Horn Lenses

As I understand it. JBL used to sell horns with acoustic lenses. Take the HL91 for example. It is the H91 horn with the L91 lens. Today many people refer to horns with no acoustic lens as a "horn lens". I see this printed in catalogs, on eBay, and hear it in everyday conversations. This is a misnomer, isn't it?

And then there are wave guides. I assume a wave guide is like a horn in that it affects dispersion characteristics but doesn't act as a true acoustic transformer to couple the driver with the air as a horn does.

IMO, it's mostly marketing strategy. To me, a "horn lens" and
"waveguide" are simply horns with a catchy name. Horns used
in microwave antenna's are called waveguides. They realize
the word "horn" can turn people off, so they think these up.

Look at the cereal isle in the store with all those sugar-
coated varieties, but guess what?, none use the word "sugar"
on the front. Same idea.

It's done alot in the speaker industry, take Polk and Bose
for example. They take an old technology from the 50's, and
attempt to make it sound like something new with a catchy name.

Yes. I think most other companies used horns that were complete units, where JBL made a lot of horn/lens conbinations. I think it was a great idea because the horn could concern itself with flare rate while the lens could deal with dispersion.
You know, it's funny to see the "development" of horns over the years. Even recently you have CD designs that claim perfection, while expotential, Triax, sectorial, multi-cell, Mantaray, bi-radials and other designs get pushed aside. And now there are the new straight-sided horns from JBL that get the glowing descriptions... yet look so primitive. Why is horn design so illusive?

Tom

Hello Widget

Yeah I would say it is a misnomer. They are two different things. If you think about it JBL used the H94 Serpentine in the L220/L222 right in front or a 5" midrange direct driver. You can also use it to shorten the throw and change the dispersion on a 2307 or any of the varoius horns with the same diameter exit. These can be exponential or conical it doesn't matter. The lense will work well with or without a horn and could care less what the flair is.

Rob:)

Yes, but the lens does care about the dispersion angle
going in. Say, you have 20 deg. going in, you get 90 going
out. If you have 40 going in you'll have say, 120 deg. out.

Yes, those new straight wall horns seem like two steps back,
I see them and say 'how the h... can that sound decent'.
Looks like honk city, baby. :confused:

MW,

For anyone pursuing design of an acoustic lens (not a wave-guide, and not a horn), the following tree articles [1], [2] and [3] are a ‘must-read’. Such devices have geometry and characteristics similar to their optical counterparts. Their geometry determines whether they exhibit convergent or divergent characteristics and likewise have an index of refraction that determines the degree of wave path alteration. They are also addressed by Olson is his book [4]. Characterization of a horn as a waveguide or a lens is an unfortunate misnomer. In the world of waves, acoustic and otherwise, horns, waveguides and lenses each have precise meanings that make them different. Without these distinctions, conversations about them become confused.

Regards,

WHG


References:

[1] Title: Theater Loudspeaker System Incorporating an Acoustic-Lens Radiator
Author: John G. Frayne
Author: Bart N. Locanthi
Publication: SMPTE-J, Vol. 63, p. 82, Sep-1954
Abstract: This paper describes a two-way loudspeaker system for presentation of stereophonic sound in motion-picture theaters. The systems presented use divergent acoustic lenses to achieve a wide dispersion pattern for high frequencies.

[2] Title: Refracting Sound Waves
Author: Winston E. Kock
Author: F.K. Harvey
Publication: ASA-J, Vol. 21, No. 21, p. 471, Sep-1949
Abstract: Structures that refract and focus sound waves are described. These include path length delay element and obstacle arrays that function as the acoustical convergent and divergent lenses.

[3] Title: An Acoustic Lens as a Directional Microphone
Author: Malcolm A Clark
Publication: ASA-J, Vol. 25, No. 6, p. 1152, Nov-1953
Abstract: An acoustic lens combined with a conical horn can be used to obtain a highly directional microphone without some of the disadvantages of a parabolic microphone. The directional characteristics can be calculated satisfactorily if one assumes that the horn provides uniform flooding of the lens aperture.

[4] Title: Acoustical Engineering
Author: Harry F. Olsen
Publication: D. Van Nostrand Co., Inc. (1957)
Professional Audio Journals, Inc. (1991)
http://www.audioxpress.com/bksprods/books/bkpa1.htm
Abstract: Comprehensive, but dated, text on the subject of acoustical engineering. Its reprinting at this late date says volumes about the value and significance of Olsen’s work. For those involved in this discipline, a copy of this book should be considered a necessary addition to their reference library.
Reference: Section 1.11 Refraction and Diffraction (Incl. Acoustic Lenses), p. 17

Quote:

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Originally posted by whgeiger
In the world of waves, acoustic and otherwise, horns, waveguides and lenses each have precise meanings that make them different. Without these distinctions, conversations about them become confused.

Regards,

WHG

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That is pretty much what I thought. I was just wondering if somewhere during the last ten years or so the definitions were changed.

