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

[jsilvela]

If they were directional, you could hear where they were. They can even stand backwards.

On this bit specifically, I've seen some comments at ASR that if pointing the driver towards a wall, one should make sure to leave enough space. Esp. with ported models, at least as much as the port diameter, but even for sealed boxes, the driver cone should be able to travel outward without colliding with the wall. Not a lot of separation needed, but some.

Aside from that caveat on separation, where the sub is "pointed" is immaterial.
Sorry, don't have specific threads at ASR, been reading too many

But also, on the "directionality", the consensus seems to be that if the subs are crossed over too high, you could hear where they are.
I.e. the radiation pattern from the sub may be a circle, but above 80Hz, your hearing would be able to locate the source of the sounds.

 

[radix]

On this bit specifically, I've seen some comments at ASR that if pointing the driver towards a wall, one should make sure to leave enough space. Esp. with ported models, at least as much as the port diameter, but even for sealed boxes, the driver cone should be able to travel outward without colliding with the wall. Not a lot of separation needed, but some.

Aside from that caveat on separation, where the sub is "pointed" is immaterial.
Sorry, don't have specific threads at ASR, been reading too many

I think different subs have different separations, depending on their build. Arendal, for example, says the 1S should be at least 4" (10cm) to the wall. The Inkognito is designed to be mounted on the wall and pointed at the wall or closely adjacent to it on its floorstand.

 

[dc655321]

I've seen some comments at ASR that if pointing the driver towards a wall, one should make sure to leave enough space. Esp. with ported models, at least as much as the port diameter, but even for sealed boxes, the driver cone should be able to travel outward without colliding with the wall. Not a lot of separation needed, but some.

From Roy Allison's paper on SBIR (see related post with link to paper here), an acoustic resonator can be formed in the space between the speaker and boundary.
See Fig 6 in the referenced paper:

 

[Tom C]

"Positioning in the corners is aimed at maximizing the excitation of standing waves (because 7/8 of all room modes have their maxima there). This is what you do with small, cheap subs that lack the power to "play with the room". Bass in such a setup is non-linear, very long reverberating and generally has nothing to do with what is recorded in the film. That subs placed in the corners generate maximum mods is not an opinion. I fight mods as hard as I can. I don't want to listen to a rambling bun, just what's in the signal.
Subwoofers are omnidirectional and this is due to the wavelengths they radiate. If they were directional, you could hear where they were. They can even stand backwards."

True or not true?

More than one assertion is put forth here.
‘I’ve read a handful of good quality papers, presentations, and books. I’m not expert, rather, an interested learner/student. Reading the papers, then discussing them with others helps the learning process, and can help clear up misunderstandings. So that’s the perspective I’m writing from.
I think the reason the output is highest when the sub is in the corner is because of the support (reflections) from the floor and two walls, so total of three boundaries. I’ve seen plenty of times people writing that corner placement is where the most modes are excited, but I’ve never seen the math model showing this is so. It may or may not be true, I simply don’t know if that’s going to excite the greatest number of nodes, or the strongest of nodes. Modes can develop in any direction, but tend to be strongest in the length and width of the room. Some nodes are weak enough in most rooms that they can be ignored. Toole has a nice little paper on this subject.
‘Corner placement can give a good result, and not just for small subs. But studies have shown that positioning the subs in other locations can give a smoother (less lumpy) response, at the expense of somewhat lower output. The quote above is kind of a mish-mosh of ideas, but it is true that subs are omni at low frequencies, but like any speaker will become more directional if playing frequencies that are high enough. I’ve never tried facing a sub toward a wall, don’t really see the point in trying, but it should work. Doesn’t mean a person should or shouldn’t use corner placement, though.

