Specifications

(4) Polarity (Phase)

The optimum polarity for the APL-10, -12, or -SB subwoofer is a function of

its placement in relation to the full-range speaker(s) it is augmenting.This is

known as the phase relationship of the two systems although absolute phase

also plays a role in the equation, as we’ll see later.

If the APL-10, -12, or -SB are directly under or over the full-range speaker(s),

in nearly all cases the polarity should be normal; that is, the same as the full-

range speaker. (NOTE: A positive signal applied to pin 2 of the XLR input

connector will result in a positive wavefront appearing at the front of the

APL-10, -12, or -SB if the Phase Reverse Switch is set in the normal position).

As long as the full-range speaker system exhibits a like response (i.e., pro-

duces a positive wavefront when excited with a positive signal on pin 2 of its

amplifier’s input), both systems will be in-phase with each other. Often,

depending on the characteristics of full-range speaker(s), when both systems

are in-phase with each other, a low frequency peak will occur in the region

where the two systems overlap.This is normal and can be dealt with by one

of the following:

(a) The low frequency peak in the overlap region can be filtered out with an

equalizer. (NOTE: Usually equalizing only the full-range system is sufficient.To

this end,Apogee’s powered full-range speakers are equipped with a 100 Hz

high-pass switch, making it easy to adapt them for use with subwoofers.)

However, in some situations (such as when a large number of subwoofers

and full-range speakers are deployed), it may be necessary to equalize both

the full-range system and the subwoofer system to achieve a perfectly flat

response through the overlap region.

(b) The full-range speaker system can be driven from the APL-10, -12, or

-SB’s high-pass output. This output effectively attenuates the energy to the

full-range speaker system in the overlap region, eliminating the low-frequen-

cy build-up. It behaves in a like manner to the 100 Hz high-pass switch sup-

plied on Apogee’s full-range powered loudspeakers.

system.This will cause a deep cancellation through the overlap region and is

not recommended. It may sound better than the low-frequency accentuation

generated by the overlap, but it can (and will) adversely affect the system’s

impulse and phase response, as well as causing the drivers to work harder

for less output (because of the cancellations taking place). It is far better

practice to properly equalize the system than to take a shortcut by using can-

cellation to shape the frequency response of the system.

If an APL-10, -12, or -SB is NOT located directly over or under the full-range

system, but rather some distance away from it, the proper phase relationship

will need to be determined.This is also true if the APL-10, -12, or -SB is off-

set in depth, such as in front of, or behind, the full-range system.