Why do most subwoofers work best in a corner?

[Loren Booda]

Besides reinforcing bass, doesn't placing a subwoofer in a corner disperse resonances more effectively throughout the room? If so, how?

 

[planish]

I don't really understand everything that goes on, but the bass reinforcement thing is called the "Klipschorn Effect" or "Klipschorn Principle", after Paul Klipsch.

From http://www.arcticcorsair.f9.co.uk/audio/terminology.html#K

Book shelf speakers seldom have efficiency above one percent. For the Klipschorn (an invention of Paul Klipsch), it's something about 30%. The horn-loading makes it far more efficient, but the speakers really have to be big. The Klipschorn principle uses the walls of the room as effective extensions of the speaker itself. This effect applies only to sub-woofer frequencies.

Low frequency audio does not suffer from multi-path interference as much as mid and high frequencies do, because the wavelength is relatively long compared to the distance to the wall surfaces.

Sorry I couldn't offer more info, but that might get you started.

 

[Loren Booda]

planish,

At least you have something to woof about! It is sometimes hard to find a room whose symmetry will accommodate Klipschorn speakers.

 

[planish]

That's the beauty of the thing. You don't need Klipschorn speakers to take advantage of the effect. An inexpensive bookshelf speaker placed in a corner will have improved bass. Or (better yet) a single sub-woofer of any design, placed in a corner.

 

[Nolen Ryba]

Whoa there...the instance of the Klipsch horn is different because it is a horn.

More generally, placing a standard monopole subwoofer in the corner as opposed to out in the room results in an increase in output for a couple reasons:

- when you place the subwoofer in the corner, you are dissipating the same power over a smaller area- notice a spherically diverging wave at a given distance in the corner has 1/8 of the surface area of one in freespace because you are radiating into 1/8 of the sphere
- the radiation impedance is higher in the corner thus increasing efficiency
- when placed in the corner, the subwoofer excites all modes in the room just as if you pluck a string at the very end, but in 3 dimensions

One thing to keep in mind is that although this does provide more output, because you are exciting all modes the frequency response will vary wildly throughout the room. If you are only concerned with sheer output, this may not be a problem, but if you want the sound to be consistent over a multi-person listening area, it probably will be. In that case other options may be more suitable.

If this has not been clear, please let me know and I will clarify. Perhaps you should check out this website http://www.kettering.edu/~drussell/demos.html to see some animations and get a feel for what I mean by "modes".