 

[Bjorn]

"Positioning in the corners is aimed at maximizing the excitation of standing waves (because 7/8 of all room modes have their maxima there). This is what you do with small, cheap subs that lack the power to "play with the room". Bass in such a setup is non-linear, very long reverberating and generally has nothing to do with what is recorded in the film. That subs placed in the corners generate maximum mods is not an opinion. I fight mods as hard as I can. I don't want to listen to a rambling bun, just what's in the signal.
Subwoofers are omnidirectional and this is due to the wavelengths they radiate. If they were directional, you could hear where they were. They can even stand backwards."

True or not true?

I thought enough measurements have been shared here here to refute that this is the general case.

But here's another example of corner placement of subwoofer. This time I'm showing the waterfall, so we can see what going on the the time domain behaviour as well. No EQ has been applied for peaks or dips.

 

[DRNNOO]

So the version with subwoofers in the corners must be as in the picture, i.e. the left subwoofer on the front facing to the right, and the right one must "look" at the left one?

No details given. I wonder the same thing. I would imagine that the woofers might need to face each other on the x or the y axis.

 

[DRNNOO]

That subs placed in the corners generate maximum mods is not an opinion

Magnitude and reverberation times are connected. Once Eq'd to a more neutral response, reverberation times go down as well. Distortion also goes down, as now the woofer has less excursion. Essentially the walls are being used as a Horn/Waveguide. The proof that a more neutral response, coming from a corner, has acceptable decay character is seen in Bjorns measurements above.

Whether you arrive at a response like above, through EQ or not, is neither here nor there.

 

[Adi777]

Distortion also goes down, as now the woofer has less excursion.

This is also interesting for me, because lot if people say that less excursion=better quality, especially in music, but when I wrote with DIY builder he wrote that in cinema rooom subwoofer should have big excursion.

 

[Adi777]

Not better make subwoofer with very big driver - 24 inch, but with less excursion?

 

[DRNNOO]

This is also interesting for me, because lot if people say that less excursion=better quality, especially in music, but when I wrote with DIY builder he wrote that in cinema rooom subwoofer should have big excursion.

You miss interpreted what he said.... A subwoofer should have a large Xmax....true. If for example, You can create 100db at 20hz with 2mm excursion, instead of 20mm excursion, the lower excursion situation will be less distorted.
So a 12" vs a 24" woofer.....The 24" will have to travel less, than the 12" to create the same spl, all other things equal....the 24" woofer will have less distortion as a result.
Having a large Xmax is desirable in order to keep distortion down, so a woofers ability to travel farther in a linear way is desirable. High Efficiency means the woofer does not need to travel very far, in order to achieve desired Spl, this is desirable as well.

The efficiency aspect is seen, in effect, in a horn. A smaller diaphragm can be used because the horn increases LF efficiency lowering the amount of excursion needed to achieve spl. You can also increase efficiency through other means, such as increasing Sd(surface area) via large woofer or accumulation of surface area, through multiple woofers. Larger enclosures create more LF efficiency as well.

 

[Adi777]

You miss interpreted what he said....

Okay, maybe, but why he didn't recommend Eminence, Lavoce, and B&C drivers to me? He didn't recommend them to me because he said they had a low deflection. I don't understand anything anymore...

On Data Bass these drivers are very good, especially Eminence and B&C.

 

[DRNNOO]

No idea who "he" is.... but if you say its because of low deflection and if you mean by low xmax... All of those brands have models of woofers displaying High and Low Xmax so it is likely that "he" isn't very knowledgeable about loudspeaker design...

 

[Adi777]

All of those brands have models of woofers displaying High and Low Xmax so it is likely that "he" isn't very knowledgeable about loudspeaker design...

Maybe he was looking at some other drivers from these companies? I don't know.

 

[Adi777]

PS You know some objective measurements about dual opposed vs single subwoofer? Dual is better? More SPL? Lower distortion?

