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Old 10th March 2013, 01:08 PM   #11
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Jmbee, yes, in LR4 both drivers go through the same 360 degrees rotation, with 180 degrees somewhere around the xover frequency. What is the problem with that? As you showed, the maximum group delay is .8 ms @ 450 Hz.

According to Blauert, I have his book on spatial hearing, but not the article Group delay distortions in electroacoustical systems | Browse - Journal of the Acoustical Society of America that explains research into threshold of the audibility of group delay, however I know the results. At 450 Hz, it is at least four times higher than the 0.8 ms in the example.

FIR filters can do away with this, but you exchange something inaudible (group delay) for something potentially audible (pre-ringing).

Experimenting is fun and I do not want to discourage anyone from doing so, but it is actually possible to learn from science published in the field. If you don't have the books, Google is a great learning tool.
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Old 11th March 2013, 11:34 AM   #12
Jmmlc is offline Jmmlc  France
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Quote:
Originally Posted by marco_gea View Post

I just wanted to report on my "reverse-angineering" studies about the TAD variant, and compare the two.


I have not had the chance of listening to otherwise identical systems employing the JMLC vs. the TAD crossover, but based on the simulations I SUSPECT that the TAD one just MIGHT sound better, that it all.
Hello,

You'll find here attached 2 screen copies. The first one shows the impulse reponse (IR) of the TAD TD2402 and the other one is the measurement of the IR of a 2 ways using nearly the same loudspeakers but with a JMLC crossover.


As you can see there is a 2nd pulse on the IR of the TAD TD2402 around 0.4ms (equivalent distance = 14 cm) fully explained by the group delay curve you shown to us.

Best regards from Paris, France

Jean-Michel Le Cléac'h
Attached Images
File Type: gif TAD_TD2402_IR.gif (21.4 KB, 518 views)
File Type: gif 2_ways_JMLC.gif (21.0 KB, 517 views)
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Old 11th March 2013, 12:10 PM   #13
Jmmlc is offline Jmmlc  France
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Quote:
Originally Posted by vacuphile View Post
According to Blauert, I have his book on spatial hearing, but not the article Group delay distortions in electroacoustical systems | Browse - Journal of the Acoustical Society of America that explains research into threshold of the audibility of group delay, however I know the results. At 450 Hz, it is at least four times higher than the 0.8 ms in the example.
Hello Vacuphile,

You don't use the Blauert criterium the right way it should.

For a given frequency if Blauert says x ms is the threshold, that means that with a delay between the 2 signals (e.g. pulses) larger than x, the 2 signals will be perceived as 2 separated signals.

Now if the delay is smaller than x then it signifies that only one "phase distorted" signal will be perceived.

(phase distortion being defined as for the "summation" signal having non constant group delay curve vs. frequency).

Best regards from Paris, France

Jean-Michel Le Cléac'h

Last edited by Jmmlc; 11th March 2013 at 12:31 PM.
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Old 11th March 2013, 12:56 PM   #14
jmbee is online now jmbee  France
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Hello Jean-Michel,

"As you can see there is a 2nd pulse on the IR of the TAD TD2402 around 0.4ms"

Well, y wonder how jou got such a big second echo impulse !
My results taking in acount this filter , even +/- aproximative, are,
as you can see, quite different.

crd

Click the image to open in full size.
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Old 11th March 2013, 01:04 PM   #15
LJNorth is offline LJNorth  United Kingdom
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The Blauert paper shows results where the experimental subjects were asked to identify the "group delay distorted signals" withing groups of two, or three, discrete distorted and non-distorted signals. His conclusion is that trained listeners listening to the "most critical test signals" with "diotic earphone presentation" couldn’t detect group delay distortion below 0.5 mS. In the paper no mention is made of differentiation between coposite signals of two impulses



regards


Laurence
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Old 11th March 2013, 01:12 PM   #16
Jmmlc is offline Jmmlc  France
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Quote:
Originally Posted by jmbee View Post
Hello Jean-Michel,
Well, y wonder how jou got such a big second echo impulse !
My results taking in acount this filter , even +/- aproximative, are,
as you can see, quite different.

Hello Jimbee,

The response of the TAD TD 2402 is taken from the firts link here (green frequency response curve) :


http://2.bp.blogspot.com/-HttNapLF7g...ction+horn.png

http://4.bp.blogspot.com/-3wCe1MaSJj...0%25A711ms.png

Both 2 measurements show that second peak,

May be it is due to some inner reflection in the TH4001 horn though.

Best regards from Paris, France

Jean-Michel Le Cléac'h

Last edited by Jmmlc; 11th March 2013 at 01:15 PM.
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Old 11th March 2013, 07:35 PM   #17
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Quote:
Originally Posted by Jmmlc View Post
Hello Vacuphile,

You don't use the Blauert criterium the right way it should.

For a given frequency if Blauert says x ms is the threshold, that means that with a delay between the 2 signals (e.g. pulses) larger than x, the 2 signals will be perceived as 2 separated signals.

Now if the delay is smaller than x then it signifies that only one "phase distorted" signal will be perceived.

(phase distortion being defined as for the "summation" signal having non constant group delay curve vs. frequency).

Best regards from Paris, France

Jean-Michel Le Cléac'h
Jaen Michel, you are talking about what Haas found out.
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Old 15th March 2013, 09:57 AM   #18
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Default More simulations, and possibly an improvement

Hello,

In response to some insightful comments made by Jean-Michel Le Cléac'h (here and on other French-language forums), I have made new simulations trying to further improve on the TAD crossover.

This is what I have come up with:

- Woofer low pass: 6th order Bessel at Fx * 1.25 (-6dB of attenuation at Fx)
- Tweeter high pass: 2nd order Butterworth at Fx * 1.3 (-6dB of attenuation at Fx)
- Offset = 0.4 * c / Fx

The result is even better phase match and a smoother Group Delay curve, still with a practical offset between Woofer and Tweeter.

Comments welcome.

Marco
Attached Images
File Type: png TADmodFR.png (34.5 KB, 464 views)
File Type: png TADmodPhase.png (31.0 KB, 449 views)
File Type: png TADmodGD.png (22.4 KB, 121 views)
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Old 15th March 2013, 02:03 PM   #19
jmbee is online now jmbee  France
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Hello,

Vacuphile : "At 450 Hz, it is at least four times higher than the 0.8 ms in the example."

That does'nt reflect the sensibility to phase distorsion , imho.
Do experiment with a soft like MacAudio Tool box, create a few sinus harmonics and change one of them from 0° to only 30°. Then 60° ect.
Click the image to open in full size.
Mac Audio Function Generator Software Macintosh
No doubt you will hear changes resulting of variations of the wave form.

crd
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Old 17th June 2013, 10:22 PM   #20
pw8888 is offline pw8888  France
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Quote:
Originally Posted by marco_gea View Post
Hello,

In response to some insightful comments made by Jean-Michel Le Cléac'h (here and on other French-language forums), I have made new simulations trying to further improve on the TAD crossover.

This is what I have come up with:

- Woofer low pass: 6th order Bessel at Fx * 1.25 (-6dB of attenuation at Fx)
- Tweeter high pass: 2nd order Butterworth at Fx * 1.3 (-6dB of attenuation at Fx)
- Offset = 0.4 * c / Fx

The result is even better phase match and a smoother Group Delay curve, still with a practical offset between Woofer and Tweeter.

Comments welcome.

Marco

HI Marco
Is there any way i could contact you ?
i have few question regarding TAD 2402 and i am sure you would have a way to help me :-)
thanks
phil
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