Here we make a brief comparison of several crossover when used for MTM systems. The first two
figure compare a 2K Hz 3rd order Butterworth MTM and MT speaker. The MTM speaker has
significantly reduced power response below the crossover frequency due to cancleation between the
M drivers. The polar response, at the crossover frequency, is much smoother for the MTM, as was
originally demonstrated by D'Appolito. however, we can expect symmetric dips in the polar response
below the crossover frequency, again, due to the interference between the M drivers.
Next we look at a lower, 1.4K Hz crossover point with a 7th order Butterworth crossover. The results a re very similar to the
B3 case, smoother polar response at the crossover point but somewhat degraded power response.
Lastly, we examine the lower crossover frequency case with an LR8 crossover. As with the LR4 crossover, the power
response of the MTM shows a deep notch and degraded polar response. In short, these results show the general trend
that even order LR type crossover can be expected to perform worse in ans MTM format than their MT counterparts both
in power and polar response. Butterworth crossovers, by contrast, show the well known improvement in polar response is
at the expense of some degradation in the power response. Still, if an MTM design is favored it would appear that odd
order crossovers are superior to even order ones.
The plots below show similar a similar comparison for a 2K Hz, 4th order linkwitz/Riley crossover. With the LR4 crossover
the dip in the power response for the MTM is both deeper and considerably more irregular than it was for the MTM with
the B3 crossover and, as expected, not as uniform as the LR4 MT. The polar response also shows that rather than
improving dispersion at the crossover frequency, the main lobe is actually narrower than the MT speaker system. Below
the crossover point the same type of cancellation between M drivers should be expects as would occur for the B3 MTM
since this is a function mainly of the driver spacing.
Consideration of Power Response in Speaker Design:
Crossover Choice and Setup.