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If One Sub is Good, Are Two Better?

post #1 of 129
Thread Starter 
If One Sub is Good, Are Two Better?
Alan Lofft, Axiom Audio


If your room has typical dimensions--20 x 14 x 8 ft., about 2,100 cu. ft.--one well-designed subwoofer with an internal amplifier equal in size to the full output of your receiver (full power for 1 channel + 1/8 power x the number of other channels) and a 10-inch or 12-inch driver should deliver solid deep bass extension and ample output for music and movie soundtracks. On the other hand, if the room is larger than usual (4,000 to 8,000 cu. ft. or bigger) or has a vaulted or cathedral ceiling, you should definitely consider running an extra subwoofer.

Big rooms, especially the "great rooms" so common in many suburban homes, really devour deep bass, so two subs will generate enough sound pressure to fill the place. They'll also give you smoother distribution of extended bass over several different listening locations. My colleagues and friends who have large vaulted-ceiling rooms all run dual subs. Taste plays a role as well. If you like your music or soundtracks really loud and deep, go for two subs. If you have a huge room and you want really loud sound and deep bass, then look at physically larger subwoofers with bigger amplifiers.

Read the complete article at HomeToys.com
post #2 of 129
I use two subs for the same reasons listed above.
I have a relatively large living room with a tall ceiling.
One sub is located front right of the room while the other sits right behind the main couch.
One added benefit to this set ups is that I can "feel" explosions, gun shots, etc. making movie watching way more fun.. and all with zero distortion
post #3 of 129
I guess it depends on what you consider deep solid bass extension. I do not know of a single 10" sub (ported, sealed, band passed or horn loaded) that does what I would consider an adequate job for HT even in a small room. A single 10" sub is not going to provide much SPL at 20hz. A single 12" is not much better. Most commercial subs are around 88db sensitive. If the listening distance from the sub is 13' then you are losing an additional 6db. That puts your starting point at 82db, not even allowing for power compression or headroom. Reference level is 115db. That is 33db to make up or 11 doublings of power. So to get to reference level the sub amp would need to provide 2,048 watts of peak power and the driver is going to have to be able to convert that to clean sound pressure. Good luck with that.

Added
Am I understanding his formula correctly? If you have a 100 watt per channel AVR and you have a 5.1 set up, then:

100 watts + (1/8 x 100) x 4 = 150 watts. So a 10" driver and 150 watts is deemed adequate for a 2,100 CF room? Personally, No way.
post #4 of 129
Dual subs is a must in a typical 20x14x8 room IMO.
post #5 of 129
post #6 of 129
Clearly someone has no clue as to the purpose behind multiple subs in small rooms...and is has nothing to do with sufficient output of the subwoofer.
post #7 of 129
Quote:
Originally Posted by mjg100 View Post


Added
Am I understanding his formula correctly? If you have a 100 watt per channel AVR and you have a 5.1 set up, then:

100 watts + (1/8 x 100) x 4 = 150 watts. So a 10" driver and 150 watts is deemed adequate for a 2,100 CF room? Personally, No way.

I think the math would actually be 450 watts, or 562.5 watts for 5 channels. Either way, its not enough for the movie watching most of us do. I have the same size room, and use a JL F113....I would say its enough, although 2 has popped in my mind from time to time. As a counter to the temptation, I put on War of the Worlds and its so violent I go back to "one is enough". Its an ongoing cycle that I'm sure will end in me getting a second one.
post #8 of 129
my room is approx 16x16 w/ 10' ceilings. My 15" fills the room just fine. I do have some extra "texture" from bass shakers. Another sub would be overkill for my environment.
post #9 of 129
Why bother pulling apart the formula when the entire thing is nonsense.
post #10 of 129
Quote:
Originally Posted by Dennis Erskine View Post

Clearly someone has no clue as to the purpose behind multiple subs in small rooms...and is has nothing to do with sufficient output of the subwoofer.

And what's that purpose? You mean to get more cash from consumers? There's no other purpose for two subs in a small or medium room.
post #11 of 129
Quote:
Originally Posted by WebEffect View Post

And what's that purpose? You mean to get more cash from consumers? There's no other purpose for two subs in a small or medium room.

I'm going to go out on a limb here. Maybe... Just maybe... it could be to even out room response. You'd figure being here for so long you'd have learned this.
post #12 of 129
there are some misconceptions about the purpose of multiple subs in this article.

I highly recommend anyone really wanting to understand the true benefits and gains and sometimes losses when employing multiple subs to pick up a copy of "Sound Reproduction: Loudspeakers & Rooms" by Dr. Floyd Toole.

I also wrote an article on this topic and it was peer reviewed by Dr. Floyd Toole and Dr. Sean Olive of Harman. I summarize associated gains/loses of multi subs when placed in common locations around the room but don't dig in as deep as Dr. Toole's excellent book. Chapter 13 of Dr. Toole's book IMO should be considered gospel on the subject matter.

