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Old 4th June 2007, 09:42 PM   #951
JoshK is offline JoshK  Canada
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Lynn,

Your design a few pages back looks to have a lot of merit. I just finished reading your latest clarisonus blog entry. I might mention that SL probably didn't report your cascade solution as it was in conflict with one of his constraints that the system be relatively small form factor. The drawing you show is clearly not that.

The trapezoidal shape has a lot of diffraction benefits, I just wished that there was a more aesthetically pleasing way to design such a speaker. I am in the brainstorm part of my OB speakers as well and that is where I am stuck; designing speakers that are meant for maximum SQ but that my wife will allow in the LR.
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Old 5th June 2007, 12:43 AM   #952
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Default EnABL & Lowthers

Bud was sent a pair of PM6A's, not EX drivers. These will be at RMAF in the fall, in an OB. FYI these have silver voils and Ticonal magnets, making them a cheap (by Lowther standards) but very nice driver.

With regards to dynamics and compression, I will state that if placed in a TQWT or bass reflex the dynamics do get restricted, but that is not a problem on an OB if you have a crossover network. I use 180 hz. on an 18" x roughly 48" baffle. Compression is caused as the driver exceeds x-max (1mm) which is easy to do when used full range without a BLH design.

The 5" drivers (which Lynn calls 6") do have less dynamics than the 8" unless horn loaded. They are also less efficient (94 dB instead of 99dB). On the other hand they have more extended highs and are cleaner sounding. It will be interesting to compare the 8" EnABL drivers to the 5" units in this regard.

I am usually very free in loaning things out, and after RMAF will be happy to let others try these drivers. Before the show there will be a bit of a learning curve and work to make them sound there best, so unless you are coming to Chicago to hear them you will have to wait.

With regards to whizzerless units: the 8" drivers typically have a mechanical crossover to the whizzer at 2.5 kHz. When poorly controlled this was the cause of the Lowther shout, but recent design changes do a much better job of control. I do not know of any measurements of the whizzerless cone. My educated guess is that use of the RAAL ribbon down to 2.5 kHz would seem to fit this driver well. The PM6A is only 96 dB efficient, fitting well with the RAAL 95 dB rating. Past experience with ribbons indicates that they lack the same dynamics as Lowthers, but the RAAL is supposed to be a lot better than what I have had.

Having played with the BassZilla design OB for awhile the sound is nicely scalable, it sounds right at low volumes and high volumes. For reasons I do not understand this is more true with the Alnico drivers (A series) than the neodymium drivers (DX and EX series). The Eminence woofer mates pretty well, albeit not perfectly, with a slight lower mid bass heaviness. This is more likely due to my crossover (a variant of what Dick Olsher recommends due to my use of the PM6A rather than his DX4) than anything else.

BTW, a thoroughly enjoyable thread, with much interesting information. It is always a treat to look at the same problems from a different angle, and this thread has it in spades.
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Old 5th June 2007, 03:05 AM   #953
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Quote:
Originally posted by JoshK
Lynn,

Your design a few pages back looks to have a lot of merit. I just finished reading your latest clarisonus blog entry. I might mention that SL probably didn't report your cascade solution as it was in conflict with one of his constraints that the system be relatively small form factor. The drawing you show is clearly not that.

The trapezoidal shape has a lot of diffraction benefits, I just wished that there was a more aesthetically pleasing way to design such a speaker. I am in the brainstorm part of my OB speakers as well and that is where I am stuck; designing speakers that are meant for maximum SQ but that my wife will allow in the LR.
Josh and Jon, thanks for the timely and informative comments. Much appreciated.

On the size issue, one of the things that appeared on this thread (or another DIYAudio OB thread) was the discovery by the European researchers that the single-point model of driver radiation, as used by HF Olson and many others, was not in fact accurate. Driver size matters. Large, diffuse sources have substantially less diffraction than small, single-point sources, and moreover, go deeper in the bass than predicted by the outdated single-point models. (This is why the Edge simulator behaves differently for different-sized drivers.)

This is a very significant finding that is still overlooked by some of the OB theoreticians. The implication is that baffles need to have a large percentage of their surface covered by drivers - I also see a corollary that drivers need to be grouped together as closely as possible so they radiate as a unit. A vertical line may not be the optimum shape, at least once you get into the 1/f rolloff region.

That's why I'm "stacking up" the drivers that are closest to the floor, creating a group of 6 drivers (including the mirror images). You could go even further and have a closely-spaced group of 8 drivers (a quartet of physical drivers) - like a Marshall stack on stage, with the WR driver above it.

A straight-line vertical stack loses the close coupling with the floor reflection, and throws away a lot of potential 1/f gain. It has to be remembered that although the floor reflection is a nuisance from a measurement perspective, it is completely natural-sounding, something we expect to hear.

It's the absence of a floor reflection that sounds unnatural - and don't expect a strong floor reflection in modern multimiked recordings, where the mike is quite close to the instrument or singer. Remember, in nature, the only time you don't hear a 2~3 mSec ground reflection is when you're sitting high up in a tree or are right at the edge of a deep canyon.
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Old 5th June 2007, 03:36 AM   #954
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Default Question for you horn guys

This is a question for all the horn enthusiasts perusing this thread:

With a good LeCleac'h profile 550 Hz horn - like, say the Azurahorn AH-550 - and a crossover around 1 to 1.4 kHz, what differences will I hear between 1", 1.4", and 2" exit compression drivers of similar high-quality design?

Looking at the Radian product line, for example, the drivers would be the 465, the 745, and the 950. The 465 has a 1.75" diaphragm, and a 1" exit. The 745 has a 3" diaphragm and a 1.4" exit. The 950 has a 4" diaphragm and a 2" exit. All of the drivers have a roughly 2:1 compression ratio, or maybe the ratio depends on the relative areas of the diaphragm and the exit.

