If the theory does predict their existence, it does seem that it would be very difficult to separate them for control isolation in measurement/testing. That is not an argument against their existence nor against their effects.
One can very clearly measure and to a certain degree control diffraction from boundaries such as baffle edges, but attributing specific audible effects separate from other influences is still not easy even in this case since the changes are global, in the polar response and not just on some particular axis. I would think that HOMs would simply be a worst case scenario for this sort of measurement/testing, especially given their smaller amplitudes. But just as it is for distortion components, very small amplitude components can indeed be audible in some situations.
Dave
Dave
Precisely correct.
I continue to work on this problem, but meet with several dead ends. Even the modal decomposition is having a difficult time seperating details. ALthough I am able to prove conclusively with measurements that the axial hole is a result of mouth edge diffraction and that was denied by some for a long time. But I am not able to resolve the modes down below the mouth dimensions because of evanescent wave problems (See Williams - Fourier Acoustics). Dead ends, dead ends.
Precisely correct.
I continue to work on this problem, but meet with several dead ends. Even the modal decomposition is having a difficult time seperating details. ALthough I am able to prove conclusively with measurements that the axial hole is a result of mouth edge diffraction and that was denied by some for a long time. But I am not able to resolve the modes down below the mouth dimensions because of evanescent wave problems (See Williams - Fourier Acoustics). Dead ends, dead ends.
There highest end product the K2 does not use the OS shape or really worry about diffraction that much. I have to conclude that maybe there isnt much diffraction (I have no idea) or its just not an audible issue in all cases because with that speaker there is no honk.
There theater designs JBL 4772 do not use OS waveguides either so its not like they believe in the OS design enough to use it on all products. btw, Im not a fan of the 4772 as a critical listening speaker (obviously it was never designed for that application).
What speaker do they use with your OS waveguide design?
btw, Im definitely curious about it all and for myself I have the QSC HPR-152i that measured very well. I also will be getting the SEOS-15 in at some point but first I will be moving over to the IWATA-300 to test 'other' horn theories.
Its just fun to try them all, I do blame all your research and contributions (Yes, I think you make a lot of sense over the years!!!) for this madness
Hello Doug20
You need to take a closer look at the throats and horn profiles they use compared to the first generation CD horns like a 2370 or a 2344. Also look at the PT waveguides. I own both Project Array Horns and PT waveguides and agree they are Honk Free. That said there are no sharp transitions or hard chines like in previous generation horns. It looks to me like they didn't eliminate the difraction slots but they modified them. They didn't do that for no reason.
In the LSR Studio Monitor Line and later versions of it for the waveguide on the tweeter. I don't think Earl considers it a true waveguide but if you read their literature they have OS Waveguide all over it
Rob
One can only be surprised over and over again what can be patented *at some places*...
Michael
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So you're saying that what you want to call CMP is a form of group delay by another name? OK.if you think so ...
Michael
Dave
And nothing new not already understood.Not exactly - as the naming says - its a delayed overlay
Greeeeeat deal !
Michael
Dave
Back in the mid 2000's he did an AES presentation on using a microflown (a hot wire microphone) to measure particle velocity in the plane of a waveguide mouth. I was at that paper. He described how the results were multi-modal, but concluded that there were of insufficient strength to affect the directivity, which is most likey quite true. But in talking with him afterward he had not considered the fact that affecting the directivity and being audible are completely different things.
He wrote up that paper for publication in the JAES and I was asked to review it. I made several corrections but in the end he did not follow through on its publication so it was only ever a preprint. I have a copy of the paper, of course, but it would be unethical to transmit it. I suspect that since he was graduating at the time that he went on to other things and never got arround to rewritting the paper.
But his conclusions on the presence of HOMs were quite clear.
As to the actual preprint date, just search AES preprints for his name, although it may not be first as I recal.
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With respect to effects related to all sort of horns that are caused by simple diffraction "HOM bogus" is more often than not used here as a "smoke discharger / mind blocker term".
Just keep it simple: this horn stuffing is mainly the same thing like transmission line stuffing = dampening of looped echoes
Michael
Well not exactly, I'd say - at least as for the second part of your statement.
*If* CMP concept were "understood" there would not be any chance at any place to file a patent on :
"Dampening measures outcarried by dampening materials stuffed into pipes of increasing cross section in order to dampen CMP effects"
As this is exactly the same as stuffing a TM for exactly the same reasons - as said already.
But -
- as far as I remember Earl has generously allowed to apply ""Dampening measures outcarried by dampening materials stuffed into pipes of increasing cross section in order to dampen CMP effects" for the DIYer elsewhere - so no DIY'er has to worry about stuffing his pipes - be they of whatever cross section
Michael
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Looks like a Bulpren S32450 (10ppi):
Filtrace vzduchu | Eurofoam - technické p?ny
Bulpren - S | Eurofoam - technické p?ny
Hi Earl,
Thanks again for another detailed explanation.
Can you clarify your use of the term "Group delay" here? I don't believe you are refering to dispersion but to the addition of delayed reflections. If that is the case then why are delayed reflections from higher order modes any different from the classic effects of mouth,throat or diffraction slot reflections? We assume that the nonflat load that a horn puts on a driver is the frequency domain view of the multiple reflections from end to end. If adding higher order modes means that there are internal lateral modes (and I don't doubt this for a moment) why are they inherently different in effect?
Each reflection from any cause (internal or external) has group delay and should be governed by the many studies on the audibility of reflections, echos, etc. Is there something unique about HOMs that makes them more distinctive? If they are a linear effects but difficult to measure, presumably due to magnitude, what makes them more significant than the classical horn reflection effects that are easy to measure?
My understanding is that the presence of higher order modes means that simplifying assumptions can only take us so far in our modeling. I get it, if we really want an accurate model of on and off axis behaviour we can't think of the wave in the throat as simply flat or spherical. But how does the presence of the modes automatically translate into artifact rather than complexity?
David
I'm an ex-JBL engineer so I can only speculate on their current view of the subject.
I use a lot of JBL systems in small cinemas. Primarily this would be the 4675 using the large 90 x 40 2360 horn. The first thing you do in the design of the sound system is look at your floor area, screen location and speaker distance. You will calculate lateral and vertical angular seating area and level drop from front to back of the audience. If you have multiple horn choices then you will be looking for something that covers the seating area, but no more, with a consistant frequency balance (EQ will be used). You also hope that off axis falloff in response can be used to balance front to back level drop. That will determine your aiming.
I think this is typical of any pro customer: the objective for the horn is to give even coverage across an intended area with consistant, equalizable frequency response. This is why the constant directivity horns were such a revelation in the pro market. Imagine trying to achieve the same goals with an older 511b radial horn.
For a diy-er the attributes may be different and we can worry about the best possible performance for one listener. That is not the market that JBL has to design for.
David S.
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