Here is a link to the article I wrote on this topic: Multiple Subwoofer Calibration & Setup Guide

I hope this helps.
post #13 of 129
Flater Bass!
post #14 of 129
Quote:
Originally Posted by Gene DellaSala View Post

I summarize associated gains/loses of multi subs when placed in common locations around the room but don't dig in as deep as Dr. Toole's excellent book. Chapter 13 of Dr. Toole's book IMO should be considered gospel on the subject matter.

One issue i have with the Harman approach to multiple subs is that they recommend mid wall placement. The Geddes approach to placement ought to be equally considered as it appears to give smoother results.
post #15 of 129
Quote:
One issue i have with the Harman approach to multiple subs is that they recommend mid wall placement. The Geddes approach to placement ought to be equally considered as it appears to give smoother results.

Assuming a standard rectangular room, midwall is fine if only done for 2 wall surfaces NOT 4 as I state in my article. I believe Harman no longer recommends 4 midwall b/c of severely reduced overall efficiency.

I have found 2 subs up front 1/4 length of front wall works very well if you can globally EQ them. JL Audio are champions of this approach.

I have also had good success with diagonal corners (again with global EQ).

For folks thatdon't have ideally rectangular rooms (myself included) experimentation is advised and global EQ recommended.
post #16 of 129
Quote:
Originally Posted by Gene DellaSala View Post

there are some misconceptions about the purpose of multiple subs in this article.

I highly recommend anyone really wanting to understand the true benefits and gains and sometimes losses when employing multiple subs to pick up a copy of "Sound Reproduction: Loudspeakers & Rooms" by Dr. Floyd Toole.

I also wrote an article on this topic and it was peer reviewed by Dr. Floyd Toole and Dr. Sean Olive of Harman. I summarize associated gains/loses of multi subs when placed in common locations around the room but don't dig in as deep as Dr. Toole's excellent book. Chapter 13 of Dr. Toole's book IMO should be considered gospel on the subject matter.

Here is a link to the article I wrote on this topic: Multiple Subwoofer Calibration & Setup Guide

I hope this helps.

Gene, I found this article extremely helpful. Thank you for publishing it. I am planning two subwoofers, one at the front of the room and one at the rear of the room. I will try diagonal corners.
post #17 of 129
For your average Joe, this formula suffices. I always tell my friends to think of getting a good subwoofer that effectively doubles the power of their current amplification.

So if your 5 channel receiver says it pumps out 100 watts RMS times 5, then look at getting a 500 watt subwoofer.

The benefits of adding 1 relatively powerful subwoofer to an average sound system is huge. It frees up the receiver from reproducing most bass, allowing the receiver wattage to be delegated more to the less power hungry mid and high frequencies.
post #18 of 129
Quote:
Originally Posted by WebEffect View Post
And what's that purpose? You mean to get more cash from consumers? There's no other purpose for two subs in a small or medium room.
You need to educate yourself a bit more before saying something like that. It's all about head room, i.e. flatter response and higher SPLs without clipping/distortion.
post #19 of 129
Quote:
Originally Posted by notnyt
Why bother pulling apart the formula when the entire thing is nonsense.
Why do you say that?
post #20 of 129
even if one sub is enough who wants to listen to just enough? the fun is having more than enough.
post #21 of 129
Quote:
Originally Posted by mjg100 View Post
I guess it depends on what you consider deep solid bass extension. I do not know of a single 10" sub (ported, sealed, band passed or horn loaded) that does what I would consider an adequate job for HT even in a small room. A single 10" sub is not going to provide much SPL at 20hz. A single 12" is not much better. Most commercial subs are around 88db sensitive. If the listening distance from the sub is 13' then you are losing an additional 6db. That puts your starting point at 82db, not even allowing for power compression or headroom. Reference level is 115db. That is 33db to make up or 11 doublings of power. So to get to reference level the sub amp would need to provide 2,048 watts of peak power and the driver is going to have to be able to convert that to clean sound pressure. Good luck with that.
Couldn't agree more! I've used lots of different kinds of subs in a quest to get at least 25hz. extension at my listening positon (mainly for music) and it simply isn't possible with a single sub - even one as impressive as the F113. I ended up with 4 subs scattered around the room in order to achieve my goal. I'm regularly amused by folks who say they get great bass, only to go and discover that they're only getting to 40 hz.
post #22 of 129
My room is 22x14x8 and I use 2 200 watt 12" subs in opposite corners along with 12" Cornwalls. I can't think anything less would suffice.

Edit. I typoed. Should be 15" Cornwalls.
post #23 of 129
My room is close to those dimensions, and one Epik 12, 300w continuous, 1500w peak, is more than enough. The Audyssey calibration sets sub out at 0 with the dial on the sub at half way, so there is plenty of head room.

The whole thing is really subjective, as it depends on how loud you like the movie to be. One of the reasons I got into HT was so I could watch movies at a lower volume than the earbleeding levels they like to use at the theater. I find the detail and sound quality is far superior at home.

