Stereo Subs Vs. Mono Subs

[hemster]

Jul 17, 2014 21:14:20 GMT -5 Priapulus said:

The second Sub outlet on the xmc-1 is for your buttkickers.
/b

Indeed, that's how I have mine hooked up. 

[hemster]

I've been reading this discussion about localization with great interest. I've had my sub exactly at midpoint (right under the center channel) in my rig. It has served me well without any localization issues!   

I dragged the little sub (Emotiva Ultra-10) out of my office and installed it directly opposite the other sub (i.e. midway on the rear wall) just to see what happens. Drove each sub via the 2 sub outs on the XMC-1. I found that the 2^nd sub really didn't do much for music. For movies there was a slightly more pronounced effect. I then repeated the exercise with a single sub-out, split because I need the other sub output for the Buttkicker. The same observations were experienced. Of course that's my situation but YMMV.. 

So the little sub is going back to the office but it was an interesting experiment. 

[pop]

Jul 18, 2014 1:46:42 GMT -5 hemster said:

I've been reading this discussion about localization with great interest. I've had my sub exactly at midpoint (right under the center channel) in my rig. It has served me well without any localization issues!   

I dragged the little sub (Emotiva Ultra-10) out of my office and installed it directly opposite the other sub (i.e. midway on the rear wall) just to see what happens. Drove each sub via the 2 sub outs on the XMC-1. I found that the 2^nd sub really didn't do much for music. For movies there was a slightly more pronounced effect. I then repeated the exercise with a single sub-out, split because I need the other sub output for the Buttkicker. The same observations were experienced. Of course that's my situation but YMMV.. 

So the little sub is going back to the office but it was an interesting experiment. 

Interesting, thanks for the testing.

Curious, did you leave the two subs at the same LPF, or did you have for example the Ultra pick up 40-80z and the sunfire everything below? I would imagine with the two sub outs that you can set two different LPF points for your subs? I actually don't remember seeing that in the manual.

Seeing as how your drivers in the subs are completely different it doesn't sound to me like they didn't play well together and were fairly easy to integrate, which is pretty good news.

I agree with you, my two subs don't make too much of a difference with music but when you get into heavy LFE movies, it is substantial.

[KeithL]

I'll pop in here with a few tips on localization of sound....

First off, research seems to show that indeed we can't hear where sounds below 80 Hz or 100 hz are coming from... unfortunately, as usual, it's not that simple...

1) No crossover is "perfectly sharp"; if I set a crossover for a particular speaker at 80 Hz, with a 24 dB/octave slope, that means that sounds at 160 Hz will be 24 dB down, and sounds at 320 Hz will be 48 dB down. (Note that, if you're playing something loud, even things that are 24 dB down from the loudest parts will still be audible.)

2) Speakers produce distortion; even if I were to play a perfectly clean 80 Hz tone from a sub, and play it loud, it will produce some second harmonic (160 Hz), and some third harmonic (240 Hz). Now, even though those will be at much lower levels than the primary tone, they are also easier to hear - and much easier to localize. At this point, if you hear the overtone, and there is no other audio being played, your brain will hear the entire thing as if the low note is localized.

3) "Factor #2" is complicated even further by the particulars of the sub itself. The distortion is produced by the driver; if the driver is front-firing, then you'll hear any distortion it makes; if it fires into the floor, or into some sort of internal loading arrangement, then those harmonics may me muffled and so less audible. Likewise if it happens to live behind your fluffy couch. Many subs also produce mechanical distortions - like whooshing noises from the port, or vibration noises from the cabinet. These all allow you to localize the sub.

4) The room also makes "distortion" (or, more properly, noise). It doesn't matter if you can't localize the sound coming from the sub if you can localize the sound of the floor and everything near it rattling. Face it, stuff closer to the sub will probably rattle more. And back to #3, a sub that fires into the floor is going to make the floor rattle more.

5) On our side, our brains base localization on various cues. When we hear a sound that includes both very low notes and higher components or harmonics, our brains "fill in" the localization based on those other sounds. When T-Rex walks, we can't tell at all where the lowest vibrations are coming from, but we "imagine" that we do, because the sounds of his foot touching the ground, and the gravel crunching, and such things are very localizable. Therefore, our brains associate the two and "imagine" that the thump of his footfall "must" be coming from the same place as the crunch of the gravel that goes with it - and so we hear it that way. This is why you may be able to localize where your sub is when playing a pure test tone (where all you have is the non-localizable bass note and a little rattle or whoosh from the sub), but it works just fine when you play that recording of T-rex. In your brain, the location information from the gravel crunching, which is coming from a main speaker or s surround, completely overrides the slight amount of conflicting "information" from the few percent of distortion produced by the sub - or other "errors" in the whole process.

