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Old 19th December 2003, 02:37 AM   #1
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Location: Brisbane Australia
Default Constant Directivity Speaker Project

This is a project I have been contemplating for some time now and although it isn't fully coherent (in my own mind) just yet I will post my musings and see if I can get some good feedback from everyone (anyone).
The idea is as follows.

A stereo speaker system with a constant and defined directivity pattern such that its interaction with the room is minimised compared to conventional speakers. The system will be a 3-way (maybe 4 a sub could be used later if deemed necessary) with the following frequency ranges (approximate only) drivers and enclosures.

Bass (50 - 400Hz)

Either a dipole, cardioid or second order gradient setup comprising 1 or 2 (depending on which alignment is used) high efficiency 15" mid bass Pro drivers. A Typical candidate would be's SN15-MB
I am leaning towards a dipole or second order gradient alignment at the moment and intending to use floor placement to help the lower end with 6dB gain.

Mid (400 - 4000Hz)

A 60 - 90 degree oblate spheroidal waveguide as described in Earl Geddes (spelling??) AES preprint. This would be loaded with a 6.5" pro midrange of between 95 and 100dB efficiency. Typical candidates would be

Audax PR170MO
PHL 1660 (others in PHL's range may also be suitable) MD-720 (

I would like to push the 4000Hz up to somewhere nearer 6000Hz or more if possible. Any thoughts on drivers or techniques which would allow me to achieve this?

Treble (4000 - 20000Hz)
Undecided but must have same directivity as mid within its passband. This means it will most probably be wavguide/horn loaded also. Maybe a waveguide for a convetional tweeter woild work, any thoughts?

The reason I am going to all this trouble is I have been experimenting with crosstalk cancellation using matlab for a while and believe that the key to its success is directional loudspeakers.

Any input on the above would be most helpful especially the following:

Drivers which are of good quality and low price for the mid & bass sections

Any info on second order gradients and how much equallization will be required (I already have olsons paper thanks to Kelticwizard)

Any info on how to realise a suitable the treble solution.


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Old 19th December 2003, 05:00 AM   #2
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You may want to investigate the Unity Horn from Tom Delany. A two way 60 x 60 constant directionality Unity horn will reach down to 300Hz, and a 3-way could reach down close to your 50Hz target. One time coherent constant directionality horn with very modest room interaction.

Your current thread mixes several radiation patterns which may be difficult to integrate.
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Old 19th December 2003, 05:04 AM   #3
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Here is the front view of 3-way Unity Horn.
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Old 19th December 2003, 07:07 AM   #4
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Thanks for your input, I have the following queries.

Your current thread mixes several radiation patterns which may be difficult to integrate.
By this do you mean the radiation patterns are different in shape from the 3 sources or that the sources are not coherent because they are originating from different positions.
If you mean the latter then that is correct. If you mean the former I tend to disagree. The polar radiation of a second order gradient is very close to that of a 60 degree waveguide and ofcourse the radiation from to 60 degree waveguides will be very close. Can you explain a little further.

How big is the mouth of a 50Hz unity horn. If I use conventional horn theory and place it on the floor I get a mouth size of 1.4x1.4 metres. Or against a wall and the floor 0.97x0.97 metres. This is pretty big and does not allow me to position the speakers where I wish (against a wall). Something which I consider important. I would have thought that introducing the low frequencys that close to the mouth would forfeit any control over directivity the waveguide has at that frequency anyway. Do you have a link to the page the 50Hz model can be found so I can read up on it a little.

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Old 19th December 2003, 04:34 PM   #5
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The 300 Hz 2-way 60 x 60 unity hors is 16.5" x 16.5" and aboout 14" deep.

