Musings and advice on in-room bass

zydeco · Oct 30, 2013

I’m trying to make sense on how to improve bass performance in my 12’ x 16’ x 10’ (w x l x h) stereo music room. Yes, I'll be doing some measurements but I though thought that y’all might be able to get me started on the right track. Some reading has guided me towards use of multiple subwoofers to smooth out the <100Hz bass response. This makes general sense but how this can be implemented is less clear – a couple of quick questions:

What is the minimum separation of subwoofers for the approach to be useful? My situation would see, for example, subwoofers in the rear corners being, say, 9’ apart (from the centre of the woofer). At what frequency, then, would these be seen as being co-located? Or, put another way, over what range would the subwoofers be separate sources? I was guessing that this would be 30 to 120Hz on the basis that the 9’ separation is roughly the wavelength of a 120Hz signal.
What are the recommendations for subwoofers for this multi-sub approach? My brain tells me to go for a small, easily placed, subwoofers (e.g., Gallo TR-3 or SVS SB12-NSD) but that sense of audio nervosa edges me towards more larger capable subwoofers (e.g., SVS SB13-Ultra) in line with the capabilities of my main speakers (Horn + pro-audio driver).
And how should one think of bass traps or Spatial Black Hole in a multi-sub set-up? I thought, at first, that bass traps violated the model of generating lots of modes from multi-subs but am now of the view that, designed correctly, the two approaches are complementary in that bass traps will reduce the ringing of a smooth listening position response. And, I guess, the Black Hole could also play a part at low frequencies at which there is effectively only one bass source?

The other part of the equation seems addressing speaker / boundary cancellations in the 100 to 300Hz region. I actually see this as more important to enjoying music but, unfortunately, more problematic as I don’t want to run subwoofers up to the these frequencies given localisation. My situation sees the main speakers against a pseudo front wall which is a 3’ bass trap and a near-field listening position that is 7’ from the back wall. I’ll do some measurements but guess that the major issue will be floor bounce. Is there a solution other than targeted room treatment for the 100 to 300Hz region?

Zydeco

DaveyF · Oct 30, 2013

I can say this with certainty....setting up subs is a PITA. Takes a lot of experimentation and patience. In my case, the small sub is the way to go...due to my room size ( opted for a REL T5). I am now contemplating adding a second T5...which I will do soon. The question in my VERY small room is will this overload the room? which is what one does NOT want to happen. ( I have bass trapping ....but there is ONLY so much that can accomplish). We shall see. You may want to consider this factor. BTW, IF you have suspended floors....all bets are off.

GaryProtein · Oct 30, 2013

DaveyF said:
. . . . IF you have suspended floors....all bets are off.

HA! You said it!

If I play music really loud--louder than I like my inner ear to experience, my room shakes and the floor feels like an earthquake with very low and sustained organ notes--and I have already had my floor joists doubled up.

With normal music this isn't a problem though.

You can overpower your room, but all it takes is a bit of volume control.

NorthStar · Oct 30, 2013

People like Ethan and Don (experts on acoustics, bass, room treatments, measurements, ...) here are well positioned to help you out.
...And there are other members too well calibrated in that department. ...With additional background experience in complementing the ordeal, resolving the task at hand; with DSP EQs (separates or internally implemented in some subs), REW, DIRAC, Perfect Room EQ & Calibration systems, ....

Nyal Mellor · Oct 30, 2013

zydeco said:
I’m trying to make sense on how to improve bass performance in my 12’ x 16’ x 10’ (w x l x h) stereo music room. Yes, I'll be doing some measurements but I though thought that y’all might be able to get me started on the right track. Some reading has guided me towards use of multiple subwoofers to smooth out the <100Hz bass response. This makes general sense but how this can be implemented is less clear – a couple of quick questions:

What is the minimum separation of subwoofers for the approach to be useful? My situation would see, for example, subwoofers in the rear corners being, say, 9’ apart (from the centre of the woofer). At what frequency, then, would these be seen as being co-located? Or, put another way, over what range would the subwoofers be separate sources? I was guessing that this would be 30 to 120Hz on the basis that the 9’ separation is roughly the wavelength of a 120Hz signal.