If the horn size and crossover frequency are the same, how would the 3 drivers sound different? This is a serious question, and I'm curious about the answer. Yes, I know, the bigger drivers get into trouble above 10 kHz. I can see that from the curves. But what about the rest of the range, from 1 to 10 Khz?
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Old 5th June 2007, 01:08 PM   #955
CV is offline CV
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Hi Lynn,
This is somewhat tangential...
Tom Danley explained how all direct radiators produce a 90 degree acoustic phase shift (when wavelength > driver size), whereas proper horns (or very large ESLs) don't.

It struck me that it might be possible that LF units on a large baffle couple to each other in such a way that the "effective" driver area (from a radiation patterb perspective) is much larger than Sd x n. May well be that a large LF array has temporal characteristics nearer to horn bass as a result.

As for compression drivers, I'd think that the higher the x/o, the smaller the throat you'd want. Just my gut feeling from the consideration of having the throat diameter << a wavelength - I'd feel weird having a source lobing away right at the throat.

This may well be an oversimplification given the action of the phase plug, but still, one wouldn't stick a Lowther in a VOTT midbass horn.

From a practical perspective, myl experience is limited to drivers of 1.4 or 1.5", all of which need tweeters. I've run S2 and RCA field coils on the same 1.5" 340Hz horn (I commissioned that and the 550 from Martin) and they sound completely different.

Speaking of phase plugs, that's what governs the compression ratio - I assume you were using the term more loosely than that as shorthand for exit/dia area...

Best and hope your recovery is proceeding well,
cv
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Old 5th June 2007, 01:28 PM   #956
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Quote:
Originally posted by CV
Hi Lynn,
This is somewhat tangential...
Tom Danley explained how all direct radiators produce a 90 degree acoustic phase shift (when wavelength > driver size), whereas proper horns (or very large ESLs) don't.
cv
But when I do a near field measurement on the direct radiator, they are square wave-like. There is no so-called phase shift. The key is flat frequency response. Maybe I never done it right

Personally I think the strength of horn speakers is their dynamics (which is a result of low memory effect and low surround/spider hysteresis). A horn speaker has a back EMF much larger than direct radiator. That means the ratio of back EMF to the impedance is much higher too, which in turn means better cone control. It can be mathematically shown that the hysteresis in those horns speakers are lower.
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Old 5th June 2007, 02:39 PM   #957
CV is offline CV
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Brian,
Very interesting! What frequency did you use?

I wonder if nearfield vs farfield is an issue here as well?

As for surrounds/spiders, I've long felt that these do more harm than they are given the blame for. I suspect adherents of true compression driver bass are hearing the absence of driver hysteresis as you imply...

best,
cv
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Old 5th June 2007, 10:25 PM   #958
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Quote:
Originally posted by rythmikaudio


But when I do a near field measurement on the direct radiator, they are square wave-like. There is no so-called phase shift. The key is flat frequency response. Maybe I never done it right

Personally I think the strength of horn speakers is their dynamics (which is a result of low memory effect and low surround/spider hysteresis). A horn speaker has a back EMF much larger than direct radiator. That means the ratio of back EMF to the impedance is much higher too, which in turn means better cone control. It can be mathematically shown that the hysteresis in those horns speakers are lower.
Reading between the lines here, that would imply as the bass array grows larger - and has more intimate coupling with the floor reflection - efficiency goes up, the ratio of diaphragm mass to air-load becomes more favorable, and by inference, back-EMF's increase as well, gradually approaching the horn condition.

This is the opposite of a ribbon or magnetic-planar, with very low BL products, which produce the characteristic flat impedance curve. As efficiency of a bass array goes up, all those little ripples in the Z curve should become more prominent, if back-EMF's are increasing (relative to DC resistance of the voice coil).

P.S. Thanks for the thoughts about the sound of different compression drivers, which I guess comes down to "listen and find out for yourself". I am told the exit pipe of a CD sometimes has a certain rate of expansion, which may not be the same as the inlet to a horn, thus causing a discontinuity, depending on the degree of mismatch. This would cause some horns to work with some CD's, but not with others. Something I need to find out more about.
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Old 6th June 2007, 12:35 AM   #959
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Default Inline resistors

Lynn ... You may have missed my question when your computer went nuts. May I ask again?

"Would you be kind enough to give the good and bad points of adding inline resistors to gain Q when it is seems necessary to bring the F3 lower?
If already mentioned will you link to post?"
Zene
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Old 6th June 2007, 06:14 AM   #960
Pano is offline Pano  United States
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Default Re: Question for you horn guys

Quote:
Originally posted by Lynn Olson
With a good LeCleac'h profile 550 Hz horn - like, say the Azurahorn AH-550 - and a crossover around 1 to 1.4 kHz, what differences will I hear between 1", 1.4" and 2" exit compression drivers of similar high-quality design?
A good question that I hoped would get a reply. Maybe it still will. It may be hard to find someone who has actually done the tests.

The 1.4" and 2" drivers I've heard, Altec, Westrex, TAD, some JBL and Renkus Heinz, all sounded very smooth to me. Very clean. They tended to be crossed lower than 1400Hz, though.

I can't say the same for 1" drivers, but they may not have been of the same quality, so that would skew results. Would be interesting to know the differences.

Meyer sound uses a 4" diaphragm compression driver coupled to an 80 x 40 horn in their CQ1. A box I used for years. Sounds very nice. Don't know the exit diameter. And of course being Meyer, it's got heavy processing in front. I always wanred to drag a pair of CQ1 home for a "Hi-Fi Listen." Never did.
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