6) Another thing to consider is that we are, to a degree, stuck with the room we listen in. Depending on the shape of your room, and where the room modes fall, you may not have a choice. If the bass "piles up" in one corner, then that corner will be the apparent source for those frequencies... and the only solution is big, possibly expensive, bass traps - with a truly awful WAF. If moving the sub to an otherwise less optimal location cures that problem, then you have a "net gain" by doing so.... and, if localization then becomes an issue (but only if), then you can work on that.


My personal advice (very generally), would be to maintain symmetry - if practical. That means, if you have one sub, put it along the centerline (front center, back center, under the coffee table dead center); if you have two subs, place them symmetrically (next to or behind your front mains, in the front or back corners, or one front center and one back center - although, if you do that, then they should be set to mono). If this setup works reasonably well - I'm happy. If not, then you "do what you gotta do" to even out the response, and to minimize anything that causes any annoying localization. (If the subs are arranged symmetrically, then any localization that occurs will be more benign; if not, then any localization that does occur will "pull" the sound to the left or right.) ALso, I'll admit, according to my personal sense of aesthetics, I simply prefer symmetrical arrangements in things that "should be symmetrical".

Also, for the record, I am quite sensitive to the sound image being "pulled" to the left or right - it drives me nuts when a center vocalist isn't in the center - but I'm much less sensitive to the width of the sound stage, or errors in front-to-back placement. Your results may, as they say, differ. You should always focus on what matters to you.

[sesquipedalian]

Jul 18, 2014 9:57:07 GMT -5 KeithL said:

I'll pop in here with a few tips on localization of sound....

First off, research seems to show that indeed we can't hear where sounds below 80 Hz or 100 hz are coming from... unfortunately, as usual, it's not that simple...

1) No crossover is "perfectly sharp"; if I set a crossover for a particular speaker at 80 Hz, with a 24 dB/octave slope, that means that sounds at 160 Hz will be 24 dB down, and sounds at 320 Hz will be 48 dB down. (Note that, if you're playing something loud, even things that are 24 dB down from the loudest parts will still be audible.)

2) Speakers produce distortion; even if I were to play a perfectly clean 80 Hz tone from a sub, and play it loud, it will produce some second harmonic (160 Hz), and some third harmonic (240 Hz). Now, even though those will be at much lower levels than the primary tone, they are also easier to hear - and much easier to localize. At this point, if you hear the overtone, and there is no other audio being played, your brain will hear the entire thing as if the low note is localized.

3) "Factor #2" is complicated even further by the particulars of the sub itself. The distortion is produced by the driver; if the driver is front-firing, then you'll hear any distortion it makes; if it fires into the floor, or into some sort of internal loading arrangement, then those harmonics may me muffled and so less audible. Likewise if it happens to live behind your fluffy couch. Many subs also produce mechanical distortions - like whooshing noises from the port, or vibration noises from the cabinet. These all allow you to localize the sub.

4) The room also makes "distortion" (or, more properly, noise). It doesn't matter if you can't localize the sound coming from the sub if you can localize the sound of the floor and everything near it rattling. Face it, stuff closer to the sub will probably rattle more. And back to #3, a sub that fires into the floor is going to make the floor rattle more.

5) On our side, our brains base localization on various cues. When we hear a sound that includes both very low notes and higher components or harmonics, our brains "fill in" the localization based on those other sounds. When T-Rex walks, we can't tell at all where the lowest vibrations are coming from, but we "imagine" that we do, because the sounds of his foot touching the ground, and the gravel crunching, and such things are very localizable. Therefore, our brains associate the two and "imagine" that the thump of his footfall "must" be coming from the same place as the crunch of the gravel that goes with it - and so we hear it that way. This is why you may be able to localize where your sub is when playing a pure test tone (where all you have is the non-localizable bass note and a little rattle or whoosh from the sub), but it works just fine when you play that recording of T-rex. In your brain, the location information from the gravel crunching, which is coming from a main speaker or s surround, completely overrides the slight amount of conflicting "information" from the few percent of distortion produced by the sub - or other "errors" in the whole process.

