Never Put Subwoofers In Corners... Even with DSP and Multi-Sub Setups?

[stevenswall]

Appreciate the help everyone. Looks like I'll need to start with two subs, and see if I can figure out Dirac bass management from multiple points for the woofers and leave GLM for the Genelecs.

...Now I just need to figure out if I'm going to get more than two subs, and adjust the prices accordingly instead of starting with $1500 Rythmiks.

 

[stevenswall]

I agree that multi sub (3+) is not worth the money. I'd rather spend it on bass trapping the ceiling, rear wall, corners, etc which will help a lot in the more important 100-1000hz region. Or don't spend anything extra and just use good placement and EQ for <100hz.

Yeah, need to figure out dampening or diffusing things when I move everything to the basement living room. Probably only going to treat the first and second reflection points on the walls to get things to sound more dry... I miss how dry and clear nearfield is from back in college.

 

[March Audio]

I agree that multi sub (3+) is not worth the money. I'd rather spend it on bass trapping the ceiling, rear wall, corners, etc which will help a lot in the more important 100-1000hz region. Or don't spend anything extra and just use good placement and EQ for <100hz.

EQ alone will indeed help taming the modes, however it won't assist in smoothing out the dips and response at different positions around the room.

The amount of improvement from 2 to 4 subs is much less than 1 to 2, but nonetheless its there. 4 subs also means you can get away with smaller cheaper ones. In the example above they were 4 B&W asw608, about $500 each.

Effective bass trapping is going to be big and expensive (not saying don't do it) and ideally will need to be tuned to the modes. I'm not sure what you refer to by bass trapping the ceiling.

Of course you are correct that you shouldn't ignore above 100Hz, but you need to deal with below as well.

 

[March Audio]

Appreciate the help everyone. Looks like I'll need to start with two subs, and see if I can figure out Dirac bass management from multiple points for the woofers and leave GLM for the Genelecs.

...Now I just need to figure out if I'm going to get more than two subs, and adjust the prices accordingly instead of starting with $1500 Rythmiks.

Start with 2 subs and see how you go. Don't forget the measurement mic.

 

[RichB]

Start with 2 subs and see how you go. Don't forget the measurement mic.

I don't have a room and spouse that is conducive to more that 2 amps. I have 2 Salk built Rythmik subs on order.
Currently, I have a single Velodyne HGS-15 flanking 1 Salon2 handling LFE and the source for the bass often identifiable.

I am hoping 2 subs will improve this.

Salk sound is building custom E22s with mahogany sides and gloss black top, front, and rear to compliment Salon2s.
They will be 14"(w) x 16.5"(D) x 30" (H). They cost about 1/2 the price of the JL Fathom 12 which was my other choice for small form factor.
I am hoping the low distortion and dual subs will improve performance and remove localization.

- Rich

 

[Duke]

My experiences with multiple subs (and the experiences related to me by customers) seem to indicate that four subs intelligently distributed are a significant improvement over two subs, though probably not as big of an improvement as going from one sub to two.

Earl Geddes on the subject:

"The use of multiple source locations in the modal region will globally yield a response curve that is closer to the natural power response of the sources and the room. Said another way, if we use multiple source locations then the frequency response at any given location in the room will become closer to the true power response (read smoother) the more sources that are used. Basically if I have one source which has a variance, V, of the frequency response (the variation of the response from the average or smooth response) of say 6 dBs, then by adding a second source we will reduce this variance by half to 3 dB. Adding a third source reduces this to 2 dB, etc. Basically the variance goes as V/N where N is the number of “independent” sources. A key requirement here is “independent”. If the added sources are close to the first source then they are not independent. And two sources in opposite corners or symmetrical locations are not as independent as two sources placed in non‐symmetrical locations. It is impossible to have two sources that are completely independent at LFs in a small room, so the effect is never as good as the formula suggests...

"To get the best possible LF response one needs to use multiple subs placed about the room in such a way as to maximize their independence from one another."

So adapting these ideas to using two subs, it seems that they should be positioned asymmetrically and fairly far apart.

By coincidence Earl was developing his asymmetrically-distributed multisub concept at the same time that Todd Welti et al was developing his symmetrical multi-sub concept. Neither was aware of the other's work at the time.

 

[RichB]

I agree that multi sub (3+) is not worth the money. I'd rather spend it on bass trapping the ceiling, rear wall, corners, etc which will help a lot in the more important 100-1000hz region. Or don't spend anything extra and just use good placement and EQ for <100hz.

I don't think bass traps are good way to address nulls.

