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Multi-Way Conventional loudspeakers with crossovers

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Old 11th September 2007, 11:25 AM   #1931
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Default Re: Other drivers worth considering?

Quote:
Originally posted by mikey_audiogeek
Hi Lynn, have you considered Triangle drivers? Bit low on efficiency, but otherwise...

Triangle drivers

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Mike
Um, I listened the Triangle speakers, and they didn't leave a strong impression. But they're hardly alone - the current fad for audiophile qualities like "fast" and "slam" has led not to lower distortion and more efficiency (which sure would have been nice), but drivers with poorer self-damping, only slightly more efficiency, and ever-more-harsh sound with very rough response at the upper edge of the band.

It seems that modern designers are reacting to these problematic drivers in two ways: the "minimalists" are going for lots of excitement and thrills, using the rock-bottom simplest crossovers possible (but with very expensive parts), and letting the peaks sail right through. Unsophisticated listeners - and worse, reviewers - interpret the peaks and harshness as "speed" and "accuracy".

There's a lower-profile school that believes in extensive computer simulation and using crossovers of almost unlimited complexity. This "objective" school of designers tend to discount esoterica like audibility of capacitor coloration - or even believe it doesn't exist - so has no problem with complex op-amp circuits, multiple transistor amps, or high-parts-count crossovers with extensive notch filters and shaping networks.

I'm not in either school. I don't want to use drivers with problematic responses - too much work for too little return. I still remember the bad old days of KEF and Audax Bextrene drivers, with their characteristic qualities of lumpy midrange, and dreadfully low efficiencies (85 dB/metre typical). Now, audiophile efficiencies have crept up to 90~93 dB/metre (with a tailwind), but the drivers have gotten really peaky, and in ways that are very hard to correct - the worst peaks are typically directional, making a crossover correction useless.
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Old 11th September 2007, 11:53 AM   #1932
soongsc is offline soongsc  Taiwan
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I quite agree it's hard to find excellent drivers these days. The development process is very complicated. With a little tweaking, or slight mod in design, the Jordans probably can become even better than they are today. These are one class of drivers that have great potential.
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Old 11th September 2007, 12:01 PM   #1933
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Quote:
Originally posted by john k...

As for extracting phase form amplitude data, at least of a single driver, minimum phase reconstruction work very well if you have good amplitude data. Maybe pro sound driver manufactures don't supply sufficiently accurate amplitude data, most reprtable hifi driver manufactures do (SEAS, Vifa Peerless, ScanSpeak, etc). While I haven't looked at large panel (like Martin Logan ELS) of horns, I have yet to measure a conventional driver, cone, dome or small ribbon, that doesn't reduce to minimum phase on axis over its useful operating range. So what that leaves is what is the driver offset, a problem which is still of concern using impulse response techniques. Of course, I wouldn't consider 1/3 octave RTA a legitimate measurement of a driver's anechoic response.
I think one difference between us is that I'm no longer interested in SEAS, Vifa Peerless, ScanSpeak, etc. They've had 15 years to respond to the vacuum-tube subculture and the constantly-expressed demand for substantially higher efficiency, and have done their best to ignore it and hope it would go away. Well, it hasn't, there's only been a trivial 1~2 dB change in efficiency in more than a decade, and to me, the mainstream audiophile drivers sound worse than what they were making 15 years ago. That's why I'm looking at different vendors than the usual mainstream candidates.

I'm surprised that you haven't seen drivers depart from minimum phase. This is one of the most direct indicators of cone breakup, and it's gotten much worse with the popularity of very rigid Kevlar, carbon-fiber, composite, ceramic, and metal cones. When a cone no longer moves as unit and enters the breakup region, there are multiple, asynchronous centers of radiation all over the cone. This is a clear indication of a "no-go" zone, and indirectly shows a requirement for an aggressive high-slope crossover to avoid gross coloration.

The drivers that are most interesting - to me - are the ones that don't require aggressive equalization to avoid harsh sound, and are characterized by smooth, well-controlled rolloff regions that retain their minimum-phase character to very high frequencies. Since the prosound manufacturers can't be bothered to supply either impulse or complete FR/phase data information, I'll be finding this out the hard ($$$) way - I'm not expecting any free loans from 18Sound, JBL, or Fertin.
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Old 11th September 2007, 12:38 PM   #1934
jzagaja is offline jzagaja  Poland
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soongsc

Do you know any other drivers than Jordan/Bandor/Goerlich that shares similar concept of using variable thickness and stiffness? For example with all-PP composites it is possible to vary local mechanical properties in in a wide range.
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Old 11th September 2007, 01:13 PM   #1935
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Quote:
Originally posted by Lynn Olson
I'm not expecting any free loans from 18Sound, JBL, or Fertin.
Maybe this is not true for 18Sound. Their headquarter is in Italy and I've seen Giacomo Previ answering kindly to an italian diy forum member. The company is 8 years old, I think a link to this thread would be enough for a loan request.
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Old 11th September 2007, 01:49 PM   #1936
Rudolf is offline Rudolf  Germany
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Quote:
Originally posted by Lynn Olson
... At 1.6 kHz, wool felt (and other damping materials) are starting work pretty well. Gary Pimm is using Bonded Logic "Ultratouch" fiber to fill his open-backed dipole woofers with great success - this recycled cotton fiber has high absorptive properties, and Pimm's system has the best, most crisp, and tonally realistic bass I've heard so far.
Ultratouch seems to have a very linear absorption capacity over a wide frequency range. I would rather imagine absorption rising with frequency, so that at 1.6 kHz the WR would be "dead" in the back. Something like 41 mm thick Basotect might achieve this:

