gedlee said:
😕 😕
You damned (!) conventional horns for their diffraction. Diffraction was bad You told anybody. Now it comes out that Your horn lacks uniformity due to some - diffraction. Diffraction will always run back into the horn, and thats HOM. If HOM is anything at all.
You as far as I know never gave any substantial data on the (huge?!) effect of that foam. If I look at Your horn it doesn't seem to be so much improved compared to so called conventional implementations.
gedlee said:
I think Your trial to degrade my social and engineering competence falls back on You. I know a lot of people who are won't discuss with You. They tried and gave up. Why?
When it comes to substantial questions Yours is to repeat bold claims, not at least regarding Your scientific standards. There's some kind of contradiction in it. As soon as someone questions Your claims he gains Your disrespect and/or ignorance. That's not scientific but simply unkind.
1) You solved the wave equation in horns
2) Your solution has to stand the same practical limitations as fomer attempts
3) You are left with the same compromises as anybody
There is NOTHING bad with an Electro Voice HP940, that old bat of mine. I own a pair of JBL 2352 too - great sounding devices within their limitations: remember that dip on axis?!
cheers
Patrick,
"The whole idea of a waveguide is to provide pattern control, and mate with a woofer. The problem with the "waveguide" used in the econo-wave is that it's a compromised design. First of all, the coverage angle in the vertical axis and the horizontal axis is different. "
To me, that's an advantage.
As Wayne Parham elucidated in Zilch's thread at AK, in the vertical axis this is neither possible, because of the vertical driver spacing, nor desirable (except perhaps for something like a stadium seating situation); why waste output creating unwanted ceiling and floor reflections?
Dr. Geddes,
Thanks for your response; I guess given your experience it's reasonable.
From the pictures of the JBL PT device, I can't really see the slope changes that would point toward diffraction; did you see them?
I guess a tipoff that they must be there would be if they are significantly shallower in depth than your WG's, adjusted for lowest operating freq; is that the case?
Something else I wonder about is the creases in the corners; even if they don't have abrupt slope changes along the axis, is there something bad about them?
I guess if they went all the way to elliptical it wouldn't give the desired coverage for most PA/pro applications.
"The whole idea of a waveguide is to provide pattern control, and mate with a woofer. The problem with the "waveguide" used in the econo-wave is that it's a compromised design. First of all, the coverage angle in the vertical axis and the horizontal axis is different. "
To me, that's an advantage.
As Wayne Parham elucidated in Zilch's thread at AK, in the vertical axis this is neither possible, because of the vertical driver spacing, nor desirable (except perhaps for something like a stadium seating situation); why waste output creating unwanted ceiling and floor reflections?
Dr. Geddes,
Thanks for your response; I guess given your experience it's reasonable.
From the pictures of the JBL PT device, I can't really see the slope changes that would point toward diffraction; did you see them?
I guess a tipoff that they must be there would be if they are significantly shallower in depth than your WG's, adjusted for lowest operating freq; is that the case?
Something else I wonder about is the creases in the corners; even if they don't have abrupt slope changes along the axis, is there something bad about them?
I guess if they went all the way to elliptical it wouldn't give the desired coverage for most PA/pro applications.
noah katz said:
Does a piano create unwanted ceiling and floor reflections?
Does a singer create unwanted ceiling and floor reflections?
That's the whole point of a waveguide; the sound is uniform on AND off axis. To get uniform coverage, you have to use a waveguide with a coverage angle that's identical vertically and horizontally. As you deviate from ninety degrees, the design becomes compromised. Check out the pic I posted; JBL's own data demonstrates that the PT Waveguide is compromised. The waveguide in the M-Pro is much better, but not as good as the Summa. If anyone wants to listen to both of them, I have 'em both 🙂 C'mon over...
As soon as you arbitrarily decide that ceiling and floor reflections aren't important, you've compromised the design.
Of course compromises are sometimes necessary, particularly in engineering.
The difference between the waveguide in the Summa and the JBL PT Waveguide is that the JBL is compromised, and the waveguide in the Summa is not.
