Why would you want 2 subwoofers in your setup?

[strammer]

I saw a 5k surround system recommendation. In it they were proposing 2 SVS 1000W subwoofers @ $1600 total.

My question is why would you need 2 subwoofers? Especially for about 1/3 of the total budget.

 

[afterlife2]

It mainly depends on your room size. If you have a small room it really is not needed.

 

[markw]

It's kind of like having two women simultaneously. It may sound like a lot to handle but don't knock it until you've tried it.

 

[walter duque]

I"ll be picking up my rear subs soon. I have a 12x12 room and there is nothing like having 4 subs. Once you get that taste of 4, there is no going back. Retail on my 7 speakers is 35k and retail on my front subs is 10.5k, rear subs are 5k (and these are passive subs-no amps included) so that ratio is just about right.

 

[Cos]

Wow 4 subs in a 12x12 room I assume you have solid sound treatments

 

[herbu]

My question is why would you need 2 subwoofers?

My room is odd shaped, with lots of corners, part with a cathedral ceiling and a bridge, and part w/ plain 9' ceiling. When I had 1 sub, no matter where I put it, the sub volume was different from chair to chair. You could hear a significant difference in bass volume, even between our 2 main chairs just 6' apart.

Think of a small pond with several stumps, boulders, and an irregular shoreline. The ripples from a stone dropped in the water bounce off the stumps & boulders, and off points on the shoreline at different times. So you have primary ripples and reflected ripples.

In some places the ripples have opposing directions and tend to cancel each other out. In other places the ripples move in the same direction and tend to amplify themselves. So different points in the pond see different intensities of ripples.

It is the same with sound waves in your room. 2 subs in different locations can even out the bass ripples, so people sitting in different chairs hear a similar intensity of sound.

Plus, 2 subs make it easier to rattle the windows, shake the floor, and thump you in the chest. Who doesn't want that?

 

[walter duque]

Wow 4 subs in a 12x12 room I assume you have solid sound treatments

None

 

[Dr. Bob]

I've wondered about this, too. It seems to me that having two subs would make interference more of a problem rather than less. Two point sources will create an interference pattern:

That means you'll have dead areas (the gray bands) where the sound cancels out, rather than adding.

Of course, reflections from the walls can create interference, too, but reflections will generally be at lower amplitude than the direct sound, so the interference will be less.

 

[Swerd]

It is the same with sound waves in your room. 2 subs in different locations can even out the bass ripples, so people sitting in different chairs hear a similar intensity of sound.

Good explanation.

I've wondered about this, too. It seems to me that having two subs would make interference more of a problem rather than less. Two point sources will create an interference pattern.

Of course, reflections from the walls can create interference, too, but reflections will generally be at lower amplitude than the direct sound, so the interference will be less.

For long wavelength signals that sub woofers produce, the reflections from ceiling, floor, and walls do significantly interfere with sound waves from the original source. Above frequencies of about 200-300 Hz, the sound wavelengths become short enough so that in rooms that most homes have, this becomes much less of a problem. See Wikipedia, Room Acoustics http://en.wikipedia.org/wiki/Room_acoustics and look for Schroeder frequency. Also here http://en.wikipedia.org/wiki/Manfred_R._Schroeder

Depending on sub woofer and listener locations (movable within limits), as well as room boundary locations (not movable), this can result in standing waves at certain frequencies that are loud enough to dominate (so called one-note bass), or standing cancellation points (nulls points) that cause a noticeable loss of bass.

With two sub woofers, you are free to move them individually until standing waves and standing null points are minimized. There is no need to place them symmetrically as shown in the diagram you posted.

 

[AcuDefTechGuy]

In my experience, if you have just one subwoofer on left front corner, then your left side of the room will have more bass than the right side of the room.

If you have one subwoofer in the Middle/Center of the front wall or rear wall, then the bass is more balanced. But the problem is, most people can't accommodate this.

So having 1 subwoofer on each of the front corners balances out the bass more.

Now, I think having 2 opposing subwoofers in the middle of opposing walls is best.

 

[shadyJ]

I think Swerd has given the best explanation of why multiple subs. For a deeper explanation, look at this white paper.

 

[Swerd]

I think Swerd has given the best explanation of why multiple subs. For a deeper explanation, look at this white paper.

Thanks shadyJ, that's great! If nothing else, it shows in detail how complex a problem bass response can be in normal sized rooms in our homes. And it shows why we use words like "optimize" or "minimize" instead of saying "flat frequency response" below ~250 Hz.

I loved slides 36-38, and I wonder who will actually ask himself this: "Hey, wait just a minute. If I have 5,000 12" woofers randomly located in the room, where will I sit?" Or, "how many power strips can I use in my room?" .

 

[markw]

Wow 4 subs in a 12x12 room I assume you have solid sound treatments

Well, these are Walters neighbors wanting to discuss the situation with him.