If you like to listen at "reference" levels, and have ideal speaker placement options, I can totally see the dual sub appeal.
post #24 of 129
Quote:
Originally Posted by ca1ore View Post

Couldn't agree more! I've used lots of different kinds of subs in a quest to get at least 25hz. extension at my listening positon (mainly for music) and it simply isn't possible with a single sub - even one as impressive as the F113. I ended up with 4 subs scattered around the room in order to achieve my goal. I'm regularly amused by folks who say they get great bass, only to go and discover that they're only getting to 40 hz.


This I cannot let stand! Check out Epik, Hsu, MFW, SUB 25hz bass extension is totally possible with one sub. You just have to spend some serious $$$ to get it. I would take my Epik for $800 over two $400 subs any day of the week. I get down to 12hz, albeit just barely, and at 16-19hz it is STRONG.

I agree on one thing though, until you actually hear(feel) sub 40hz bass, you have no idea how immersive surround sound can be.
post #25 of 129
If your really want to be smart then use a design with a front pointing woofer. This allows for the best imaging. Then have two passive radiators on each side of the enclosure. This distributes the bass and couples it to the room better. Also, since the forces are 180 degrees out of phase the tremendous pressure on the enclosure is canceled. Then equalize it for extended deep bass response.
Then make the woofer speaker NOT round (say 6*9) so the box can be quite narrow in the front. This too improves the sound quality as large footprint speakers always degrade imaging and the soundstage. Now there is only a need for one separate, sealed subwoofer. What speaker has such an intelligent design and is priced inexpensively?
post #26 of 129
Quote:
Originally Posted by Gaborik View Post

This I cannot let stand! Check out Epik, Hsu, MFW, SUB 25hz bass extension is totally possible with one sub. You just have to spend some serious $$$ to get it. I would take my Epik for $800 over two $400 subs any day of the week. I get down to 12hz, albeit just barely, and at 16-19hz it is STRONG.

I think this is a area where we must 'agree to disagree'. I've played with far better subs that you cite and, frankly, they simply don't cut the mustard much below 30hz. at any sort of useful output. It took four very good subs for me to get balanced output down to 25hz. at my lsitening position and I have never heard a home-based system that performs as well (and I've heard a lot of home systems).

Further, much below 25 hz. is not heard so much as felt, so how are you judging that your sub produces 16-19 hz.? Are you are judging that based on how much the driver flaps back and forth?
post #27 of 129
Quote:
Originally Posted by HiFiFun View Post

If your really want to be smart then use a design with a front pointing woofer. This allows for the best imaging. Then have two passive radiators on each side of the enclosure. This distributes the bass and couples it to the room better. Also, since the forces are 180 degrees out of phase the tremendous pressure on the enclosure is canceled. Then equalize it for extended deep bass response.
Then make the woofer speaker NOT round (say 6*9) so the box can be quite narrow in the front. This too improves the sound quality as large footprint speakers always degrade imaging and the soundstage. Now there is only a need for one separate, sealed subwoofer. What speaker has such an intelligent design and is priced inexpensively?

Hmmn, not sure where to start. I pretty much disagree with everything you said, beginning with the notion that an important criteria for a subwoofer is 'imaging'.
post #28 of 129
Quote:
Originally Posted by ca1ore View Post

Hmmn, not sure where to start. I pretty much disagree with everything you said, beginning with the notion that an important criteria for a subwoofer is 'imaging'.

If the floor of the room is raised & hollow (to improve subsonic tactile 'feel'), then it's been my experience that there is what I call "tactile imaging". You may not be able to "hear" the direction the bass is coming from, but you can FEEL where it's coming from. And in a movie experience, if I 'feel' vibration coming from a direction other than indicated visually, it tend to take me out of the movie. My home theater has a sub in the front/right corner and I wish I could find a used 'slave' sub to match up with my CSW PSW1 to go on the left side of the room.
post #29 of 129
Quote:
Originally Posted by WebEffect View Post

And what's that purpose? You mean to get more cash from consumers? There's no other purpose for two subs in a small or medium room.

Might want to read up on who Dennis is. I would think that him being an acoustical architect would give you a hint that he might know what he is talking about. Getting deep flat even room response is not possible using a single sub if you have more than one seat in our HT.
post #30 of 129
It is much easier to get a flatter response curve at multiple points in the room with multiple subs, carefully placed.

When I used a single sub (an eD A7-600 with dual 12" drivers - is that still a single sub?) I could get measured in-room extension to 20Hz and below, but the measured response curve was far from flat and varies from seat to seat to seat. One can equalize to help somewhat, but even then you're fighting a battle of averages, and the result will always be a compromise.

I use three subs now, which (when carefully placed) significantly reduced the peaks and valleys in my frequency response curve, and showed much less variation when measuring at different listening points in the room. From there, I still use a Behringer DSP in a dual-channel configuration to further tame that response. The resulting curve is VERY close to flat, and much more uniform when measured across different seats.

One single sub (even if it's the world's greatest sub) may very well get you both the volume and the low Hz you require, but it won't get a flat response, and it will vary at different points in your room, even after you equalize.
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