Unlike
a typical consumer speaker's passive crossover, the analogue
crossover in an active speaker runs at Preamp line level,
and so does not have to handle the high power from the power
amp. This gives the active speaker's crossover more flexibility
to compensate for frequency-response errors, as well as offering
higher order filters (typically to 24dB/octave) with fewer
side effects such as phase distortion. Importantly, it takes
a load away from the amplifiers, because although more amplifiers
are required (usually one for each driver), each amp needs
to only operate ideally over four or five octaves instead
of ten to twelve. This is why active speakers are virtually
essential for professional sound and are also chosen by many
home audio users despite their utilitarian looks.
Lower
Distortion
DEQX's
digital crossovers with individual driver anechoic
correction take the advantages of active speakers to their
logical conclusion; providing very high order digital filters
typically from 48dB/octave to 300dB/octave (instead
of 12dB/octave to 24dB/octave achievable using either passive
or active analogue crossovers.) Importantly, DEQX's
digital crossovers automatically phase and time align themselves
to the enclosure design, whereas analogue active
crossovers do not compensate for time alignment errors.
DEQX's
precisely phase and time aligned high-order filters,
combined with an absence of electronic or filter related
phase distortion, virtually eliminate the effects of crossover
distortion and comb-filtering.
Power Handling
Power
handing is a critical issue in speaker design. It is
desirable that a speaker can create a peak volume without
noticeable distortion in the order of 110 dB SPL, and we
suggest that more is preferable for an effortless presentation
even at moderate listening levels.
Power
handing in speaker drivers is often limited in passive
speakers, which are inherently forced to use low-order
crossover filters, which themselves are sources of
power loss. When the crossover from a 6" woofer to a 1" tweeter
occurs at say 3kHz, and a 12dB/octave passive filter
is used, then at 1.5kHz (one octave below 3kHz), there
is still considerable power being sent to the tweeter,
which becomes increasingly distorted as that power increases.
Using
a DEQX crossover of 100dB/octave, for example, in the
same speaker cabinet described above, the power to the
tweeter at 1,500Hz is virtually zero, and the -12dB point
is only about one semitone below the 3kHz crossover frequency.
This means that the tweeter can handle more power with
less distortion, and/or, the crossover frequency can
be dropped to gain more purity in the critical high-midrange
area, where the woofer is struggling to stay clean
and disperse. A similar improvement can be gained in the
crossover from the woofer to sub-woofer or mid-range driver
to bass woofer. In all cases, distortion can be minimized
at higher volume.
Dispersion
The
effect noted above is also the reason that passive
speakers tend to 'beam' high frequencies at the listening
position in the 2kHz to 6kHz region. Beaming occurs to
any speaker driver for frequencies it produces above its
comfort zone. In the case of a 6" woofer, beaming becomes
significant in the 3kHz region whereas a 1" tweeter is
virtually omni-directional at that frequency but starts
to beam above about 10kHz. (As an aside, this may be why
super tweeters can give the impression of high frequency
'air'. They have wide dispersion in the 10kHz to 20kHz
region where the 1" tweeter, despite
its flat on-axis frequency response to 20KHz,
has fallen away off axis. This means that the high
octave (10kHz to 20kHz) is not being supported by the
room, which the supertweeter can help resolve).
In
a typical 6" woofer
with 1" tweeter two-way configuration for example, it is
immediately apparent when using DEQX's PDC-2.6 high-order
crossovers that dispersion dramatically improves off axis
in the vital mid-range crossover region, with beaming from
the woofer becoming virtually inaudible.
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