BMS 4554/4555, 1.4"/1.5", with 44mm coil/cone
I wonder how the phase plug looks on those compression drivers where the coil and exit are almost equal
I wonder how the phase plug looks on those compression drivers where the coil and exit are almost equal
Yesterday I noticed that the LeCleach curve and the spherical horn curve are basically a circle. And that the JBL wavguides are similar in shape, but elliptical instead of circular.
So I was curious to see what wave shape would be produced if you took that all the way around the cabinet. This yields a few possible shapes:
1) A figure eight shape
2) The same figure eight shape, but 'squashed' to form an ellipse, like the JBL horns
3) A figure eight shape that's open to the back, which forms a bipole
Here's what the wavefronts look like. Horn 3 is at the bottom, 2 is in the middle, 1 is at the top. Some observations:
1) The figure eight shaped horn has really well behaved wavefronts. Nice and spherical with no weird discontinuities. The conical and OS curves appear to flatten the wavefronts to a degree, but not 100%. So the conical and OS curves seem to produce elliptical wavefronts.
2) The beamwidth of the figure eight horn is quite wide.
3) The elliptical horn seems to work about as well as the figure eight horn. Downside to the elliptical shape appears to be that the beamwidth narrows as the waves get larger than the horn. Note that the 500hz waves are basically cardioid, and have narrowed a great deal when compared to 1khz.
4) Turning the figure eight horn into a bipole seems to work quite well too, and basically makes the horn omnidirectional. I'm not real keen on omnidirectional speakers, but if someone was, the bipole figure eight horn might be worth a look.
Here's some ideas on how you could build these horns out of PVC pipe:
A monopole figure eight might look something like this, minus the conical part at the center.
If you wanted to extend the curve to a full figure eight you could.
This could be built with a miter saw in about an hour.
If you fed the horn with a ribbon it would look like this
A torus would work too, but it's a bit difficult to build.
An externally hosted image should be here but it was not working when we last tested it.
That horn shape looks familiar...
This video of a trombone's shock wave demonstrates the shape of the wavefront pretty well:
Trombone's shock waves caught on film - YouTube
That is patently untrue (pun intended) and only shows how completely unaware of the technology that you actually are. JBL licensed my ideas from me back in the 90's - why would they do that if they already knew about them. And the Peavy rip-off has been described here so many times that I won't go over it again. And let's not even mention the foam!!!
I understand that two-way horn systems have been around for a long time. I owned JBL 4430's for decades - but they were pretty poor designs when compared to the modern stuff. My goal was to facilitate that improvement.
Why do you think that everybody now uses "smooth contours" with matching throat angles. This is all stuff that I promoted in my earliest papers and people simply ripped-off with no acknowledgement for the precedence. That's just the way audio is - everybody is cut-throat. But if you really look at the provenance of the designs you will see my work all over them.
And yes, I do take offense at comments like yours that exhibit very little understanding of the history of things and make a joke about it all.
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And as long as we are on this subject maybe its time to tell the story of JBL and me.
In 1991 after I published my papers on Waveguide Theory, JBL, through John Eargle, who was a good friend, approached me about licensing my ideas. I agreed and we went forward with a patent filing.
But if you will remember back in 1991, Ford, my employer at the time, was entering into a contract with JBL for Auto sound system development, etc. To make a long story short I was told that it would be a conflict of interest for me to continue a professional interest with JBL outside of my employment at Ford. I had to terminate the agreement with JBL or terminate my employment at Ford, which was kind of a no-contest (I was at a very high level at Ford at the time).
This left all of my ideas completely open ground for JBL, or anyone else, to use at will. They all took great advantage of this fact.
In 1991 after I published my papers on Waveguide Theory, JBL, through John Eargle, who was a good friend, approached me about licensing my ideas. I agreed and we went forward with a patent filing.
But if you will remember back in 1991, Ford, my employer at the time, was entering into a contract with JBL for Auto sound system development, etc. To make a long story short I was told that it would be a conflict of interest for me to continue a professional interest with JBL outside of my employment at Ford. I had to terminate the agreement with JBL or terminate my employment at Ford, which was kind of a no-contest (I was at a very high level at Ford at the time).
This left all of my ideas completely open ground for JBL, or anyone else, to use at will. They all took great advantage of this fact.
