dipole affect on apparent sealed cab size

toobhed

Member
2010-06-04 1:36 am
...probably a silly question to those who understand but....
I'm looking at a cheap 3" 4ohm FR driver that calls for a 2 liter sealed cab...fair enough. But what if I were to wire a second driver on the rear facing cabinet panel in series and out of phase wrt the front driver in dipole fashion?

I understand the amp would see an 8 ohm load, but do my drivers basically see no cabinet "seal" since one is pushing when the other is pulling? Does this not work as the driver(s) may no longer "see" a 2 liter sealed cab? Thanks for your indulgence.

Mario
 
If there was no baffle between the two boxes, ...
I believe that's what Mario is talking about.
... the drivers will act as if they are in free air.
This is true, but only up to a frequency, where the wavelength becomes less than half the distance between the front and rear panel. Above that frequency resonances will build up between those panels.
 

toobhed

Member
2010-06-04 1:36 am
Thanks for your thoughts and let me clarify:

The situation that prompted my post yesterday: I'll be using a cheap small cabinet and 3 or 4 cheap 8 ohm drivers for a fun experiment. The cabinet, (5.6 liters knock-down) and its small front baffle will barely fit a line array of three drivers whose recommended cabinet volume is 2 liters each and sealed.

I'll try three different wiring/driver combinations to discover which sounds best, or least worst as the case may be.

Alternative 1): Use three drivers. Wire 2 of the 3 in series. Parallel the series to the 3rd driver which has a resistor to bring it up to a 16 ohm load. As a result, the amp will see an 8 ohm load.

Alternative 2): Instead of using a resistor with the third driver, add a fourth driver on the rear baffle (in phase with the front three), wired in series with the 3rd. Then parallel the two series so the amp will again see an 8 ohm load.

Alterative 3): Same as the second alternative but wire the forth, rear driver out of phase wrt to the front three for quasi dipole. This alternative was hatched as a "guess-solution" to the fundamental problem of alternative 2....cabinet volume that is too small for 4 drivers.

I hope to discover whether adding a forth driver out-of-phase mitigates the need for greater cabinet volume that may otherwise be required for adding a forth driver.

Describing the experiment in written English seems harder than actually executing it. I need a drink now :)