Patrick Bateman said:
There's a difference between a sound producer and reproducer. Comb filtering effects will be present within the recording as amplitude effects. A reproducer should not add its own fault on top of these where avoidable.
The vertical CTC is another valid point. In some ways the more conventional horn + woofer approximates a "point source" better, (CTC spacing), in some ways the OS waveguide does (symmetrical dispersion of waveguided freqs).
The waveguide in the Summa is compromised by its large vertical dimension, and other issues such as the 8kHz hole mentioned by Xpert. No such thing as a perfect solution in this world. I'd love to play with the doc's waveguides but I'm more interested in coming up with a good low-diffraction waveguide in elliptical format.
My personal opinions of various design philosophies
I respectfully disagree. Not so much about the specific implementation of the JBL PT waveguides but about the idea that asymmetrical patterns are a compromise. If you're mouting drivers vertically on a baffle, the pattern is asymmetrical even if the horn or waveguide itself is not. I would suggest that it is important to consider this as a part of the system design.
The vertical nulls make CD impossible along movement in the vertical plane, regardless whether or not the horn/waveguide itself is CD. At least with an asymmetrical device, you can decrease center-to-center spacing, which moves the nulls further apart, giving a larger, more useful forward lobe. Further, reducing the vertical pattern is useful for limiting ceiling reflections.
I think you'll find Dr. Geddes agrees with that assessment.
To me, this is the holy grail, so to speak: A waveguide with 90° horizontal beamwidth and 40° vertical beamwidth through the passband, and mouth small enough that vertical nulls could be set outside the pattern. If that is achieved, I'd say you have a no-compromise design.
The problem is, I am not at all sure those competing priorities can be realized simultaneously. Pattern control down low requires large mouth size yet widely spaced vertical nulls requires small mouth size. The compromise I choose is to use a horn that provides CD horizontal beamwidth and gently collapsing vertical beamwidth. I think it's the best compromise, as it allows the verical nulls to be spaced far apart and still provides CD along the horizontal.
This can be accomplished with an asymmetrical flare having a horn mouth that is not very tall. What it gives you is the desired uniform beamwidth along the horizontal and smooth transitions in the vertical that don't cause ripple by quick transition to CD within the passband. You can't get around the vertical nulls, but you can make them far enough apart that they don't hurt anything. You can also limit HF at large vertical angles, both of which are useful.
Probably the only thing I don't like about some of the recent asymmetrical waveguides is they try to be CD in the vertical without the necessary mouth area. What that does is make them gain pattern control abruptly within the passband, and that results in some ripple. If the horn/waveguide cannot have uniform vertical beamwidth through the whole passband I'd prefer it to have gently collapsing directivity in the vertical plane.
Again, I think we should strive to make a horn or waveguide that was CD in both horizontal and vertical, with beamwidth around 90°x40° and small vertical mouth size. This is a very worthy goal. However, I am not sure you could realize mouth dimensions that keep the beamwidth constant and within the vertical nulls through the passband.
Patrick Bateman said:
I respectfully disagree. Not so much about the specific implementation of the JBL PT waveguides but about the idea that asymmetrical patterns are a compromise. If you're mouting drivers vertically on a baffle, the pattern is asymmetrical even if the horn or waveguide itself is not. I would suggest that it is important to consider this as a part of the system design.
The vertical nulls make CD impossible along movement in the vertical plane, regardless whether or not the horn/waveguide itself is CD. At least with an asymmetrical device, you can decrease center-to-center spacing, which moves the nulls further apart, giving a larger, more useful forward lobe. Further, reducing the vertical pattern is useful for limiting ceiling reflections.
I think you'll find Dr. Geddes agrees with that assessment.
To me, this is the holy grail, so to speak: A waveguide with 90° horizontal beamwidth and 40° vertical beamwidth through the passband, and mouth small enough that vertical nulls could be set outside the pattern. If that is achieved, I'd say you have a no-compromise design.
