The flatness/smoothness of the direct signal is the most important. (Note this need not be "on-axis".) There can be a small falloff of the direct field at HFs, in fact this is highly desirable if the system is CD. Nothing can make up for a bad direct sound.
Next would be the control of the early reflections through directivity. The directivity has to be below 90 degrees or the side walls will get too much sound. this should be done down to about 700 Hz below which this factor becomes less important. The directivity must be well controlled out to +- 30 degrees so that you can toe-in the speakers and because if you do this then the direct signal is not the axial signal its an off axis response - typically 20-25 degrees.
A diffraction free design is important as well, but this is very hard to quantify.
Thermal modulation is important as well, but this not a factor when you use 15" pro woofers and compression drivers.
After that one gets into the smaller things that don't rate very high. Things like THD just aren't a factor in a speaker like mine so I don't rate it. Not that in an arbitrary design its not a factor because it can be. But with the driver set that I typically use the nonlinearities at normal listening levels are simply not a factor.
Next would be the control of the early reflections through directivity. The directivity has to be below 90 degrees or the side walls will get too much sound. this should be done down to about 700 Hz below which this factor becomes less important. The directivity must be well controlled out to +- 30 degrees so that you can toe-in the speakers and because if you do this then the direct signal is not the axial signal its an off axis response - typically 20-25 degrees.
A diffraction free design is important as well, but this is very hard to quantify.
Thermal modulation is important as well, but this not a factor when you use 15" pro woofers and compression drivers.
After that one gets into the smaller things that don't rate very high. Things like THD just aren't a factor in a speaker like mine so I don't rate it. Not that in an arbitrary design its not a factor because it can be. But with the driver set that I typically use the nonlinearities at normal listening levels are simply not a factor.
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Earl, I was wondering what your thoughts are on the "image control waveguide" that JBL uses in their M2 speaker, which might be a competitor of the uber-Summa. I wonder what would happen in the furrows, can't see how it would be an improvement over an oblate spheroid unless it's generating reflections that help normalize the off-axis response, and that's a questionable improvement because it's the sort of thing a diffraction horn does. Is that what it is, a "kinder, gentler" diffraction horn?
By the way, it sounds like JBL is using your 6% nickel-copper alloy, or something similar, in the "patented" voice coil of their woofer.
JBL Professional :: Recording & Broadcast :: M2 Master Reference Monitor
An externally hosted image should be here but it was not working when we last tested it.
By the way, it sounds like JBL is using your 6% nickel-copper alloy, or something similar, in the "patented" voice coil of their woofer.
JBL Professional :: Recording & Broadcast :: M2 Master Reference Monitor
audiokinesis,
There was a discussion about perhaps a month ago on this subject and both Earl and others did discuss the theory and principal of this JBL horn design. Not sure how far back you have to go to read that but it is here in this thread.
There was a discussion about perhaps a month ago on this subject and both Earl and others did discuss the theory and principal of this JBL horn design. Not sure how far back you have to go to read that but it is here in this thread.
Thank you. I searched before posting and didn't find, but I will search again.
Yes, I see it as "kinder, gentler" diffraction horn. That's a good way of putting it.
Actually the JBL patent on voice coil wire uses a different composition that includes silicon. It works a little better than nickel, but has a much higher cost and is not as readily available. That and they have a patent on it, which they wouldn't with nickel.
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I don't see how all that follows. I don't think that there is never a situation that requires a diffraction slot. There is always a solution without one. What is the claimed coverage angle?
Earl, I was wondering what your thoughts are on the "image control waveguide" that JBL uses in their M2 speaker, which might be a competitor of the uber-Summa. I wonder what would happen in the furrows, can't see how it would be an improvement over an oblate spheroid unless it's generating reflections that help normalize the off-axis response, and that's a questionable improvement because it's the sort of thing a diffraction horn does. Is that what it is, a "kinder, gentler" diffraction horn?
By the way, it sounds like JBL is using your 6% nickel-copper alloy, or something similar, in the "patented" voice coil of their woofer.
JBL Professional :: Recording & Broadcast :: M2 Master Reference Monitor
IMHO, the M2 looks this way for the following reasons:
1) A wide waveguide generally has flatter response than a narrow waveguide. One way to examine this is to look at the measurements of Danley's narrow angle synergy horns, like the SH25, versus the SH50 or SH60. Narrow angle waveguides have more ripple.
2) A narrow waveguide has higher output on-axis. This is simple; it's the same amount of energy focused into a narrower 'cone'
So we have a couple of competing criteria. If you want it smooth, you want a wide angle waveguide. If you want it to have very high output, you want a narrow angle waveguide.
