Phase linear subtractive crossover for subwoofer / speakers

[Yevhen]

Hi all. I want to extend the bottom of my floorstanding speakers with a new 12" diy subwoofer. Probably, the sub will be covering the 20-40Hz range.

Does it make sense to use a subtractive filter to align the delays in sub and speakers?

Subtractive Crossover Networks

Derived (or Subtractive) Crossovers - are they any good? Why aren't they used everywhere?

sound-au.com

This setup will be used in the 9m2 office. Some time ago I tried different subs in my 40m2 living room but it always felt like the sub was way too slow compared to speakers. Was it indeed slower because of the delay in the low-pass filters or it was just triggering the low-freq modes of the room and causing more echo?

 

[voodooless]

Why would you want to make your life hard with analogue crossovers? Just get an amp with DSP, then there is no need to worry about that stuff. In any case EQ ability will be much more important.

Alignment should be done with delay. Usually the sub is not next to the mains, so you’ll need to compensate that distance. These delays are always much larger than what those filter topologies might introduce.

 

[Yevhen]

Ah, excellent point! I just wanted to put the sub in the middle of the long wall. But that will be 2m from the speakers! Didn´t even consider the physical delay of the soundwave, so that will be ~6ms. The simplest RC low-pass filter will also introduce 5-10ms.

 

[Yevhen]

What if I put the sub 2m closer to my ears to compensate for that 5ms delay in the low-pass filter? It should be nice at one point in the room, right?

 

[Yevhen]

Why would you want to make your life hard with analogue crossovers? Just get an amp with DSP, then there is no need to worry about that stuff. In any case EQ ability will be much more important.

I don't want to use a DSP because of religious reasons
Analog high-performance crossover also seems to cost less, I can build the boards myself.

 

[abdo123]

I don't think a crossover is necessary, just measure your floor standers' LF cutt-off frequency and slope and implement a complementary low pass filter on the subwoofer. This way minimum phase distortion is introuduced (the audibility of it is in question though).

I'm interested in doing a DIY sub for that region too, mind sharing your plans / design?

 

[ppataki]

Or you can go for a fully software-based DSP solution just like I did with my 2-way DIY system:

DIY Audio Nirvana 12" + Dayton Reference FAST project

I am sharing with you yet another DIY project we have done with my neighbor (who is a carpenter...:)) much earlier this year It is a FAST (Fullrange Assisted Subwoofer Technology) system consisting of 12" Audio Nirvana Classic fullrange speakers and Dayton Audio RSS315HF-4 subs I could not find...

www.audiosciencereview.com

I am using Jriver with various VST plugins, for crossover I am using Acon Equalize 2 in mixed phase mode. I have tried tons of EQ plugins for the crossover and this is by far the best I managed to find
You can see on the below how the wavelet diagram (=impulse response by frequency) looks like when using mixed phase mode crossover vs. traditional minimum phase crossover (that equals to hardware based crossovers)

Mixed phase mode:

Min phase mode:

In both cases crossover was set to 80Hz, 24dB/octave slope

 

[pjug]

I don't want to use a DSP because of religious reasons
Analog high-performance crossover also seems to cost less, I can build the boards myself.

Did you already build the sub? I am running my main speakers full range and using an SVS subwoofer to extend and smooth the low end. The DSP done by SVS has a lot of flexibility (separate control of LP filter cutoff and slope, polarity, phase, and PEQ). I only apply this at the very low end so it doesn't seem like too much of a religious violation!

 

[ppataki]

Or you can go for a fully software-based DSP solution just like I did with my 2-way DIY system:

DIY Audio Nirvana 12" + Dayton Reference FAST project

I am sharing with you yet another DIY project we have done with my neighbor (who is a carpenter...:)) much earlier this year It is a FAST (Fullrange Assisted Subwoofer Technology) system consisting of 12" Audio Nirvana Classic fullrange speakers and Dayton Audio RSS315HF-4 subs I could not find...

www.audiosciencereview.com

I am using Jriver with various VST plugins, for crossover I am using Acon Equalize 2 in mixed phase mode. I have tried tons of EQ plugins for the crossover and this is by far the best I managed to find
You can see on the below how the wavelet diagram (=impulse response by frequency) looks like when using mixed phase mode crossover vs. traditional minimum phase crossover (that equals to hardware based crossovers)

Mixed phase mode:
View attachment 155491

Min phase mode:

View attachment 155492

In both cases crossover was set to 80Hz, 24dB/octave slope

Forgot to add that I tried many linear phase crossovers too but I always heard the pre-ringing hence I moved to mixed phase mode instead
Btw the graphs of the linear phase crossover look almost the same as those of the mixed phase mode except for the longer pre-ringing that is visible on the step response curve too

 

[ernestcarl]

Forgot to add that I tried many linear phase crossovers too but I always heard the pre-ringing hence I moved to mixed phase mode instead
Btw the graphs of the linear phase crossover look almost the same as those of the mixed phase mode except for the longer pre-ringing that is visible on the step response curve too

I haven't always found the step response to be obviously correct (i.e. audible to me) when it comes to diagnosing pre-ringing. Besides select clips of bass-focused music tracks, I now mostly use Neumann's looping subwoofer kick drum test to quickly do my post-DSP-xo-correction listening check for the sub and mains: Download "TEST SIGNALS"

I'm curious if you, or anyone else who's reading this for that matter, have any other sub-to-mains xo test tracks to recommend?

