Pointing Subwoofer into a Wall or Corner

aboroth00

As I'm tweaking my room for optimal bass response with acoustic treatments, a new topic surfaced that I never really entertained. Facing your subwoofer into a wall or corner. Josh Ricci who runs data-bass.com advocates facing his subwoofer into the wall.

From my brief reading and understanding, bass below 125hz radiates spherically and boundaries such as walls causes the bass to reflect back into the room. By placing the driver closer to the wall it pushes the reflected frequencies higher and therefore makes them more easily treatable with absorption treatments or inaudible for a sub. This would prevent a lot of cancellations from the reflected bass in the room which can cause notches in the freq response.

All great in theory, but i was used to pointing the sub into the LP and wasn't too happy with the bass. But now that I have the sub pointed away into the corner or wall, the bass sounds tighter and less localizable. So win-win. Doesn't look as cool... but that's the price to pay for good sound. I haven't been able to take out my measurement mic so this is all anecdotal for now. Just some food for thought that's contrary to accepted thought. But at the same time, downfiring subwoofers do the same thing! Place the driver very close to a boundary.

aboroth00

My very humble desktop setup with some klipsch speakers, monoprice subwoofer and monoprice tube amp. The bass sounds quite good actually pointed into the wall.

afterburnt

Very good question that I myself would have asked when I move. I can either aim my subs at the end of the couches or aim them at the wall. Kinda no other choices but I could aim one at my equipment rack but that don't seem like such a good idea lol.

aboroth00

afterburnt wrote: »

Very good question that I myself would have asked when I move. I can either aim my subs at the end of the couches or aim them at the wall. Kinda no other choices but I could aim one at my equipment rack but that don't seem like such a good idea lol.

Haha indeed, who knows what all those vibrations are gonna do to all that expensive circuitry! I think ideally all that gear should be in another room entirely!

Generally all the subs I own are near a corner because of aesthetics and space limitations. At my desk setup it made a pretty big difference pointing the sub into the wall instead of outward toward my office chair. I'm interested to see other people try just rotating their subs around will improve the bass response. For my desk setup, it was remarkably better!

pitdogg2

My cerwin vega CVT 300 faces the wall no complaints here.

mhardy6647

The trick of using a corner to reinforce very low frequencies (essentially creating a low-frequency horn) is (almost) as old as the dynamic loudspeaker itself.

The wavelength of low frequency sound (bass frequencies) is so long that which way the driver faces probably doesn't much matter.

Col. Paul Wilbur Klipsch was a particularly vocal proponent of the approach.

aboroth00

mhardy6647 wrote: »

The trick of using a corner to reinforce very low frequencies (essentially creating a low-frequency horn) is (almost) as old as the dynamic loudspeaker itself.

The wavelength of low frequency sound (bass frequencies) is so long that which way the driver faces probably doesn't much matter.

Col. Paul Wilbur Klipsch was a particularly vocal proponent of the approach.

I believe orienting the driver into the wall is aimed at alleviating boundary cancellations instead of boundary reinforcement. The concern is that the reflected bass causes cancellations at the LP and thus dips in the frequency response which is the enemy of smooth bass. This is explained by the Allison effect and the big concern of speaker boundary interference response (SBIR). The closer the driver is to the wall, the higher we push the cancellation in frequency. If the driver is close enough to the wall the cancellation occurs well above the operating frequencies of the subwoofer and doesn't become a concern. Plus a 200hz peak is a helluva lot easier to treat with absorption panels and bass traps than a 40hz peak. I pulled this quote below from another website that explains the concern about orienting the driver into the wall.

"If you place your speaker 1/2 a wavelength away from a boundary then, at the frequency that corresponds to that wavelength, the sound will be reinforced significantly. We're talking the kind of boost you get from cranking a parametric EQ with Q narrow. If this particular frequency is a boomy/muddy one, it will not be fun.

The flipside: If you place your speaker 1/4 wavelength away from a boundary, then at the frequency that corresponds to that wavelength (twice the previous frequency if the speaker hasn't moved) the sound will be cancelled significantly. A typical amount would be -15dB at the null frequency. Nasty. Truly tone sucking.

The solution? Place your cab so it's less than 1/4 wavelength (of the upper bass range i.e. 100Hz) away from any boundaries OR more than 1/2 wavelength (of your lowest frequency) from any boundary.