@ dumptruck
What is interesting to me as little as I apparently know regarding smooth entry of horns and given that I have unknowingly taken Dr. Geddes smooth throat transition for granted, is what appears to be the best and brightest of the speaker DIY club back engineering Synergy horns, which as far as I can tell, can't perform Dr. Geddes throat smoothing trick. In fact I recently discovered that thread and there gained what I do know about this whole thing. I really don't know the whole smoothing story yet. I purposely killed my own thread about Synergies pointing to that one as where the real deal was happening.
What is interesting to me as little as I apparently know regarding smooth entry of horns and given that I have unknowingly taken Dr. Geddes smooth throat transition for granted, is what appears to be the best and brightest of the speaker DIY club back engineering Synergy horns, which as far as I can tell, can't perform Dr. Geddes throat smoothing trick. In fact I recently discovered that thread and there gained what I do know about this whole thing. I really don't know the whole smoothing story yet. I purposely killed my own thread about Synergies pointing to that one as where the real deal was happening.
Riiight. So, anyway, to someone like me, the question remains.. which horn to get?!?! (from the available horns on the market). And for me, it must be a 3" diaphragm, so at least 1.4" exit. So far, the Eighteen Sound XT1464 seems to be the best option..
Here are measurements of XT1464 with DE700:
http://www.prodance.cz/files/dl/1/969/18Sound_XT1464+DE700.pdf
What does Dr. Geddes think?
Here are measurements of XT1464 with DE700:
http://www.prodance.cz/files/dl/1/969/18Sound_XT1464+DE700.pdf
What does Dr. Geddes think?
A 1.75" driver is not pistonic. 3/4" is pistonic in the right designs Mag or Al Mag. 1.75" is limited to mid treble limit.This has been known widely in the driver world. 15KHz would be a realistic limit for many and perhaps 18kHz or so for the few.
The 3" - 4" diaphragms can only do treble if the diaphragm is made very rigid. Not possible for proper HiFi with FLAC type quality where you really want subtle clear articulate top treble.
Yuo have to use a supertweeter and roll the big diaphragm off
..and did you negotiate an excellent employment contract and severance package knowing this? 😉
The Synergy horn throat transition can be smoothed like Geddes', no problem- just takes some careful filing (and some Bondo work if you are not too careful).
They also can be made circular, like Yorkville's Unity series.
I have always assumed that bumps in the path of things cause deflection, just didn't realize the gravity of this assumption or the physics involved in non bumpyness, as making something bumpy would seem to required even more thought than making it smooth, like say Mantaray diffraction horns or the hall of mirrors at old carnivals. I always figured sound was like an explosion it wanted to be round and anything in its way would deform it. I am now learning this is not necessarily what most people assumed.
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You know, I would never consider myself to be overtly gifted like some here are but I'm really having a hard time accepting that that is not just a natural thing to expect to have to do when mating one shape to another shape. Makes you wonder what else has not been quantified and harvested by those gifted enough to truly understand the physics involved.
nanos gigantum humeris insidentes
“If I have seen further it is by standing on the shoulders of giants.” Isaac Newton
Hughes cited your work in his paper [1] but failed to reference the derivative work of Freehafer [2] (and earlier [3],[4] & [5]) from which your work is based as well.
Regards,
WHG
Reference:
[2]
Title: The Acoustical Impedance of an Infinite Hyperbolic Horn
Author: J. E. Freehafer
Publication: ASA-J, Vol. 11, No. 4, p. 467-476 (Apr-1940)
Abstract: In discussing the acoustical properties of horns, it is in general a mathematical necessity to assume plane waves. In the case of a horn in the form of a hyperboloid of one sheet, however, it is possible to avoid this assumption and to obtain an exact solution to the problem. The analysis, carried through with the aid of the differential analyzer, leads to curves representing the acoustical resistance and reactance as functions of the ratio of the radius of the throat to the wavelength. Comparison with the conical horn shows that the hyperbolic is superior.
“If I have seen further it is by standing on the shoulders of giants.” Isaac Newton
Hughes cited your work in his paper [1] but failed to reference the derivative work of Freehafer [2] (and earlier [3],[4] & [5]) from which your work is based as well.
Regards,
WHG
Reference:
[2]
Title: The Acoustical Impedance of an Infinite Hyperbolic Horn
Author: J. E. Freehafer
Publication: ASA-J, Vol. 11, No. 4, p. 467-476 (Apr-1940)
Abstract: In discussing the acoustical properties of horns, it is in general a mathematical necessity to assume plane waves. In the case of a horn in the form of a hyperboloid of one sheet, however, it is possible to avoid this assumption and to obtain an exact solution to the problem. The analysis, carried through with the aid of the differential analyzer, leads to curves representing the acoustical resistance and reactance as functions of the ratio of the radius of the throat to the wavelength. Comparison with the conical horn shows that the hyperbolic is superior.
