Hi gedlee,
Some measurements done by POS can be seen here:
D2430K compression driver information? - Page 3
regards
ivica
To me those measurements support what I was saying - that all those drivers are basically the same. Of course those are far from a comprehensive set of measurements.
old patents don't have to be avoided - after 20 years they expire - you can make, sell, use any idea in expired patents - that's the whole point - to promote the progress of the useful arts - by fully disclosing/publishing the patented concept - in exchange for a limited time monopoly
in addition in the US maintenance fees have to be paid to keep a patent active - if something never makes money it may not be paid up and is again open for use
in addition in the US maintenance fees have to be paid to keep a patent active - if something never makes money it may not be paid up and is again open for use
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Hi GEDLEE,
If we are talking that all the mentioned drivers: JBL 2435, JBL 2450SL and JBL D2430K, are operating on the principle that the moving diaphragm(s) is producing sound, I can agree with You that "...all those drivers are basically the same..." and in order to enhance the sensitivity they applied a kind of 'compression', but technical realization , seems to me to be quite different, especially for D2430K, where two diaphragms are operating in parallel.
Talking about the measurements that our member POS has done, I can only emphasize that these are one of the first (I have seen) independent measurements of D2430K drivers, so I want to encourage him to continue in that way.
From time to time we have to trust each-other, not to believe that our-self work is the only "thrust".
regards
ivica
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I agree that those three drivers have a lot in common, with superb performance, and are difficult to distinguished once properly EQed (the 2435HPL phasing plug has "problems" with that horn though, as can be seen at ~13kHz)
But let's consider what drivers we have here:
- 2435HPL: 3" Beryllium diaphragm, similar to the 435Be used in the JBL K9800
- 2450SL-Be : 4" Beryllium diaphragm, similar to the 476Be used in the JBL D67000
- D2430K: dual 3" ring radiator, used in the JBL M2
These ain't no DE250 😉
I could probably include a 1" compression driver on the 1" PT waveguide (I am using the 1.5" version here), just for comparison...
Hi POS,
It would be , for me , more interesting if measurements can be done with PT-H95HF horn, but.....
I would expect that LF loading (under 2kHz) for D2430K would be better, but have no idea about HF response, may be a kind of HF cancellation can be get, and so no so good HF response would be.
regards
ivica
Frayne & Locanthi
See the attached article [1]
Regards,
WHG
[1] Theater Loudspeaker System Incorporating Acoustic-Lens Radiator
SMPTE-J, Sep-1954
See the attached article [1]
Regards,
WHG
[1] Theater Loudspeaker System Incorporating Acoustic-Lens Radiator
SMPTE-J, Sep-1954
I for one will say that these lenses never worked well. I have been around those horn and lens combinations since over 40 years ago and that was not a great idea. This idea is really based on optic principals and not audio wavelength properties. Just because you can write a coherent sounding paper does not make something true. Since the patents on this type of device are long since open to the public to use if this was such a great idea why is it that you don't see this combination of horn and lens used today? Bottom line is they didn't sound very good. The compression drivers themselves were fine, some of the best made at the time. The horns and lenses in combinations just didn't compare to a well designed horn itself. An attempt to make a to small horn work and still have any chance of dispersion.
I did my MS thesis on these devices and I agree they did not work very well. The levels of Index of Refraction that one could achieve were just not great enough to have a major effect. I first tried foam as a means of shaping the wave fronts, but that didn't work too well either - hardly any effect. But then I discovered that the foam had other benefits.
Truism
Truism
The assertion that all compression drivers “are basically the same" is nothing more than a truism that begs the question: What are their differences? And, are they important? E.G., One can say that all loudspeaker drivers "are basically the same"...; But redact the important part: ... because they are all electromagnetic to acoustical transducers. Such statements do not substantiate the assertion that driver performance differences are not evident.
The caveat accompanying the graphs shown later in the referenced thread [1] follows:
"Each graph shows a different harmonic distortion order as the lower traces.
The mic is not calibrated, so disregard the (heavily smoothed) upper curve.
The drivers where grossly EQed for CD compensation and midband matching."
The lower graphs show lower HD for orders 2nd. through 6th. for the D2 driver; only the 1st. order is higher.
The other graphs appearing earlier in the thread [1], show marked and improved frequency response above 6 kHz for the D2.
Unfortunately these tests were not performed using a PWT, so what we are seeing here is an on-axis response laced with horn artifacts, not a 'clean' power response.
None the less, this data does constitute sufficient evidence to demonstrate that there are measurable differences between the DUTs that are left to the auditors hearing acuity to detect.
Regards,
WHG
[1] Lansing Heritage Thread
D2430K compression driver information? - Page 3
Regards,
WHG
Truism
The assertion that all compression drivers “are basically the same" is nothing more than a truism that begs the question: What are their differences? And, are they important? E.G., One can say that all loudspeaker drivers "are basically the same"...; But redact the important part: ... because they are all electromagnetic to acoustical transducers. Such statements do not substantiate the assertion that driver performance differences are not evident.
The caveat accompanying the graphs shown later in the referenced thread [1] follows:
"Each graph shows a different harmonic distortion order as the lower traces.
The mic is not calibrated, so disregard the (heavily smoothed) upper curve.
The drivers where grossly EQed for CD compensation and midband matching."
