Dayton Audio BR-1 6-1 - Manual (Page 6)

Most loudspeakers including the BR-1 use drivers mounted on a flat baffle. One problem encountered here is the fact
that the tweeter’s relative acoustic center is set ahead of the woofer’s relative acoustic center. In general, a flush
mounted tweeter’s acoustic center is aligned with the front baffle. A typical 6.5” woofer’s relative acoustic center is
set about 1-1/2” behind the tweeter. This means that when fed a signal at the crossover frequency, the woofer’s
output will be delayed 110uS relative to the tweeter. For successful filter summation, this must be dealt with.
The method used to compensate for this delay in the BR-1 is the use of asymmetrical filters. Normally one would
use the same crossover topology for both high pass and low pass filters. A 3
rd order high pass acoustic slope is
used with a 2 nd order low pass acoustic slope to allow for the time delay. This technique takes advantage of the
phase delay differences between the two filter types and results in a flat summation and allows both drivers to be
acoustically in-phase with one another at the crossover frequency.
The crossover filters were designed to achieve a flat overall response. The BR-1 measures on axis within +/- 2.0dB
from 100 Hz -12 KHz. Flat frequency response is desirable so that all frequencies are reproduced with the same
loudness over the loudspeaker’s bandwidth. In itself, flat frequency response does not ensure a good sounding
loudspeaker. But targeting flat on axis performance is the first step in designing a high performance loudspeaker.
Another, arguably more important goal is flat off axis frequency response. Many times a speaker can measure flat on
axis, but the off axis curves suffer from dips in the response. This is due to insufficient driver overlap, usually
caused by using too high of a crossover point for the low frequency driver. Good off axis performance will avoid the
so-called Venetian blind effect. What is the Venetian blind effect? When the seated listener moves horizontally from
directly in front of the speaker, the treble or high frequency response drops off dramatically. A loudspeaker which
exhibits good off axis response can be listened to well away from directly in front of the speakers and excellent
performance will still be enjoyed.
Note that even 60 degrees off axis, the woofer is producing a reasonably flat response without deep nulls or
cancellations throughout the crossover region.
Page 6
On/Off Axis Response of BR-1 System