I'd like to invite everybody to a technical discussion about simple shaped reflectors/deflectors mounted in front of common piston drivers. Here's an example:
What is its task?
What are the working principles?
Are there any real world measurements that confirm functionality?
How does shape, size and distance from driver affect the performance?
How does the driver affect performance?
Can the behavior be modeled?
Any references and measurements are welcome.
An externally hosted image should be here but it was not working when we last tested it.
What is its task?
What are the working principles?
Are there any real world measurements that confirm functionality?
How does shape, size and distance from driver affect the performance?
How does the driver affect performance?
Can the behavior be modeled?
Any references and measurements are welcome.
The reflector’s ”task” is to provide 360 degree coverage in the high frequency range of the speaker.
The working principle is high frequency sound waves reflect like a ray of light off a mirror.
A simple cone shape as depicted will have a very narrow vertical dispersion at high frequencies.
The size of the reflector must be around a wavelength long to be effective, wavelengths longer than the reflector will diffract around the reflector rather than reflect.
Different shapes will reflect in different directions.
Different drivers will have different radiation patterns at different frequencies, emanating from different parts of the cone. The larger the driver, the lower the frequency that the speaker narrows in HF dispersion.
For a model to be useful, it would have to use the complex radiation pattern of a specific driver , which would require measurement of the driver prior to creation of the model.
Hi Markus
Digging down deep for topics? I cannot imagine such a device working well. The B&O device didn't.
"Fluid mechanics" versus "ray tracing"!? Thats a new one. So "Acoustics" is now "Fluid Mechanics"? Well I guess that it always was, its just that Fluid Mechanics is mostly a static flow analysis and acoustics is a dynamic one where any static flow is ignored. So I guess that B&O is interested in the air currents arround the room and their effect on the sound?
Digging down deep for topics? I cannot imagine such a device working well. The B&O device didn't.
"Fluid mechanics" versus "ray tracing"!? Thats a new one. So "Acoustics" is now "Fluid Mechanics"? Well I guess that it always was, its just that Fluid Mechanics is mostly a static flow analysis and acoustics is a dynamic one where any static flow is ignored. So I guess that B&O is interested in the air currents arround the room and their effect on the sound?
That rattle you just heard was me preparing my correction for that problem if I ever owned these speakers
That rattle you just heard was me preparing my correction for that problem if I ever owned these speakers
lol!
possibly Puffery - but Moulton has the PHD, papers
I assume Moulton was referring to some Ansoft style multiphysics modeling, maybe compressibility, flow losses from the cavity, edges - I agree that Hemholtz, Diffraction, acoustic impedance may the more common/useful engineering aproximations - didn't you find anything in phase plug design that needed a little more than linear acoustic modeling?
maybe it was just meant to contrast real Acoustic modeling vs Ray Tracing
he does post polar response Moulton Laboratories :: A new loudspeaker design
I assume Moulton was referring to some Ansoft style multiphysics modeling, maybe compressibility, flow losses from the cavity, edges - I agree that Hemholtz, Diffraction, acoustic impedance may the more common/useful engineering aproximations - didn't you find anything in phase plug design that needed a little more than linear acoustic modeling?
maybe it was just meant to contrast real Acoustic modeling vs Ray Tracing
he does post polar response Moulton Laboratories :: A new loudspeaker design
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Yes, correct. B&O did not renew the license. If it had been successful they certainly would have.
There is nothing of interest in loudspeaker design that cannot be done with standard linear acoustic modeling. Fluid dynamics, ala the full Bernoulli equations, are never necessary when static flow is ignored. Even in nonlinear acoustics, the static flow terms are ignored , but the dynamic nonlinearity of the air is retained. But nothing in "audio" requires this kind of analysis.
Yes, he does show polar responses - they prove my point. There is nothing "good" about them. This whole concept was ill-conceived and fell flat in the marketplace. I first saw it at Dave's studio way back before it was even a patent. It didn't interest me then and still doesn't now. We always say "time will tell!" - it did.
Here's my more or less random prototype:
Driver is a Visaton B200. The reflector angle is about 45° and its circumference matches that of the driver's cone.
0° to 90° in 10° steps - box without reflector/with reflector:
Box only:
Box with reflector:
An externally hosted image should be here but it was not working when we last tested it.
Driver is a Visaton B200. The reflector angle is about 45° and its circumference matches that of the driver's cone.
0° to 90° in 10° steps - box without reflector/with reflector:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Box only:
An externally hosted image should be here but it was not working when we last tested it.
Box with reflector:
An externally hosted image should be here but it was not working when we last tested it.
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Eh? Are we talking about the same thing? B&O bought the Patent(s) and split the Rights of usage; its been instrumental in turning Bang & Olufsen's fortunes around.
Originally Posted by gedlee
Hi Markus
Digging down deep for topics? I cannot imagine such a device working well. The B&O device didn't.
Dispersion is usually specified with -6 dB points, note that the -6 dB point of the Soundsphere Model 110B from 3 kHz to 8 Khz is perhaps 7 degrees, while the Architects and Engineers Specifications states the vertical polar coverage shall be 180°.
They didn’t lie completely, the vertical polar coverage is around 180° at 250 Hz, of course a conventional speaker has nearly that dispersion that low too.
The B&O / Sausalito “lens” basically is a fancy looking version of a similar reflector, which offers very wide horizontal dispersion, but extremely narrow vertical dispersion.
The coverage pattern goes from roughly spherical at low frequencies to a disc shape at high frequencies.
As David Moulton wrote: “The full reasoning regarding why such performance is desirable is well beyond the scope of this paper. “
It is also beyond the scope of my imagination why such performance would be desirable .
As Earl Geddes wrote, “This whole concept was ill-conceived and fell flat in the marketplace. I first saw it at Dave's studio way back before it was even a patent. It didn't interest me then and still doesn't now. We always say "time will tell!" - it did. “
Hi Markus
Digging down deep for topics? I cannot imagine such a device working well. The B&O device didn't.
Soundsphere has been peddling the reflector “technology” since 1976.
Dispersion is usually specified with -6 dB points, note that the -6 dB point of the Soundsphere Model 110B from 3 kHz to 8 Khz is perhaps 7 degrees, while the Architects and Engineers Specifications states the vertical polar coverage shall be 180°.
They didn’t lie completely, the vertical polar coverage is around 180° at 250 Hz, of course a conventional speaker has nearly that dispersion that low too.
The B&O / Sausalito “lens” basically is a fancy looking version of a similar reflector, which offers very wide horizontal dispersion, but extremely narrow vertical dispersion.
The coverage pattern goes from roughly spherical at low frequencies to a disc shape at high frequencies.
As David Moulton wrote: “The full reasoning regarding why such performance is desirable is well beyond the scope of this paper. “
It is also beyond the scope of my imagination why such performance would be desirable .
As Earl Geddes wrote, “This whole concept was ill-conceived and fell flat in the marketplace. I first saw it at Dave's studio way back before it was even a patent. It didn't interest me then and still doesn't now. We always say "time will tell!" - it did. “
Attachments
The Soundsphere fails as a speaker but survives as a business venture using PT Barnum’s “a sucker is born every minute” approach since 1976, they are selling to a new generation of suckers now
.The Soundsphere suffers from the same problem that the B&O / Sausalito lens has, wide horizontal dispersion, but extremely narrow vertical dispersion.
Of course, David Moulton seems to think that problem is a virtue
.One man’s meat is another man’s poison
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