Nousaine wrote:

There's no 60 Hz cancellation at 3-feet.

Tom....

Lets pretend were in an open field
There is a woofer in a box thats playing a 60Hz tone and its about 5 ft from us.
There is another woofer 9 ft beyond the first woofer that we can turn on and off
the second woofer plays the exact tone from the same amp as the first woofer.

Now when we turn the second woofer on, so it plays along with
the first woofer are we going to hear MORE 60Hz sound or less sound???


?????????????????????????????????????????????????? ?????

Come on Tom..
This example makes it easy....

The second wave travels 9ft before it gets to the first wave now
both waves are coming at you together!

At 60hz this will put the two waves aprox 180degrees out of
phase with each other....

So the resulting sound to your listening position is reduced with
the second speaker playing....

Im sure your with me so far TOM....

------------------------------------ NOW!

The sound from the first woofer goes in all directions, so it not only
comes at you it goes in all directions. it did in the first example but
because we were in an open field the sound just went off and was
eventually lost, with the exception of the sound that came directly to us.

Lets loose the second speaker and instead build a wall at 1/2 the distance
about 4.5 ft behind the first woofer....

Some sound that goes out of the first woofer comes to us
and some hits the wall and bounces to us....

That *bounced sound* has traveled the same 9 ft (to the wall (4.5
and back (another 4.5)) and will be just like the sound from the
second woofer thats not there anymore.... ;-)

Now are you getting it Tom??

The bounced wave, is 180 degrees out of phase with the first wave
so the sound WITH THE WALL will be less sound that WITHOUT
THE WALL....

This is (even though you dont believe me) a standing wave.!


I dont know how you can miss this Tom...
Maybe you want to ignore it or something because you dont want
to appear to be WRONG in all your previous statements....

BTW, the wall would have to be further away at lower frrequencies
and closer for higher frquencies.....

About 14ft at 20Hz
about 2 ft at 120 Hz

SO the range of my sweeps cover standing wave cancelation
from 2ft and longer.. ;-)

Get it now TOM??

Eddie Runner
http://www.installer.com/tech/