What are the recommendations for subwoofers for this multi-sub approach? My brain tells me to go for a small, easily placed, subwoofers (e.g., Gallo TR-3 or SVS SB12-NSD) but that sense of audio nervosa edges me towards more larger capable subwoofers (e.g., SVS SB13-Ultra) in line with the capabilities of my main speakers (Horn + pro-audio driver).

And how should one think of bass traps or Spatial Black Hole in a multi-sub set-up? I thought, at first, that bass traps violated the model of generating lots of modes from multi-subs but am now of the view that, designed correctly, the two approaches are complementary in that bass traps will reduce the ringing of a smooth listening position response. And, I guess, the Black Hole could also play a part at low frequencies at which there is effectively only one bass source?

The other part of the equation seems addressing speaker / boundary cancellations in the 100 to 300Hz region. I actually see this as more important to enjoying music but, unfortunately, more problematic as I don’t want to run subwoofers up to the these frequencies given localisation. My situation sees the main speakers against a pseudo front wall which is a 3’ bass trap and a near-field listening position that is 7’ from the back wall. I’ll do some measurements but guess that the major issue will be floor bounce. Is there a solution other than targeted room treatment for the 100 to 300Hz region?

Zydeco

Multi-subs only work in the frequency you are running them up to and have some beneficial effects maybe 1/2 an octave above. So if you use a 80Hz XO then you should get good results under that and improvements up to 120Hz. Multi-subs is a good idea because down in this frequency range you are in the 'sparsely populated room mode' region where there are a few axial modes that are very powerful and spread quite far out, so they are very audible.

You can determine where to place subs mathematically in a rectangular room without doing any trial and error. They should be placed to actively cancel the major problem room modes. Depending on your room and it's issues you may only need one sub, or you may need 4.

Because multi-subs only works up to 80Hz well and 120Hz ok you need bass traps to take care of the range up to the end of the room's modal region. Commercial bass traps are only really working in that 80Hz+ region anyway so the two approaches are complimentary.

Adding some parametric EQ capability will help flatten any remaining bass issues. Any audiophiles who are still anti-EQ for philosophical 'signal chain purity' reasons need their heads examined.

Finally if you are running multi-subs it is pretty critical that they behave the same. Most of the time this means using identical subs. Reason is that under 50Hz manufacturers put in a bunch of EQ to get the subs flat. Different manufacturers use different EQ, resulting in different phase shifts. Sometimes it is impossible to actively cancel room modes using subs with very different EQ / phase shift.

Properly implemented active room mode cancellation through multi-subs and EQ is magical, although to do it properly is beyond the skill of most. Luckily most have no reference for what good bass is so happily they are not missing much.

NorthStar · Oct 30, 2013

- Your room is 12' by 16' (10' high) => Two twelve-inch subs would do nicely (even quality 10-inchers).
- Try to position them first one at each front corner (6" from the front wall and 2.5" from the side wall).
- What equipment (electronic audio gear) are you using (preamp or SSP)? ...Does it have a Room EQ & Correction system integrated?
- Bass traps; one on each front corner. ...Now you can put the subs in front of them (nearer the side walls).
- Parametric EQ: This Yamaha one can be found on eBay for only $150 (was retailing for $2,400). ...The YDP2006
1 => http://usa.yamaha.com/products/live_sound/processors/ydp2006/?mode=model
2 => http://www.musiciansfriend.com/pro-...-digital-parametric-equalizer/180713002000000 ... Scroll down a bit.
3 => http://www.hometheatershack.com/for...ha-ydp2006-audio-control-c131.html#post492801

zydeco · Oct 30, 2013

Nyal Mellor said:
You can determine where to place subs mathematically in a rectangular room without doing any trial and error. They should be placed to actively cancel the major problem room modes. Depending on your room and it's issues you may only need one sub, or you may need 4.

Now that’s interesting if it helps me avoid purchasing an unnecessarily large number of subs. What information is needed to get an accurate assessment for a real room? And how does this work for rooms, like mine, that have the complications of windows, fixed bookshelves and in-built bass traps?

Nyal Mellor said:
Finally if you are running multi-subs it is pretty critical that they behave the same. Most of the time this means using identical subs. Reason is that under 50Hz manufacturers put in a bunch of EQ to get the subs flat. Different manufacturers use different EQ, resulting in different phase shifts. Sometimes it is impossible to actively cancel room modes using subs with very different EQ / phase shift .

