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Multi-Way Conventional loudspeakers with crossovers

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Old 15th May 2009, 04:49 AM   #5601
Pano is offline Pano  United States
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Bass speed, slam and weight?
Try the good old 40Hz square wave test. It tells a lot.
Enough said.

(electronics, not speakers)
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Old 15th May 2009, 06:46 AM   #5602
Jmmlc is offline Jmmlc  France
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Hello,

As I am not the one who introduced the "enveloppe theme" in this disussion, preferring for my own part to speak about the relationship between harmonics and fundamental,it seems that we agree for a large part.

(see my initial message : http://www.diyaudio.com/forums/showt...66#post1827566 )


It is on such subjects that psychoacoustic studies fail for a part. As, for frequencies lower than 150Hz, it is difficult to obtain a low phase distortion acoustic signal arriving at the listener ear due to the lack of loudspeaker having such beahviour, we still don't know alot about the relation between what we hear in the bass and what we can measure.

Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally posted by Elias
Hello,



Well, to be accurate the envelope does not exist in real world since it's not a physical quantity, rather it's a mathematical measure only. The thing is at low freqs the ear does not detect the envelope but what is perceived is the phase difference of the ear signals, or possibly the phase relations of harmonic components. It is the fundamental component below the envelope where the phase is detected, not the phase of the envelope, and reflections alter the phase of the fundamental. Actually in a mathematical sense the envelope can remain the same altough the phase of the fundamental is varied since the envelope is a result from amplitude modulation and not related to the phase of the carrier.

Of course then comes the question what is the detection threshold.

The case of the closed box and reflex box comparison is an exellent showcase to demonstrate that any resonance should not be part of a high quality reproduction system.

Make another comparison in a room between a closed box bass and a dipole bass. There is a diference in accuracy, speed or whatever one likes to call it, and it's because of less reflections of the directional source altering the amplitude and phase of the original waveform.

- Elias
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Old 15th May 2009, 07:24 AM   #5603
xpert is offline xpert  Afghanistan
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Quote:
Originally posted by Jmmlc
... psychoacoustic studies fail for a part. As, for frequencies lower than 150Hz, it is difficult to obtain a low phase distortion acoustic signal arriving at the listener ear due to the lack of loudspeaker having such beahviour, ...
Did You ever have heard from equalizers?
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Old 15th May 2009, 07:44 AM   #5604
Jmmlc is offline Jmmlc  France
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Hello Xpert,

In the quasi general case, the use of an equalizer will linearize only the frequency response but they'll make worst the group delay curve.

As an example I smile when I read that someone saying that he plan to reduce the rise of group delay of a horn near it's cut-off just using equalization...

That's easy to understand, high frequencies travel fast inside most filters (even high pass) and grossly low frequencies are delayed versus the high frequencies. If I would do some humour I'll say that the ability of equalizers to reverse time is very small. ;-)

When the order of the transfer function of the system became large (let's say over 2) it became quite impossible to linearize phase by minimum phase equalization.

Best regards from Paris, France.

Jean-Michel Le Cléac'h
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Old 15th May 2009, 09:00 AM   #5605
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I remember an article in HiFi News and Record Review back in the days when it was a magazine worth reading. (cira 2000 ish please bear with me, this is all from memory)

Keith Howard took a pair of B&W 802s (I think). He used a DSP algorithm to effectively phase equalise the speaker by processing the .WAV files used for audition. This was applied between reasonable limits, I think he "let the speaker go" below port resonance.

As we would expect, the two major points of departure from minimum phase behaviour were around the crossover points and around the bass reflex tuning. The published before and after graphs showed markedly improved phase behaviour.

The subjective results he reported included an improvement in bass speed and impact. It makes sense to me that the phase relationship between the LF and directly associated instrument harmonics plays are large part in the "quality" of the bass. Over-damped IB always sound speedier than mis-tuned reflexes in the bass. I believe this is largely down to more accurate phase tracking between the instrument fundamental and harmonics, as Lynn points out LF is, in theory, the easiest bit to do!
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Old 15th May 2009, 10:19 AM   #5606
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Quote:
Originally posted by Jmmlc
Hello Xpert,
When the order of the transfer function of the system became large (let's say over 2) it became quite impossible to linearize phase by minimum phase equalization.
Group delay is something different than "travel time". On the other hand for the sake of simplicity, would it help to delay the higher tones a bit?
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Old 15th May 2009, 11:01 AM   #5607
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Old 15th May 2009, 11:13 AM   #5608
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by Jmmlc
In the quasi general case, the use of an equalizer will linearize only the frequency response but they'll make worst the group delay curve.

As an example I smile when I read that someone saying that he plan to reduce the rise of group delay of a horn near it's cut-off just using equalization...

That's easy to understand, high frequencies travel fast inside most filters (even high pass) and grossly low frequencies are delayed versus the high frequencies. If I would do some humour I'll say that the ability of equalizers to reverse time is very small. ;-)

When the order of the transfer function of the system became large (let's say over 2) it became quite impossible to linearize phase by minimum phase equalization.
Is there really any reason to go higher orders than 2, if we are thinking about bass? Higher orders than that will only bring problems (BR etc) as indicated earlier.

If we stay in second order system, phase linearisation is quite straight forward by using pole/zero cancellation and generating desired new poles and zeros. Can be done in analog domain too with one opamp like in Linkwitz transform. Well, it cannot make linear phase from DC, but what it does it pushes the group delay lower in freq below audibility range. It's only mathematics of linear transfer functions. Of course it can bring other problems like increased nonlinear distortion because drivers have to work harder after equalisation.

- Elias
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Old 15th May 2009, 11:22 AM   #5609
Elias is offline Elias  Finland
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Hello,

Quote:
Originally posted by xpert
On the other hand for the sake of simplicity, would it help to delay the higher tones a bit?
Yes it helps, but it's not feasible to do in passive crossovers. Try delaying 20kHz signal for 10ms, for example. Phase linear systems only exist in digital domain, well but that is not news. Still, even you would have a phase linear speaker, you have the room reflections which will defeat your painfully earned victory over nonlinear phase.

- Elias
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Old 15th May 2009, 12:00 PM   #5610
Jmmlc is offline Jmmlc  France
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Hello Elias,

I agree with most of what you wrote. I guess the (non)feasibility to design that kind of poles/zeros cancellation with passive components only and the mainstream use of bass-reflex enclosure is surely the major limit to their generalisation.

As an example at the moment only one of my numerous friends use a close enclosure to reproduce the bass register.

Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally posted by Elias
Hello,



Is there really any reason to go higher orders than 2, if we are thinking about bass? Higher orders than that will only bring problems (BR etc) as indicated earlier.

If we stay in second order system, phase linearisation is quite straight forward by using pole/zero cancellation and generating desired new poles and zeros. Can be done in analog domain too with one opamp like in Linkwitz transform. Well, it cannot make linear phase from DC, but what it does it pushes the group delay lower in freq below audibility range. It's only mathematics of linear transfer functions. Of course it can bring other problems like increased nonlinear distortion because drivers have to work harder after equalisation.

- Elias
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