I'm new to CDs and Horns.
I'm thinking about a coax CD playing through a JBL 2390 horn lens. The idea is to smooth response in general and disperse the high frequencies. The JBL document shows pretty good dispersal of 10K. This would be for home use. The only report I found cautions against beaming with coax CDs (BMS 4590 for example).
The ideal is to use a separate driver for bass with an active XO.
I'm wondering if anyone's tried this route, and what people's experience is in general with horn lens CD combos.
I'm thinking about a coax CD playing through a JBL 2390 horn lens. The idea is to smooth response in general and disperse the high frequencies. The JBL document shows pretty good dispersal of 10K. This would be for home use. The only report I found cautions against beaming with coax CDs (BMS 4590 for example).
The ideal is to use a separate driver for bass with an active XO.
I'm wondering if anyone's tried this route, and what people's experience is in general with horn lens CD combos.
The JBL 2390 horn lens has a sound I would describe as "warm and fuzzy".
It does have wide dispersion, but just does not sound "real", compared to the same driver, same horn, lens removed.
I have used the 2385, 2390, 2308, and the 2301 "potato masher".
They all sound goofy, but not unpleasant.
An approach best left back in the 1970s.
I would not recommend a horn lens to anyone who is interested in accurate reproduction of recorded (or live) sound.
Art Welter
I have found that diffraction lenses of the sort that use the "venetian blind" approach have multiple problems, not the least of which is the vibration of the metal parts... they might be somewhat better if well damped by some means...
I think the "potato masher" concept has some merits, but requires a very different implementation if it is going to reach past the old perf-metal set up... but that's a story for another day.
It is very difficult to disperse very HF sound after it has been transmitted any significant distance from the diaphragm - thus the use of phase plugs in compression drivers... the issue of reflections and interference once the dimensions get >1/4 wave are difficult to deal with.
Once you have a coax driver you're going to have compromises and issues to cope with WRT the HF dispersion and diffractions... difficult to overcome.
So, with that in mind, it might be sonically acceptable to experiment with various sorts of dispersion techniques.
I think the UREI or older Altec 604 drivers that are already fitted with a horn assembly (or a newer one that is also so fitted) might be easier to work with?
Keep in mind the highs coming off the main cone will be banging off the back of anything that sticks out... that is maybe one reason that Tannoy did things way they did...
_-_-bear
I think the "potato masher" concept has some merits, but requires a very different implementation if it is going to reach past the old perf-metal set up... but that's a story for another day.
It is very difficult to disperse very HF sound after it has been transmitted any significant distance from the diaphragm - thus the use of phase plugs in compression drivers... the issue of reflections and interference once the dimensions get >1/4 wave are difficult to deal with.
Once you have a coax driver you're going to have compromises and issues to cope with WRT the HF dispersion and diffractions... difficult to overcome.
So, with that in mind, it might be sonically acceptable to experiment with various sorts of dispersion techniques.
I think the UREI or older Altec 604 drivers that are already fitted with a horn assembly (or a newer one that is also so fitted) might be easier to work with?
Keep in mind the highs coming off the main cone will be banging off the back of anything that sticks out... that is maybe one reason that Tannoy did things way they did...
_-_-bear
My recommendation would be a single horn like DSL's SH-50 (a Synergy or Unity style horn), with subwoofers below if desired.
An open baffle has sound from the back reflecting off rear walls, floors and ceiling, adding additional room reverb to the recorded sound.
Horns with good pattern control down below 1000 Hz can eliminate much of the room reflections, so you hear more of what the recording sounds like rather than what your room sounds like.
Horns will also be more efficient, so distortion may be less, and less power needed for a given volume.
If an acoustic lens is designed properly, the only audible difference will be an improved dispersion pattern of the signal passing through it.
Like a horn, an acoustic lens it is a band-pass device. At its lower limit, when overall dimensions are comparable to signal wave length, it is acoustically transparent. At its upper limit, when signal wavelength is comparable to element spacing, irregularities in frequency response occur. Also the elements themselves must be designed so that they do not resonate at frequencies within the pass-band.
Most derogatory ovseravtios come from listening to acoustic singles having frequency content outside the pass-band of the acoustic lens they are passing through.
If you want design information, come back an I will provide some references.
Regards,
WHG
I concur, I'm using 2308 lens clones (well damped plastic vanes) with some JBL 2440 CD on 2311 horns and of the several combinations I have tried in my small room including 2397 Smith Horns I think these work the best.
