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Multi-Way Conventional loudspeakers with crossovers

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Old 5th July 2010, 03:13 PM   #6601
Jmmlc is offline Jmmlc  France
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Hello,

Here is (attached) the theorical impulse response of a subwoofer dipole calculated using Hornresp and its spectrogram (new feature added in Hornresp).

As we can see the impulse response due to the "back" wave arrives latter than the "front" wave. I really cannot see how a simple minphase equalisation will lead to a grouping of the 2 single pulses!

Best regards from Paris, France

Jean-Michel Le Cléac'h


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Originally Posted by john k... View Post
Dipole response is minimum phase. Thus when a dipole response source is equalized, using minimum phase equalization, to the same band pass response as a direct radiator the impulse response is also the same.
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File Type: gif dipole.gif (30.1 KB, 537 views)
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Old 5th July 2010, 03:15 PM   #6602
Pano is offline Pano  United States
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Thanks for the info, Lynn. Interesting concept.

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Originally Posted by Lynn Olson View Post
Widerange 15" driver - AESpeakers TD15M or Altec/GPA 416. Both drivers have similar efficiency (97~98 dB/metre)
Be sure to measure and don't count on that number. Some of the 416s fall out at about 94dB/W. They are very smooth on top, to be sure.
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Old 5th July 2010, 03:42 PM   #6603
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Jmmlc View Post
Hello,

Here is (attached) the theorical impulse response of a subwoofer dipole calculated using Hornresp and its spectrogram (new feature added in Hornresp).

As we can see the impulse response due to the "back" wave arrives latter than the "front" wave. I really cannot see how a simple minphase equalisation will lead to a grouping of the 2 single pulses!

Best regards from Paris, France

Jean-Michel Le Cléac'h
Jean-Michel

I can confirm that there are two distinct impulses to a dipole as thats what appears in the measurements of the Orion. But I don't see why this cannot be considered minimum-phase at LFs. The two distinct impulses, as you show them, are only visible as such because of the HFs. Remove them and the two "bumps" blur together into a single waveform that would be minimum-phase.

It's the diffraction that is almost always present in a dipole that is non-minimum phase. But there isn't much diffraction -per se - at LFs.

Last edited by gedlee; 5th July 2010 at 03:50 PM.
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Old 5th July 2010, 03:49 PM   #6604
gedlee is offline gedlee  United States
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Quote:
Originally Posted by Lynn Olson View Post
In the worst case with digital time-domain equalization, you'd get three signals arriving at the ear, the first arrival from the front of the driver, the delayed and inverted arrival from the back of the driver, and the mistimed digital correction signal.
Welcome to the reality of electronic EQ.

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appealing concept: a closed box for a widerange bass driver ... and large-format horn have a conventional passive crossover, while the lower-efficiency ... has an active parametric EQ and power amplifier.
Where have I seen that before?
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Old 5th July 2010, 03:55 PM   #6605
Pano is offline Pano  United States
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Quote:
Originally Posted by gedlee View Post
The two distinct impulses, as you show them, are only visible as such because of the HFs. Remove them and the two "bumps" blur together ...
As is nicely shown in the spectrogram that Jean-Michel provides. What would the section below ~300Hz look like if the reflection were removed? Much different?

J-M, can you run the sim again without the reflection so we can see the difference in the low end? It would be interesting to see what happens.
Thanks!
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Old 5th July 2010, 04:16 PM   #6606
gedlee is offline gedlee  United States
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What "reflection"? There is one impulse from the front and another from the rear. But Jean-Michels impulses are idealized and could not be correct for a real system since each impulse would have to be a doublet and they would ring because of the HP characteristic. Filter out the highs and you just have two near sine waves that would blend together and become a single waveform without distinct peak arrivals.
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Old 5th July 2010, 04:19 PM   #6607
Pano is offline Pano  United States
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Sorry, reflection is the wrong word. I should have said "rear wave." What does the same simulation look like without the rear wave?
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Old 5th July 2010, 05:12 PM   #6608
Jmmlc is offline Jmmlc  France
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Hello Panomaniac,

Here is the frequency response of the simulated subwoofer (actually this is an Infraplanar as the one used by Marco Henry in the to complement the 2010 version of La Grande castine) just using the front wave.

See attached file.

Best regards from Paris, France

Jean-Michel Le Cléac'h


Quote:
Originally Posted by panomaniac View Post
What would the section below ~300Hz look like if the reflection were removed?

J-M, can you run the sim again without the reflection so we can see the difference in the low end?
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File Type: gif front_subwoofer.gif (31.1 KB, 506 views)
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Old 5th July 2010, 05:26 PM   #6609
Jmmlc is offline Jmmlc  France
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Hello Earl,

Your explanation is OK for me as long as we don't ask the woofer to reproduce frequency at which the wavelength becomes short.

In order to see what happens at low frequency, I filtered the simulated Impuse response of the dipole (front + rear wave with a difference of path of 1 meter) using a 4th order low pass filter of the 4th order with F-3dB = 100Hz.

You'll see in attached file both, the shape of the pulse, the frequency response, the phase curve and the group delay curve (from ARTA).

Wish that measured real system could behave the same in the low frequency! (group delay variation lesser than time equiavalent to the difference of path between the rear and the front wave, very few phase variation, excellent frequency response.)

At very low frequency the wave drag along the baffle and turn around the baffle edge but from which frequency can we say that the rear wave of a dipole needs a reflection on a wall to interfer with the front wave...(if we consider the directivity of the piston, it should depend on the size of the OB I guess).

Best regards from Paris, France

Jean-Michel Le Cléac'h

P.S.: that dipole subwoofer is Claude Lacroix's Infraplanar.

Quote:
Originally Posted by gedlee View Post
What "reflection"? There is one impulse from the front and another from the rear. But Jean-Michels impulses are idealized and could not be correct for a real system since each impulse would have to be a doublet and they would ring because of the HP characteristic. Filter out the highs and you just have two near sine waves that would blend together and become a single waveform without distinct peak arrivals.
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Old 5th July 2010, 05:46 PM   #6610
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I agree entirely. This thread was an opportunity for some of the greatest minds in our hobby to brainstorm, even if much like a brainstorming session it got off track sometimes and was hard to follow. There's lots of good info in here, even if it takes a couple days of reading to find it. Honestly, someone should take this offline someplace and index it for topics.

John
So how would you do that? I mean, can you download the entire thread at one time without going page by page using a screen capture program?
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