6) Another thing to consider is that we are, to a degree, stuck with the room we listen in. Depending on the shape of your room, and where the room modes fall, you may not have a choice. If the bass "piles up" in one corner, then that corner will be the apparent source for those frequencies... and the only solution is big, possibly expensive, bass traps - with a truly awful WAF. If moving the sub to an otherwise less optimal location cures that problem, then you have a "net gain" by doing so.... and, if localization then becomes an issue (but only if), then you can work on that.


My personal advice (very generally), would be to maintain symmetry - if practical. That means, if you have one sub, put it along the centerline (front center, back center, under the coffee table dead center); if you have two subs, place them symmetrically (next to or behind your front mains, in the front or back corners, or one front center and one back center - although, if you do that, then they should be set to mono). If this setup works reasonably well - I'm happy. If not, then you "do what you gotta do" to even out the response, and to minimize anything that causes any annoying localization. (If the subs are arranged symmetrically, then any localization that occurs will be more benign; if not, then any localization that does occur will "pull" the sound to the left or right.) ALso, I'll admit, according to my personal sense of aesthetics, I simply prefer symmetrical arrangements in things that "should be symmetrical".

Also, for the record, I am quite sensitive to the sound image being "pulled" to the left or right - it drives me nuts when a center vocalist isn't in the center - but I'm much less sensitive to the width of the sound stage, or errors in front-to-back placement. Your results may, as they say, differ. You should always focus on what matters to you.

Thanks for the detailed response.

I have two subs--mostly because of a perceived pressure differential in my ears. This happened when I had one sub to the left or right of center--even in a back corner near the seating position. I purchased a second sub place it on the opposite side of the first one, and it immediately produced equilibrium without and weird ear pressure perception. Is this pressure localization normal?

[pop]

@keithl

Thanks for the response. Would you mind attributing some comments on 2 or more subs configured in stereo vs. mono with the XMC? Basically opinions on the sound qualities between the two.

[Deleted]

FYI, Just allow me to slip in here some audio tests links you might enjoy.  There is a wealth of information here:



www.audiocheck.net/audiotests_frequencychecklow.php

(See bottom of page for) 

Other Subwoofer Tests
Subwoofer Harmonic Distortion Test
Subwoofer Transient Response Test
Design your Custom Sub-Bass Sweeps
Low Frequency Sound Localization Test
High Frequency Audibility Test
High Frequency Response and Audibility Test

External Links
Frequency Range of the Human Hearing
Frequency Range of Loudspeakers



www.audiocheck.net/blindtests_index.php

(Includes)

.....Find the smallest difference in sound levels you can detect.
The Level Series: 6dB 3dB 1dB 0.5dB 0.2dB 0.1dB

.....Find the highest frequency you can reliably hear.
The Frequency Series: 10kHz 11k 12k 13k 14k 15k 16k 17k 18k 19k 20kHz

.....Find the smallest difference in pitch (frequency) you can hear.
The Pitch Series: 50c 20c 10c 5c 2c 1c

.....Find the highest dynamic range offered by your listening environment.
The Dynamic Range Series: 36dB 42dB 48dB 54dB 60dB 66dB 72dB 78dB

.....Do you have the absolute hearing ability?
The Perfect Pitch Blind Test: C Scale Chromatic

.....Are your ears sensitive to Absolute Phase?
The Absolute Polarity Blind Test: Here

.....Can you hear a difference between 16-bit and 8-bit audio files?
The 16-bit v/s 8-bit Blind Test NEW

[hemster]

Jul 18, 2014 9:02:33 GMT -5 pop said:

Jul 18, 2014 1:46:42 GMT -5 hemster said:

I've been reading this discussion about localization with great interest. I've had my sub exactly at midpoint (right under the center channel) in my rig. It has served me well without any localization issues!   

I dragged the little sub (Emotiva Ultra-10) out of my office and installed it directly opposite the other sub (i.e. midway on the rear wall) just to see what happens. Drove each sub via the 2 sub outs on the XMC-1. I found that the 2^nd sub really didn't do much for music. For movies there was a slightly more pronounced effect. I then repeated the exercise with a single sub-out, split because I need the other sub output for the Buttkicker. The same observations were experienced. Of course that's my situation but YMMV.. 

So the little sub is going back to the office but it was an interesting experiment. 

Interesting, thanks for the testing.