The lower graphs show lower HD for orders 2nd. through 6th. for the D2 driver; only the 1st. order is higher.
The other graphs appearing earlier in the thread [1], show marked and improved frequency response above 6 kHz for the D2.
Unfortunately these tests were not performed using a PWT, so what we are seeing here is an on-axis response laced with horn artifacts, not a 'clean' power response.
None the less, this data does constitute sufficient evidence to demonstrate that there are measurable differences between the DUTs that are left to the auditors hearing acuity to detect.
Regards,
WHG
[1] Lansing Heritage Thread
D2430K compression driver information? - Page 3
Regards,
WHG
Bad Horn, Good Lens, Bum Rapp
The principal reasons acoustic lenses are not used is, cost, fragility, and the lack of research.
The most likely reason for the bad sound, was due to the horn used or other reasons. Unless you audited the system with and without the lenses present, you do not know what was causing the anomalies you were hearing.
In comparison to the research work done on horns, that done on acoustic lenses is miniscule.
The slant plate lens is only one of several different varieties of acoustic lenses.
For most of the ones I have audited, what I heard that was bad, I attributed to horn artifacts and diaphragm breakup. When we removed the lenses, the sound did not change character except for the presence of HF beaming.
Regards,
WHG
The principal reasons acoustic lenses are not used is, cost, fragility, and the lack of research.
The most likely reason for the bad sound, was due to the horn used or other reasons. Unless you audited the system with and without the lenses present, you do not know what was causing the anomalies you were hearing.
In comparison to the research work done on horns, that done on acoustic lenses is miniscule.
The slant plate lens is only one of several different varieties of acoustic lenses.
For most of the ones I have audited, what I heard that was bad, I attributed to horn artifacts and diaphragm breakup. When we removed the lenses, the sound did not change character except for the presence of HF beaming.
Regards,
WHG
No.
I have done several tests on the subjective audibility of differences like this and they have all concluded that differences like this are not audible.
If people want to nibble away at small details and call them important that's up to them. As for me, it is all down in the noise. The waveguide makes all the difference, the driver hardly any.
sorry Earl but its getting difficult to sort out what you're objecting too and the reasons
I thought you did think wavefront pressure, velocity shape was important in the throat
did you comment on the paper/image from http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-686.html#post3945668
isn't the right side better in your own terms?
why or why not?
I thought you did think wavefront pressure, velocity shape was important in the throat
did you comment on the paper/image from http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-686.html#post3945668
isn't the right side better in your own terms?
why or why not?
Who is Doing the Listening Matters.
I have read the papers on the referenced work and find that the methods and subjects used do not provide sufficient statistical inference to support this claim. The average typical listener is quite satisfied with the sound coming from a Bose Wave Radio. To suggest that their untrained observations bear any relevance to the mission here is simply absurd. I suspect most participants were probably young, avid rock concert and night club attendees with no top-end listening acuity left, due to repeated exposure to over-loud sound systems always found at these venues.
I have read the papers on the referenced work and find that the methods and subjects used do not provide sufficient statistical inference to support this claim. The average typical listener is quite satisfied with the sound coming from a Bose Wave Radio. To suggest that their untrained observations bear any relevance to the mission here is simply absurd. I suspect most participants were probably young, avid rock concert and night club attendees with no top-end listening acuity left, due to repeated exposure to over-loud sound systems always found at these venues.
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whgeiger,
On the point of little research going on with slant plate combinations with horns you are probably correct that there is little. I think most concluded early on that the premise of using optic principals was a flawed concept. That is what I understand and have been told by others who's opinions I hold highly.
On the differences in compression drivers I believe you are correct. While keeping the horn or waveguide constant and only changing compression drivers, no changes in eq and using similar types of drivers, short pancake vs short pancake style and older typical drivers with longer throat sections vs the same, it is rather easy to hear a difference between devices and sound quality across the entire pass-band. Yes you can eq any driver but the inherent quality of the driver will not change.
On the point of little research going on with slant plate combinations with horns you are probably correct that there is little. I think most concluded early on that the premise of using optic principals was a flawed concept. That is what I understand and have been told by others who's opinions I hold highly.
On the differences in compression drivers I believe you are correct. While keeping the horn or waveguide constant and only changing compression drivers, no changes in eq and using similar types of drivers, short pancake vs short pancake style and older typical drivers with longer throat sections vs the same, it is rather easy to hear a difference between devices and sound quality across the entire pass-band. Yes you can eq any driver but the inherent quality of the driver will not change.
The AES journal that published them did not agree with you, but your objection is to be expected, noted and filed where it belongs.
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The principles are not "flawed" at all. It is the fact that audio encompasses many times the bandwidth of optics (in decades). Getting the principles to work over such large bandwidth is just not feasible. An optical lens operates only over less than a octave.
I learned a lot of my acoustics from books like Fourier Optics and the like and I strongly recommend them.
No data shown here gives any indication of the wave front shape or coherence. Yes, that coherence would be important to me should some data ever be shown that indicates it.
The only thing that I object to is making something out of nothing. Every subjective test that I have done implies that distortion in a compression driver is irrelevant, that the waveguide response dominates the perception making all drivers virtually identical in that regard, and that virtually nothing of what is usually measured will ever show anything that will adequately differentiate subjective perceptions of one driver from another.