 

[Tangband]

This article seems to go against a lot of what I hear on the forum: (Is this guy just trying to sell something?)

https://www.acousticfields.com/why-you-should-never-place-subwoofers-in-your-corners/

"So don’t buy into this culture of putting the subwoofer in the corner. And definitely don’t buy into the culture of multiple subs will smooth out the frequency response. Yes, technically it will but the smoothness, the level of smoothness that you get in the bump is so minuscule, it’s maybe 1 or 2 dB."

Pretty sure it's going to sum and be +3dB or -3dB, plus a MiniDSP should be able to help even more.

Also, if it's just adding a bunch of gain putting it in the corner, DSP would fix that too it seems: I have my Genelec's in a corner and they measure flat down to 18hz or so.

I remember another user who said that it's all about controlling the peaks and nulls in the room, and even ringing and smear can be controlled just by having a DSP system take care of the peaks, which goes against what this guy says about treatment:

"Put that money in treatment. You’ll be way better off. Use less energy, more treatment and balance it out that way. It’s better to reduce the response."

Looking at getting a pair of Rythmik FV15 subwoofers to use as stands once I move everything to the basement, but apparently corner placement is bad even if I run things from a MiniDSP.

Also of Note: Speakers that go low enough not to "need" subwoofers... Just make me want subwoofers more because now I know what things can sounds like and sometimes want it louder when watching Interstellar.

He is right .
Not only this, but the fact is : The perceived pitch of bass notes will be clearer with two subwoofers in stereo mounted a bit above the floor - next to each speaker. You want to excite less room modes, not more.

This is one of the many reasons that a full register floorstander often sound better than small speakers with subwoofers in the corners or on the floor.

Edit: Genelec 8361 on stands sound better than 8351 with floorstanding subwoofers, partly because of this.

 

[DRNNOO]

PS You know some objective measurements about dual opposed vs single subwoofer? Dual is better? More SPL? Lower distortion?

I have a pair of PPSL(push push slot loaded) subwoofers. Remember as I said earlier, the more surface area(Sd) you have, the less excursion a woofer will have to use to create Spl. So if a woofer has to move 6mm to create 100db/1m/30hz, if there are two woofers, now it may only move 3mm to create the same levels....This is inturn, lowers distortion. If your goal is to reach higher spls then also, headroom is higher with 2 woofers. If you do dual opposed, this configuration also allows the woofers to cancel each others mechanical vibrational energy, which can lower distortion as well. The woofers can also be place on the opposite, outside walls to create the same vibration cancelling effect.

 

[ozzy9832001]

He is right .
Not only this, but the fact is : The perceived pitch of bass notes will be clearer with two subwoofers in stereo mounted a bit above the floor - next to each speaker. You want to excite less room modes, not more.

This is one of the many reasons that a full register floorstander often sound better than small speakers with subwoofers in the corners or on the floor.

Edit: Genelec 8361 sound better than 8351 with subwoofers, because of this.

I tested my sub in various positions and found that about 12" from any boundary and about 18" off the floor gave the best response. Second best position was about 6' off the floor sitting on top of a massive 16" bass trap.

 

[Adi777]

The woofers can also be place on the opposite, outside walls to create the same vibration cancelling effect.

When I was writing dual opposed, I was thinking about subwoofers like Rythmik G25HP.
What about dual opposed vs subwoofer with 2 drivers like JTR Captivator R2?

 

[sigbergaudio]

When I was writing dual opposed, I was thinking about subwoofers like Rythmik G25HP.
What about dual opposed vs subwoofer with 2 drivers like JTR Captivator R2?

A dual opposed will be 3-6dB louder than a single sub with the same driver (3dB if same amplification power and 6dB if amplification power is also doubled). Due to the the added headroom, distortion will naturally be lower as well.

If you compare two single driver subs vs one dual opposed subwoofer (with the same total power, volume and number of drivers), the practical differences in distortion will be minimal.

 

[Adi777]

A dual opposed will be 3-6dB louder than a single sub with the same driver

So, more dB is only one profit with dual opposed?