[tomlinmgt]

Just watched Ron's (NRD) new video on subwoofer implementation.  He offered a lot of great info, but didn't really address the one subtopic to subwoofer integration I was hoping he would...which is subwoofer distance from listing chair compared to main speakers distance from listening chair. He did discuss phase, but didn't relate it to distance between subs/mains and listening spot. So it left me wondering just how important subwoofer distance from the listening spot compared to the main speakers distance from listening spot really is?

One configuration he suggests is subwoofers between and behind the mains and also a subwoofer on each side wall and even with the listening spot. With three different distances between the subs and mains, is there no potential timing issue here since information from the mains will arrive at the listening spot before the subs that are behind the speakers and after the subs that are on the side walls?  Would the phase adjustment correct this?

I've used subs behind the listening spot and it sounded and measured great...although the subs were about 6' closer to the listening spot than the main speakers. And I've had subs about 6' further away from the mains and got good integration with some speakers and not great with others. Now I question if I should be focusing more effort  on getting the distances between sub/listening spot and mains/listening spot equal or as close as possible. And this is for box subs...not OB.  Am I'm overthinking all this?

[Mike-48]

The issue is that the acoustic distance from the subs and mains to the listening chair should be the same. This may not be the same as the physical distance, because most subs these days use DSP, which adds latency (delay).

The best way to align subs and mains is is by using a measurement mic. You run a low-frequency sweep, measure at the listening spot, and adjust phase and polarity of the sub -- or its distance from the listener -- to get the smoothest frequency response. I have wound up with subs in front of the listener, or in corners, or behind the listening chair. In other words, there's no a priori way to know what will work best.

Adjusting a phase control is obviously more convenient, though not all sub positions will give great results even if you can adjust phase. If a sub doesn't have control of phase in fine increments (45 degrees or less), moving things around is the only method I know of to optimize phase alignment. You could also Google the phrase sub crawl.

The purpose of phase alignment is to avoid the destructive nulls that can cause large (> 20 dB) variations in bass frequency response.

[Early B.]

Your subwoofer setup experiences answer your question. There's no ideal formula for subwoofer distance to the listening chair. It depends on the room, your limitations within the room, the type of sub, and a host of other considerations. The general advice is to place the sub in various positions in the room and see which one yields the best bass response. Corners matter. Room boundaries matter. Inches matter.   

[tomlinmgt]

Thanks for the replies and info, Early B and Mike-48.  So then the things I've always focused on before...locating the sub(s) to minimize the effects of modal activity so that there is better integration with the mains...is the primary objective over timing issues? Manufacturers put so much effort into time-aligning drivers, I figured the subs should be part of that too. But is time alignment really only critical for all energy above the first octave?

[TRADERXFAN]

This subject is a deep rabbit hole...

So depending on your rooms Schroeder frequency -- where the room dominates what you hear, based on room modes.

Here is a quick article i found on it for you...
https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1

You may or may not find any spot that is actually "good".  Thats where the multiple subwoofer strategy comes in like Dukes Swarm subs or Geddes methods etc.

More than 1 low frequency source below the Schroeder freq to drive it from different points in the room, and flatten the modes.

at low frequency, our ears need multiple cycles to even register the sound to our perception. So it is not like time alignment is a "thing" to worry about below a certain frequency.

The bigger the room = the lower the Shroeder frequency (each parameter matters height, width, length etc)

The open baffle subs, because of dipole cancellation to the sides,  help reduce some of the room reflections. (and btw. top is a "side" too that is also being canceled)

[HAL]

If the subs are located in front of the main speakers, then the phase control would work.

If the subs are located behind the main speakers then the mains need to be delayed so the wavefronts will match at the listening position.  Subs do not have negative time controls to advance the wavefront, since this is a causal universe.

I use a measuring tape and do the time alignment that way to calculate the time delay for the mains needed to the subs.  Since subs cutoffs are usually below the 200Hz frequency range, that is 5.65ft wavelength.  At 1/4 wavelength or ~1.41ft you will start having interference.   A tape measure usually gets me in a few inches of alignment. 

A measurement mic and REW will let you do this as well as discussed above. 

[TRADERXFAN]

My comment above was about finding the smoothest response from a dip/null perspective.

But another factor that is related to benefit of finding actual time alignment is that the subwoofer will play higher than the electronic crossover point. And the steepness of rolloff of that matters.  So keep that in mind where the intended play range may not be localizable, but the acoustic output can be above that.  Which can interfere with localization of the mains. 

[tomlinmgt]

My comment above was about finding the smoothest response from a dip/null perspective.

But another factor that is related to benefit of finding actual time alignment is that the subwoofer will play higher than the electronic crossover point. And the steepness of rolloff of that matters.  So keep that in mind where the intended play range may not be localizable, but the acoustic output can be above that.  Which can interfere with localization of the mains.  That is why Geddes recommends bandpass designs (but hard to get good ones). Because the nature of that design had a sharp acoustic rolloff above the port tuning limiting higher frequency output much better than others.