How does this relate to the real bass playing world? A 41Hz (low E) sound has a wavelength of 27.5 feet (I'm sorry, I'm still hanging onto the Imperial system). A 31Hz (low sound has a wavelength of 36.5 feet. So, fellow four stringers, you need to place your cab at least 13'9" away from any walls (fivers, 18'3"). So that's how to avoid peaky boundary reinforcement.

To avoid notching boundary cancellation you need to be within 1/4 wavelength of a boundary in the range of 31 to 100 Hz. So really you need to get your cab within 2'10" of a boundary. Which part of the cab, you may ask? The bit that's making the sound, i.e. the bass speakers themselves and the ports. So given that most bass cabs are 14"-20" deep, you need to get the cab really close to the back wall, but not so close that the ports' operation (if rear-ported) is affected. Think 6"-12" away."



At the end of the day, give it a shot! Fire that puppy into a wall and hear for yourself. I tried it and was astonished by the difference it made. It seems backed up by the science too but I trust my ears if anything.

mhardy6647

I think there'll be multiple effects -- but I thoroughly concur that empiricism can't be beat!

Jstas

It's called "corner loading".

The way subs work is like any other speaker, they pressurize air in a room.

Corner loading can be helpful to make your sub out a bit more efficient if it's, say, slightly smaller than it needs to be for the room.

The reason it works is that there is less space for air to move from in front of the sub driver when facing a corner. So it pressurizes that air more which increases the energy stored in it so it has more energy when it hits your ear drums or when you feel it in your butt. This all makes it seem louder. All you are really hearing and feeling here, though, is harmonics emphasizing certain frequency ranges.

It does have drawbacks though. If the sub already is powerful enough for the room, corner loading can make things boomy.

At high volumes, the reflection from the wall can cause the cone itself to start vibrating out of phase. That can cause not only coloring to the sound but leads to distortion that can destroy a driver.

Those harmonics? They can also turn your sub into a one-note-wonder like what a poorly design band-pass box is like.

So you have to be careful with placement.

As far as theories on wavelengths, subwoofer frequency ranges have very long wavelengths and your 1/2 wavelength has a good chance of being physically outside the room. Also, wavelengths radiate in every direction so you need to consider positive and negative axis as well as your Y and Z axis for that theory to work in practice. Otherwise, your sub might be correct for one wall but not the others, or the ceiling and certainly not the floor. Makes it a daunting task for sub placement.

aboroth00

Jstas wrote: »

It's called "corner loading".

The way subs work is like any other speaker, they pressurize air in a room.

Corner loading can be helpful to make your sub out a bit more efficient if it's, say, slightly smaller than it needs to be for the room.

The reason it works is that there is less space for air to move from in front of the sub driver when facing a corner. So it pressurizes that air more which increases the energy stored in it so it has more energy when it hits your ear drums or when you feel it in your butt. This all makes it seem louder. All you are really hearing and feeling here, though, is harmonics emphasizing certain frequency ranges.

It does have drawbacks though. If the sub already is powerful enough for the room, corner loading can make things boomy.

At high volumes, the reflection from the wall can cause the cone itself to start vibrating out of phase. That can cause not only coloring to the sound but leads to distortion that can destroy a driver.

Those harmonics? They can also turn your sub into a one-note-wonder like what a poorly design band-pass box is like.

So you have to be careful with placement.

As far as theories on wavelengths, subwoofer frequency ranges have very long wavelengths and your 1/2 wavelength has a good chance of being physically outside the room. Also, wavelengths radiate in every direction so you need to consider positive and negative axis as well as your Y and Z axis for that theory to work in practice. Otherwise, your sub might be correct for one wall but not the others, or the ceiling and certainly not the floor. Makes it a daunting task for sub placement.

Definitely agree that sub placement is going to have a big effect on how it interacts with your rooms axial modes, the most prominent modes. But I believe the boundary effects I'm talking about are beyond what is typically thought of in "corner loading." Basically what I believe is happening via the SBIR and the Allison effect is that the proximity of the driver to a boundary affects the frequency in which constructive interference (peaks) and destructive interference (nulls) occurs. The conversation I'm trying to have isn't relevant to the power of the subwoofer but how the reflections off of boundaries causes smearing (dips and nulls) of bass.