The problem is, I am not at all sure those competing priorities can be realized simultaneously. Pattern control down low requires large mouth size yet widely spaced vertical nulls requires small mouth size. The compromise I choose is to use a horn that provides CD horizontal beamwidth and gently collapsing vertical beamwidth. I think it's the best compromise, as it allows the verical nulls to be spaced far apart and still provides CD along the horizontal.
This can be accomplished with an asymmetrical flare having a horn mouth that is not very tall. What it gives you is the desired uniform beamwidth along the horizontal and smooth transitions in the vertical that don't cause ripple by quick transition to CD within the passband. You can't get around the vertical nulls, but you can make them far enough apart that they don't hurt anything. You can also limit HF at large vertical angles, both of which are useful.
Probably the only thing I don't like about some of the recent asymmetrical waveguides is they try to be CD in the vertical without the necessary mouth area. What that does is make them gain pattern control abruptly within the passband, and that results in some ripple. If the horn/waveguide cannot have uniform vertical beamwidth through the whole passband I'd prefer it to have gently collapsing directivity in the vertical plane.
Again, I think we should strive to make a horn or waveguide that was CD in both horizontal and vertical, with beamwidth around 90°x40° and small vertical mouth size. This is a very worthy goal. However, I am not sure you could realize mouth dimensions that keep the beamwidth constant and within the vertical nulls through the passband.
- Waveguides vs Horns (on AudioRoundTable.com)
- My personal opinions of various design philosophies
badman said:
The oft-mentioned 8khz hole only exists on-axis; and you're not supposed to listen on axis.
Here's the data; note the hole disappears off axis:
An externally hosted image should be here but it was not working when we last tested it.
I'm listening to a Gedlee waveguide right now. They sound lovely, and they're on the other side of the room, and I'm well off axis.
Here's the response of that crummy PT Waveguide; note the off axis response is atrocious. In the vertical axis it's abysmal. Can you say "compromised?"
Honestly, this whole argument seems a bit silly to me. We're comparing a ten dollar waveguide that's full of design compromises to a no-compromise solution. It reminds me of those letters in car magazines where someone is trying to convince the editor that their ten year old Mustang LX is just as good as a Porsche 911 Turbo. It's a nice car for the money, but there's a reason why a 911 costs $60,000...
Wayne from a total power response perspective how can a high directivity device mated to a much lower one (the woofer) be superior to a device that matches woofer directivity in the vertical plane? You are going to have a low SPL about the crossover no matter which method you use, but at least with matching directivity it will resume a more even level above and below the crossover. Your idea sounds like it would have a smoothly falling level for the woofer passband (as you move vertically), then a steep drop around the crossover, and then continuing low level due to the horn directivity up into the higher frequencies. I just don't see how this is smoother. I'd rather just have the null about the crossover to deal with, at least I can optimize that by manipulating crossover slope, etc.
Second concern, is as the lobing is an issue of CTC versus crossover frequency, you can lower the frequency to adjust it just the same as changing the CTC distance. Earl uses (I believe) 1khz crossover, while most of the people using the JBL econo waveguide are using 2.5khz. I'm sorry but the 4" CTC decrease from using the JBL is NOT going to compensate for the 2.5khz crossover, especially wrt the Geddes waveguide @ 1khz crossover.
Second concern, is as the lobing is an issue of CTC versus crossover frequency, you can lower the frequency to adjust it just the same as changing the CTC distance. Earl uses (I believe) 1khz crossover, while most of the people using the JBL econo waveguide are using 2.5khz. I'm sorry but the 4" CTC decrease from using the JBL is NOT going to compensate for the 2.5khz crossover, especially wrt the Geddes waveguide @ 1khz crossover.
Another thought, while typically pushing everything together to push the nulls far apart is indeed the way to, this is rarely achievable in reality. Almost certainly not with the large pro drivers. Perhaps it is better to manipulate the CTC and crossover frequency to "aim" the null. For example at the ceiling and/or floor bounce angle, resulting in less interference (negative summing) at the seating area. This seems to me that it would preserve the response at the seating area quite well.