I would not say that my work is based on Freehafer because I used nothing from his papers in mine. It is true that he too wrote about the OS waveguide, but he did not discuss the general usage of any waveguide based on separable coordinates. Freehafer used a rather obscure form of solution, the Harmonic Analyzer, an analog computer used to solve differential equations. I did not have access to such a machine (and he did not have a PC!), so I did mine using numerical methods.
In fact, I did not even know about Freehafer until after I had started writing my first paper. So I referenced it, that was only fair, but nothing in it was very useful to me except to confirm that my approach was correct for the special case of the OS coordinate systems.
Charley Hughes was never the guy who wrote about the Quadratic Waveguide without giving any credit to my influence over this design. It was another guy at Peavey who claimed to not know anything about my relationship with Charley, but was trying to promote the Peavey device as "revolutionary". I hold no ill will towards Charley because he has always come clean about how the Quadratic approach came about as a simplification to the exact OS equations using a circle, which is all that was possible in his drafting program. He was trying to do an OS curve, but that was too hard in his program at that time (its not too hard these days using parametric spline curves.) JBL later admitted to doing the same thing, so their EOS really isn't even OS, its Quadratic.
In the end the Peavey patent was not very well written and could be easily circumvented so it never became very important. I later concluded that any effective patent protection on any form of curve would be difficult to impossible because precise specification, as required by a patent, could always be circumvented with a small variant on the claim that would end up having a very small effect on the results, but not fall within the claim language. Any attempt at patent coverage would and did, end up being just mater of chasing ones tail.
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Bill
It is also interesting to note: I reread the Hughes paper, as it has been decades since I had done so and was surprised to see that he got his description of my work wrong. He describes my approach as being "One -parameter" but yet I was very clear that my approach was NOT one parameter except in the few cases as defined by Putland (except that I described these back in 1987 while Putland did so in his early 90's work), which are not of much practical value.
In general there is no such thing as a "one parameter" solution and I have written about this fact on several occasions since. I can only imagine that my idol, Prof. Phillip Morse, was quite embarrassed by having written these claims back in his first book on Acoustics. By the 50's when he wrote Methods of Theoretical Physics, he had gotten it completely correct when no mention is made of "one parameter" solutions and he correctly shows the very limiting assumptions that must hold for Webster's Equation to hold. It is indeed unfortunate that Morse's first work is rather well known (the incorrect one) while his later work (the correct one) is rather obscure (except by a small class of theoretical physicists). So the "one-P" discussion goes on despite the fact that its original "inventor" later realized that it was a mistake!
It is also interesting to note: I reread the Hughes paper, as it has been decades since I had done so and was surprised to see that he got his description of my work wrong. He describes my approach as being "One -parameter" but yet I was very clear that my approach was NOT one parameter except in the few cases as defined by Putland (except that I described these back in 1987 while Putland did so in his early 90's work), which are not of much practical value.
In general there is no such thing as a "one parameter" solution and I have written about this fact on several occasions since. I can only imagine that my idol, Prof. Phillip Morse, was quite embarrassed by having written these claims back in his first book on Acoustics. By the 50's when he wrote Methods of Theoretical Physics, he had gotten it completely correct when no mention is made of "one parameter" solutions and he correctly shows the very limiting assumptions that must hold for Webster's Equation to hold. It is indeed unfortunate that Morse's first work is rather well known (the incorrect one) while his later work (the correct one) is rather obscure (except by a small class of theoretical physicists). So the "one-P" discussion goes on despite the fact that its original "inventor" later realized that it was a mistake!
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Earl was that pun not intended? 😀
After three years of unexpectedly losing my listening space I will finally get to build my Abbeys and listen to them in a fair comparison.
Horn Potpourri
Earl,
The books by Philip Morse and Herman Feshbach are not as obscure as you suppose. [1] Herman’s son continues to publish them at a price under $200 for the two volumes. My copies are in PDF format. I am well aware of the 1-p horn issue raised in Gavin Putland's tome [2] and elsewhere [3].
Regards,
Bill
[1] Feshbach Publishing - Home
[2] Gavin R. Putland: <i>Modeling of Horns and Enclosures for Loudspeakers</i> (PhDthesis)
[3] For those that might be interested, I have added some references here as well.