Bass pretty much is spherically radiated below 500hz and then it pretty much bounces around your room until it decays. But the peaks and nulls we see are usually caused by the room's reflections. For example, 80hz an all too important frequency has a wavelength of 14ft, and if the speaker (or sub) is placed 3.5ft (quarter wavelength) it'll cause a null at 80hz. But if the speaker or sub is placed within a foot (face the driver into the wall), it'll push the null frequency above 250hz, well above the sub's operating frequencies. I believe, I'm hearing smoother bass due to less cancellations and peaks due to those reflections. But you're basically right that bass is traveling in three dimensions which is something I hadn't really entertained! But now thinking about it, those are just the room's axial modes if the sub is placed in the corner and all the axial modes are being excited which can be favorable.

I haven't heard about distortion from reflections killing a driver though. I would imagine a downfiring driver would be adversely affected by this?

Here are some links which helped me understand the concept better. But give it a shot! Maybe it'll be completely different sounding! I was pretty astonished that the peaks and boominess I heard pretty much went away after I faced the sub in a different direction but pretty much left it in the same spot.

http://www.gikacoustics.com/speaker-boundary-interference-response-sbir/
http://david-janszen.squarespace.com/blog/speaker-setup-minimizing-the-allison-effect2015321
http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

Jstas

Not necessarily. Mainly because a down firing sub would be designed to be positioned that way. You don't get much more help in corner loading a down firing sub. My sub is in a corner and there is a specific cross-over setting for corner placement because of all of that.

While you are correct about the null frequencies, I think your interaction distances are a bit off. You might get reflections within the room on stuff like 250 Hz scale you are talking about but if your sub is crossed over where it should be (i.e.: 80 Hz or lower) then you aren't going to get cancellations unless your room is large enough that the sound pressure can complete a waveform within the room space.

Otherwise, you're just getting resonances that aren't necessarily reflections. At least not any that would cause null values at the listening point.

If you have noticed smoother bass from corner loading I would be more inclined to think that because of the efficiency increase of the corner loading, you are not having to drive the amplification for your sub so hard thereby reducing your distortion.

There's so much affecting waveforms and reflections in your typical, imperfect home listening environment that to say the null cancellations on reflections is the reason for your listening changes is a bit over-simplifying it.

For your thoughts to be the culprit here, you would have to get your sub hovering some place in the middle of the room so that each direction has an equal and opposite distance to it. Then you'd be able to tell.

But, like if you have a 14 foot wave form and your room is 15 feet long by 12 feet wide, even if the reflection off the 15 foot wall cancels something out at the listening position, that still doesn't account for that 12 foot distance or you 7-9 foot ceiling height or the inches off the floor.

Also, sub placement in the room matters because if you have a 15 foot long room and you have your sub 5 feet from the corner on that 15 foot wall then the 14 foot wave form is now going to only have 10 to reach a full cycle.

In other words, if your waveform is longer than the room then all the reflections you get on it will be harmonics and not the actual programming material. That will cancel out frequencies but harmonics are rarely at the same frequency and amplitude as the program material.

aboroth00

Jstas wrote: »

It's called "corner loading".

The way subs work is like any other speaker, they pressurize air in a room.

Corner loading can be helpful to make your sub out a bit more efficient if it's, say, slightly smaller than it needs to be for the room.

The reason it works is that there is less space for air to move from in front of the sub driver when facing a corner. So it pressurizes that air more which increases the energy stored in it so it has more energy when it hits your ear drums or when you feel it in your butt. This all makes it seem louder. All you are really hearing and feeling here, though, is harmonics emphasizing certain frequency ranges.

It does have drawbacks though. If the sub already is powerful enough for the room, corner loading can make things boomy.

At high volumes, the reflection from the wall can cause the cone itself to start vibrating out of phase. That can cause not only coloring to the sound but leads to distortion that can destroy a driver.

Those harmonics? They can also turn your sub into a one-note-wonder like what a poorly design band-pass box is like.

So you have to be careful with placement.

As far as theories on wavelengths, subwoofer frequency ranges have very long wavelengths and your 1/2 wavelength has a good chance of being physically outside the room. Also, wavelengths radiate in every direction so you need to consider positive and negative axis as well as your Y and Z axis for that theory to work in practice. Otherwise, your sub might be correct for one wall but not the others, or the ceiling and certainly not the floor. Makes it a daunting task for sub placement.

