I'm inclined to agree. The horizontal planes should be fine, as there is lateral symmetry to a stacked pair. There would be all sorts of comb effects in the vertical direction. A three-foot offset is a LOT for a point source, though that really is the case only for the higher frequencies.
He has a two pairs, though, so it would be easy enough to try.
The traditional way to increase output from the 63 is to add a dipole woofer that operates below about 100 Hz. Gradient made a commercial unit, and some DIY builds can be found on the Web. Most use the woofer as a stand for the 63.
None of this comb-effect problems are found with stacked old Quads, where the panels run vertically. Stacking a pair merely extends the panel lengths.
I'll note that I may have over-complicated the simple math analysis I suggested. The case for a single point source, or for a known radius, has been solved. One can use superposition to obtain the combined response, and this is not that difficult. One can use Excel to evaluate the results if desired.
Got say ...if were talking Acoustats the spectra setup is a big step forward in dynamics....but the Spectra11-1100 is the only one that I can get real dynamic rang out of...with the bias ,panel frame fix....why....the panels only see above 100hz.....but I gess were talking full rang...so I gess the tube servos amp are the winners....or any other ESL with drack drive tube amps
I have the Spectra 3,an the 1+1s sound slow next to the spectra11....
I have the Spectra 3,an the 1+1s sound slow next to the spectra11....
I sure do. I knew Thiele-Small theory back then, and knew nothing about dipoles. I thought they were very odd, and wondered how they possibly could provide bass of any sort. Celestion made very good or better products, but I found these to be mystifying.
It was only when Linkwitz started posting about dipoles that it made sense.
Are the 6000s still available new?
Stereophile review of Celestion System 6000
Celestion System 6000 loudspeaker system | Stereophile.com
White paper on bass unit here
https://www.diyaudio.com/forums/multi-way/46111-legacy-whisper-bass-2.html#post3897099
Celestion System 6000 loudspeaker system | Stereophile.com
White paper on bass unit here
https://www.diyaudio.com/forums/multi-way/46111-legacy-whisper-bass-2.html#post3897099
Thanks for the links!
I looked at some pictures of the 6000 subwoofer, and indeed it uses two drivers, one on either end of the "box." What seems odd is that the box contains a few inch slot near the center all the way around it. It would largely suppress cavity resonances, I suppose, but I'd think sound would leak through it.
Maybe the impedance is high enough that there is little acoustic output. It could also be that the size is such that it would pass only higher frequencies that are removed by the crossover. I don't know.
Linkwitz looked at it and had no trouble with it. It must work OK or Celestion would not have released it.
I looked at some pictures of the 6000 subwoofer, and indeed it uses two drivers, one on either end of the "box." What seems odd is that the box contains a few inch slot near the center all the way around it. It would largely suppress cavity resonances, I suppose, but I'd think sound would leak through it.
Maybe the impedance is high enough that there is little acoustic output. It could also be that the size is such that it would pass only higher frequencies that are removed by the crossover. I don't know.
Linkwitz looked at it and had no trouble with it. It must work OK or Celestion would not have released it.
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Because it is a dipole, both cones should move together so that there should be no differential pressure change between them, and hence no air 'squirted' in or out through any hole, contained in cavity between them; constant distance between the cones under travel, ideally that is.
I would like to have heard one, they were praised.
I would like to have heard one, they were praised.
As I posted elsewhere, a box is not a good thing; it is one way to deal with the rear wave. Better to think in terms of how to work with the rear wave. Simply have the rear wave waft into the room after some twists and turns is a satisfactory approach and the results in a real room with complex surfaces are nothing like the textbook annihilation diagram. Leaky sealed boxes are an esp good solution. Ditto for labyrinths.
Long pipe to sequester rear wave
Long pipe to sequester rear wave
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Pharos,
I was trying to figure that out too. The maximum SPL is limited by Xmax, which doesn't change if you have one woofer or two. They would be have a greater SPL per watt, if implemented properly. Perhaps it helps performance to have one pulling while the other is pushing? It might minimize the effect of the slots. I might also affect reflections on the far side of a single woofer, and hence minimize cavity resonances.
These purely are speculations. It does make it twice as expensive. Celestion's engineers are good, so they must have had a reason. It just is not clear to me what it is.
I was trying to figure that out too. The maximum SPL is limited by Xmax, which doesn't change if you have one woofer or two. They would be have a greater SPL per watt, if implemented properly. Perhaps it helps performance to have one pulling while the other is pushing? It might minimize the effect of the slots. I might also affect reflections on the far side of a single woofer, and hence minimize cavity resonances.
These purely are speculations. It does make it twice as expensive. Celestion's engineers are good, so they must have had a reason. It just is not clear to me what it is.
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The Celestion paper says: "By setting two dipoles with specific effective path lengths for each dipole, we can see the effect of spacing of our two dipoles, as increasing the spacing brings the broadside null lower in frequency."
That seems imprecise to me, but I'm assuming the Legacy Whisper layout is doing something similar:
Project Whisper | An Engineers Perspective | Legacy Audio - Building the World's Finest Audio Systems
"The low frequency drivers operate in phase with each other and combine acoustically as a pair of figure-of-eights, one behind the other. The result: a compound null formed at the sides of the enclosure, which minimizes resonances and room reflections."
That seems imprecise to me, but I'm assuming the Legacy Whisper layout is doing something similar:
Project Whisper | An Engineers Perspective | Legacy Audio - Building the World's Finest Audio Systems
"The low frequency drivers operate in phase with each other and combine acoustically as a pair of figure-of-eights, one behind the other. The result: a compound null formed at the sides of the enclosure, which minimizes resonances and room reflections."
mattstat,
Thanks, I think. I have no idea what these mean in terms of the fundamental physics. Do either have any graphs or polar plots (for example) to illustrate what they mean?
Pharos,
Peak limiting I'd think would be set by the drive Xmax, which doesn't change if you use one or two woofers. But you may be right about non-linearities; I just don't know. If that is so, it might help lower the cost of the woofer so that it is competitive with a single, high-quality one. Those can be frighteningly expensive, at least for the best ones.
Thanks, I think. I have no idea what these mean in terms of the fundamental physics. Do either have any graphs or polar plots (for example) to illustrate what they mean?
Pharos,
Peak limiting I'd think would be set by the drive Xmax, which doesn't change if you use one or two woofers. But you may be right about non-linearities; I just don't know. If that is so, it might help lower the cost of the woofer so that it is competitive with a single, high-quality one. Those can be frighteningly expensive, at least for the best ones.
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I followed the Whisper link, and to me these look like standard dipoles with small baffles that would need a lot of power. With two large woofers they can get away with this approach. How the configuration creates deeper nulls is not clear to me.
In my opinion, the site contains lots of audio mumbo jumbo that does not tell me anything. Linkwitz's site is much better in that regard, but obviously the purpose is different. I'm probably one of the few audio kooks who used to read JAES for pleasure, though I have not done so for over 20 years. Clearly a commercial web site serves a different purpose.
In my opinion, the site contains lots of audio mumbo jumbo that does not tell me anything. Linkwitz's site is much better in that regard, but obviously the purpose is different. I'm probably one of the few audio kooks who used to read JAES for pleasure, though I have not done so for over 20 years. Clearly a commercial web site serves a different purpose.
The Celestion paper has some polar plots, but they aren't modern and didn't make a lot of sense to me on a quick glance.
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