I've been toying with this idea for awhile, to build subwoofers like the Genelec W371A. I've read about DSP for multiple subwoofers for years, so I feel this is a clever application of those ideas. But I'm not sure if there is an off the shelf DSP that can do the job? A MiniDSP 4x10 would have enough channels. The mains would have to be on the same DSP
For background, what Genelec is doing is combining a front firing 14" woofer and a rear firing 12" subwoofer in the same cabinet. The frequency range of the 2 drivers overlap, and the different placement of the 2 drivers is enough to create different room nodes. The EQ takes advantage of the different room nodes from each driver and adjusts both drivers individually so together they create a flat response.
I already did some rudimentary testing of this concept. I have 2 M-Audio BX subwoofers, and I stacked them on top of each other, with the bottom speaker facing the rear and the top facing the front. The height of the two subs stacked was 34". I also added spacers to get 41", and again raised it to match the Genelec's 43" height. This test is NOT meant to represent what Genelec's product does, but it is intended to see how much of an effect this unique speaker alignment makes.
I found that the 34" height showed the most difference in room nodes, in my very not good room. (The subs were spaced ~32" from the wall.) The effect seemed to diminish with height, but I expect it begins increasing again at a certain height.
I also found that it works for a limited frequency range, between 60hz and 200hz. The response curve above and below were identical in all tests.
This leads me to believe that Genelec have a trick they do not mention in their marketing--they sum the low frequencies below ~60hz and below! The driver separation on the individual w371 is not enough, so the low frequencies are split between the two W371 units, using the same DSP trick.
I think this last trick is the one that is hardest to pull off for an off the shelf DSP? Is it possible to low cut two stereo channels at 60hz, sum everything below 60hz, and combine that summed signal back into the original stereo signals?
Measurements via FuzzMeasure:
34" stack
41" stack
43" stack
For background, what Genelec is doing is combining a front firing 14" woofer and a rear firing 12" subwoofer in the same cabinet. The frequency range of the 2 drivers overlap, and the different placement of the 2 drivers is enough to create different room nodes. The EQ takes advantage of the different room nodes from each driver and adjusts both drivers individually so together they create a flat response.
I already did some rudimentary testing of this concept. I have 2 M-Audio BX subwoofers, and I stacked them on top of each other, with the bottom speaker facing the rear and the top facing the front. The height of the two subs stacked was 34". I also added spacers to get 41", and again raised it to match the Genelec's 43" height. This test is NOT meant to represent what Genelec's product does, but it is intended to see how much of an effect this unique speaker alignment makes.
I found that the 34" height showed the most difference in room nodes, in my very not good room. (The subs were spaced ~32" from the wall.) The effect seemed to diminish with height, but I expect it begins increasing again at a certain height.
I also found that it works for a limited frequency range, between 60hz and 200hz. The response curve above and below were identical in all tests.
This leads me to believe that Genelec have a trick they do not mention in their marketing--they sum the low frequencies below ~60hz and below! The driver separation on the individual w371 is not enough, so the low frequencies are split between the two W371 units, using the same DSP trick.
I think this last trick is the one that is hardest to pull off for an off the shelf DSP? Is it possible to low cut two stereo channels at 60hz, sum everything below 60hz, and combine that summed signal back into the original stereo signals?
Measurements via FuzzMeasure:
34" stack
41" stack
43" stack
So you want to put both channels sub 60hz signal into both channels while maintaining the separate channels above that? I don’t think that is possible off any DSP I know of. You can sum channels but not only over a certain freq range like that. If you are running separate sub amps you can sum both channels from 60 down. Look at the mini DSP or DSP-408 from PE.
Cardioid Sub woofer or in this case woofer
since the genelec is advertised for controlling directivity of low bass , not sub bass
One facing forward one facing backward.
Gets you almost there.
you delay the rear driver. so basically to make it adjustable as promoted by genelec you would have to adjust the delay time.
Every ones room is different so it is a good sales point.
In most set installations they adjust the delay time and speaker locations for the specific room.
once the achieve the cardioid pattern and direction wanted for the location. no need to adjust it.
For a marketable box where the speakers are pre mounted and fixed.
In order to control the directionality in many rooms then yes a adjustable delay time is needed.
but the speaker location is set.
A diy type project would allow you to change speaker location and adjust delay time.
just like it is done in for large installs or clubs etc etc.
either way one rearward on forward gets you there, then just a delay line.
Most multi channel DSP should do it. for around 55 to 60 hz believe your looking at around 3 to 4ms of delay
could likely be done with a All pass filter, but depending how low in frequency you want to control directivity.
you will need longer delay times to get the phase cancelation. Hence easier to use Delay for low frequency
no fancy summing etc etc. just rear / forward speakers with one delayed.
otherwise known as a cardioid.
since the genelec is advertised for controlling directivity of low bass , not sub bass
One facing forward one facing backward.
Gets you almost there.
you delay the rear driver. so basically to make it adjustable as promoted by genelec you would have to adjust the delay time.
Every ones room is different so it is a good sales point.
In most set installations they adjust the delay time and speaker locations for the specific room.
once the achieve the cardioid pattern and direction wanted for the location. no need to adjust it.
For a marketable box where the speakers are pre mounted and fixed.
In order to control the directionality in many rooms then yes a adjustable delay time is needed.
but the speaker location is set.
A diy type project would allow you to change speaker location and adjust delay time.
just like it is done in for large installs or clubs etc etc.
either way one rearward on forward gets you there, then just a delay line.
