LCR subwoofers with center subwoofer playing out of phase sounds?

[olds1959special]

I have three subwoofers in front of the room, set up as LCR. I have two rear speakers playing out of phase sounds ("Hafler circuit"). Today I decided to try something, I split one of the outputs going to the rear speakers and sent it to the center subwoofer. I decided to flip the phase on this sub since it is supposed to go with the rear speakers. Are there are any potential downsides to this situation?

EDIT: I am thinking of moving furniture around (if I can) to get the center subwoofer in the back with the rear speakers since this makes more sense.

 

[Doodski]

Erm... I have been observing your experiments and see that you have a interest in electronics. I followed you until the now. Why are you using the rear for the sub etc?

 

[olds1959special]

Erm... I have been observing your experiments and see that you have an interest in electronics. I followed you until the now. Why are you using the rear for the sub etc?

It’s just an extension of the rear speakers to add low bass. They are small speakers.

Pics showing back of room and front. The subs in the front are in phase with the front speakers. The sub in the back is in phase with the rear speakers.

It seems to add a bit of dimension to the sound from the back.

 

[Wayne Highwood]

There really isn't much bass in the rear signal anyway, and a host of problems created by arbitrarily swapping polarity on one of three subs. You would be better off calibrating all the subs with the front channels.

Did you read the article that someone posted in your other thread, about the guy with the Dunleavys in a Hafler rig? He seemed overly focused on the rears being extended or full range. I personally don't buy that. You have the equipment on hand to calibrate one of your subs to the rear speakers, so give it a whirl if you want (it would take more than merely flipping a phase switch), but I doubt it's worth the hassle.

 

[olds1959special]

There really isn't much bass in the rear signal anyway, and a host of problems created by arbitrarily swapping polarity on one of three subs. You would be better off calibrating the subs with the fronts.

What if flipped the phase of the rear sub to 180?

(At least the middle sub doesn't block my feet anymore!)

 

[Wayne Highwood]

Was anticipating your question...I subsequently added some more specifics to my prior post.

 

[Wayne Highwood]

(At least the middle sub doesn't block my feet anymore!)

Yeah, no reason for that third sub to be in the way of your feet. There is a lot of flexibility with sub placement. The use of multi subs is all about improving modal response, smooth bass throughout the listening area.

 

[Wayne Highwood]

Furthermore, what if I flip the phase on the rear speakers with in-line adapters to be in phase with the rear subwoofer, which is flipped to 180 degrees because it's in the back of the room?

I'm looking for that article now. This one?

Build a High-end Surround Stereo System

Technical paper explaining how to construct a surround sound system from off-the-shelf audio components. Also a guide to using MLSSA to measure and adjust other surround sound systems for best performance.

web.archive.org

If you don't disrupt the difference signal, it might work for the ambience recovery part of the equation, but severely mess with your bass.

The article kind of confirmed the appropriate level and delay settings being recommended by us in the thread. The author suggested staggered delay for the rears (not sure that's necessary), and full range rears (again, not convinced that's necessary).

So compartmentalize sub integration from playing with abience recovery.

 

[olds1959special]

I like the middle sub being in the back for the sake of my leg room. Since the rear speakers are small (I also reduced the low end with the trim control), why can't they match with the sub that's there, if set to be in phase with each other? This way they are basically acting as full-range speakers.

I don't like the effect of delays. I tried around 10ms but prefer the natural delay from distance only.

 

[Wayne Highwood]

Sure, you can play around with it, but I still think that's an avenue to mess up bass response in the room. And again, most bass in recordings is monoized, so the rear difference signal won't have any bass.

 

[olds1959special]

Sure, you can play around with it, but I still think that's an avenue to mess up bass response in the room. And again, most bass in recordings is monoized, so the rear difference signal won't have any bass.

Another thing is I run my subs with the LPF disabled so I'm getting some higher frequencies too. The back sub is also smaller, 10" vs the 12" fronts. To integrate the rears with the back sub better I turned down the low end trim control a notch on those. Next I'll try flipping the direction the back sub is facing.

 

[Wayne Highwood]

That's a bit unconventional and idiosyncratic. Subs reproducing localizable higher frequencies is not optimal. I suggest a more conventional, proven approach to sub integration.

 

[olds1959special]

That's a bit unconventional and idiosyncratic. Subs reproducing localizable higher frequencies is not optimal. I suggest a more conventional, proven approach to sub integration.