Title: Acoustic Waveguide Theory
Author: Earl R. Geddes
Publication: AES-J, Vol. 37, No. 7, p. 554 (1989)
Abstract: In 1919, A. G. Webster published a paper on the theory of horns. Webster's horn equation is based on a plane-wave assumption that is incorrect and this assumption severely limits the applicability of this theory to modern directivity-controlling devices ...
Title: Every One-Parameter Acoustic Field Obeys Webster's Horn Equation
Author: Gavin R. Putland
Publication: AES-J, Vol. 41, No. 6, p. 435 (1993)
Abstract: The Helmholtz equation admits one-parameter (1P) solutions in , that is, solutions depending on a single spatial coordinate ,..
Title: Acoustic Waveguide Theory Revisited
Author: Earl R. Geddes
Publication: AES-J, Vol. 41, No. 6, p. 452 (1993)
Abstract: Abstract: The concept of waveguides was introduced by Geddes in 1989. That paper showed how Webster's horn equation lacked a sufficient description of the wave propagation in the horn to be accurate in directivity simulations. The concept of a waveguide as a direc
Title: Comments On "Acoustic Waveguide Theory"
Author: Gavin R. Putland
Publication: AES-J, Vol. 39, No. 6, p. 469 (1991)
Abstract: An Oblate Spheroidal Horn does not emit acoustic waves expressible in one parameter,
Title: Author's Reply to "Comments on 'Acoustic Waveguide Theory'"
Author: Earl R. Geddes
Publication: AES-J, Vol. 39, No. 6, p. 471 (1991)
Abstract: Qualified acknowledgement of the error by Geddes
Title: A Generalized Horn Design to Optimize Directivity Control and Wavefront Curvature
Author: Charles E. Hughes
Publication: AES-P, No. 5016, Cnv. 107, (1999-9)
Abstract: A new horn design is presented. This approach yields good loading characteristics and reduced harmonic distortion. The new horns polar patterns are that of a constant directivity type horn. The novel feature of this new horn is that its apparent apices for the horizontal and vertical planes are in the same physical location regardless of coverage angle for the horizontal or vertical plane.
Title: The Quadratic-Throat Waveguide
Author: Charles E. Hughes
Author: By John Murray
Publication: Peavey Electronics Corp. "A White Paper On An Invention"
Abstract: Simplified version of the AES Convention Preprint presented in 1999
Author: Gavin R. Putland
Publication: Dept.: Electrical & Computer Engineering, University of Queensland. 6-Feb-1996
Abstract: It is shown that the ``Webster'' horn equation is an exact consequence of ``one-parameter'' or ``1P'' wave propagation. If a solution of the Helmholtz equation depends on a single spatial coordinate, that coordinate can be transformed to another coordinate, denoted by xi, which measures arc length along the orthogonal trajectories to the constant-xi surfaces.
Webster's equation, with xi as the axial coordinate, holds inside a tube of such orthogonal trajectories; the cross-sectional area in the equation is the area of a constant-xi cross-section. This derivation of the horn equation makes no explicit assumption concerning the shape of the wavefronts. It is subsequently shown, however, that the wavefronts must be planar, circular-cylindrical or spherical, so that no new geometries for exact 1P acoustic waveguides remain to be discovered.
It is shown that if the linearized acoustic field equations are written in arbitrary curvilinear orthogonal coordinates and approximated by replacing all spatial derivatives by finite-difference quotients, the resulting equations can be interpreted as the nodal equations of a three-dimensional L-C network. This ``finite-difference equivalent-circuit'' or ``FDEC'' model can be truncated at the boundaries of the simulated region and terminated to represent a wide variety of boundary conditions.
The presence of loosely-packed fibrous damping materials can be represented by using complex values for the density and ratio of specific heats of the medium. These complex quantities lead to additional components in the FDEC model.
Two examples of FDEC models are given. The first example predicts the frequency response of a moving-coil loudspeaker in a fiberglass-filled box, showing the effects of internal resonances. Variations of the model show how the properties of the fiberglass contribute to the damping of resonances and the shaping of the frequency response. It is found that viscosity, rather than heat conduction, is the dominant mechanism of damping.
The second example addresses the classical problem of radiation from a circular rigid piston, and confirms that a free-air anechoic radiation condition with oblique incidence can be successfully represented in the FDEC model.
Earl,
The books by Philip Morse and Herman Feshbach are not as obscure as you suppose. [1] Herman’s son continues to publish them at a price under $200 for the two volumes. My copies are in PDF format. I am well aware of the 1-p horn issue raised in Gavin Putland's tome [2] and elsewhere [3].
