Ashly Electronic Amplifier none - Manual (Page 22)

that low frequency amps can be overdriven without affecting the sound of the
high frequency drivers. Low frequency information requires significantly more
power from a system than high-frequency audio, and typically it is this low
frequency audio that drives a system into distortion. If only one amp is
powering a system, as in a passive or full-range setup, then important
midrange and high frequency audio will be distorted every time a deep bass
note overloads the amplifier. In a multi-amplified system, a low-frequency
amp can overload without affecting higher frequency audio in any way. But
that's
not all. Fortunately, our hearing is less sensitive to distortion of
low frequencies than midrange. Large multi-amped systems are frequently
operated with what would be considered "unthinkable" levels of distortion in
the lower bass region, and yet the system may sound very clean and loud to
even a knowledgeable listener.
Some problems remain. The initial cost and complexity of a multi-amplified
system are usually greater than passive systems, but it can be reasonably
argued that the investment pays for itself in better sound per dollar.
FILTERS
Whether your crossover is a passive, high-level type, or an active, low-level
type,
it employs filters to accomplish its dividing job. Therefore, a quick
look at the nature of filters seems relevant to an understanding of your
crossover.
A filter is a frequency-selective electrical network which is designed to pass
a
certain range of frequencies while rejecting other frequencies. All
crossovers are made with filters, but not all filters are identical. Filters
may have a variety of characteristics and these are chosen to suit a
particular audio requirement. The most common types of filters used in
crossovers are low-pass, band-pass, and high-pass filters, supplying low-
frequency, midrange, and high-frequency outputs respectively. A low-pass
filter, as the name implies, passes low frequencies, up to a certain maximum
frequency.
Above this cutoff frequency, the signal will be attenuated
(rejected) to some degree. A bandpass filter will pass a certain median band
of frequencies while attenuating any frequencies above or below those desired.
A high-pass filter performs the opposite function of the low-pass, passing all
frequencies above a certain cutoff frequency while attenuating those below.
These
basic filter characteristics are usually shown in graph form as
frequency vs. amplitude, as in figure 22 below.
Figure 22 Basic filter characteristics
21