Curious, did you leave the two subs at the same LPF, or did you have for example the Ultra pick up 40-80z and the sunfire everything below? I would imagine with the two sub outs that you can set two different LPF points for your subs? I actually don't remember seeing that in the manual.

Seeing as how your drivers in the subs are completely different it doesn't sound to me like they didn't play well together and were fairly easy to integrate, which is pretty good news.

I agree with you, my two subs don't make too much of a difference with music but when you get into heavy LFE movies, it is substantial.

I left them both at the same LPF. In practice I intend to use only one sub out for sub duty and the other for my Buttkicker. 

[panheadxxx]

Ive come to the conclusion that running dual sub's in a HT or Stereo set up add's more problems than benifits , i find that running a single stereo sub offers a cleaner & tighter bass response vs dual subs , or single summed L & R sub , they are more expensive but are much easier to incorporate into the system .

[bootman]

Jul 20, 2014 12:25:00 GMT -5 panheadxxx said:

Ive come to the conclusion that running dual sub's in a HT or Stereo set up add's more problems than benifits , i find that running a single stereo sub offers a cleaner & tighter bass response vs dual subs , or single summed L & R sub , they are more expensive but are much easier to incorporate into the system .

Have you read this?

www.audioholics.com/subwoofer-setup/subwoofer-connection-guide

[panheadxxx]

Jul 20, 2014 12:27:29 GMT -5 bootman said:

Jul 20, 2014 12:25:00 GMT -5 panheadxxx said:

Ive come to the conclusion that running dual sub's in a HT or Stereo set up add's more problems than benifits , i find that running a single stereo sub offers a cleaner & tighter bass response vs dual subs , or single summed L & R sub , they are more expensive but are much easier to incorporate into the system .

Have you read this?

www.audioholics.com/subwoofer-setup/subwoofer-connection-guide

Yup , i read it as well as several other sub set up guides but it still dont change my views on subs , it isnt that running dual sub's for stereo effect cant be done it's just far easier to obtain the same or better results with a single stereo sub , the key here is stereo , Most sub out's dont even present a proper signal for true stereo unless the signal is a dedicated L & R signal vs sub 1 & 2 , or a Y splitter, as Chuckienut pointed out in his post summed sub out's do not produce true stereo , even with 2 seperate sub's .

[Deleted]

FYC:

So, as the frequency drops below a critical frequency - usually around 80 Hz - it becomes very difficult to determine a sound's location. This current page tests the exact frequency when this phenomenon happens, in your particular audio setup.

If you are using a subwoofer, its crossover frequency should ideally be located below this critical frequency: only then will the lower frequencies be perceived as if they were coming from your main speakers, not the corner of your listening room where your subwoofer is often placed.


Low Frequency Sound Localization Test
www.audiocheck.net/audiotests_basslocalization.php

[urwi]

More like 4.
www.aes.org/e-lib/download.cfm?ID=13680&name=harman

Jul 17, 2014 19:15:54 GMT -5 DYohn said:

The main reason for using multiple subwoofers (besides increasing SPL) is to cancel room modes. Many theorists, including my hero Dr. Earl Geddes, thinks three sources for LF information is ideal. Others, such as Dr. Floyd Toole, think it's more like six. So bottom line it' about creating a uniform LF sound field.

[ludi]

I just came across an article about stereo subwoofers. In this article the writer takes an historical view on why one or two subwoofers. He also gives another argument why stereo subwoofers are of a benefit. It has to do with th out-of-phase information: with mono sub you loose it while with stereo it is reproduced. This is the link to the article.

[urwi]

The room itself acts as a filter. Phase information is completely distorted by that filter. Any directional low frequency information that might have been recorded is completely scrambled. There will be some perceivable directional information from pressure gradients caused by room modes but this is not spatial information from the recording but from the playback room. Playing a slow sine sweep will create similar directional perceptions. You'll hear the sound swirling around your head.

Jul 27, 2014 5:50:36 GMT -5 ludi said:

I just came across an article about stereo subwoofers. In this article the writer takes an historical view on why one or two subwoofers. He also gives another argument why stereo subwoofers are of a benefit. It has to do with th out-of-phase information: with mono sub you loose it while with stereo it is reproduced. This is the link to the article.

[geebo]

Jul 27, 2014 5:50:36 GMT -5 ludi said:

I just came across an article about stereo subwoofers. In this article the writer takes an historical view on why one or two subwoofers. He also gives another argument why stereo subwoofers are of a benefit. It has to do with th out-of-phase information: with mono sub you loose it while with stereo it is reproduced. This is the link to the article.

