Improving Two–Way Loudspeaker Directivity by Olli Kantamaa, February 2020 discusses a two-way speaker that uses gradient signal processing to control middle and low frequency radiation pattern. The goal was to narrow the low/middle directivity of a two-way speaker by using a rear driver 180 degrees out of phase with the front driver.
https://aaltodoc.aalto.fi/bitstream...Kantamaa_Olli_2020.pdf?sequence=2&isAllowed=y
Citations include a reference to "Low frequency directivity control" by Olivier, L. B. (2010) that discusses using spectral delay filtering in order to modify the directivity of low frequencies.
I understand the basic concepts but not the math. The 2010 research paper is a decade old now so I wonder if there are plug-n-play algorithms available for Sigma Studio/DSP software. It would be nice if you could plug in a distance between the front and rear woofer to get the proper algorithm for active control of the low/mid frequencies.
Does anything like that exist yet?
https://aaltodoc.aalto.fi/bitstream...Kantamaa_Olli_2020.pdf?sequence=2&isAllowed=y
Citations include a reference to "Low frequency directivity control" by Olivier, L. B. (2010) that discusses using spectral delay filtering in order to modify the directivity of low frequencies.
I understand the basic concepts but not the math. The 2010 research paper is a decade old now so I wonder if there are plug-n-play algorithms available for Sigma Studio/DSP software. It would be nice if you could plug in a distance between the front and rear woofer to get the proper algorithm for active control of the low/mid frequencies.
Does anything like that exist yet?
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I believe it is what Kii3/D&D use. DIYAudio forum members have said they like how LowMid frequency directivity sounds. Olli Kantamaa researched that opinion and determined increased/ing directivity using active DSP control of a rear woofer subjectively improves the sound.
There might be passive methods that work better or as well, but active is successful. I'm hoping there's a way to get and use the algorithms that doesn't require a PhD.
There might be passive methods that work better or as well, but active is successful. I'm hoping there's a way to get and use the algorithms that doesn't require a PhD.
I thought this final conclusion from Kantamaa's paper was interesting as well,
An industry standard might not be substantiated by the science. Maybe it just came from pragmatism.
An industry standard might not be substantiated by the science. Maybe it just came from pragmatism.
The industry standard is @ss-backwards..
It should be increasing directivity as freq.s lower and decreasing as freq.s raise.
Unfortunately this is the most difficult pattern to achieve..
The D&D is actually mostly passive for the midrange. That's what those slots on the sides are for
A less "technical" paper on the subject. https://electrovoice.com/media/downloads/wp_subwoofer_arrays_v04.pdf
The industry standard is @ss-backwards..
It should be increasing directivity as freq.s lower and decreasing as freq.s raise.
Unfortunately this is the most difficult pattern to achieve..
I've heard people share that same opinion. The author of the paper only researched LowMidFrequency directivity. If active LMF directivity becomes easier & cheaper maybe more DIYers will start designing speakers with narrow LMF & wide HighFrequency.
Unless I'm wrong, DIYers seem to approach LMF directivity by controlling HF first and working their way down into the mids, a large waveguide that can push down into the mids. But if active LMF directivity was easy maybe they'd start widening the HFs.
I tried to build a lazy man's narrow LMF wide HF to see what it sounds like. The 5.5" speaker is open baffle, 3" & 3/4" are closed. 5.5" to 3" speakers are 4.5" center to center. 3" to 3/4" is 2.5" center to center. Crossover @2970Hz, and 5350Hz. Cone diameter of 5.5" speaker is 3.75". Cone diameter of 3" speaker is 2".
I don't know what I'm doing but it looks like I get beaming with the 5.5" up to 4kHz before breaking up. Maybe I could have crossed straight to the 3/4" tweeter at 4100 with a center to center distance of 3.25" but I played it safe at 2970Hz because I don't know what I'm doing or if I properly identified breakup. https://www.scan-speak.dk/datasheet/pdf/15w-8424g00.pdf
Trying to do this using passive methods seems sort of restrictive. It feels like a digital Cardioid/Gradient LMF would make things easier (if the DSP algorithm is plug-n-play.) For example, I tried to get the 5.5" driver to beam but was restricted by center to center spacing. I could hear the difference when I ignored center to center spacing to increase beaming of the 5.5" driver at 4,000Hz. With Cardioid/Gradient DSP you wouldn't have to worry about getting your driver to beam based on geometry, you could just make it beam.
I don't know what I'm doing but it looks like I get beaming with the 5.5" up to 4kHz before breaking up. Maybe I could have crossed straight to the 3/4" tweeter at 4100 with a center to center distance of 3.25" but I played it safe at 2970Hz because I don't know what I'm doing or if I properly identified breakup. https://www.scan-speak.dk/datasheet/pdf/15w-8424g00.pdf
Trying to do this using passive methods seems sort of restrictive. It feels like a digital Cardioid/Gradient LMF would make things easier (if the DSP algorithm is plug-n-play.) For example, I tried to get the 5.5" driver to beam but was restricted by center to center spacing. I could hear the difference when I ignored center to center spacing to increase beaming of the 5.5" driver at 4,000Hz. With Cardioid/Gradient DSP you wouldn't have to worry about getting your driver to beam based on geometry, you could just make it beam.
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The opposite.
Increasing directivity increases apparent spl..
It's counter-intuitive. 😱
Treble horns mated with "omni" midbass drivers usually need to be "padded-down" with lower pressure than the midbass drivers for subjectively proper summation between the two. The same is also true for Coaxial drivers.
Subjectively IF you don't do this then not only is the treble apparently louder, it also seems to *"push" the soundstage/imaging forward from the plane of the loudspeakers. When it's "correct" (or with a subjectively balanced pressure level broad-band), then sound (all of it unless some weird phase processing was done to the signal) should start at the plane of the loudspeakers and expand rear-ward from the loudspeakers.
*though note that there are quite a few people that like this result, sounds more "exciting" to them.
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Oh, but I did build the lazy man platform using DSP + individual amps. Made it easy to switch crossover frequencies to see how the sound changed. If I wasn't so lazy I would have placed another 3/4" tweeter below the woofer so I could have tried the 5.5" to 3/4" crossover.
Unfortunately "omni" high freq. is ALSO difficult to achieve, with the typical solution being some sort of radial design, usually "up-firing" (as in a tweeter on a very small spherical "baffle" pointed up at the room's ceiling). Problematically: moving that far off-axis (70-90 degrees depending on the listener's vertical angle relative to the treble driver) results in pressure loss in the top two octaves.
As for most DIY'ers: they are typically emulating the rest of the industry. 😱
Plus, though still complex - trying to controlled directivity down to the midrange with a typical "omni" result below that, is much easier than the directive low freq. to omni high freq. result.
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Mount a driver flush into a wall and you have better than cardioid. Trying to do as good using any kind of processing will be challenging.
And not very expensive if you already DIY things like sheetrock and finishing trim.
Sounds like a good idea for a center channel. A waveguide as wide as the TV might get you down to the Schroeder transition. And you could use it as a cabinet to store the equipment.