- Rich

 

[ChoiceCriticism]

I actually installed my second PB16-Ultra last night so have fresh experience here.

Room is roughly 24’ x 19’ x 8’
Because of furniture and aesthetic constraints, sub(s) placement is limited to wall with TV. Corner placement not possible.
SVS PB16-Ultra. One port plugged in Extended mode.

Sub crawl with one sub along wall shows optimal position with EQ has two large nulls (-10 and -).

After adding second sub, doing independent sub crawls, then summed EQ, shows +/-4Db response from 16-100Hz.

 

[KaiserSoze]

There was a pretty good article in Audiohlics fifteen years ago.
https://www.audioholics.com/subwoofer-setup/subwoofer-placement-the-place-for-bass-part-1

The rectangular solid images you see on the 1st page, showing how sound pressure peak values are different for different parts of the room, will play with your brain until you correctly sort out which of the two possible 3-D interpretations is the correct one. The box has one vertical corner at the top of the image and one vertical corner at the bottom of the image. You are looking into the box and seeing one of these corners as an interior vertical corner. The other one is effectively an exterior vertical corner. If you can consciously force your brain to see the upper vertical corner as an interior corner, that you see when looking the box, it will then make visual sense. But not if you see it the other way.

Down at the bottom of the page there is a drop-down scroll box for selecting the next page to "jump to". If you don't manage this selection you can end up taking a sort of random walk through the various pages, and it will be confusing. The pages I found most interesting are the ones dealing with dual sub placement.

According to the simulations presented, the best dual-sub placements are at the midpoints of opposing walls. The front/back wall alternative seems better than the side walls. The two front corners are not great but neither is this configuration particularly bad. Ditto for placement near the L&R main speakers.

My sense is that there is an inherent conflict between optimal location for mitigating room modes vs. placement where you won't always have the sense that the bass is coming from somewhere besides the main speakers. Different people seem to have a different sense of what does or does not constitute proper integration of the main speakers with the subs. An option not often given the consideration that is deserved is the use of main stereo speakers with deep bass capability augmented with a single high-quality subwoofer located at the rear wall. If the subwoofer located at the rear wall is capable of truly deep bass, down to 20 Hz or close to it, and if the crossover point between it and the main stereo speakers is in the vicinity of about 50 Hz, then because of the overlap, the main stereo speakers will provide useful output down close to 20 Hz, and the big subwoofer in the back will provide useful overlap up to 100 Hz or higher depending on the steepness of the LP filter. Thus, through most of the low-bass and mid-bass frequencies you actually have three subwoofers, two located at the front wall and potentially near the front corners, and one in the back. There can be little doubt that this is an exceedingly good arrangement from the standpoint of mitigation of room modes. And with this arrangement there is no issue with integration of the main speakers with the subwoofer. This may well be the only arrangement that appreciably avoids the compromise between the two conflicting needs. The only way to get this arrangement without a kludgy hookup of subwoofers to the main speaker wiring is with main stereo speakers that have true deep bass capability. Sealed (acoustic suspension) speakers are desirable so long as the F3 point is below about 40 Hz. Ported speakers are good so long as the port tuning is similarly low (which is necessary because of the steep rolloff), which generally implies large floor-standing ported speakers. As someone who owned a pair of Advent 5012 (the last before Jensen took over and replaced the woofer with one of their cheaper commodity woofers), I know from personal experience that a pair of acoustic suspension speakers of this type, augmented with a single high-quality subwoofer located at the rear wall, leaves little to be desired for anyone whose objectives include not spending the cost of an automobile on a home audio setup.

 

[win]

Other things worth considering that I haven't seen pointed out here:

* you get a lot more value per dollar with subs than you do with mains. I'd focus more on aesthetics of the subwoofer than price. Most have class d amps and some even have dsp built in. Seems wasteful to splurge on subwoofers when even having two low range ones will be a massive improvement over one expensive one. Ported subs are a lot larger than sealed ones, and they are typically a lot uglier. It's easier to hide multiple subwoofers if you don't hate the way they look.

*you get a lot more value from multiple subs, but that's mainly if you run them mono. I would not recommend running subs in stereo to extend your mains to low frequencies. It sounds great in theory, and I wanted to make it work as my favorite program material is orchestral (I.e. stereo bass ostensibly matters because bass is on the right in orchestral settings). But I got way flatter response tuning two subs as mono. The one in the corner masks the other's deep 90hz null. This also allows you to play with phase individually, which can make surprisingly large impacts to frequency response.