Thanks.

NorthStar said:
- Your room is 12' by 16' (10' high) => Two twelve-inch subs would do nicely (even quality 10-inchers).
- Try to position them first one at each front corner (6" from the front wall and 2.5" from the side wall).

What’s the thinking behind this recommendation? I was thinking that at least one of the first two subs would be on the back wall (behind listener).

NorthStar said:
- What equipment (electronic audio gear) are you using (preamp or SSP)? ...Does it have a Room EQ & Correction system integrated?
- Bass traps; one on each front corner. ...Now you can put the subs in front of them (nearer the side walls).
- Parametric EQ: This Yamaha one can be found on eBay for only $150 (was retailing for $2,400). ...The YDP2006
1 => http://usa.yamaha.com/products/live_sound/processors/ydp2006/?mode=model
2 => http://www.musiciansfriend.com/pro-...-digital-parametric-equalizer/180713002000000 ... Scroll down a bit.
3 => http://www.hometheatershack.com/for...ha-ydp2006-audio-control-c131.html#post492801

My speakers are active horns sitting upon sealed bass bins with 18” pro-audio drivers. I’m managing the x/o via convolution within J River Media Centre on a purpose built computer that is connected to a multi-channel (Exasound e18) USB DAC that has in-built volume control. If I do add subwoofers then these will run off the remaining (4) channels of the USB DAC and I’ll be able to do some Room EQ via J River etc.

Cheers
Zydeco

NorthStar · Oct 30, 2013

1. Two subs are better than a single one. ...Better overall balance over a larger listening area of those lower sub frequencies.
...Less modal interference, and cancellation.
2. Two smaller subs (with a 12" maximum size driver) are better/easier to integrate with other speakers than larger subs (15" and 18" drivers).
3. The two subs positioned at the front, in each corner is a good positioning start, and easier to integrate with your front mains; that's all.
{But do try at the rear, after.}

__________________

4. You don't need subs.
5. You seem to know what you're doing.

FrantzM · Oct 31, 2013

Nyal Mellor said:
Multi-subs only work in the frequency you are running them up to and have some beneficial effects maybe 1/2 an octave above. So if you use a 80Hz XO then you should get good results under that and improvements up to 120Hz. Multi-subs is a good idea because down in this frequency range you are in the 'sparsely populated room mode' region where there are a few axial modes that are very powerful and spread quite far out, so they are very audible.

You can determine where to place subs mathematically in a rectangular room without doing any trial and error. They should be placed to actively cancel the major problem room modes. Depending on your room and it's issues you may only need one sub, or you may need 4.

Because multi-subs only works up to 80Hz well and 120Hz ok you need bass traps to take care of the range up to the end of the room's modal region. Commercial bass traps are only really working in that 80Hz+ region anyway so the two approaches are complimentary.

Adding some parametric EQ capability will help flatten any remaining bass issues. Any audiophiles who are still anti-EQ for philosophical 'signal chain purity' reasons need their heads examined.

Finally if you are running multi-subs it is pretty critical that they behave the same. Most of the time this means using identical subs. Reason is that under 50Hz manufacturers put in a bunch of EQ to get the subs flat. Different manufacturers use different EQ, resulting in different phase shifts. Sometimes it is impossible to actively cancel room modes using subs with very different EQ / phase shift.

Properly implemented active room mode cancellation through multi-subs and EQ is magical, although to do it properly is beyond the skill of most. Luckily most have no reference for what good bass is so happily they are not missing much.

Zydeco

Please read and re-read Nyles post. Excellent advice to which In entirely agree. You also have a system that can actually help you go into this. THis will not be a simple, plug and play issue. it will require time, research, forethought and work, lot of work. The results will be very very good. Just so that you know you could use inexpensive DACs down there for the additional subs. While this would make the system complex in term of logistics (more cables) the results will be wel worth the effort and more than satisfying.
Additionally and not speaking for Nyal, give him a call or a PM. That would be time well spent.