Oops. Accidently deleted my response. But I believe the conversation goes beyond the typical conversation with corner loading. I'm trying to entertain the effects of reflected bass causing cancellations and peaks in the room and thus unsmooth bass. For example, if the speaker or sub is 3.5ft (quarter wavelength) from a boundary, it'll cause a null at 80hz (14ft wavelength). Put it within a foot, the null will occur well above 250hz, higher than the subwoofer range.

I believe the boominess you're referring to are the room's axial modes which can make things boomy but is different than speaker boundary interference response which I'm referring to which might even make things worse than the room modes!

Here are some links that really helped me understand the phenomenon and made me re-think how I place the sub and speakers!

http://www.gikacoustics.com/speaker-boundary-interference-response-sbir/
http://arqen.com/acoustics-101/speaker-placement-boundary-interference/
http://david-janszen.squarespace.com/blog/speaker-setup-minimizing-the-allison-effect2015321

aboroth00

Jstas wrote: »

Not necessarily. Mainly because a down firing sub would be designed to be positioned that way. You don't get much more help in corner loading a down firing sub. My sub is in a corner and there is a specific cross-over setting for corner placement because of all of that.

While you are correct about the null frequencies, I think your interaction distances are a bit off. You might get reflections within the room on stuff like 250 Hz scale you are talking about but if your sub is crossed over where it should be (i.e.: 80 Hz or lower) then you aren't going to get cancellations unless your room is large enough that the sound pressure can complete a waveform within the room space.

Otherwise, you're just getting resonances that aren't necessarily reflections. At least not any that would cause null values at the listening point.

If you have noticed smoother bass from corner loading I would be more inclined to think that because of the efficiency increase of the corner loading, you are not having to drive the amplification for your sub so hard thereby reducing your distortion.

There's so much affecting waveforms and reflections in your typical, imperfect home listening environment that to say the null cancellations on reflections is the reason for your listening changes is a bit over-simplifying it.

For your thoughts to be the culprit here, you would have to get your sub hovering some place in the middle of the room so that each direction has an equal and opposite distance to it. Then you'd be able to tell.

But, like if you have a 14 foot wave form and your room is 15 feet long by 12 feet wide, even if the reflection off the 15 foot wall cancels something out at the listening position, that still doesn't account for that 12 foot distance or you 7-9 foot ceiling height or the inches off the floor.

Also, sub placement in the room matters because if you have a 15 foot long room and you have your sub 5 feet from the corner on that 15 foot wall then the 14 foot wave form is now going to only have 10 to reach a full cycle.

In other words, if your waveform is longer than the room then all the reflections you get on it will be harmonics and not the actual programming material. That will cancel out frequencies but harmonics are rarely at the same frequency and amplitude as the program material.

Give the links a read. I may not be explaining it as well. SBIR is a big issue it seems and may be more critical to smooth bass than room mode interactions. The acoustics guys on other forums as well as bass heads seem to take it very seriously.

Here are some guys talking about it over at audioholics.

http://forums.audioholics.com/forums/threads/facing-a-subwoofer-towards-a-wall.97740/

Jstas

Oh, I take it very seriously too.

I used to build subwoofer enclosures for sound competitions. Just because it's in a car doesn't mean the same physics as a home installation doesn't apply.

I'll peruse the articles a little later when I have more time.

aboroth00

Jstas wrote: »

Oh, I take it very seriously too.

I used to build subwoofer enclosures for sound competitions. Just because it's in a car doesn't mean the same physics as a home installation doesn't apply.

I'll peruse the articles a little later when I have more time.

For sure buddy! That sounds pretty awesome and deafening... I hope to get some measurements of the setup soon with the sub in the corner but oriented in different directions, i.e. out toward LP, toward corner, toward either wall and see how it measures. I don't think the orientation is gonna give me more headroom since it's already corner loaded, maybe a tiny bit more... and thus a tiny bit less distortion.