Most multi channel DSP should do it. for around 55 to 60 hz believe your looking at around 3 to 4ms of delay
could likely be done with a All pass filter, but depending how low in frequency you want to control directivity.
you will need longer delay times to get the phase cancelation. Hence easier to use Delay for low frequency
no fancy summing etc etc. just rear / forward speakers with one delayed.
otherwise known as a cardioid.
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To start with, WhiteDragon is probably right, cardioid radiation pattern is a thing.
Mini DSP or DSP0408 are pretty limited in their process flows. Though I think they both have digital delay, like WhiteDragon mentions. There are more flexible DSP alternatives if you really want to sum portions of a channel. You could do a 2 channel XO at 60 Hz, sum the 2 LF channels (and reduce by 6 dB) so it was a mono channel, and then add the result back into your HF Left and right.
You could do that sort of thing in software with Max / MSP, as long as you have a computer and the audio ins and outs in sufficient quantity. There are probably other packages to do it also, but Max is the one I know.
https://cycling74.com/products/max
If you wanted a hardware solution you could do it in Sigma Studio, with
https://www.parts-express.com/Dayto...B-KE-Kernel-DSP-Expansion-2-In-3-Out-325-1300
or
https://www.parts-express.com/Dayto...io-Amplifier-Board-with-Bluetooth-5.0-325-505
Either one would be a bit of a rabbit hole to fall into.
Mini DSP or DSP0408 are pretty limited in their process flows. Though I think they both have digital delay, like WhiteDragon mentions. There are more flexible DSP alternatives if you really want to sum portions of a channel. You could do a 2 channel XO at 60 Hz, sum the 2 LF channels (and reduce by 6 dB) so it was a mono channel, and then add the result back into your HF Left and right.
You could do that sort of thing in software with Max / MSP, as long as you have a computer and the audio ins and outs in sufficient quantity. There are probably other packages to do it also, but Max is the one I know.
https://cycling74.com/products/max
If you wanted a hardware solution you could do it in Sigma Studio, with
https://www.parts-express.com/Dayto...B-KE-Kernel-DSP-Expansion-2-In-3-Out-325-1300
or
https://www.parts-express.com/Dayto...io-Amplifier-Board-with-Bluetooth-5.0-325-505
Either one would be a bit of a rabbit hole to fall into.
I should be possible. One need to split L and R into 2 new channels L2 and R2 then:
- sum the L2 and R2 (mono) into M2
- HP M2 at 60 Hz
- Sum M2 with L and R so to get L' and R'
This can be made with e.g the exquisite and free CamillaDSP - see thread... CamillaDSP - Cross-platform IIR and FIR engine for crossovers, room correction etc.
Here ending with a 120Hz LP for the subs...
//
- sum the L2 and R2 (mono) into M2
- HP M2 at 60 Hz
- Sum M2 with L and R so to get L' and R'
This can be made with e.g the exquisite and free CamillaDSP - see thread... CamillaDSP - Cross-platform IIR and FIR engine for crossovers, room correction etc.
Here ending with a 120Hz LP for the subs...
//
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Thanks for the responses!
Yes, I agree it is a rabbit whole. But what a rabbit hole! 🙂
And to the original point I was asking about, it is what I was stuck on at the moment, but I'm realizing that it's probably a non-issue. Mdpaudio's comment is a workable solution, but now I found an off the shelf solutions in pro audio. And with some help from the internet I could make my own if I really want to.
https://www.bhphotovideo.com/c/product/333330-REG/Galaxy_Audio_JIB_C_JIB_C_Jack_In_The.html
I mentioned the MiniDSP 4x10, which I think is ideal for integrating all the components. At the moment I am expecting to use 8 channels. The break down:
(Left Main) + (Left LF 1) + (Left LF 2) + (Mono Sub 1)*
(Right Main) + (Right LF 1) + (Right LF 2) + (Mono Sub 2)*
* LF 2 and Mono Sub signals will be combined into a single signal after the DSP as discussed above
The mains will be my current active studio monitors.
LF 1 is the front facing woofer near the top. Genelec uses a 14" woofer (not a subwoofer). It looks like a PA type woofer that only goes down to 50 or 60hz. I think I'll end up using a 15", since 14" is an odd size.
LF2 is the rear facing woofer at the bottom. It is a high excursion 12" subwoofer.
As far as DSP processors, are there other viable options besides MiniDSP for an 8+ channel processor? I've been browsing, but nothing has jumped out at me.
Yes, I agree it is a rabbit whole. But what a rabbit hole! 🙂
And to the original point I was asking about, it is what I was stuck on at the moment, but I'm realizing that it's probably a non-issue. Mdpaudio's comment is a workable solution, but now I found an off the shelf solutions in pro audio. And with some help from the internet I could make my own if I really want to.
https://www.bhphotovideo.com/c/product/333330-REG/Galaxy_Audio_JIB_C_JIB_C_Jack_In_The.html
I mentioned the MiniDSP 4x10, which I think is ideal for integrating all the components. At the moment I am expecting to use 8 channels. The break down:
(Left Main) + (Left LF 1) + (Left LF 2) + (Mono Sub 1)*
(Right Main) + (Right LF 1) + (Right LF 2) + (Mono Sub 2)*
* LF 2 and Mono Sub signals will be combined into a single signal after the DSP as discussed above
The mains will be my current active studio monitors.
LF 1 is the front facing woofer near the top. Genelec uses a 14" woofer (not a subwoofer). It looks like a PA type woofer that only goes down to 50 or 60hz. I think I'll end up using a 15", since 14" is an odd size.
LF2 is the rear facing woofer at the bottom. It is a high excursion 12" subwoofer.
As far as DSP processors, are there other viable options besides MiniDSP for an 8+ channel processor? I've been browsing, but nothing has jumped out at me.