@North'

NorthStar said:
1. Two subs are better than a single one. ...Better overall balance over a larger listening area of those lower sub frequencies.
...Less modal interference, and cancellation.
2. Two smaller subs (with a 12" maximum size driver) are better/easier to integrate with other speakers than larger subs (15" and 18" drivers).
3. The two subs positioned at the front, in each corner is a good positioning start, and easier to integrate with your front mains; that's all.
{But do try at the rear, after.}

__________________

4. You don't need subs.
5. You seem to know what you're doing.

Your point #2 : Why would a 12" be easier to integrate than a a 15" or 18", aside from logistics (weight of subs, girth, etc)? I hope you are not trying to revive this old and tired cliche of "fast' sub?

4) How can you conclude that" You don't need subs?"
5) My opinion too and a route I will follow with the built for the purpose HTPC with likely the Lynx Audio PCI card. An ongoing project that is been on hold because of various business (fortunately) related issues thus lack of time.

Nyal Mellor · Oct 31, 2013

zydeco said:
Now that’s interesting if it helps me avoid purchasing an unnecessarily large number of subs. What information is needed to get an accurate assessment for a real room? And how does this work for rooms, like mine, that have the complications of windows, fixed bookshelves and in-built bass traps?

The key three things are room dimensions, speaker / listener position and room acoustic measurements. From the room acoustic measurements you work out which room modes are causing issues (the 2nd axial length, the 4th axial height, etc) and then from there determine placement of subs for active room mode cancellation. If one is clever with crossover points and relatively lucky with which room modes are problematic then speakers can be used as balancing sound sources, essentially becoming one component of a multi-sub array.

Generally in a rectangular room windows, bookshelves and bass traps do not substantially change the spatial distribution of room modes.

In odd shaped rooms then some more sophisticated modeling techniques can be used (boundary element models) to give you the sub placement answers required.

The cool thing about this is that it can all be done remotely, including sub integration, as long as the person on the other end of the phone has an acoustic measurement rig.

FYI in our home theater demo room we are running 12 channels off JRiver, with multi-sub array and a bunch of EQ. Works great. The ExaSound is a nice unit, we just signed on as a dealer for them and sold our first unit this week.

audioguy · Oct 31, 2013

zydeco said:
The other part of the equation seems addressing speaker / boundary cancellations in the 100 to 300Hz region. I actually see this as more important to enjoying music but, unfortunately, more problematic as I don’t want to run subwoofers up to the these frequencies given localisation. My situation sees the main speakers against a pseudo front wall which is a 3’ bass trap and a near-field listening position that is 7’ from the back wall. I’ll do some measurements but guess that the major issue will be floor bounce. Is there a solution other than targeted room treatment for the 100 to 300Hz region?

Zydeco

I've had that issue in my last two rooms and in both cases is was the floor/ceiling interaction. I suspended 4 GIK 244 Bass Traps on the ceiling between the LP and the front speakers and no more problems. If you have a measuring system (REW, OmniMic, etc) you can easily determine is that is the issue by putting the mic at the LP and move it up and down to see if it address the issue.

Just a thought.

NorthStar · Oct 31, 2013

NorthStar said:
1. Two subs are better than a single one. ...Better overall balance over a larger listening area of those lower sub frequencies.
...Less modal interference, and cancellation.
2. Two smaller subs (with a 12" maximum size driver) are better/easier to integrate with other speakers than larger subs (15" and 18" drivers).
3. The two subs positioned at the front, in each corner is a good positioning start, and easier to integrate with your front mains; that's all.
{But do try at the rear, after.}

__________________

4. You don't need subs.
5. You seem to know what you're doing.

FrantzM said:
@North'

Your point #2 : Why would a 12" be easier to integrate than a a 15" or 18", aside from logistics (weight of subs, girth, etc)? I hope you are not trying to revive this old and tired cliche of "fast' sub?
4) How can you conclude that" You don't need subs?"
5) My opinion too and a route I will follow with the built for the purpose HTPC with likely the Lynx Audio PCI card. An ongoing project that is been on hold because of various business (fortunately) related issues thus lack of time.

Happy Halloween Frantz! :b

#2 - I don't think you know me well; I'm not the type of "fast" and "slow" this or that; in particular when it comes to loudspeakers and drivers (electricity travels at a certain speed, and the only way to slow it down is to ...). :b
-> Smaller size drivers, in closed enclosures, are simply better/easier to cross and integrate with your mains. ...And lower order crossovers (6dB/octave).
For more on this, search articles by Richard Hardesty; who has his own ultra high-end audio journal (subscription required, and it's not cheap).