Click the image to open in full size.
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Old 11th September 2007, 02:48 PM   #1937
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by jzagaja
soongsc

Do you know any other drivers than Jordan/Bandor/Goerlich that shares similar concept of using variable thickness and stiffness? For example with all-PP composites it is possible to vary local mechanical properties in in a wide range.
Above 300Hz or so, I have not come across any as good. Bear in mind that certain material characteristics are just not documented, unless one has dedication as Ted did, it is very difficult to find the right formula without massive trial and error. The one I'm tweaking does better in the lower frequencies, but is not as good in the higher frequencies. The region from 15KHz~30KHz is the most difficult region to tweak in small metal drivers and very critical. I remember that Ted mentioned it just extented to 30KHz by chance, I wish I had that kind of luck. I understand that some people are trying some alloy with lithium that seeminly has better damping characteristics, but have not seen any on the market yet.
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Old 11th September 2007, 03:02 PM   #1938
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soongsc

So above 10kHz it is not possible to use polypropylene? (5-6"). It is 7 times less stiff than aluminium (oriented).

I'm wondering about Jordan's 30K ability - my friend ordered faulty units and then changed them to Vifa 10BGS. It looks much cleaner on CSD but he likes JXR6 more for its highs. For him Vifa is too dry.
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Old 11th September 2007, 04:47 PM   #1939
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by jzagaja
soongsc

So above 10kHz it is not possible to use polypropylene? (5-6"). It is 7 times less stiff than aluminium (oriented).

I'm wondering about Jordan's 30K ability - my friend ordered faulty units and then changed them to Vifa 10BGS. It looks much cleaner on CSD but he likes JXR6 more for its highs. For him Vifa is too dry.
If the cone is soft, the sound will not be as crystal clear because of how much vibration wave exists on the cone at the same time. The right combination of stiffness is necessary. I'm not familar with the 10BGS and could not find data on it. Soft cone material generally sounds dry because the soft cone absorbs some of the detail where the VC former meets the cone. This is the main reason alluminum is better in revealing detail.

I just went back to check my measurements, and my CSD are actually better than the Jordans. Now if I can get them to go to 30KHz, it would be nice.
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Old 11th September 2007, 05:25 PM   #1940
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Quote:
Originally posted by Lynn Olson


I think one difference between us is that I'm no longer interested in SEAS, Vifa Peerless, ScanSpeak, etc. [...] That's why I'm looking at different vendors than the usual mainstream candidates.

I'm surprised that you haven't seen drivers depart from minimum phase. This is one of the most direct indicators of cone breakup, and it's gotten much worse with the popularity of very rigid Kevlar, carbon-fiber, composite, ceramic, and metal cones. When a cone no longer moves as unit and enters the breakup region, there are multiple, asynchronous centers of radiation all over the cone. This is a clear indication of a "no-go" zone, and indirectly shows a requirement for an aggressive high-slope crossover to avoid gross coloration.

The drivers that are most interesting - to me - are the ones that don't require aggressive equalization to avoid harsh sound, and are characterized by smooth, well-controlled rolloff regions that retain their minimum-phase character to very high frequencies. [...]
Yes, I realize that you are looking at different types of drivers. And I'll be the first to admit that I'm not part of the SET subculture though I do like and have in the past (and will in the future) owned tube amps. I had a wonderful pair of EAR 509's designed by Tim de Paravicini (100 w into 4, 8, or 16 ohms). I had to opportunity to meet and talk with Tim at the time I bought them, back in the 80's. Don't know why I sold them.

On the other issue, break up is not necessarily a departure from minimum phase. This thread went through the multiple source/minimum phase thing when we were discussing diffraction(or was it in Earl's thread) and I don't think there is any reason to go there again other to say that as far as I recall for every conventional driver I have measured it has been possible to get a near perfect minimum phase reconstruction of the measured phase, on axis, well into the breakup even with highly resonance metal cone like the Seas W18 and W22. And is it really break up or uncontrolled resonance at and above breakup that are the issue. Assume for the moment that breakup is still minimum phase, at least in some cases. If the breakup is well damped and retains minimum phase behavior, how would it be identified from either the amplitude or phase response? I think the only way to verify breakup is viewing the cone motion with a laser scan or the like. And if there is a departure from minimum phase is that necessarily an indication of breakup or just that the size of the radiating area is much greater than the wave length?

It's not a big deal though. I understand you desire for better driver data supplied from the manufacture. I think one of the issues regarding phase is that it is a relative quality. There needs to be a clear reference point. For example, assuming minimum phase for the moment, the driver is minimum phase relative to the acoustic center. But where is the AC? That isn't an easy question to answer since the only way to accurately locate the AC is by constructing the minimum phase response and then removing delay from the measured phase until they match. And while that is easy to do, there are a number of parameters in the minimum phase reconstruction that must be specified some what arbitrarily which can alter the AC position. A physical reference is a better idea and for that reason I always reference the phase to the driver mounting flange.
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