Widget

MW,

The source of the misnomer as far as can be determined, starts with Geddes [2] and was based on a 1P assumption for a class of horns where the assumed isophase wave shape was that of an oblate spheroid bounded by a hyperboloid. Freehoffer addressed this class of horns in an earlier paper [1]. Following Geddies’ article [2], Putland in [3] disputed the 1P claim of Geddies, who subsequently retracted it in [4]. Later, Hughes [5] and [6], presented a similar horn that is also asymptotically conical and characterized it as a waveguide. This is all a very amusing read when prefaced by [1], as nothing particularly original beyond that presented by Freehafer (under the horn heading) has been revealed under the heading of “waveguide”.

Regards,

WHG

References:

[1] 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 horn is superior.

[2] Title: Acoustic Wave guide Theory
Author: Earl R. Geddes
Publication: AES-J, Vol. 37, No. 7, pp. 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.

[3] 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,

[4] 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

[5] Title: A Generalized Horn Design to Optimize Directivity Control and Wave front 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.

[6] Title: The Quadratic-Throat Waveguide
Author: Charles E. Hughes
Author: By John Murray
Publication: Peavey Electronics Corp. "A White Paper On An Invention"
URL: http://aa.peavey.com/Media/pdfs/qwp1.pdf
Abstract: Simplified version of the AES Convention Preprint presented in 1999

Hi, everyone:

IMHO, horn-related technology has really taken an unfair beating over more recent years, especially on behalf of marketing stratagists who are promoting designs which are far more efficient to manufacture (i.e. bass reflex designs; accoustical lenses VS. CD horns; a single, so called "sub-woofer" with satellites :barf: ).

They've been successful through what I've called brain washing on prior posts; they (marketing stratagists) have been reaching the public through channels which are generaly precieved as highly authoritative, be it all the Stereo Review-type publications, the sales staff at the retail outlets, and so forth. I come across people more often as time goes on who have absoluely no idea - no concept - of what they're missing in terms of how good sound reproduction can really, well, sound.

From time to time I'll have an opportunity to visit someone's house and get a chance to experience their latest and greatest (and usually very expensive) 5.1 suround system, and while they rest on their pride I'll be polite and say nice things about their system while thinking to myself, "...here's another lost soul...". What they really have is mostly a result of years of spin they've been believing as gospel.

Then there are the self proclaimed audio experts who I get over to my house. They see my sound room packed full of what they initially preceive as junk ("...Charley, where's your sub-woofer?"), and snicker as the tubes warm up. Then the music starts to play. Aint nothin' like the sight of watching the jaws hit the floor on these people during a session which leaves them crushed and humiliated.

Sorry I got off track there...

If one observes what goes into manufacturing a line of CD horns, VS. a line of accoustical lense-horn assemblies, It's too obvious to see which would be more appealing to a manufacturer.

Regards,
Charley

WHG's post should have read as follows: (the URL was wrong)


Very interesting paper..
JCD


[6] Title: The Quadratic-Throat Waveguide
Author: Charles E. Hughes
Author: By John Murray
Publication: Peavey Electronics Corp. "A White Paper On An Invention"
URL: http://www.peavey.com/Media/pdfs/qwp1.pdf
Abstract: Simplified version of the AES Convention Preprint presented in 1999



Report

Quote:

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Originally Posted by jcdahl

WHG's post should have read as follows: (the URL was wrong)


Very interesting paper..
JCD


[6] Title: The Quadratic-Throat Waveguide
Author: Charles E. Hughes
Author: By John Murray
Publication: Peavey Electronics Corp. "A White Paper On An Invention"
URL: http://www.peavey.com/Media/pdfs/qwp1.pdf
Abstract: Simplified version of the AES Convention Preprint presented in 1999



Report

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Just correct URLs, together much easier to understand:

http://www.excelsior-audio.com/Publi...201999-09).pdf

http://www.excelsior-audio.com/Publi...WhitePaper.pdf

Quote:

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Originally Posted by Charley Rummel

Hi, everyone:

IMHO, horn-related technology has really taken an unfair beating over more recent years, especially on behalf of marketing stratagists who are promoting designs which are far more efficient to manufacture (i.e. bass reflex designs;...

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You forgot to mention manufacturers of 1000watt power amps. They are the ones that need to go with subs and bass reflex enclosures ;)

Quote:

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Originally Posted by Mr. Widget

<snip> ... and hear it in everyday conversations. This is a misnomer, isn't it? ... <snip>
<snip> ... that it affects dispersion characteristics but doesn't act as a true ...<snip>

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Yes, it is a missnomer. There are many more: just think about all those CD horns named "biradial", though their construction may be completely different, such as Manta Ray.

"Dispersion" is the dependency of wave properties on the wavelength, e.g. the dependency of the speed of light in glass on the wavelength. In an optical lense this leads to an error called "chromatic aberration".

Ruediger