subs and small room

The first thing you need to determine is how low your sub is going to operate. Room modes occur higher 80-200 (mid-bass) region in smaller rooms. Check the internet on how to determine where room modes occur based on the distance between two walls. So it will be your main speakers that will excite room modes. The sub if it operates below 40Hz with a XO of 24dB/octave won't really cause a problem but may even help smoothen out nodes that may occur with proper placement and being a bit frugal with the sub's volume control.

Don't know your price point but I use a small Velodyne SPL800 in a small dedicated room. It took some experimentation but after I realized the sub wasn't going in the corner things got a lot easier. I don't know how people get their subs to sound good in room corners. Click on my system page for a pic of what I mean.

Athipaul, I may have this wrong, but doesn't frequency doubling occur with room modes? That is, a given mode will be excited by a wave at half its length?

Thanks for any help with this.

Small rooms are the hardest to get smooth bass in. If you are really serious about getting good bass in a small room, there is a solution but I must warn you - at first glance is seems insane.

First a bit of background. You may have noticed that moving the speakers, or moving a subwoofer, changes the bass at the listening position. This is because how the low frequencies interact with the room depends not only on the room's dimensions, but also on the location of the low-frequency source(s) in relation to the room's boundaries as well as the listening position.

Using multiple subwoofers will result in smoother in-room bass because where the response of one sub is "zigging" due to its room interaction, the response of another sub is "zagging" - so the net result is smoother than any one sub could be. This isn't my original idea; I learned it from Earl Geddes, but it is also supported by Todd Welti.

"With enough subwoofers, it is theoretically possible to cancel out all modes in a room." - Todd Welti, "How Many Subwoofers are Enough". In a small room, the problem is modes that stick out like a sore thumb, and using multiple subs is the solution. Small subs though - we don't need big ones.

"The spatial variations, and to a certain extent the frequency response variations, will go down (get smoother) as 1/N, where N is the number of independent sources." - Earl Geddes, Speaker Asylum Post 10-30-05. This give us an idea of how much improvement to expect from each additional sub.

As a practical matter, Welti suggests four subs as enough to get a significant smoothing of the bass. Here is a paper he wrote on the subject:

http://www.harman.com/wp/pdf/multsubs.pdf

Whereas Welti recommends symmetrical placement of the subs, Geddes advocates asymmetrical placement:

http://www.gedlee.com/downloads/sub%20study%20.pdf

I suggest using four small subs that have a steep-slope low-pass filter (4th order, rather than the more common 2nd order) to allow greater flexibility in sub placement. If you can't hear the location of the subs, you have more freedom to experiment. I use a four-sub setup in my listening room when I'm using speakers that call for subs (like hotrodded Maggies).

Duke

Small rooms are the hardest to get smooth bass in. If you are really serious about getting good bass in a small room, there is a solution but I must warn you - at first glance is seems insane.

First a bit of background. You may have noticed that moving the speakers, or moving a subwoofer, changes the bass at the listening position. This is because how the low frequencies interact with the room depends not only on the room's dimensions, but also on the location of the low-frequency source(s) in relation to the room's boundaries as well as the listening position.

Using multiple subwoofers will result in smoother in-room bass because where the response of one sub is "zigging" due to its room interaction, the response another sub is "zagging" - so the net result is smoother than any one sub could be. This isn't my original idea; I learned it from Earl Geddes, but it is also supported by Todd Welti.

"With enough subwoofers, it is theoretically possible to cancel out all modes in a room." - Todd Welti, "How Many Subwoofers are Enough". In a small room, the problem is modes that stick out like a sore thumb, and using multiple subs is the solution. Small subs though - we don't need big ones.

"The spatial variations, and to a certain extent the frequency response variations, will go down (get smoother) as 1/N, where N is the number of independent sources." - Earl Geddes, Speaker Asylum Post 10-30-05. This give us an idea of how much improvement to expect from each additional sub.

As a practical matter, Welti suggests four subs as enough to get a significant smoothing of the bass. Here is a paper he wrote on the subject:

http://www.harman.com/wp/pdf/multsubs.pdf

Whereas Welti recommends symmetrical placement of the subs, Geddes advocates asymmetrical placement:

http://www.gedlee.com/downloads/sub%20study%20.pdf

I suggest using four small subs that have a steep-slope low-pass filter (4th order, rather than the more common 2nd order) to allow greater flexibility in sub placement. If you can't hear the location of the subs, you have more freedom to experiment. I use a four-sub setup in my listening room when I'm using speakers that call for subs (like hotrodded Maggies).

Duke
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