A 65 Hz 3-way 60 x 60 unity horn would be about 29" x 29" and about 23" deep. A 40 x 40 horn about 19" x 19"

Controlled directionality speakers that can be placed close to a wall look attractive for home theater. High efficiency HT speakers can save substantial amplifier cost.

unity horn
Yorkville unity horn
sound physics Lab

The Sound Physics Labs SPL-td1 is a unique combination of compact size and extended coverage capabilities, designed by Thomas Danley to deal with the real world problems faced by systems contracting professionals every day.
The SPL-tdl is a distinctive multiple entry horn. Precise mechanical time correction is achieved through proper placement of transducer exits along the body of the horn. The size, angle, and spacing of these apertures was mathematically determined using a proprietary new modeling system (patent pending). The mathematical model used allows scaling to whatever size may be required. The final voicing was done using both industry standard measurement and subjective analysis. As a result the SPL-tdl has excellent, documented polar response, and subjectively delivers an unusually neutral sonic presentation. What you hear is the signal not the loudspeaker!

Frequency Response 65 Hz-20kHz 3dB (2 or more boxes)
Sensitivity 103 dB @ 2.8v/1m
Power Handling 600 Watts Continuous
Peak SPL 137dB @ 800 Watts Pink Noise (6dB Crest Factor)
Nominal Impedance 8 Ohms Average
Coverage Pattern 60V x 40H
Transducers LF 2 x 12"
Transducers MF 4 x 5"
Transducer HF 1 x 1"
Weight 130 lbs.
Dimensions 29" H x 23"D x 19"W
Construction 13 Ply Baltic Birch
Finish Black Catalyzed Texture Coat,
White Catalyzed Texture Coat
Line X Exterior Coating
Box Angle 30 Degree Trapezoid
Connectors 2 x NL4 (Passive)
2 x NL4 & 2 x NL8 w/pin swap switch (Active)

================================================== =====================

This patent-pending technology is based on utilizing a pyramid-shaped, multi-band wave guide, to properly combine the amplitude and phase from a multiple number of drivers into a single coherent acoustic output. It is in effect a 2-way horn, 5 driver system including a simple passive crossover network that effectively acts as a single driver on and off axis. Unlike similar sized enclosures, the 16-inch square horn exit provides an essentially constant 60 x 60 degree pattern down to several hundred Hz. Using this technology, more of the sound is aimed directly to where the cabinet is pointed minimizing side and floor reflections. This benefit assists in controlling sound in highly reverberant rooms or where the maximum preservation of a recording's stereo image is desired.

Clarity Unmatched voice intelligibility and precise music reproduction due to the time-aligned phase coherent design. This is the only multi-way design to accomplish such in both the on and off axis response.
Controlled Directivity 60 x 60 dispersion pattern provides superb energy time curve response over an extended bandwidth while lowering undesirable side wall and floor reflections from reaching the listener and clouding the sound.
Frequency Response 300hz ~ 22,000Hz +/ - 3dB
Efficiency 100dB @ 1W1m with an 8ohm nominal load
Power Handling 100W RMS (120dB) typical music program assuming 6dB high pass crossover at 300hz
Distortion @ 112dB/1M 300 Hz = .477%
600 Hz = .194%
1200 Hz = .386%
2400 Hz = .967%
4800 Hz = 1.5%

Distortion @ 90dB/1M 300 Hz = .078%
600 Hz = .029%
1200 Hz = .062%
2400 Hz = .110%
4800 Hz = .049%

Unparalleled Performance Very low distortion, very high output. Consider at even 116dB each 5" mid range driver is receiving only 1W, the power compression and harmonic distortion levels of the speaker rivals those that only amplifiers could previously attain.
Dimensions 16.5" x 16.5" at the mouth outer lip, 14" deep overall, very small size for such high performance.
No "Horn" Sound! Due to the large radiating area of the 4 midbass drivers, the "horn" sound has been eliminated in this advanced patented design.
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Old 19th December 2003, 07:59 PM   #6
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Default Marketing hype


Have you actually listened to a unity horn? I have not, but until I have some other opinion or personal experience other than a marketing spiel I am not inclined to consider them for this particular project.

Has anyone else listened to unity horn in any of its incarnations? If so what did you think?

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