Acoustic Lenses & Other Dispersive Devices
A list of references follows. They include reflecting surfaces that have a similar mission.
The most important of these are the work of Kock & Harvey followid by that of Frayne & Locanthi.
Regards,
WHG
File: AESP1401.pdf
Title: Acoustic Lens, Their Design and Application
Author: Earl Geddes
Affiliation: Department of Physics, Eastern Michigan University, Ypsilanti, Michigan
Publication: AES-P, No. 1401, Cnv. 79 (Nov-1978)
Abstract: A simple criterion for the design of acoustic lenses is developed. An experimental study of a lens designed to increase the dispersion at 4000 Hz of the far field of a seven inch driver is described and compared to the theoretical predictions.
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.
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.
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.
Title: The Acoustical Lens
Author: George L. Augspurger
Publication: Wireless World Magazine, Dec-1962
Abstract: Operation and performance of various type of devices use professionally and in home hi-fi speakers systems to disperse and shape sound energy from horn type driver units are discused.
File: AESP-2267
Title: Wide Dispersion Frequency Invariant Acoustic Lens
Author(1): Ferralli, Michael W.
Author(2): Moulton, David; Brugger
Author(3): Brugger, David
Author(4): White, Jeffrey
Author(5): Hebrock, Steven
Affiliation(1): Phase Coherent Audio, Inc., Girard, PA
Affiliation(2): Audio-Techniea U.S., Inc., Stow, OH
Publication: AES-P No. 2267, Cnv. 79 (Oct-1985)
URL: AES E-Library Wide Dispersion Frequency Invariant Acoustic Lens
Abstract(1): A novel acoustic lens has been devised which allows the acoustic radiation field of two or more transducers to be coupled in phase such that the resultant acoustic radiation pattern is interference-free at all frequencies, and displays wide and nearly frequency independent beam width.
Abstract(2): The lens is utilized in the high frequency transduction system of a loudspeaker array in order to achieve high frequency beam widths which approach that of the low frequency components while eliminating beaming, upper frequency beam collapse, and combing.
File: AESP-2392
Title: 360 Degree Dispersion Frequency Invariant Acoustic Transduction System
Author(1): Ferralli, Michael W.
Author(2): Moulton, David
Affiliation: Phase Coherent Audio, Inc.,Girard, PA
Publication: AES-P No. 2392, Cnv. 81 (Nov-1986)
URL: AES E-Library 360 Degree Dispersion Frequency Invariant Acoustic Transduction System
Abstract(1): An acoustic transduction system has been designed which couples the sound field of two transducers in phase and produces a resultant acoustic radiation pattern which has a full 360 degree horizontal by 90+ degree vertical frequency invariant beamwidth. The system incorporates an acoustic lens, rather than a phased array or electronic technique, to couple the sound fields and produce the wide dispersion.
Abstract(2): The system is used in a loudspeaker to achieve a 360 degree sound field which is devoid of high frequency beam collapse, and combing.
File: AESP-5648
Title: Driver Directivity Control by Sound Redistribution
Author(1): Pedersen, Jan Abildgaard
Author(2): Munch, Gert
Affiliation: Acoustics Research, Bang & Olufsen, Struer, Denmark
Publication: AES-P No. 5648, Cnv. 113 (Oct-2002)
URL: AES E-Library Driver Directivity Control by Sound Redistribution
Abstract(1): The directivity of a single loudspeaker driver is controlled by adding an acoustic reflector to an ordinary driver. The driver radiates upwards and the sound is redistributed by being reflected off the acoustic reflector. The shape of the acoustic reflector is non-trivial and yields an interesting and useful directivity both in the vertical and horizontal plane. 2D FEM simulations and 3D BEM simulations are compared to free field measurements performed on a loudspeaker using the acoustic reflector.
Abstract(2): The resulting directivity is related to results of previously reported psychoacoustic experiments.
A list of references follows. They include reflecting surfaces that have a similar mission.
The most important of these are the work of Kock & Harvey followid by that of Frayne & Locanthi.
Regards,
WHG
File: AESP1401.pdf
Title: Acoustic Lens, Their Design and Application
Author: Earl Geddes
Affiliation: Department of Physics, Eastern Michigan University, Ypsilanti, Michigan
Publication: AES-P, No. 1401, Cnv. 79 (Nov-1978)
Abstract: A simple criterion for the design of acoustic lenses is developed. An experimental study of a lens designed to increase the dispersion at 4000 Hz of the far field of a seven inch driver is described and compared to the theoretical predictions.
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.
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.
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.
