JBL horn?

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buzzforb

buzzforb

Member
Joined 2010
Thnka you for the correction. I tihnk it is a popular bit of misinformation in regards to the A290, of which I was a part. As for JBL 9800, it is one of things that puzzles me and why i started the thread. JBL must know what they are doing, but they do seem to make a number of choices that do not coincide with what some of the more knowledgable members of this forum would suggest.
 
J

JR_W

Member
Joined 2009
The TH-4003 isn't symmetrical between the top and bottom halves, I'm pretty sure the H9800 is.

The contour of the bottom half of the TH-4003 looks similar to the contour of both halves of the H9800, IMHO.

ETA: I was confusing your last 2 posts and missed the 290C part.
 
Kindhornman

Kindhornman

Member
Joined 2012
Buzz,
It seems that you are confusing what is happening in a normal dome tweeter and cone loudspeaker application where you see a tilt in the on axis response due to the offset in distance from the listeners axis and the two devices. It is hard to equate that with what is going to happen in an individual horn or waveguide. At the same time I would expect some differences in the polar response out of an asymmetrical horns response in the vertical axis if that is what they are doing, at least in regards the on axis response.
 
pos

pos

Member
Joined 2008
rephase.org/
Jmmlc said:
Hello Pos,

The oblate spheroidal profile doesn't allow the mouth to roll back for itself and my spreadsheet doesn't allow a mouth part to be added.

But there is a horn very similar to what you described I use to design many years ago. Too bad it was never built.

See attached 3D view graph.

Best regards from Paris, France

Jean-Michel Le Cléac'h
Click to expand...
Thanks for the drawing!
What is the frequency and T of that horn?
Does its horizontal profile open faster than the E-JMLC?
 
Wayne Parham

Wayne Parham

Member
Joined 2004
PiSpeakers.com
buzzforb said:
Wayne,
How similar is the cross section of the 290C in comparison to the TH-4003 shown in the link?
https://www.google.com/search?q=th4...26start%3D8550%26sort%3D1%26number%3D;496;701
Click to expand...

I lifted the equations used to describe the H290C waveguide/horn from a document describing the device:

H290C_equations.gif


That shows in some detail the flare profile I used. What is not shown by those formulas are the mouth radius and the profile at the edges.

The mouth radius is borrowed from LeCleach, but it is not a large part of the total profile so in truth, it could have been a tractrix or some other shape, even an arbitrary radius. I just wanted to avoid any sharp edges.

Similarly, I wanted to provide smooth features on the diagonals, but also to maintain as much of the area as possible, which is why I chose a rectangular profile. I think the super-ellipse would have been fine too, but I saw no reason to take that shape, so what I did was to use the same formula as shown above and apply it for the oblique angles, but just enough to provide a round entrance that gradually blends the sides with top and bottom so that the exit is rectangular.

The end result is a shape that has slightly wider tangential angles on the diagonals. The profile starts off round, then slowly changes to elliptical, then towards more of a super-ellipse, then finally to a rectangular exit. But the profile at every point - horizontal, vertical or obliques - is described by the trigonometric formula above.

My design goals were to create a device that had uniform directivity but not at the expense of response smoothness. I also wanted an asymmetrical flare, because I like the ability to minimize the vertical spacing of MF and HF sound sources.

I always thought that discontinuities inside the horn caused response ripple due to impedance spikes. They also cause diffraction, which may be useful for widening the pattern but it destroys imaging. So waveguides are attractive in that they limit these problems, but many of them aren't so good at acoustic loading, and so suffer from response ripple. I wanted the best of both worlds, and I found that it is possible, provided you design the waveguide paying attention not only to flare profile but also area expansion and length.
 
Last edited:
ivicai

ivicai

Member
Joined 2009
Hyperbolic Horn from y:1937-1938

Wayne Parham said:
Earlier we were talking about giving credit where credit is due.

I remember 10 or 12 years ago, when I first became interested in the catenary flare profile, doing a lot of research and finding catenoid horns were popular in another field. Seems like ultrasonics, maybe. I also remember reading about an early adopter of catenoid horns, someone that promoted the flare shape long before any of us here were using them.

Does any of you know that researcher's name or the reasons he preferred catenoid horns? Might be an interesting factoid, one that I have long since forgotten.
Click to expand...

Hi Wayne Parham,

May You have these in mind:
from the forum member whgeiger [ diyAudio - View Profile: whgeiger ]

http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-715.html#post4059281

".....
Some Horn History

The hyperbolic horn (A.K.A. O.S. Waveguide) is not new in the field of acoustics.

While At M.I.T.,
[1] John Freehafer submitted his PHD dissertation,
“The Velocity Potential of a Hyperbolic Horn”
On 13-May-1937
https://dspace.mit.edu/bitstream/han...pdf?sequence=1

Shortly thereafter,
[2] Vincent Salmon submitted his PHD dissertation
“The Sound Field and Radiation Impedance of a Hyperbolic Horn”
on 6-Dec-1938
http://dspace.mit.edu/bitstream/hand...pdf?sequence=1

Regards,
WHG
...."

regards
ivica
 
ivicai

ivicai

Member
Joined 2009
Kindhornman said:
Earl Geddes,
I guess it was the same way I felt when I read your paper on the oblate spheroid design that I had previously written a private paper to Bayer corp for funding. Called it something else but was convinced that paper was shown to you at Ford. I think now we can agree that it was simultaneous invention but we did have the same idea at the same time. Still a slightly different perspective on how we did it , you from the mouth backwards and me from the driver outwards but they couldn't have been closer in theory how they worked. You published your paper and I didn't. You win!
Click to expand...

May be these (on hyperbolic flare horn, as OSWG) can help:

http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-715.html#post4059281

regards
ivica
 
ivicai

ivicai

Member
Joined 2009
Hi Wayne Parham,

May You have these in mind:
from the forum member whgeiger [ diyAudio - View Profile: whgeiger ]

http://www.diyaudio.com/forums/multi-way/103872-geddes-waveguides-715.html#post4059281

".....
Some Horn History

The hyperbolic horn (A.K.A. O.S. Waveguide) is not new in the field of acoustics.

While At M.I.T.,
[1] John Freehafer submitted his PHD dissertation,
“The Velocity Potential of a Hyperbolic Horn”
On 13-May-1937

https://dspace.mit.edu/bitstream/handle/1721.1/46001/35368752.pdf?sequence=1


Shortly thereafter,
[2] Vincent Salmon submitted his PHD dissertation
“The Sound Field and Radiation Impedance of a Hyperbolic Horn”
on 6-Dec-1938

http://dspace.mit.edu/bitstream/handle/1721.1/45994/35167649.pdf?sequence=1


Regards,
WHG
...."

regards
ivica[/QUOTE]
 
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