 

[ppataki]

Hi @ernestcarl
Yes, I personally use this track: Jazzanova - Boom Clicky Boom Klack
Right during the first 5 seconds you can hear the pre-ringing (if there is any)

 

[Yevhen]

I don't think a crossover is necessary, just measure your floor standers' LF cutt-off frequency and slope and implement a complementary low pass filter on the subwoofer. This way minimum phase distortion is introuduced (the audibility of it is in question though).

I'm interested in doing a DIY sub for that region too, mind sharing your plans / design?

The sub is still in an early stage. I ordered 35€ 600W class D amp board on TI chip from AliExpress . Will do the filter part myself. That's why can put that phase linear filter on board for free.

Speaker: https://www.soundimports.eu/en/sb-acoustics-sb34swpl76-4.html

http://www.troelsgravesen.dk/ports_files/18W_2.xls

This xls gives the optimum volume of 25l. I think I'll go for 30l. Can share box plan when finished.

 

[voodooless]

The sub is still in an early stage. I ordered 35€ 600W class D amp board on TI chip from AliExpress . Will do the filter part myself. That's why can put that phase linear filter on board for free.

And you worry about the quality of DSP

Speaker: https://www.soundimports.eu/en/sb-acoustics-sb34swpl76-4.html

That should make a fine sub.

http://www.troelsgravesen.dk/ports_files/18W_2.xls

This xls gives the optimum volume of 25l. I think I'll go for 30l. Can share box plan when finished.

Probably good to verify with something like Hornresp or WinISD. 25l seems small? It is closed?

 

[abdo123]

That should make a fine sub.

Do you think two of them in a dual opposed configuration would make a good subwoofer for the 20Hz-45Hz region?

 

[voodooless]

Do you think two of them in a dual opposed configuration would make a good subwoofer for the 20Hz-45Hz region?

I would say so. Parameters favor a ported design though, but with some power it will do well closed as well probably. One should look at the max power and excision graphs to see if that would be enough for the purpose. It does have some high inductance though, but that should not matter as much for that frequency range. Also note that these are 4 Ohm, so you’ll need a beefy amp to drive them in parallel, or use two amps.

 

[richard12511]

I don't think a crossover is necessary, just measure your floor standers' LF cutt-off frequency and slope and implement a complementary low pass filter on the subwoofer. This way minimum phase distortion is introuduced (the audibility of it is in question though).

I'm interested in doing a DIY sub for that region too, mind sharing your plans / design?

Subwoofers are the one channel I always recommend to DIY. Really difficult to DIY something that beats a JBL 308 for the same price, but it’s not very difficult to outdo its companion subwoofer.

 

[abdo123]

Subwoofers are the one channel I always recommend to DIY. Really difficult to DIY something that beats a JBL 308 for the same price, but it’s not very difficult to outdo its companion subwoofer.

I've always been pushed away by the learning curve, do you have any sources i can read about subwoofer design (Sorry OP for hijacking your thread).

 

[Frgirard]

Why would you want to make your life hard with analogue crossovers? Just get an amp with DSP, then there is no need to worry about that stuff. In any case EQ ability will be much more important.

Alignment should be done with delay. Usually the sub is not next to the mains, so you’ll need to compensate that distance. These delays are always much larger than what those filter topologies might introduce.

The dsp has a delay. You want to make the life of the OT hard.

 

[voodooless]

The dsp has a delay. You want to make the life of the OT hard.

Then I’d say: good luck soldering your analogue EQ room correction every time you decide to move the sub. If you really go the analogue route, at least make sure you have the usual sub controls like phase and crossover pots.

 

[Yevhen]

And you worry about the quality of DSP

I don't mind to use a DSPs in subwoofer channel, but delay is needed for for the floorstanders and there I prefer to keep it simple: DAC -> potentiometer -> Purifi amp.

The 35€ amp from AliExpress will be used as the donor board. I planned to make a filter (or a phase linear crossover ) on opa1612 and 600W final on 2xTPA3255. As the backup I can always add 3rd Purifi module to main stereo amp. Just feels a bit like a waste, when Purifi is only used in 20-40Hz range