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Old 13th May 2008, 06:45 AM   #21
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Quote:
Originally posted by Diogenes
crossover schematics
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Old 13th May 2008, 06:24 PM   #22
Salas is offline Salas  Greece
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I have registered in the Dahlquist Yahoo Group and have read the patents. Jon Dahlquist had grasped the importance of timing errors in multi way dynamic speakers back then. He talked about common large baffle diffraction problems and need for coherent rise time between sources.
He also talked about the staggered baffle sizes. He used them to aid the lower extension of each driver's passband. But before they created diffraction effects in the upper range he said. He integrated their lowering extension effects into his crossover design. He must have had some rise time criterion that he measured when designing the relative distances of the sources in the Z plane.


To grasp all that back then, is brilliant! I can imagine him performing literally hundreds of trials with a square wave generator a microphone, and an oscilloscope!

Ok, today we would talk about impulse response, edge diffraction, radiation centers, cardioid mids etc.
We could probably find many mistakes, do it better with the benefit of hindsight, FFT, internet etc.

But the dynamic speaker ground that Jon Dahlquist broke back then, and his guts to bring it down to an actual product that is still considered excellent, and worthy of a restoration cult, is amazing!

To be fair to the audio patriarchs, he is the interpreter of Quad's founder Peter J. Walker in the voice coil domain IMHO. But that was no mean feat!

RESPECT!

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Old 13th May 2008, 06:56 PM   #23
chrisb is offline chrisb  Canada
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Yup, no dummy that boy.


One can only dream what he could accomplish with today's driver and digital electronics technology. At the very least, the number of drivers and complexity of XO required to achieve the same sonics could be reduced.
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Old 13th May 2008, 07:09 PM   #24
Salas is offline Salas  Greece
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Quote:
Originally posted by chrisb
Yup, no dummy that boy.


One can only dream what he could accomplish with today's driver and digital electronics technology. At the very least, the number of drivers and complexity of XO required to achieve the same sonics could be reduced.

I can envisage a clone, which does not change the polar behavior between woofers and mid-woofer, so to cancel the original DQ-10 sonic discontinuity there as Gordon Holt spotted. That 600Hz cross between omni and semi cardioid was most likely causing the problem. That is why Jon Dahlquist was at a loss, by researching just the bass alignment. Also, much better sensitivity and nice impedance can be done today. A four way is very doable with much better drivers in the detail department too. Alignment and diffraction control can be well attained with today's knowledge and digital tools. As for the crossover, I would keep it first order series.
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Old 14th May 2008, 12:58 AM   #25
holdent is offline holdent  Canada
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In the early 1980's I fell in love with some DQ-10s but couldn't afford them as a student. So I think Salas' idea of recreating the sound as a DIYer is excellent.

I already have the 15" version of the Goldwood woofers Salas mentioned and think that the Eminence Alpha 15As are are a much better bang for the buck. So I'd argue for one Alpha 15A per side.

I tried modeling this using Martin King's OB worksheet for two drivers and the following parameters:
- the Alpha 15A and TangBand W6 789S Salas mentioned above
- a 32 x 22" baffle (no stand included),
- the Alpha 15A centered 10" up from the bottom
- mid-woofer directly above the Alpha off the baffle
- 1st order crossover at 200Hz as suggest by Salas
This is the result:

Click the image to open in full size.

As the TangBand is off the baffle its response drops off earlier but the result is still very good. The modeled impulse response appears to be excellent. [Note that the model assumes no rear wall]. Adding a 6" stand flattens the response curve. Going up to a 12" stand actually flattens the woofer response but requires minor crossover changes.
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Old 14th May 2008, 01:02 AM   #26
Salas is offline Salas  Greece
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The Alpha crossed my mind too. Nothing against it. Your cross looks over 300Hz to me. Use a little individual baffle for the TB and cut at 200Hz. Try to de-bump the low mids.
Because there is going to be a rear wall, I suggest thick foam behind the Alpha, and thick felt behind the TB as per the original mid-woofer.
Slow transition to cardioid will be achieved. Excellent for music's power range in a small room. Get those bands acoustically right, and the original DQ-10 will be a poor relative to the brave brand new -sensitive- clone.
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Old 14th May 2008, 01:15 AM   #27
holdent is offline holdent  Canada
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Incidently I would've liked to model the four GW-210s Salas suggested but Martin's OB worksheets will only model up to two woofers and I need the BL and Sd of the drivers - PE's website doesn't have them listed.
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Old 14th May 2008, 01:24 AM   #28
Salas is offline Salas  Greece
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Quote:
Originally posted by holdent
Incidently I would've liked to model the four GW-210s Salas suggested but Martin's OB worksheets will only model up to two woofers and I need the BL and Sd of the drivers - PE's website doesn't have them listed.
I suggested them as a nice dirt cheap example of a high qts assortment of enough square area. No need to stick with them.
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Old 14th May 2008, 01:56 AM   #29
holdent is offline holdent  Canada
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Quote:
Originally posted by salas
Your cross looks over 300Hz to me. Use a little individual baffle for the TB and cut at 200Hz.
Unfortunately the TangBand's low Qts (0.37) means that even in a 12 x 12" baffle the acoustic response will begin to naturally drop off higher. Adding the 200Hz 1-order electrical filter doesn't help... If you don't add the filter you'll hit the xmax limit of the TangBand with as little 3 watts. I'd actually go with a 300 Hz or higher 2-order (electrical) filter here or a higher cross with a 1st order filter.

Quote:
Because there is going to be a rear wall, I suggest thick foam behind the Alpha, and thick felt behind the TB as per the original mid-woofer.
I'd be worried that the cardiod response you're looking for will at least partially disappear as the materials won't uniformly reduce the rear output across the driver's frequencies. But I can't back this up with a reference or by modeling with Martin's worksheets.

Note that the modeled response with the rear wall set to be 1 m away is still very good:

Click the image to open in full size.
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Old 14th May 2008, 02:02 AM   #30
Salas is offline Salas  Greece
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Quote:
Originally posted by holdent
Unfortunately the TangBand's low Qts (0.37) means that even in a 12 x 12" baffle the acoustic response will begin to naturally drop off higher. Adding the 200Hz 1-order electrical filter doesn't help... If you don't add the filter you'll hit the xmax limit of the TangBand with as little 3 watts. I'd actually go with a 300 Hz or higher 2-order (electrical) filter here or a higher cross with a 1st order filter. I
Jon Dahlquist used first order -electrical-. at 600Hz. Look for second order acoustical, the lower you can.


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