Audio Engineering

Loudspeaker Enclosures 717

also absent in active powered enclosures and is the rather the reverse—1 integrated active
cabs are “ plug in and go ” systems. For everyone else, more care is needed when connecting
up an active system, taking care that the drive units are going to be fed their appropriate
band. In professional systems, multipin speaker and line connectors are commonly used so
that the two or more frequency bands ’ connections are always routed correctly.

Notable advantages compared to the common, high-level passive crossover are:

1. Reduced “ congestion ” and similar intermodulation distortion symptoms as each
   power amplifi er handles only a section of the audio range.


2. Differences in driver sensitivities (considered under “ matching levels, ”
   see earlier discussion) are ironed out and without compromise, except the
   requirement for, or use of amplifi er headroom, by simply adjusting gain controls.


3. Higher dynamic headroom by diversity , as the program peaks occurring in the
   respective out-of-band frequency ranges do not steal any headroom. Also, brief
   clipping (overdrive) of the bass band (etc.) has little effect on clarity when the
   other bands are not driven into clipping at the same time.


4. Amplifi ers are connected directly to their respective drive-unit(s). There are no
   reactive components (i.e., the passive crossover) to steal current, but the drive-unit’s
   impedance dips may still demand signifi cant current headroom from the amplifi er.


5. The ease and capability of creating highly conjugate, highly matched, and
   closely toleranced crossover functions.

Of these, the low-level passive crossover potentially has all the same advantages—except
possibly this last item.

24.1.4.8 Active Manifestations

Active crossovers commonly take one of three forms. In pro-audio, “ the crossover ” is
commonly used packaged in its own box, like other signal processors, as a stand alone.
As a power amplifi er presents a (literally) well-placed opportunity to share a box and
a power supply, a few power amp makers offer a pluggable option or “ octal socket, ”
where a crossover module or card can be retrofi tted. Often, the performance of the card’s
fi ltering (e.g., the frequency and slope rate) may be decided upon by the user. This is
often a low-budget option limited to installation work, but while it can save money, it
need not be shoddy. If carried out with as much care as any crossover is due, turning an