714 Chapter 24
routing ” that ensures different drivers receive their intended range, and not other
frequencies, is thecrossover (no relation to crossover distortion ).
The crossover may also perform phase shifting or signal delay in one or more bands.
Principally this is to synchronize (UREI use the phrase “ time align ” ) the signals delivered
by the drive-units, for example, because the sound from some has slightly further to
travel.
A variety of crossover types exist, with the more sophisticated designs aiming to have the
bands meld neatly in the crossover regions, without boosting or cutting any frequencies.
24.1.4.4 Crossover Point (XOF)
The crossover frequency or “ point ” is chosen by speaker designers on the basis of:
1. Power handling. Drops dramatically if the XOF is too low for the higher driver.
Caused by the exponential increase in excursion as LF limits are reached.
Distortion. For the same reason, rises rapidly for the higher driver below a
comfortable XOF.
Frequency response , both on- and off-axis. If either of these changes abruptly,
near the proposed XOF, the XOF had better be moved. But with some drive-unit
combinations, there is no ideal XOF.
24.1.4.5 Passive Crossovers
In the majority of domestic speaker systems, but particularly where low cost or simplicity
is paramount, the crossover is passive (unpowered) and operates at a “ high level, ” being
placed within and supplied as part of the speaker cabinet ( Figure 24.4 ).
In this form, the crossover comprises physically large and heavy, high voltage-rated
capacitors, high current-rated inductors (coils), and high power-rated resistors.
24.1.4.6 Passive Low Level
It is possible (but not very common) to have a passive crossover operating at line level
installed before the signal enters the power amplifi er, or otherwise before the power stage
( Figure 24.5 ). The crossover parts can then be smaller and lighter, as the voltage and
current ratings (that in part determine size) can then be 30 to over 100 times lower. This is
a fi ne arrangement for all-integrated active cabinets.