Pat wrote:
On Sat, 30 Nov 2013 07:00:29 +1100, "Phil Allison"
wrote:


Phasing similar speakers is all about making the low frequency output from
each *reinforce* the others rather than cancel.

Compared to the wavelengths of low frequency sound, woofers are a point (
hence omnidirectional ) source of sound pressure - so it is irrelevant
which way the cone faces.


... Phil


Hi Phil,
I was away for a while, so this thread is new to me today. Your
comments above make sense, but bring up a question I have had for many
years. I own a pair of ESS AMT Monitor speakers that I purchased new
back in the 80's. Each has a pair of 12" woofers - one active (ie, a
normal speaker) and the other passive. I would think that when the
active one is compressing the air in the cabinet, the passive one
would be pushed out thereby appearing to be out of phase to a
listener. That doesn't appear to be the case because these speaker
have a great low end sound. Can you explain why they work? (I am
just picking you because you seem to know something about the subject,
but others are welcome to explain my misunderstanding as well.)

Thanks,
Pat

I heard the ess once, in a Vegas disco, of all places. Just a fill in
speaker.

On a port or passive, most of the output is from the port or passive, so
they don't cancel. This is around th tuned frequency. Woofer movement
becomes minimal. If you drove it with an oscillator you could probably find
this out.

Greg