Astounding
misconceptions abound on this subject. A flat, or even frequency
response is the reference standard to which all electronics
are designed, and to which recording studio monitor speakers
and (to a lesser extent) room acoustics are designed, albeit
sometimes with varying success.
We don't tolerate even one
decibel of variation from a perfectly flat frequency response
for CD players and amplifiers, so why should we for loudspeakers?
DEQX Calibrated™ means by definition that the anechoic
(native) behavior of the speaker is flat at least through
the upper bass to 20 kHz. In the lower octaves the placement
in the room has an extraordinary effect on bass response.
This means that room correction and/or careful placement
of the speaker can vary bass response considerably, making
the anechoic (native) accuracy of the speaker's low bass
less vital provided that room effects can be dealt with.
Therefore,
it is not a question of 'does flat sound better or worse?'
in a context where there is no other standard to choose
from. It is simply a fact that flat is the only standard
by which all music production is mixed and monitored, subject
only to room dispersion effects and intended shelving for
film mixes due to cinema sound requirements.
Production mixing
requires monitors that have frequency response accuracy
to within two or three decibels (plus/minus 1.5dB), which
is almost impossible to achieve with passive speakers. Active
speakers are usually required to achieve this, whereby
each driver has its own amplifier and the analogue active
crossover works at line level.
Active analogue speakers allow
higher order crossovers of typically 24dB/octave and compensation
filtering with less phase corruption than passive speakers
allow. The monitoring room itself is usually the subject
of expensive acoustic treatment whose goal is to provide
a reasonably flat overall response, although measurements
from the listening position will tend to show slight attenuation
at the highest octave/s and possibly slight boost in the
lowest octave/s. This response is a result of the room
and speaker placement - the flat response refers to the speaker
itself, whilst the high-end rolloff and slight bass boost
refers to the speaker coupled into the room. Considering
the two responses separately allows the tightest control
over the resulting overall frequency response.
The reason
that 'flat' has not always been recognized as 'right' is
that many productions are not monitored using accurate
monitoring and the user is forced to equalize to compensate.
Flat
- but what about phase errors.
Another misunderstood effect
that may lead one to say that flat is not good, is where
analogue filters, active or passive, are used to make a
speaker's frequency response more flat. The problem is that
analogue filters, particularly passive (inside the speaker
as part of the crossover) can cause significant phase errors
that extract the 'life' from the sound. In many cases a flat
frequency response, if at the expense of phase linearity,
may provide inferior sound. Since hi-fi reviewers often,
and correctly, use measured frequency-response as a guide
to accuracy, it is also true that this is far from the whole
story.
Note that DEQX Calibrated™ not only corrects
frequency response without introducing more phase errors,
but can also correct existing phase errors.
Flat - but what
about time alignment.
Another problem with analogue crossovers,
whether passive or active, that may have led to the 'flat
is not ideal' syndrome is that drivers must be mechanically
time aligned. For manufacturers this is often too expensive
to implement because the tweeter's diaphragm would typically
need to be recessed to be level with the woofers centre
dome, where the woofers high-end must cross over to the tweeter.
Unless this is done mechanically, the woofer's impulse
response will lag behind the tweeter, causing significant
comb filtering in, at least, the one octave wide crossover
region. The fix is sometimes to drop that region's frequency
response by several dB and suggest that the marketing department
proclaim that 'flat is bad'. Even active speakers using line-level
analogue crossovers cannot solve this problem (although
their higher order slopes will limit the crossover distortion
to a narrower frequency spectrum of perhaps one octave wide
instead of two octaves wide). Note that the DEQX PDC-2.6's
digital crossovers provide automatic and precise time alignment,
regardless of mechanical placement of drivers.
Flat - but
what about room effects.
This is the area where it can be
argued that flat is not necessarily best, but even here
we need to remember that 'flat' or 'sort of flat' is the
only reference that the professional engineer and artists
can work towards. For film cinema soundtrack there are variants
of flat that are adhered to in order to compensate for
screen effects and distances to the average listener. For
this reason, although native behavior of speakers is essentially
made flat so that phase behavior through the mid and high
frequencies is accurate, DEQX Calibrated™ processors do allow
user preferences for a variety of room equalizations that
can be chosen as required.
What cannot be argued is the effect
that speaker placement and the room effects have on the overall
sound. Some might point to the fact that when installed in
a room, the frequency response at the listening position
is much worse than the speaker's own native behavior especially
at lower frequencies, and they might ask "What's the
problem with plus and minus 3dB response at the speaker itself,
especially if room correction can be used to compensate?"
The
answer is that speaker correction, not room correction,
must be used to correct the mid to high frequency range so
that phase, as well as frequency response, can be corrected.
A room measurement (taken from the listening position) is
unable to provide the required resolution. Although room
correction may also correct frequency response of mid to
high frequencies in the room, it is usually better to rely
on the native speaker accuracy (provided by DEQX Calibrated™)
in this range and implement relatively simple room dampening
on walls and/or floors. This is often relatively easy to
do if the room is overly live, for example, by introducing
bookshelves or hanging curtains or rugs on side walls.
In
the bass frequencies however, the considerable interaction
between speaker position and room acoustics is harder to
handle without relatively complex acoustic design leading
to potentially expensive building works. Fortunately, using
DEQX Room Correction, this should be unnecessary.
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