That's one reason I really like using miniDSP for the crossover...it has slopes up to -48 db. Going from the -24db fixed slope on the Ashly active crossover I was using to the -48db slope on the miniDSP changed the game when I was trying to integrate subs with my LS6's. I just couldn't get any good results with the Ashly but with the miniDSP set to -48db slope it sounded significantly better.

[listenermark]

Small square weird room, this is what eventually worked:

[Mike-48]

@tomlinmgt, You have accurately summed up my view. As @TRADERXFAN said, at lowest frequencies if the subs are off a cycle or two, it'd doubtful anyone would hear it. But you will hear large nulls caused by significant out-of-phase conditions.

Using a measuring tape will not give good results in most cases, because of the latency in modern subs. I suppose there are a few subs that do not add latency, but I'm pretty sure they are in the minority.

Also as mentioned by others, use of >1 sub can be helpful to smooth out response. I use four.

Have fun!

[tomlinmgt]

@tomlinmgt, You have accurately summed up my view. As @TRADERXFAN said, at lowest frequencies if the subs are off a cycle or two, it'd doubtful anyone would hear it. But you will hear large nulls caused by significant out-of-phase conditions.

Using a measuring tape will not give good results in most cases, because of the latency in modern subs. I suppose there are a few subs that do not add latency, but I'm pretty sure they are in the minority.

Also as mentioned by others, use of >1 sub can be helpful to smooth out response. I use four.

Have fun!

All of my subs are passive...but I do use a miniDSP 2X4 HD to handle adjustments. Does that unit introduce latency?

[WGH]

All of my subs are passive...but I do use a miniDSP 2X4 HD to handle adjustments. Does that unit introduce latency?

Yes, but it may not matter if you can't hear it. Have you listened without the DSP?

REL designs their subwoofers to have very low latency:

"We spent a lot of time testing various filters during development of our Reference filters and determined that 8 ms is where “fast” begins, meaning that anything that can crossover and filter high frequencies out of a REL that takes 8 ms (our “standard” filter speed) or less. Hence our Reference filters require just 4 ms and yes, you CAN hear the difference instantly and easily if you were to compare them directly."

REL Blog - DSP Versus Analog Filters
https://rel.net/blog/2021-10-20/setup-deep-dive/dsp-versus-analog-filters/?srsltid=AfmBOootJPe3BU1I7zgWsBjstYmI_-5DRQ37iQSe_jqubvZXhfDtbls4


I have owned two REL subs in their Reference series, a 10" Gibraltar G2 and the 12" G1 MkII and can attest both are fast. REL's Reference subs easily keep up with Magnepan speakers and blend in seamlessly. I sold my REL G2 to a friend who has Magnepan 2.5i speakers and he loves the way it sounds with his Maggies.


The new REL No.31 and No.32 Reference subs now include a Dual Parametric EQ. Perlisten subs also have a parametric EQ.
https://rel.net/shop/powered-subwoofers/reference-series/no-31/

[Mike-48]

All of my subs are passive...but I do use a miniDSP 2X4 HD to handle adjustments. Does that unit introduce latency?

Yes, my understanding is that any digital filter will add latency.

As to statements by manufacturers, I take them with a grain of salt. Manufacturers tend to believe that their own technology is the best way to achieve highest fidelity. I don't think most manufacturers are trying to fool or con people, but I do believe there are many ways to get great sound.

[dallaire1]

I have struggled with the same subject regarding timing of the subs, I have two GR research open baffle subs mating with a pair of special audio M3's. I use REW and a calibrated mic. A lot of people are going with placing the subs right behind the listening position. Sounds crazy, if you look at the step response after shooting a measurement in REW, you can clearly see the frequencies that are smacking the mic at whatever particular time. There's latency factors galore, passive crossovers, digital enhancements etc etc. I'm about to set up my system again in a new room, I will definitely be playing around with this in particular. Obviously, bass frequencies take longer to produce than high frequencies. This is a simple matter of physics. I understand what your concerns are regarding timing. I also think our human hearing and integration play a large role. For instance, if you look at Danny's set up, his subs are behind his mains. I don't think phase control will offer the fix for this problem. If you have the means, try placing the subs much much closer to your listening position, perhaps behind your seated position. Again check the step response in REW it will let you know for certain which frequencies have the most latency. Again though going through a passive crossover you will see all sorts of delays. Custom audio is always a challenge and sometimes a let down. Digital might help in some forms and will create havoc in other ways. They're truly is no silver bullet for audiofiles unfortunately. Perhaps someday..

[MttBsh]

The (single driver) Cain and Cain Abbys I have been using for many years are a bit bass shy, so I have subs behind and to the right and left of my listening position. It creates a wonderful sound stage and I'm continually amazed by the strength of the illusion that the bass is coming from the Abbys - 12 feet in front of me - rather than from the subs behind me, I guess you'd call it an "aural" illusion.

[Mike-48]

I have subs behind and to the right and left of my listening position. It creates a wonderful sound stage and I'm continually amazed by the strength of the illusion that the bass is coming from the Abbys - 12 feet in front of me - rather than from the subs behind me. . ..

