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A third- or fourth-order acoustic crossover often has just a second-order electrical filter. This requires that speaker drivers be well behaved a considerable way from the nominal crossover frequency, and further that the high-frequency driver be able to survive a considerable input in a frequency range below its crossover point.
This is the biggest advantage of L-R crossovers compared to even-order Butterworth crossovers, whose summed output has a +3 dB peak around the crossover frequency. Since cascading two n th -order Butterworth filters will give a (2 n ) th -order Linkwitz–Riley filter, theoretically any (2 n ) th -order Linkwitz–Riley crossover can be designed.
In electronics and signal processing, a Bessel filter is a type of analog linear filter with a maximally flat group delay (i.e., maximally linear phase response), which preserves the wave shape of filtered signals in the passband. [1] Bessel filters are often used in audio crossover systems.
The midwoofer-tweeter-midwoofer loudspeaker configuration (called MTM, for short) was a design arrangement from the late 1960s that suffered from serious lobing issues that prevented its popularity until it was perfected by Joseph D'Appolito as a way of correcting the inherent lobe tilting of a typical mid-tweeter (MT) configuration, at the crossover frequency, unless time-aligned. [1]
A simple example of a Butterworth filter is the third-order low-pass design shown in the figure on the right, with = 4/3 F, = 1 Ω, = 3/2 H, and = 1/2 H. [3] Taking the impedance of the capacitors to be / and the impedance of the inductors to be , where = + is the complex frequency, the circuit equations yield the transfer function for this device:
The output power of the two carriers (M1 and M2) increases by about 1 dB in each frame, while the 3rd order intermodulation products (D3 and D4) grow by 3 dB in each frame. Higher-order intermodulation products (5th order, 7th order, 9th order) are visible at very high input power levels as the amplifier is driven past saturation.
Third- and higher-order filters are defined similarly. In general, the final rate of power rolloff for an order- n all-pole filter is 6 n dB per octave (20 n dB per decade). On any Butterworth filter, if one extends the horizontal line to the right and the diagonal line to the upper-left (the asymptotes of the function), they intersect at ...
As for "bringing the acoustic network in line with the crossover" - all it means is that the speaker's acoustic output is corrected for dips/peaks by using extra circuitry - the impedance equaliser is just one such in the scheme of things - the impedance equaliser makes the driver appear resistive to the crossover and the contour network simply ...