Jaybeez

Thanks for the links. I need to do a bit of research on this. My trial and error approach with HT turned out quite well, with older/ lower cost Polk subs pointed into the room from opposing corners. I still haven't figured out the perfect setup for my listening space though with a much better Rhythmik sub that I picked up from a certain Polkie a bit over a year ago.

afterburnt

This all sounds very dangerous. I am gonna aim mine at the couch, besisides I don't want to have anymore children.

aboroth00

Jaybeez wrote: »

Thanks for the links. I need to do a bit of research on this. My trial and error approach with HT turned out quite well, with older/ lower cost Polk subs pointed into the room from opposing corners. I still haven't figured out the perfect setup for my listening space though with a much better Rhythmik sub that I picked up from a certain Polkie a bit over a year ago.

Hey Jay! I'm glad that Rythmik sub is still working out for you! Opposing corners for HT is one of those generally good recommendations for placement. Maybe try pointing those woofers toward the corner and see how it sounds!

aboroth00

afterburnt wrote: »

This all sounds very dangerous. I am gonna aim mine at the couch, besisides I don't want to have anymore children.

LOL! I'm surprised they haven't invented a subwoofer couch yet! They already have subwoofer end tables. Why not a couch!

Jstas

Actually, I have seen couches with bass shakers in them. It'd be hard to put a woofer in a couch, though. They require sealed enclosures with specific dimensions which makes end tables good for the job. Coffee tables too. Couches and chairs, not so easy to work with.

aboroth00

Jstas wrote: »

Actually, I have seen couches with bass shakers in them. It'd be hard to put a woofer in a couch, though. They require sealed enclosures with specific dimensions which makes end tables good for the job. Coffee tables too. Couches and chairs, not so easy to work with.

Haha for sure. I was imagining some sort of tapped horn bench subwoofer type business. The couch has a port! Bet you never heard that before.

gp4jesus

You got my attention! I find this thread as fascinating as it is paramount to good sound. Set up* and the room* itself, ignored, can make great gear sound only fair. Given its* due* ok gear can sound impressive. Though I'm sure we can agree you can't short-change a good sub versus bad and the same can break an otherwise good system.

I have two Audio Pro subs in a 15 wide by 16' long room, the right side open to the kitchen.
1. The front sub: a floor-firing 10" w/a rear firing port, rated to 20hz, 7-8" from the wall, handles my LCR's heavy lifting. I want to enhance & enable those elusive, challenging low 20s that many subs including my rear sub can't reach. A 20hz 1/4 wave length ~14'. Your thoughts on placement? Closer or further away?

2. The rear sub: a front firing 8" w/a floor firing* port (weird* huh?) rated to 27hz helping the surrounds. Anyway when I bought and placed the (now front) sub I decided w/the (now rear) sub to try similar tricks for more and lower frequency enhancement. I've started w/its against the wall, driver pointing 2-3" into a cabinet/room divider. I've known for years this could provide a little attenuation to the higher frequencies while boosting overall output. Your thoughts on placement? Up to a foot away?

Side note: Historically, Audio Pro subs meet or exceed their specs w/ lower low-end distortion than the competition.

Unfortunately, for me, quality & quantity time to evaluate is scarce in my house. As I type God has provided a wonderful backdrop in the form of a thunderstorm. Thus, while my family has granted me time alone, my remains unplugged until the storm passes.

Thanks for the great info, Tony

gp4jesus

nbrowser wrote: »

but eh...I'm not gonna get her approval for this system.

LOL!

aboroth00

gp4jesus wrote: »

You got my attention! I find this thread as fascinating as it is paramount to good sound. Set up* and the room* itself, ignored, can make great gear sound only fair. Given its* due* ok gear can sound impressive. Though I'm sure we can agree you can't short-change a good sub versus bad and the same can break an otherwise good system.

I have two Audio Pro subs in a 15 wide by 16' long room, the right side open to the kitchen.
1. The front sub: a floor-firing 10" w/a rear firing port, rated to 20hz, 7-8" from the wall, handles my LCR's heavy lifting. I want to enhance & enable those elusive, challenging low 20s that many subs including my rear sub can't reach. A 20hz 1/4 wave length ~14'. Your thoughts on placement? Closer or further away?

2. The rear sub: a front firing 8" w/a floor firing* port (weird* huh?) rated to 27hz helping the surrounds. Anyway when I bought and placed the (now front) sub I decided w/the (now rear) sub to try similar tricks for more and lower frequency enhancement. I've started w/its against the wall, driver pointing 2-3" into a cabinet/room divider. I've known for years this could provide a little attenuation to the higher frequencies while boosting overall output. Your thoughts on placement? Up to a foot away?