* 'premium' subwoofers like REL tout their usage of high level speaker inputs. Don't use them. The idea of matching subs to your amplifier sound is a poor one when instead you can tune them individually.
(Don't do this https://rel.net/what-is-a-high-level-connection/ )

*get dsp for every channel. So minimum 2x4 crossover.

*dont forget that your mains are also a source for bass. Better not to waste this fact with an artificial high pass. I would only high pass my mains to make their integration smoother (not to make their workload easier like people proclaim).

And a question I have: to me it seems like having 4 subs is better, but just due to room construction I imagine it's a lot harder to align 4 subs on the same radius to the listening position than 2. And if one is further away than that radius, you'd have to delay all your other channels for proper alignment. Since bass sound waves are so long, I'd figure that having subs out of alignment would be noticeable and might diminish the benefits somewhat. Thoughts?

 

[Duke]

And a question I have: to me it seems like having 4 subs is better, but just due to room construction I imagine it's a lot harder to align 4 subs on the same radius to the listening position than 2. And if one is further away than that radius, you'd have to delay all your other channels for proper alignment. Since bass sound waves are so long, I'd figure that having subs out of alignment would be noticeable and might diminish the benefits somewhat. Thoughts?

The ear's time-domain resolution is poor at low frequencies so I do not think that "time alignment" of multiple subwoofers is critical. The ear is incapable of even detecting the presence of bass energy from less than one wavelength, and must hear multiple wavelengths to begin to detect pitch. So imo optimizing for "first arrival sound" in the bass region is of academic interest only; by the time we begin to hear bass energy, what we are hearing includes multiple bounces off of multiple room boundaries.

On the other hand the ear has an arguably heightened sensitivity to SPL differences in the bass region, as shown by the closer spacing of equal-loudness curves south of 100 Hz.

So I would position and adjust multiple subs to optimize for in-room frequency response smoothness rather than for time domain precision.

 

[QMuse]

The ear's time-domain resolution is poor at low frequencies so I do not think that "time alignment" of multiple subwoofers is critical. The ear is incapable of even detecting the presence of bass energy from less than one wavelength, and must hear multiple wavelengths to begin to detect pitch. So imo optimizing for "first arrival sound" in the bass region is of academic interest only; by the time we begin to hear bass energy, what we are hearing includes multiple bounces off of multiple room boundaries.

On the other hand the ear has an arguably heightened sensitivity to SPL differences in the bass region, as shown by the closer spacing of equal-loudness curves south of 100 Hz.

So I would position multiple subs to optimize for in-room frequency response smoothness rather than for time domain precision.

While it is true that ear's time domain resolution is poor, especially at low freqeuncies, time (phase) aligning multiple subwoofer is important to achieve smooth frequency response, otherwise, if their phase is not aligned, subs may easilly come to situation where they will partialy cancel each other's output which would make their joined output sub-optimal.

 

[Chris A]

Dave Griesinger has a good paper on this subject apparently written in 2005. This one is pretty interesting. You can go to the last page (pg. 21) for the punchline(s) of course, but you may need to read the article to understand everything that he's saying: www.davidgriesinger.com/asa05.pdf

If you don't know who this guy is, I recommend taking a look around his site and reading some of his presentations and articles. Everything I've read by this guy has impressed me, especially his presentation on clarity, starting at slide 13.

Chris

 

[patate91]

EQ alone will indeed help taming the modes, however it won't assist in smoothing out the dips and response at different positions around the room.

The amount of improvement from 2 to 4 subs is much less than 1 to 2, but nonetheless its there. 4 subs also means you can get away with smaller cheaper ones. In the example above they were 4 B&W asw608, about $500 each.

Effective bass trapping is going to be big and expensive (not saying don't do it) and ideally will need to be tuned to the modes. I'm not sure what you refer to by bass trapping the ceiling.

Of course you are correct that you shouldn't ignore above 100Hz, but you need to deal with below as well.

I placed rockwool bagged in corners : cheap, effective below 100 hz. Sure esthetics needs work : some curtains or reflective material can do the trick. Sure baggeg rockwool is not the most efficient way to use it, but there's no mess (easy To handle and move) thing to build. Corners, especially behind speakers are not use anyway.

 

[watchnerd]

(Is this guy just trying to sell something?)

Yes, of course he is.

This is content marketing.

A person selling acoustic treatments says to spend your money on acoustic treatment, not more subwoofers.

+1

Follow the money.

This is not peer-reviewed research.

It's a sales pitch.

