Changing the Tonal
Balance
Over the years, many audio purists have held the belief
that tone controls are the work of the devil and should never be set at anything but their
neutral positions. After all, the reasoning goes, if flat frequency response is the
ultimate audio virtue, why use a device that deliberately unflattens it?
The attitude has always been particularly strong amongst
British audiophiles, and many of the amps and preamps designed there omit tone controls
altogether. Most equipment includes them, however, and they do indeed have a number of
useful purposes.
For one thing, flat frequency response is only a reality up
to the speaker terminals of an audio amplifier. Once you get into the realm of speakers --
the devices that actually reproduce the music -- you find frequency response curves that
look like the Himalayas. Of course, speaker designers do what they can to tame these
curves, sometimes very successfully, but the combination of physical factors and tiny bits
of interference and such conspire to make speaker response curves quite jagged even in the
best of cases.
Then, when the sound is emitted into a listening room, all
sorts of dramatic things happen as it bounces off walls and excites resonances. What
arrives at your stereo seat is anything but flat, although it's often very pleasant.
Choosing a pair of speakers is a difficult task at the best
of times, and we do it without really knowing how they will sound when we get them home.
If they sound awful, and if experimenting with positioning doesn't help, other speakers
should be chosen. But if the problems are small, often they can be cured simply by a small
tweak of the tone controls. If they're a bit boomy, pulling them away from the walls a bit
and rolling off the bass control may well make the difference between dubious and perfect.
Most built-in tone controls are fairly coarse, to be sure,
with a broad range of frequencies over which they operate and often a rather limited range
of boost or cut, so they can only really be used for macro rather than micro corrections.
The upscale cousin of the tone control is the equalizer,
which offers adjustment for anywhere from five to 30 chunks of the audio spectrum rather
than two or three. In the right hands, an equalizer can be used to compensate not only for
mild speaker-vs.-room problems, but also for spectral irregularities within the speakers
themselves. But beware: if a speaker really needs that sort of fine-tuning, it's probably
not a very good speaker in the first place.
Also, except maybe for pros, practically everyone who gets
their hands on an equalizer overdoes it. That pounding bass and zingy treble usually means
that the fi is significantly lower than what you started with.
Where both tone controls and equalizers can provide some
benefit, if used with a light touch, is in undoing the aggressive equalization built into
some recordings (especially older CD transfers of music originally recorded for LP).
Problems here are often overbrightness (to add impact on cheaper systems) or lack of bass
(to fit more on an LP). If these are subtle enough, a little tone adjustment may make
something that was painful, listenable.
One specialty sort of tone adjustment that few people
really understand is the "loudness contour" switch on many receivers and
amplifiers. Our ability to hear bass is less as the overall level of a sound drops, so
unless we crank our stereos to symphonic levels, the sound may be a bit thin. The loudness
control boosts bass at low levels to overcome this.
Trouble is, the maker of your receiver has no idea what
level you are listening at, as that has to do with the original recording level, the
sensitivity of your speakers, the size of your room, and a host of other factors. As a
result, an "average" value is chosen that may or may not come anywhere close to
your conditions.
One exception comes on some older components, which offer a
sliding control. This consists of a pair of volume controls, for overall level and for
loudness. To operate it, you turn the loudness control all the way clockwise (its flat
position) and set the volume control for a comfortably loud listening level, the sort you
use when auditioning a favorite piece by yourself. Then, when you want to listen at lower
levels, you reduce the volume using the loudness control, which not only turns things
down, but gradually applies the bass correction as it does so. The lower you go, the
greater the boost.
It's the only sensible approach. Every other loudness
switch is really just a bass gooser.
...Ian G. Masters
ian@mastersonaudio.com
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