The link just brings me back to this page...

[ludi]

Jul 27, 2014 7:38:52 GMT -5 geebo said:

Jul 27, 2014 5:50:36 GMT -5 ludi said:

I just came across an article about stereo subwoofers. In this article the writer takes an historical view on why one or two subwoofers. He also gives another argument why stereo subwoofers are of a benefit. It has to do with th out-of-phase information: with mono sub you loose it while with stereo it is reproduced. This is the link to the article.

The link just brings me back to this page...

Sorry, my mistake. Fixed it in the original post. This is the correct link.

[ludi]

Jul 27, 2014 6:40:26 GMT -5 urwi said:

The room itself acts as a filter. Phase information is completely distorted by that filter. Any directional low frequency information that might have been recorded is completely scrambled. There will be some perceivable directional information from pressure gradients caused by room modes but this is not spatial information from the recording but from the playback room. Playing a slow sine sweep will create similar directional perceptions. You'll hear the sound swirling around your head.

Jul 27, 2014 5:50:36 GMT -5 ludi said:

I just came across an article about stereo subwoofers. In this article the writer takes an historical view on why one or two subwoofers. He also gives another argument why stereo subwoofers are of a benefit. It has to do with th out-of-phase information: with mono sub you loose it while with stereo it is reproduced. This is the link to the article.

Sure, you are right. But if the info is missing in the first place you get nothing. This quote explained it nicely, although is is not exactly in the same context:

Bass management electrically combines the bass from all of the channels together. Even if you had full range monitors, with say a subwoofer spliced to each of the five or more main channels, you would then be hearing an acoustical summation of the multichannel bass in your room. The two levels, acoustically summed or electrically summed, could be very different. Let's say front and surround channels are out-of-phase with each other. Then electrically they will cancel, but acoustically, depending on where you are standing, you may hear them sum (the room standing wave adds its own phase shifts!).

Link to the full article: www.tmhlabs.com/products/bassmanager.pdf

[urwi]

Exactly why monophonic bass is preferable. You don't get any unpredictable performance. In-room frequency response will be the same regardless which channel carries the low frequency signal. This helps in optimizing bass performance in rooms.

Jul 27, 2014 8:11:03 GMT -5 ludi said:

Jul 27, 2014 6:40:26 GMT -5 urwi said:

The room itself acts as a filter. Phase information is completely distorted by that filter. Any directional low frequency information that might have been recorded is completely scrambled. There will be some perceivable directional information from pressure gradients caused by room modes but this is not spatial information from the recording but from the playback room. Playing a slow sine sweep will create similar directional perceptions. You'll hear the sound swirling around your head.

Sure, you are right. But if the info is missing in the first place you get nothing. This quote explained it nicely, although is is not exactly in the same context:

Bass management electrically combines the bass from all of the channels together. Even if you had full range monitors, with say a subwoofer spliced to each of the five or more main channels, you would then be hearing an acoustical summation of the multichannel bass in your room. The two levels, acoustically summed or electrically summed, could be very different. Let's say front and surround channels are out-of-phase with each other. Then electrically they will cancel, but acoustically, depending on where you are standing, you may hear them sum (the room standing wave adds its own phase shifts!).

Link to the full article: www.tmhlabs.com/products/bassmanager.pdf

[igorzep]

Jul 27, 2014 8:11:03 GMT -5 ludi said:

But if the info is missing in the first place you get nothing.

So, instead of nothing do you want something.. that has nothing to do with what is recorded? Can be it called reproduction? I think no.

And... with all respect to Ken Rockwell he is a great photographer, but not an acoustician. He loves to write about everything but here he starts with wrong assumptions and then builds a theory. Well... hypothesis, that is unfounded.

And... summing acoustically IS the same as summing electrically! There are just many ways to sum it depending on where are you in the room when electrically you do it predictably and the same for all listeners. If you are exactly in between of two sources and have no room effects (large room or free space, or good symmetry in the room) out-of-phase will null just like with electrical summing. If you move off the centre sum will change, the same as with electrical sum will change if you do it with different delays.

But, as was noted above - in real small room practically all the phase-difference between the ears will not come from the direction of the bass source, but from the room modes. So, again no point in stereo anyway as you will get this kind of 'room ambiance' anyway (if it is something you want to have).