Regards,
Bill
[1] Feshbach Publishing - Home
[2] Gavin R. Putland: <i>Modeling of Horns and Enclosures for Loudspeakers</i> (PhDthesis)
[3] For those that might be interested, I have added some references here as well.
Title: Acoustic Waveguide Theory
Author: Earl R. Geddes
Publication: AES-J, Vol. 37, No. 7, p. 554 (1989)
Abstract: In 1919, A. G. Webster published a paper on the theory of horns. Webster's horn equation is based on a plane-wave assumption that is incorrect and this assumption severely limits the applicability of this theory to modern directivity-controlling devices ...
Title: Every One-Parameter Acoustic Field Obeys Webster's Horn Equation
Author: Gavin R. Putland
Publication: AES-J, Vol. 41, No. 6, p. 435 (1993)
Abstract: The Helmholtz equation admits one-parameter (1P) solutions in , that is, solutions depending on a single spatial coordinate ,..
Title: Acoustic Waveguide Theory Revisited
Author: Earl R. Geddes
Publication: AES-J, Vol. 41, No. 6, p. 452 (1993)
Abstract: Abstract: The concept of waveguides was introduced by Geddes in 1989. That paper showed how Webster's horn equation lacked a sufficient description of the wave propagation in the horn to be accurate in directivity simulations. The concept of a waveguide as a direc
Title: Comments On "Acoustic Waveguide Theory"
Author: Gavin R. Putland
Publication: AES-J, Vol. 39, No. 6, p. 469 (1991)
Abstract: An Oblate Spheroidal Horn does not emit acoustic waves expressible in one parameter,
Title: Author's Reply to "Comments on 'Acoustic Waveguide Theory'"
Author: Earl R. Geddes
Publication: AES-J, Vol. 39, No. 6, p. 471 (1991)
Abstract: Qualified acknowledgement of the error by Geddes
Title: A Generalized Horn Design to Optimize Directivity Control and Wavefront Curvature
Author: Charles E. Hughes
Publication: AES-P, No. 5016, Cnv. 107, (1999-9)
Abstract: A new horn design is presented. This approach yields good loading characteristics and reduced harmonic distortion. The new horns polar patterns are that of a constant directivity type horn. The novel feature of this new horn is that its apparent apices for the horizontal and vertical planes are in the same physical location regardless of coverage angle for the horizontal or vertical plane.
Title: The Quadratic-Throat Waveguide
Author: Charles E. Hughes
Author: By John Murray
Publication: Peavey Electronics Corp. "A White Paper On An Invention"
Abstract: Simplified version of the AES Convention Preprint presented in 1999
Author: Gavin R. Putland
Publication: Dept.: Electrical & Computer Engineering, University of Queensland. 6-Feb-1996
Abstract: It is shown that the ``Webster'' horn equation is an exact consequence of ``one-parameter'' or ``1P'' wave propagation. If a solution of the Helmholtz equation depends on a single spatial coordinate, that coordinate can be transformed to another coordinate, denoted by xi, which measures arc length along the orthogonal trajectories to the constant-xi surfaces.
Webster's equation, with xi as the axial coordinate, holds inside a tube of such orthogonal trajectories; the cross-sectional area in the equation is the area of a constant-xi cross-section. This derivation of the horn equation makes no explicit assumption concerning the shape of the wavefronts. It is subsequently shown, however, that the wavefronts must be planar, circular-cylindrical or spherical, so that no new geometries for exact 1P acoustic waveguides remain to be discovered.
It is shown that if the linearized acoustic field equations are written in arbitrary curvilinear orthogonal coordinates and approximated by replacing all spatial derivatives by finite-difference quotients, the resulting equations can be interpreted as the nodal equations of a three-dimensional L-C network. This ``finite-difference equivalent-circuit'' or ``FDEC'' model can be truncated at the boundaries of the simulated region and terminated to represent a wide variety of boundary conditions.
The presence of loosely-packed fibrous damping materials can be represented by using complex values for the density and ratio of specific heats of the medium. These complex quantities lead to additional components in the FDEC model.
Two examples of FDEC models are given. The first example predicts the frequency response of a moving-coil loudspeaker in a fiberglass-filled box, showing the effects of internal resonances. Variations of the model show how the properties of the fiberglass contribute to the damping of resonances and the shaping of the frequency response. It is found that viscosity, rather than heat conduction, is the dominant mechanism of damping.
The second example addresses the classical problem of radiation from a circular rigid piston, and confirms that a free-air anechoic radiation condition with oblique incidence can be successfully represented in the FDEC model.
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