On Fri, 6 Dec 2013 09:16:21 +1100, "Phil Allison"
wrote:


"Pat"
"Phil Allison"


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.


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.)


** Using a "passive radiator" is just a variation of the ported enclosure -
it allows a small box to be tuned to a lower frequency and with a larger
radiating surface area than is possible with a conventional port.

Drawbacks are increased cost and non-linearity in the radiator's suspension.

The radiator and the driven cone operate essentially in phase over the
octave above radiator resonance.


.... Phil






ESS also had a version where the passive radiator was on the rear. (I
think it was AMT 1's vs. my AMT Monitors). I had previously wondered
how the rear facing passive in the AMT 1 and the front facing passive
in the ATM Monitors both could work well. Now, I think I understand.

Thanks,
Pat