Speaker Directivity

Apr 3, 2010
Seattle, WA
I went looking for a video for this fundamental acoustics/speaker concept called directivity. To my surprise, I could not find anything but this video that is being translated into Korean. If you know a better video post it but in absence of that, this is important enough topic to put up with the translations:

Also talked in there is the interference between multiple drivers.
Dec 13, 2010
Hi Amir,

I went looking for a video for this fundamental acoustics/speaker concept called directivity.
The first part looks as if it was about what I call the Allison-effect, i.e. increase in power output caused by near room boundaries.

Allison, “The influence of room boundaries on loudspeaker power output”, J. of the Audio Engineering Society 1974, p.314

Allison, “Influence of listening rooms on loudspeaker systems”, Audio Magazine Aug. 1979, p.37

See also

Waterhouse, “Output of a sound source in a reverberation chamber and other reflective environments”, J. of the Acoustical Society of America 1958, vol.30, no.1, p.4

Also talked in there is the interference between multiple drivers.
The ultimate question is how much of that does one hear when playing music? I can imagine that you hear these comb-filter effects nicely when playing noise but what do you hear of these combs when playing a Mahler Symphony? Would'nt that driver interference generate just another comb filter to be added to those already existing (cabinet edge diffraction, first reflections), in which case it would be welcome since it helps to smooth the overall response?

Salomons, “Coloration and binaural decoloration of sound due to reflections”, Dissertation, TU Delft 1995

Bilsen, “Binaural modeling of spaciousness and coloration”, Music and Concert Hall Acoustics, Conference Proceedings from MCHA95, Kirishima International Concert Hall, Japan, May 1995, p .327-335, Editor: Y. Ando & D. Noson

This feature of delaying one speaker and lowering volume of the other is interesting, has it been put to the test, i.e. playing music and under blind conditions?

Apr 3, 2010
Seattle, WA
Hi Klaus. I have Roy Allison's paper in my library and read it long time ago. I have not however heard of the term "Allison effect." The common terminology I have heard is boundary gain.

I did not post the video for that but the polar plots he uses to show directivity. That said, I thought the early part are also good with respect to use of subs and the gains one gets by putting them next to walls.

I didn't pay attention to the end where he tries to optimize multiple horns :). I assumed that stuff was specific to whatever they were selling.

I really wish there was a video on driver and speaker directivity, waveguides, etc. Have to keep looking. Let me know if you know any.


WBF Technical Expert (Speakers & Audio Equipment)
Sep 6, 2010
Seattle, WA
Amir, from my fuzzy recollection there was quite a bit of research done at Mackie with regards this. In the pro-sound, they use multiple speakers on stage, and this caused "lobing" due to speaker directivity. What the video mentioned about lowering the level and phase delaying the other speaker rang a bell.

See if you can find Jeff Hammerstrom. He worked for me for a couple of years, and then went on to Apple. He's one of the good engineers in audio - but he fought tooth and nail with Arnie and we eventually had to let him go.

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