal") like a minimum phase system.
So if your speaker uses BR, PR or TL for a better low bass response, then it is no longer a minimum phase system, because in these cases there is again a kind of high pass - low pass summation.
 

dasdoing

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in a minimum phase system FR deviations are caused by cancelation and/or sumation, right? I can understand that his is the case for dips and peaks for a driver, but what about the roll-offs? if they are not caused by a filter they can't be minimum phase, right?
 

René - Acculution.com

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in a minimum phase system FR deviations are caused by cancelation and/or sumation, right? I can understand that his is the case for dips and peaks for a driver, but what about the roll-offs? if they are not caused by a filter they can't be minimum phase, right?
It is not whether or not the response was modified by a 'filter' or not that determines the minimimum phase aspects. The roll-off at lower frequencies will be a result of the mass-spring characteristics of the driver, and that can be seen as a high pass filter, just as an electrical filter. That will be minimum phase, although borderline.
 

dasdoing

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It is not whether or not the response was modified by a 'filter' or not that determines the minimimum phase aspects. The roll-off at lower frequencies will be a result of the mass-spring characteristics of the driver, and that can be seen as a high pass filter, just as an electrical filter. That will be minimum phase, although borderline.

thanks, could we say that a driver's roll-off is basicly (mostly?) caused by delayed output close to it's mecanical limits?
 

René - Acculution.com

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thanks, could we say that a driver's roll-off is basicly (mostly?) caused by delayed output close to it's mecanical limits?
I would not say it is related to delay. It is just that for the particular transductance principle used in most driver (electrodynamics, Lorentz force) an applied constant (as function of frequency) voltage will give a constant acceleration above the resonance frequency, where all applied force goes to accelerating the mass, but below it the force goes into compressing the "spring" with more of constant displacement, which does not produce much sound. So it is a result of the applied force and the impedance the force sees.
 

dasdoing

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I would not say it is related to delay. It is just that for the particular transductance principle used in most driver (electrodynamics, Lorentz force) an applied constant (as function of frequency) voltage will give a constant acceleration above the resonance frequency, where all applied force goes to accelerating the mass, but below it the force goes into compressing the "spring" with more of constant displacement, which does not produce much sound. So it is a result of the applied force and the impedance the force sees.

ok, I thought I was starting to understand the corelation between phase and magnitude in a minimum phase system, but Dunning-Kruger now hit me
 

René - Acculution.com

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ok, I thought I was starting to understand the corelation between phase and magnitude in a minimum phase system, but Dunning-Kruger now hit me
I have been there many times. Oftentimes it is some misunderstandings that block the learning process. You can ask here when you have some specific questions.
 
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