"Aiming" the nulls has always been my approach, as is I believe the goal of any competent designer. And you're right, it's a function of crossover and driver spacing.
I'm not here to defend or attack any designs in particular, but I do suggest that round horns and square horns are not as useful as elliptical and rectangular ones, at least not for speaker systems like this designed for high-quality home hifi.
One issue is the nulls that form from vertical spacing preclude constant directivity in the vertical plane. Whether or not the horn is axisymmetrical, the pattern generated by the loudspeaker is not.
A second issue is the reflections from boundaries. One of the best things about directional speakers is their ability to reduce early reflections. In my opinion, it is desirable to reduce ceiling slap using a horn or waveguide with limited vertical beamwidth.
I'm not here to defend or attack any designs in particular, but I do suggest that round horns and square horns are not as useful as elliptical and rectangular ones, at least not for speaker systems like this designed for high-quality home hifi.
One issue is the nulls that form from vertical spacing preclude constant directivity in the vertical plane. Whether or not the horn is axisymmetrical, the pattern generated by the loudspeaker is not.
A second issue is the reflections from boundaries. One of the best things about directional speakers is their ability to reduce early reflections. In my opinion, it is desirable to reduce ceiling slap using a horn or waveguide with limited vertical beamwidth.
badman said:
Hi,
The JBL 2352 performs typically. The pattern narrows between 500Hz and 3kHz and widens above. There are some irregularities at 8 to 10kHz.
http://www.jblpro.com/pages/pub/components/23525354.pdf
Same with EV HP940 (the 940 features that fins within the throat to cure early reflections, though).
http://pdf.textfiles.com/manuals/STARINMANUALS/Bosch - EV/HP940.pdf
Not at last, Geddes' OS waveguide does equally, if smoothing is taken into account. If it comes to "HOM" the JBL and EV realize a +/- 1dB over the whole spectrum if equalized for the CD rolloff. That should be THE annoyance of conventional vs. Geddes' horns!? That +/- 1dB is by far better than with conventional direct radiating speakers in typical boxes! For my uderstanding both Geddes' and conventional waveguides are in the first place compromized by the transition to the baffle. At least Geddes'. The major vendors as JBL and EV, nowadays 18s too,
http://www.eighteensound.it/index.aspx?mainMenu=view_product&pid=178
have the advantage of a lot more money and manpower to spend on trials, simulations etc. Look at the outdated RCF H100, nearly perfect:
http://www.rcf.it/c/document_library/get_file?p_l_id=20071&folderId=22488&name=DLFE-2191.pdf
(where's the HOM?!)
It is Geddes' honor to have solved the wave equation within a (special) horn to an analytical equation. But it is less use in it if practical limitations are taken into account. In the end it comes to simulations and endless trials again. That is what JBL and others are well trained in ... .
so long
"Does a piano create unwanted ceiling and floor reflections?... As you deviate from ninety degrees,"
Others have ably responded, but I'll add this - why draw a line in the sand at 90 deg? Does a piano not also radiate more than 90 deg?
"the JBL econo waveguide are using 2.5khz"
I believe the acoustical XO, and the woofers electrical XO freq, is much lower.
Re vertical lobing, perhaps it could be mostly addresses with digital electronic XO w/very steep slopes to limit the overlap to <1/6 octave.
Others have ably responded, but I'll add this - why draw a line in the sand at 90 deg? Does a piano not also radiate more than 90 deg?
"the JBL econo waveguide are using 2.5khz"
I believe the acoustical XO, and the woofers electrical XO freq, is much lower.
Re vertical lobing, perhaps it could be mostly addresses with digital electronic XO w/very steep slopes to limit the overlap to <1/6 octave.
Wayne Parham said:
I understand. The problem is the average diy'er is taking what you say and making very incorrect conclusions regarding their particular design. Resulting in them focusing on CTC without regard to crossover frequency.