Side note: Historically, Audio Pro subs meet or exceed their specs w/ lower low-end distortion than the competition.

Unfortunately, for me, quality & quantity time to evaluate is scarce in my house. As I type God has provided a wonderful backdrop in the form of a thunderstorm. Thus, while my family has granted me time alone, my remains unplugged until the storm passes.

Thanks for the great info, Tony

Orientation of the subwoofer in the same spot isn't going to affect the really long wavelengths. SBIR is more concerning the frequencies around the crossover point and above. For sub placement, it's a trial and error process with so many different factors with the dimensions of your room affecting room modes and the construction of the materials. Sorry I can't be of more help but my advice is mostly trial and error. If your'e curious about a different approach for subwoofer integration, check out the Geddes' method.

https://mehlau.net/audio/multisub_geddes/

aboroth00

nbrowser wrote: »

Jstas wrote: »

Oh, I take it very seriously too.

I used to build subwoofer enclosures for sound competitions. Just because it's in a car doesn't mean the same physics as a home installation doesn't apply.

I'll peruse the articles a little later when I have more time.

I don't build for cars but I know the basics on how to place them and turn the things around so it fires towards the back to get the best output in "most" cases. Even in my truck...yes truck I manged to aim it backwards, works great considering it's right behind my seat. Placement of a sub is crucial in any environment to be honest, my own home sub crawl had it end up right in front of my electronics rack side firing as it has a Active driver on one end and a passive on the other, sure 0 GAF factor but eh...I'm not gonna get her approval for this system.

LOL! Subwoofers facing the "wrong" definitely doesn't look like the most attractive things, especially considering they're not very attractive to the opposite sex when they're facing the "right" way!

Cars and rooms being of much different dimensions are going to affect different "room" modes but whether it's audible is still a trial and error process... tedious! But good to hear people are interested in turning their subs around for optimum performance!

SCompRacer

Best placement for subs in my two channel system are between speakers, facing out and against back wall. I tried corners, facing corners, outside of speakers and it didn't work as well.

My listening room is open to main level so over 10,000 cubic feet of space. The subs shore up the 25 to 40Hz range. First I swept room and moved speakers until I got best response across the frequency range. Then I added subs and adjusted them.

mhardy6647

That looks like a hard (as in "reflective", not necessarily as in "difficult"!) acoustic space.

gp4jesus

mhardy6647 wrote: »

That looks like a hard (as in "reflective", not necessarily as in "difficult"!) acoustic space.

Yeah, I cringed a bit too the moment I laid eyes on the pic.

My wife scours the FB yard sale sites frequently. Looking for a wider area rug, 12' for our LR/HT. Just put up thicker, heavier drapes - no more mid day glare on the screen

SCR: 2 thumbs up for appearance!

SCompRacer

Thanks for the kind words!

I used to have wall treatments and an area rug. The area rug had to go due to the wife's allergies of latex. She is also allergic to anything with perfumes.

It still sounds very good without. There are two stacked bass traps in left corner and one where the pic was taken from along with the one visible in pic.

mhardy6647

Real rugs are made out of wool -- just thought now might be a good time to point that out

(although there's probably a good chance she's allergic to wool, too?)

Seriously, and sort of back on topic -- I am sure the bass traps add much value in that room (or any other rooms, for that matter); how is the "slap echo in that space"? My experience with rooms like that is a liveliness that's nice for live singing or conversation, but often makes good hifis unbearably (to me, that is) bright. Treble brightness (in the realm of 5 to 10 kHz) is the one thing I for which I have a very low tolerance (which is why my Klipsch Cornwalls are long gone, and why I resisted the classic JBL drivers for soooooo long).

I'll bet a pair of B&W or Vandersteen loudspeakers in SCompRacer's space would violate the Geneva Convention

SCompRacer

mhardy6647 wrote: »

Real rugs are made out of wool -- just thought now might be a good time to point that out

I'd have to point out that it had a latex rubber non slip backing.

Ask Victor (halo) what it sounds like, he was just here the other day. Everybody seems to assume the worst, when I don't have worst.