DEQX User Manual
Each speaker in Figure 4 has an internal crossover network consisting of passive
components – inductors (coils), capacitors, and resistors. This passive network divides
the frequency range into high frequencies for the tweeter and low frequencies for the
woofer. The transition between the two drivers is gradual, with a slope ranging from
very shallow to moderate. The passive network typically also does some response
shaping to compensate for the natural response of the drivers and the acoustic effect of
the speaker cabinet.
By removing the passive crossover network and instead using a DEQX to divide the
frequency range “in front of” the amplifiers, an active speaker is realized, as illustrated
in Figure 5 on the next page. Each amplifier is thus required to deliver only a portion of
the full frequency range. The passive crossover is no longer present
, removing any
possibility of non-linearities in the passive components and giving the amplifiers direct
control over each individual driver. The DEQX adjusts the response of each driver in
minute detail, reducing group delay and amplitude errors dramatically and providing
accurate acoustic transitions between the drivers with steep linear phase filter slopes.
13.1.1 Active speaker design considerations
There are many design considerations when implementing an active speaker: raw driver
response (both on-axis and off-axis), driver sensitivity, baffle size and shape, power
handling versus frequency vs crossover slope, and so on. With a DEQX at hand, the
designer may make different choices than when designing a passive speaker.
The bi-amp and tri-amp modes should therefore be considered advanced modes of
operation. The following paragraphs discuss specific considerations when using a DEQX
to implement an active speaker:
1. As indicated in Figure 5 and Figure 6, a protection capacitor (a high voltage film
capacitor) in series with the tweeter is generally recommended. This will help
protect it from DC offsets and turn-on and turn-off transients. If there is any
question that the amplifier and upstream equipment is not perfectly behaved or
that the tweeter is fragile, the capacitor is strongly recommended.
Unlike other systems, the DEQX will compensate for the roll off and phase shift
introduced by the capacitor. The capacitor therefore does not have to be large (a
common rule of thumb is to size it so that its roll off starts two octaves below the
crossover frequency), but sized to roll off at the anticipated crossover frequency.
Since it is relatively small in size, a very high quality capacitor can be used.
2. The analog gains post-DEQX should be reasonably well matched. If there are
significant discrepancies in amplifier gain and driver sensitivity (greater than 5 dB),
it is recommended that you adjust output analog gain as described in Appendix D.
With the exception of a protection capacitor on the tweeter. See the section “Active speaker
design considerations.”
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