 

[Duke]

While it is true that ear's time domain resolution is poor, especially at low freqeuncies, time (phase) aligning multiple subwoofer is important to achieve smooth frequency response, otherwise, if their phase is not aligned, subs may easilly come to situation where they will partialy cancel each other's output which would make their joined output sub-optimal.

"Partial cancellation" among subwoofers is highly desirable. Partial cancellation and partial reinforcement are mechanisms by which multiple subs result in smoother in-room response. IF you had NO partial cancellation then adding more subs WOULD NOT IMPROVE the summed in-room response. The peaks would be just as tall, and the dips would be just as deep. Fortunately that is not the case.

Imo there is nothing of value to be gained by trying to phase-align multiple subs. By the time you hear the low frequencies, the room's effects are dominant. From a perceptual standpoint, in home-audio-sized listening rooms, there is no such thing as direct sound (which is completely different from the perceptual standpoint further up the spectrum). Fix the low-frequency in-room frequency response and you will have fixed what matters.

By way of anecdotal evidence (I don't have Harman-class resources), I have many customers who report subectively and (when available) measurably improved in-room bass from deliberately introducing significant phase differences into their distributed multi-sub systems.

 

[Duke]

Dave Griesinger has a good paper on this subject apparently written in 2005. This one is pretty interesting. You can go to the last page (pg. 21) for the punchline(s) of course, but you may need to read the article to understand everything that he's saying: www.davidgriesinger.com/asa05.pdf

If you don't know who this guy is, I recommend taking a look around his site and reading some of his presentations and articles. Everything I've read by this guy has impressed me, especially his presentation on clarity, starting at slide 13.

David Griesinger's ideas inform design decisions in both my multi-sub system and in my main speakers. Even though he's primarily writing about concert halls and lecture halls, the principles he has discovered are often applicable or adaptable to home audio.

 

[ernestcarl]

"Partial cancellation" among subwoofers is highly desirable. Partial cancellation and partial reinforcement are mechanisms by which multiple subs result in smoother in-room response. IF you had NO partial cancellation then adding more subs WOULD NOT IMPROVE the summed in-room response. The peaks would be just as tall, and the dips would be just as deep. Fortunately that is not the case.

Imo there is nothing of value to be gained by trying to phase-align multiple subs. By the time you hear the low frequencies, the room's effects are dominant. From a perceptual standpoint, in home-audio-sized listening rooms, there is no such thing as direct sound (which is completely different from the perceptual standpoint further up the spectrum). Fix the in-room frequency response and you will have fixed what matters.

By way of anecdotal evidence (I don't have Harman-class resources), I have many customers who report subectively and (when available) measurably improved in-room bass from deliberately introducing significant phase differences into their distributed multi-sub systems.

I wondered about this... I haven't experimented with multiple subs.

For a system employing multiple subs, say, 80hz or 120Hz down, what amount of group delay do you think is acceptable?

I've read from at least two sources that subs should not be over 20 to 50ms late. Although, I personally suspect, anything up to 80 to 100ms probably's just fine with most people, but even more so below 20Hz.

 

[Duke]

For a system employing multiple subs, say, 80hz or 120Hz down, what amount of group delay do you think is acceptable?

I don't remember. I looked into group delays of vented box systems years ago and concluded that the calculated group delay of my system was perceptually benign, but don't remember the specifics of where the perceptual thresholds are. And I'm not aware of how that would be any different for multiple subs versus a single sub.

I've read from at least two sources that subs should not be over 20 to 50ms late. Although, I personally suspect, anything up to 80 to 100ms probably's just fine with most people, but even more so below 20Hz.

If you're talking about arrival time differences, 20 milliseconds of relative delay corresponds to a path length difference of about 22 feet, which is imo a much greater path length difference than we're likely to have in a home audio listening room.

 

[BostonJack]

Dave Griesinger has a good paper on this subject apparently written in 2005. This one is pretty interesting. You can go to the last page (pg. 21) for the punchline(s) of course, but you may need to read the article to understand everything that he's saying: www.davidgriesinger.com/asa05.pdf

If you don't know who this guy is, I recommend taking a look around his site and reading some of his presentations and articles. Everything I've read by this guy has impressed me, especially his presentation on clarity, starting at slide 13.

Chris

I worked with Dave Griesinger at Lexicon years ago. At that time, he was concerned with acoustically realistic reverb effects, and he raised the bar in that area for commercial products. I was a software guy at the time with no detailed audio knowledge. Dave always struck me as intelligent, dedicated, and honest in his work. I would recommend taking his thoughts on this seriously.