#4 - His mains have already 18" drivers in them! ...But true, he might experiment with additional separate subs, in his 12' by 16' room.

#5 - Obviously.

Nyal Mellor · Oct 31, 2013

audioguy said:
I've had that issue in my last two rooms and in both cases is was the floor/ceiling interaction. I suspended 4 GIK 244 Bass Traps on the ceiling between the LP and the front speakers and no more problems. If you have a measuring system (REW, OmniMic, etc) you can easily determine is that is the issue by putting the mic at the LP and move it up and down to see if it address the issue.

Just a thought.

The ceiling is often missed, even by "experienced" designers...quite why makes no sense to me since most speakers people are using are a collection of vertically stacked point source drivers which have in 99% of cases some lobing or vertical off axis sound spectrally different to the on axis sound. Since our brain fuses direct + indirect sound together this vertical reflection causes timbral shifts.

With respect to SBIR it is a difficult thing to fix and it is generally not as bad audibly as it looks on the graph. I did a room recently for someone and we did our best with the ceiling SBIR but still had a 10dB+ dip there (it was 20dB before we treated with RPG BAD panels on an airgap) but interestingly enough I gave the client some test tones that crossed through the dip frequency and he could not hear it at all. So one has to know how to read the graphs also and how they correspond to what we hear (or don't in this case).

microstrip · Oct 31, 2013

Nyal Mellor said:
(...) Finally if you are running multi-subs it is pretty critical that they behave the same. Most of the time this means using identical subs. Reason is that under 50Hz manufacturers put in a bunch of EQ to get the subs flat. Different manufacturers use different EQ, resulting in different phase shifts. Sometimes it is impossible to actively cancel room modes using subs with very different EQ / phase shift.

Properly implemented active room mode cancellation through multi-subs and EQ is magical, although to do it properly is beyond the skill of most. Luckily most have no reference for what good bass is so happily they are not missing much.

Nyal,

Although the part of your comment I have quoted in bold is very true, people should know that there are many ways of adding subwoorfers to a room. As my room is very long and I could afford a few feet to built large tuned bass traps I preferred this approach, but I also looked around for other solutions. When looking at subwoofer placement rules one must remember that some were studied for subwoofers with only a common filter, level and eq control, others for separate controls in each subwoofer.
I have played a little with three subs added to the two subs of the main speakers in my room, using REW as the measuring system, and I found that for an amateur with little experience the Earl Geddes system and placing rules, using three subs with independent controls, is one of the easiest and most rewarding systems.
http://mehlau.net/audio/multisub_geddes

zydeco · Nov 1, 2013

FrantzM said:
… Just so that you know you could use inexpensive DACs down there for the additional subs. While this would make the system complex in term of logistics (more cables) the results will be wel worth the effort and more than satisfying.

…
5) My opinion too and a route I will follow with the built for the purpose HTPC with likely the Lynx Audio PCI card. An ongoing project that is been on hold because of various business (fortunately) related issues thus lack of time.

My set-up is similar to that which you’re targeting but with a 8-channel USB DAC rather than Lynx Audio PCI card. The thinking is that I’ll do the cross-over to the subs – as well as room eq – using the JRiver / e18 DAC combination. I’m not too worried about all the cables but don’t have room for additional amplifers so the subs will need to have an on-board amplifier.

Nyal Mellor said:
If one is clever with crossover points and relatively lucky with which room modes are problematic then speakers can be used as balancing sound sources, essentially becoming one component of a multi-sub array.

It’d be great if my main speakers became part of the multi-sub array given that this would save both cost and space. What do you mean by “if one is clever with cross-over points”?

Nyal Mellor said:
The cool thing about this is that it can all be done remotely, including sub integration, as long as the person on the other end of the phone has an acoustic measurement rig.

That’s food for thought.

audioguy said:
I've had that issue in my last two rooms and in both cases is was the floor/ceiling interaction. I suspended 4 GIK 244 Bass Traps on the ceiling between the LP and the front speakers and no more problems. If you have a measuring system (REW, OmniMic, etc) you can easily determine is that is the issue by putting the mic at the LP and move it up and down to see if it address the issue. Just a thought.