Yes, I have experienced that, too -- for years I had a pair of subs in the rear corners, and they were undetectable. I think that the harmonics of the bass notes, coming from the main speakers, convince the ear that the nondirectional bass notes belong there, as well.

[dallaire1]

I had the opportunity a few months ago to measure a gentlec system at our church. It was just a set of genelec monitor set up in the near field listening position with a small sub positioned beneath the control console. Genelec are all actively crossed over. I don't know how they do it, but it sounds phenomenal ! There's something to be said about near field listening. After I got home, I got more into the data that I'd recorded. The step response was flat. Meaning all frequencies were hitting the mic at the same time. I to this day, don't know if it was a recording error regarding REW or not. But it was one of the most immersive experiences I've ever listened to. Genelec does not have rights to this property, however, I can honestly say it was amazing to say the very least.

[Danny Richie]

Some things to consider....

Let's say I cross my mains to my subs at 50Hz. That is a 22 foot long wavelength. So with the subs set back two feet behind the mains that is about a 16 degree phase rotation (or something like that). That was off of the top of my head.

Consider that amount of phase rotation to the delay caused by room reflections as the lower end bounces through the room a few times.

Once you get real close to being in phase, fine tuning gets really hard to distinguish or hear. 

[tomlinmgt]

Yes, but it may not matter if you can't hear it. Have you listened without the DSP?

REL designs their subwoofers to have very low latency:

"We spent a lot of time testing various filters during development of our Reference filters and determined that 8 ms is where “fast” begins, meaning that anything that can crossover and filter high frequencies out of a REL that takes 8 ms (our “standard” filter speed) or less. Hence our Reference filters require just 4 ms and yes, you CAN hear the difference instantly and easily if you were to compare them directly."

REL Blog - DSP Versus Analog Filters
https://rel.net/blog/2021-10-20/setup-deep-dive/dsp-versus-analog-filters/?srsltid=AfmBOootJPe3BU1I7zgWsBjstYmI_-5DRQ37iQSe_jqubvZXhfDtbls4


I have owned two REL subs in their Reference series, a 10" Gibraltar G2 and the 12" G1 MkII and can attest both are fast. REL's Reference subs easily keep up with Magnepan speakers and blend in seamlessly. I sold my REL G2 to a friend who has Magnepan 2.5i speakers and he loves the way it sounds with his Maggies.


The new REL No.31 and No.32 Reference subs now include a Dual Parametric EQ. Perlisten subs also have a parametric EQ.
https://rel.net/shop/powered-subwoofers/reference-series/no-31/

Yes...when I was using the Ashly active crossover and hadn't yet introduced the DSPeaker Anti-Mode there was no DSP in the subwoofer circuit. Adding the Anti-Mode was an improvement because it smoothed the modal peaks I was hearing. Next I changed from the Ashly to the miniDSP 2X4 HD and heard further improvements since I was able to dial in a steeper crossover slope (-24 db with the Ashly, -48 db with the miniDSP).  If the DSP devices are introducing any adverse effects from latency, it's being overshadowed by the benefits they bring to the table.

[tomlinmgt]

I have struggled with the same subject regarding timing of the subs, I have two GR research open baffle subs mating with a pair of special audio M3's. I use REW and a calibrated mic. A lot of people are going with placing the subs right behind the listening position. Sounds crazy, if you look at the step response after shooting a measurement in REW, you can clearly see the frequencies that are smacking the mic at whatever particular time. There's latency factors galore, passive crossovers, digital enhancements etc etc. I'm about to set up my system again in a new room, I will definitely be playing around with this in particular. Obviously, bass frequencies take longer to produce than high frequencies. This is a simple matter of physics. I understand what your concerns are regarding timing. I also think our human hearing and integration play a large role. For instance, if you look at Danny's set up, his subs are behind his mains. I don't think phase control will offer the fix for this problem. If you have the means, try placing the subs much much closer to your listening position, perhaps behind your seated position. Again check the step response in REW it will let you know for certain which frequencies have the most latency. Again though going through a passive crossover you will see all sorts of delays. Custom audio is always a challenge and sometimes a let down. Digital might help in some forms and will create havoc in other ways. They're truly is no silver bullet for audiofiles unfortunately. Perhaps someday..

Yes, the best results I've achieved with subwoofer sound quality and integration with the mains have been in my prior listening space when the subs were on the rear wall approx 5-6' away from the listening spot with mains around 11-12- away. Acoustats, DIY OB speakers using 15" LF drivers, inefficient vintage Infinity using 12" LF drivers, super efficient vintage Altec using 15' LF drivers, sorta efficient vintage JBL using 14" LF drivers...the 12" DIY sealed subs (using Dayton Titanic drivers) just melted right in with all of them
producing articulate, musical, dense, deep and authoritative bass every time. In my new space... which is larger than my prior listening space (19'x26'x14' vaulted vs 16'x20'x8')...subs on the rear wall (in the corners) just didn't work as well as having them on the front wall (in the corners).  But those are the only two places I've tried them in the new room...well, I did also try them away from the rear corners about three feet on the rear wall (no good)...and am ready to start trying other locations and also would like to try the two 12" DIY subs on the side walls near the listening spot.