Sub facing out worked best, in phase with corresponding speakers. I turned the LPF down on all the subs to 100Hz for now. I use the HPF at 80Hz on the front speakers and the low trim on the back pair.

 

[Wayne Highwood]

Sub facing out worked best, in phase with corresponding speakers. I turned the LPF down on all the subs to 100Hz for now. I use the HPF at 80Hz on the front speakers and the low trim on the back pair.

That still seems a bit haphazard.

You have some sort of rta, right? Sub calibration is when you should put it to use. It will save a lot of time over incrementally fiddling around and relying on your ears to dial it in, which may never quite get you there. Your ears will thank you for the results, though.

 

[DVDdoug]

Phase/polarity issues are the worst when two signals are identical and out-of-phase. In the bass range you can get almost complete subtraction/cancelation. But if one is louder than the other you can't get complete cancelation... They can't subtract to zero and the side-effects are minimized. But if all the subs are not the same level and in-phase you're also not getting the full advantage of multiple subs.

Things get "strange" with L-R or R-L subtraction. With L-R, the left is in-phase with the rear so the signals add. The Right (-R) is inverted so out-of-phase with the front. If you do R-L you get the opposite with the right is in-phase and the left (-L) is out-of-phase and subtracted.

With the old Dolby surround, the rear signal was encoded with a +90 degree phase shift on one channel and a -90 degree shift in the other* to get the 180 degree difference, without it being completely in or out of phase with the left or right,





* There is something called a Hilbert transform filter that can apply the same phase shift to all frequencies. (The Internet says the audio that will become the left rear is shifted +90 and the audio for the right rear -90.)

 

[SHB]

A few things to consider:

• The Hafler Circuit subtracts one stereo channel from the other to eliminate most of the info panned to phantom center and leaves the information that differs between the stereo channels. A lot of that info is ambient sounds. Ideally, you’re running a pair of speakers in the rear (L-R, R-L). The circuit works even better if you delay it 40-80 milliseconds and add some reverb via DSP. If you’re playing vinyl, you’ll want to run a 100Hz high pass filter on the circuit so you aren’t pumping a lot of rumble and low bass garbage into your surround speakers.

• Most modern, multitracked recordings have the low end panned either exactly in the center or close to it. The reason for this is because, historically, most people don’t have speakers with huge woofers or have subwoofers in their systems. Mix engineers would keep instruments that create low bass centered so regular speakers could more easily recreate low frequency content by working together to move air.

•Given that most of the low end of the music is cancelled by the Hafler Circuit, there’s no reason to add a sub to the surround speakers.

My thought is this: feed the rear sub a mono signal and add a small digital delay to it. Play it loud enough that it adds to the low end without calling much attention to itself.

If you are experiencing any listening room modes at your listening position, play around with the delay to see if it can smooth out the low end. I did this in this past with 2 subs in opposite corners and it worked great.

 

[Chrispy]

You have some odd ideas about multich speakers let alone subs....this still with 2ch gear?

 

[olds1959special]

I moved the center subwoofer back to the front. I'm pretty sure it sounds better this way.

You have some odd ideas about multich speakers let alone subs....this still with 2ch gear?

2 channel inputs with the MiniDSP, 4 channel outputs.

 

[olds1959special]

That still seems a bit haphazard.

You have some sort of rta, right? Sub calibration is when you should put it to use. It will save a lot of time over incrementally fiddling around and relying on your ears to dial it in, which may never quite get you there. Your ears will thank you for the results, though.

I used REW with my measurement mic (ECM8000 with cal file) and ended up adjusting the LPF on the subs to around 120 Hz (the middle sub is at about 110 Hz) If I had the LPFs turned up higher I was getting peakiness around 120Hz. So right now the subs are in the front and I'm not needing any EQ.

 

[olds1959special]

You have some odd ideas about multich speakers let alone subs....this still with 2ch gear?

There is nothing odd about what I'm doing, I don't think and to me it sounds great. It's a new way to hear stereo recordings.

I'm not running the subs full-range anymore. That idea started with the miniDSP where I could add the crossover myself, but in this setup the subs are coming from the same channels the mains are, so I can't do that.

Stereo subwoofers is not a new idea and some people like it. LCR subwoofers is not much different, and it works for me because the center sub doesn't have to match. The center sub is like a mono fill channel for the bass and seems to add a little more homogeneity to the lows.