So the JBL has both. At 0, 90, 180, and 270 degrees it's a narrow angle waveguide. At 45, 135, 225, and 315 degrees it's a wide angle waveguide.
(Note that I'm only talking about the first couple inches of the waveguide.)
I think another factor is that the waveguide shape also varies the pathlength with angle. From reading the AES paper of the designer, he uses 'randomization' in the phase plug of the compression driver. So the pathlength variation might be another way to 'randomize' the response.
Plus, it just looks cool.
Now you're talking. I think it's a marketing gimmick. Not a horribly performing device, but still a gimmicky way of doing it.
Out of curiosity, I built some waveguides using a similar idea. Basically a conical horn. And then I added some 'vanes' to reduce the volume of the horn.
And it actually improved the frequency response. Go figure.
Twenty years ago there was a set of car audio horns that were 'pinched' on axis, and I'm guessing it was for a similar reason?
120° H x 100° V - 1,5 inch throat without DS ? how?
One more thing, For large studio monitors there are "almost" PA demands SPL wise. Certainly in 115-120db range. No 1 inch throat CD can do 800hz at 120° H x 100° V.
For given conception is not gimnick it is quite rational design.
Ok, you can make 3 way...
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Romtom,
Perhaps a 1" compression driver might have a problem meeting your spl level but I see no reason to believe that no compression driver can operate down to 800hz. Now why you would want to have the dispersion angle you are listing of 120 x 100 degrees I am not sure, but that shouldn't preclude a large enough horn with a small driver from getting down to 800hz. Now yes it may have a beaming high frequency but that has much to do with the actual waveguide design more than the fact that it is a small format driver.
Perhaps a 1" compression driver might have a problem meeting your spl level but I see no reason to believe that no compression driver can operate down to 800hz. Now why you would want to have the dispersion angle you are listing of 120 x 100 degrees I am not sure, but that shouldn't preclude a large enough horn with a small driver from getting down to 800hz. Now yes it may have a beaming high frequency but that has much to do with the actual waveguide design more than the fact that it is a small format driver.
Thanks for replying and correcting my misconception on their voice coil.
On another subject, after stumbling across your recommendation, I ordered Kahneman last night.
Thank you for the insightful analysis!
Eyeballing it, the new JBL waveguide looks to me sort of like an evolution of the bi-radial.
I wonder if randomizing the pathlengths in the phase plug of the compression driver is an intended goal, or justifiction for an inevitable consequence of the push-push diaphragm geometry. Which may work great, I don't know.
Your last point however is probably the most important one for the success of the product. It is pretty much unforgettable after one glance.
Please, just think about it realistic - this is not DIY, They have design constrain from beginning - size and dispersion was clearly set as objectives.
besides how will vertical lobe looks with larger horn. I not talking about what is ultimate possible dont take it literary. And why dispersion. The Toole things i suppose
And everybody in studio wants to good sound. Do take it wrong but why from DIY POV every commercial attempt must be wrong. I think that this particular monitor is very ballanced set of compromise.
Tomtom,
I didn't see any specific information in your post about any real commercial product so just assumed you were speaking in generalities. Personally I have never come across a horn with that wide a dispersion angle, that would be difficult with any compression driver to truly achieve 120 degrees of dispersion. A waveguide would be more like it for that type of angular dispersion. Most compression drivers with any kind of throat length would never be able to match a dispersion angle that wide. I would think the only practical way to do anything like that would be one of the newer compression drivers that really have no throat section and end at the tip of the phasing plug. One or 2 inches of straight conic throat section would make that wide a dispersion without a diffraction slot pretty much impossible.
I didn't see any specific information in your post about any real commercial product so just assumed you were speaking in generalities. Personally I have never come across a horn with that wide a dispersion angle, that would be difficult with any compression driver to truly achieve 120 degrees of dispersion. A waveguide would be more like it for that type of angular dispersion. Most compression drivers with any kind of throat length would never be able to match a dispersion angle that wide. I would think the only practical way to do anything like that would be one of the newer compression drivers that really have no throat section and end at the tip of the phasing plug. One or 2 inches of straight conic throat section would make that wide a dispersion without a diffraction slot pretty much impossible.
I think it more like conical with second flare and "distibuted mode diffraction slot"
and definitely good and unique look was in priority list. It looks good and from what i hear it works very very well.
Sorry i was talking about JBL M2 only not general.
Yes throatless driver was necessary to make this /D2 is throatless/. And i think we agree that with 1,5 inch constrain /wide dispersion small horn and 800hz XO/ difraction slot is necessary.
Whole discussion as i see it was about that M2 - is just gimmick to look good.
As i see it /given design constrain and objectives/ it is very clever engineering.