Wayne Parham said:
CD will still have considerable room influence. And whether a person is designing for wide dispersion or narrow, you must still aim for even and smooth response off axis, no matter the actual level, don't you agree? That's where I have concerns with matching drivers with very different directivity. Although I must say that sins in the vertical domain are not near as bad as in th horizontal, and at least there the JBL is about the same directivity as the woofer.
"CD will still have considerable room influence."
But there are "good" and "bad" ones - the latter being early reflections.
90 deg horizontal w/lots of toe-in is good, but this can't be done in the vertical so a narrower pattern to limit them is better IMO.
But there are "good" and "bad" ones - the latter being early reflections.
90 deg horizontal w/lots of toe-in is good, but this can't be done in the vertical so a narrower pattern to limit them is better IMO.
noah katz said:
Hi Noah. Problem is the directivity of the JBL has gone to hell by 2khz. Which means you should cross considerably higher.
noah katz said:
Yes narrower, but still smooth response no? Directivity will never be zero degrees, so we must still have smooth response off axis.
BTW pushing drivers apart increases vertical directivity, not pushing them together. What now? I don't think the issue is as clear as supposed.
Patrick Bateman said:
This is why Earl diffuses the ceiling reflection and damps the floor bounce, right? Ask him. If he could be making a successful axi-asymmetric version of his waveguide, he'd be doing it.
Patrick Bateman said:
And this you consider "no compromise?"
Patrick Bateman said:
You're comparing the JBL vertical to the Geddes horizontal. Ask Earl to post his vertical response system polars, and I believe we'll see a different picture. He earlier refused to do it in the Nathan thread here, as I recall.
Notwithstanding the apples and oranges issue, it's easily seen that at 30° the JBL horizontal is doing just as well.
You are posting vertical polars for what JBL product, please?
augerpro said:
Has it? Here's Earl's measurement of the JBL waveguide vertical polars, and despite it being a 50° axi-asymmetric, it's doing nearly as well at 30°:
Attachments
"Problem is the directivity of the JBL has gone to hell by 2khz."
I see what you mean; I hadn't looked at the curves closely enough before.
Seems like the EconoWG should be used with an 8" woofer.
I see what you mean; I hadn't looked at the curves closely enough before.
Seems like the EconoWG should be used with an 8" woofer.
I read Geddes's explanation of how the foam worked.
And I did question in a very direct way:
I went to a foam shop and bought, for $30, (is that costly?) some 30 ppi reticulated polyurethane foam which I stuffed into a set of exponential horns I built in 1965 following Klipsch's model.
The improvement in performance was vast and unsubtle. The horn coloration was much diminished.
There was also confirmation of Geddes's and Lee's psychoacoustic work on diffraction (linear, time based) distortion becoming unmasked at higher SPL's. Before the foam treatment these speakers were unpleasant to listen to much above 85- 88dB. Now they are good for around a 100 dB before the inherent defects of the design become apparent. Yes, I measured.
Casual visitors remarked they sound more pleasant than previously and these speakers are not eye candy with the foam modification. More significantly, sometimes they asked for the sound to be turned up which they did not before the foam installation.
Putting foam in a modern, well designed waveguide leads to less dramatic improvement because they initially produce fewer diffraction or time based components and thus produce less coloration or timbre modifications.
The importance of such distortion is due to the very short, (less than 1 ms) delay of the components compared to the original signal. They are fused by our hearing into the original signal. Thus the energy components of overtone and undertone structures are psychoacoustically modified and we do not hear the original signal faithfully reproduced. The foam reduces this effect considerably
This is particularly important with classical music reproduction because recorded classical music tends to have a large dynamic range and the diffraction components become unmasked at higher SPLs. So, because the harmonic components of violins and voices often carry as much or more energy than the fundamental, then as they play or sing louder and higher in the presence of diffraction effects we hear their timbre absurdly modified, sometimes unpleasantly.
You have the wrong end of the stick in your criticism of Geddes's foam insert. It is an acoustic filter that solves an acoustic problem that has psychoacoustic effects due to the non-linearity of our hearing with respect to time based distortion at increasing SPLs. What's not to like?
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