Title: The Acoustical Lens
Author: George L. Augspurger
Publication: Wireless World Magazine, Dec-1962
Abstract: Operation and performance of various type of devices use professionally and in home hi-fi speakers systems to disperse and shape sound energy from horn type driver units are discused.
File: AESP-2267
Title: Wide Dispersion Frequency Invariant Acoustic Lens
Author(1): Ferralli, Michael W.
Author(2): Moulton, David; Brugger
Author(3): Brugger, David
Author(4): White, Jeffrey
Author(5): Hebrock, Steven
Affiliation(1): Phase Coherent Audio, Inc., Girard, PA
Affiliation(2): Audio-Techniea U.S., Inc., Stow, OH
Publication: AES-P No. 2267, Cnv. 79 (Oct-1985)
URL: AES E-Library Wide Dispersion Frequency Invariant Acoustic Lens
Abstract(1): A novel acoustic lens has been devised which allows the acoustic radiation field of two or more transducers to be coupled in phase such that the resultant acoustic radiation pattern is interference-free at all frequencies, and displays wide and nearly frequency independent beam width.
Abstract(2): The lens is utilized in the high frequency transduction system of a loudspeaker array in order to achieve high frequency beam widths which approach that of the low frequency components while eliminating beaming, upper frequency beam collapse, and combing.
File: AESP-2392
Title: 360 Degree Dispersion Frequency Invariant Acoustic Transduction System
Author(1): Ferralli, Michael W.
Author(2): Moulton, David
Affiliation: Phase Coherent Audio, Inc.,Girard, PA
Publication: AES-P No. 2392, Cnv. 81 (Nov-1986)
URL: AES E-Library 360 Degree Dispersion Frequency Invariant Acoustic Transduction System
Abstract(1): An acoustic transduction system has been designed which couples the sound field of two transducers in phase and produces a resultant acoustic radiation pattern which has a full 360 degree horizontal by 90+ degree vertical frequency invariant beamwidth. The system incorporates an acoustic lens, rather than a phased array or electronic technique, to couple the sound fields and produce the wide dispersion.
Abstract(2): The system is used in a loudspeaker to achieve a 360 degree sound field which is devoid of high frequency beam collapse, and combing.
File: AESP-5648
Title: Driver Directivity Control by Sound Redistribution
Author(1): Pedersen, Jan Abildgaard
Author(2): Munch, Gert
Affiliation: Acoustics Research, Bang & Olufsen, Struer, Denmark
Publication: AES-P No. 5648, Cnv. 113 (Oct-2002)
URL: AES E-Library Driver Directivity Control by Sound Redistribution
Abstract(1): The directivity of a single loudspeaker driver is controlled by adding an acoustic reflector to an ordinary driver. The driver radiates upwards and the sound is redistributed by being reflected off the acoustic reflector. The shape of the acoustic reflector is non-trivial and yields an interesting and useful directivity both in the vertical and horizontal plane. 2D FEM simulations and 3D BEM simulations are compared to free field measurements performed on a loudspeaker using the acoustic reflector.
Abstract(2): The resulting directivity is related to results of previously reported psychoacoustic experiments.
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That's an impressive list, all but one of the references are beyond my reach. Are there more mainstream materials?
Also, can more folks post their home results - that's really what I'm trying here/
Acoustics
Is not Rocket Science, its worse!
However, in this case, if you understand how a camera lens works, then the leap to an acoustic one will be just a small step forward. You will still be dealing with two surfaces and the index of refraction of the medium in between.
If you want a copy of the two articles mentioned, I can send them to you.
Regards,
WHG
Is not Rocket Science, its worse!
However, in this case, if you understand how a camera lens works, then the leap to an acoustic one will be just a small step forward. You will still be dealing with two surfaces and the index of refraction of the medium in between.
If you want a copy of the two articles mentioned, I can send them to you.
Regards,
WHG
Please send the references, that would be great. I've PMed you my email address.
That may be the *theory*, but having heard several I'd disagree.
For one thing it disrupts the pressure gradient, making detection more difficult.
Note that the "lens's" were dropped in favor of larger mid-treble horns without lens's (in a variety of designs). Most had better "image" localization as a result.
Of course above 3-4 kHz in a moderately spaced loudspeaker pair, poorer localization probably is *not* a bad thing. Unfortunately because JBL used larger mids, they usually had a crossover more than an octave lower (..under 1.5 if I remember correctly) for better horizontal coverage. The models that had "lens" horns down to 800 Hz were even worse with respect to localization.
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