Good point. I’d kind of assumed that I’d deal with the ceiling interaction via the multi-sub on the basis that the path length different will be quite long (say 7’ to 10’) so the frequency will be <100Hz. You point about bass traps on the ceiling is a good idea though and I’ll have a natural point to figure it out as the ceiling itself needs to be replaced. Hmm – perhaps an IB sub in the roof? (I guess I’m concerned about the floor bounce as it will be a short path length that, roughly, equates to somewhere from 150 to 250Hz.)

Nyal Mellor · Nov 2, 2013

zydeco said:
It’d be great if my main speakers became part of the multi-sub array given that this would save both cost and space. What do you mean by “if one is clever with cross-over points”?

An example is if you want to cancel a 1st order length mode. Speakers in the front of the room can be balanced with a subwoofer in the back of the room. Pick the subwoofer crossover frequency that corresponds to the 1st order length mode, level match the sub to the front speakers playing together, and voila, room mode canceled.

See below on an example - before / after waterfalls where I did exactly the above with a client. Wasn't bad before, but better now. The 1st order length mode is 48Hz. Cool huh, it's completely gone, gotta love acoustics

microstrip · Nov 2, 2013

Nyal Mellor said:
An example is if you want to cancel a 1st order length mode. Speakers in the front of the room can be balanced with a subwoofer in the back of the room. Pick the subwoofer crossover frequency that corresponds to the 1st order length mode, level match the sub to the front speakers playing together, and voila, room mode canceled.

See below on an example - before / after waterfalls where I did exactly the above with a client. Wasn't bad before, but better now. The 1st order length mode is 48Hz. Cool huh, it's completely gone, gotta love acoustics

View attachment 12445 View attachment 12444

Nyal,
Very nice result. I have found that peaks are usually easier to solve than nulls - and the null around 100 Hz seems deeper in the second picture. How did you solve it?
BTW, it seems that some other treatments other than the sub were added between the two measurements.

Nyal Mellor · Nov 3, 2013

microstrip said:
Nyal,
Very nice result. I have found that peaks are usually easier to solve than nulls - and the null around 100 Hz seems deeper in the second picture. How did you solve it?
BTW, it seems that some other treatments other than the sub were added between the two measurements.

Yes - well spotted - other things were added but nothing effective at 48Hz.

The SBIR null at 100Hz is inconsequential. The client can't hear it. It is very interesting when to see a big dip on a graph that you can't hear in real life! More interesting still is the fact the client could hear a 5dB peak at 120Hz in the left speaker (which we fixed second time around), right after that null, but could not hear the null!

j_j · Nov 8, 2013

Nyal Mellor said:
Yes - well spotted - other things were added but nothing effective at 48Hz.

The SBIR null at 100Hz is inconsequential. The client can't hear it. It is very interesting when to see a big dip on a graph that you can't hear in real life! More interesting still is the fact the client could hear a 5dB peak at 120Hz in the left speaker (which we fixed second time around), right after that null, but could not hear the null!

Are those Omni mic measurements? The idea of cancelling something in the pressure domain has interesting implications for the velocity domain, which is 3/4 of the soundfield information, give or take.

dallasjustice · Nov 8, 2013

Fwiw, I've always found that SBIRs don't always sound the way they look in magnitude response using a single measurement from an omnimic.

Mr. j_j,
I've read your comments on this forum concerning omnimic limitations in the frequency domain above 100hz. Could that problem be overcome by taking a significant number of measurements at different locations within the listening area and combining them in a sensible way?

j_j said:
Are those Omni mic measurements? The idea of cancelling something in the pressure domain has interesting implications for the velocity domain, which is 3/4 of the soundfield information, give or take.

Musings and advice on in-room bass

Well-Known Member

Well-Known Member

VIP/Donor

Member

Industry Expert

Member

Well-Known Member

Member

Member Sponsor & WBF Founding Member

Industry Expert

WBF Founding Member

Member

Industry Expert

VIP/Donor

Well-Known Member

Industry Expert

VIP/Donor

Industry Expert

New Member

Member Sponsor

Similar threads