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ACTIVE CROSSOVERS 

1) Loudspeaker drive units of different sensitivities may be used in one system without the need for lossy resistive networks ( and L-Pads ) or transformers

( DEQX lets me use 98 dB/meter/watt planar magnetic tweeters with 105 dB+ horn drivers ).

2) Distortions due to overload in any one band are captive within that band, and cannot affect any of the other drivers - eg. occasional low frequency overloads do not pass distortion products into the high-frequency drivers, and therefore instead of being objectionable they may, if slight, be inaudible.

3) Amplifier power and distortion characteristics can be optimally matched to  drive unit sensitivities and frequency ranges.

4) Driver protection, if required, can be precisely tailored to the needs of each driver ( DEQX cuts off low frequencies at 20 Hz to protect my subwoofer drivers ).

5) Complex frequency response curves can easily be realized in the electronics to deliver flat acoustic responses at the listening position. Inherent driver irregularities can be easily regularized ( the DEQX processor/crossover 'corrects' my horn's imperfect phase and frequency responses ).

6) There are no complex load impedances as found in passive crossovers, making amplifier performance (and whole system performance) more dynamically predictable. 

8) System intermodulation distortion can be significantly reduced. ( Less band overlap = less i.m. distortion )

9) Cable problems can be dramatically reduced.

10) Low source impedances at the amplifier outputs can damp out-of- band resonances in drive units. A passive filter may function as a buffer and prevent effective amplifier damping.

11) Drive units are essentially voltage-controlled. When coupled directly to a power amplifier, (most of which act as voltage sources) drivers are more optimally driven than with passive filters which can alter impedances between the source and load . When ‘seen’ from the point of view of a voice coil, passive crossover components represent an irregularity in the amplifier output impedance.

12) Direct connection of the amplifier and loudspeaker is a useful distortion reducing system. It can eliminate the strange currents which can often flow in complex passive crossovers.

13) Steeper filter slopes can easily be achieved without loss of system efficiency.

14) Low frequency to high frequency driver+cabinet time alignments are possible which, by passive means, would be more or less out of the question.

15) Drive unit production tolerances can easily be trimmed out ( = perfectly matched drivers ).

16) Driver 'drift' from aging ( less flux = lower spl ) can easily be trimmed out.

17) Subjectively, clarity and dynamic range are generally considered to be better on an active system compared to a passive equivalent (with the

same enclosure, and the same drive units). 

18) Amplifier designs may be simplified, sometimes to sonic benefit.

19 ) In passive loudspeakers used at high levels, voice-coil heating will change the impedance of the drive units, which in turn will affect the crossover termination. Crossover frequencies, as well as levels, may dynamically shift. Actively crossed-over loudspeakers are immune to such crossover frequency changes.

20) Problems with inductor location (to minimize interaction with drive unit voice coils at high current levels) do not occur.

Digital Active Crossovers 

A digital crossover with lower bit depth and sampling rate than the recordings it's processing won't deliver maximum sound quality; unfortunately my DEQX crossover is limited to 24/96 so it can't process hi-res digital files ( early DEQX processors were limited to16/48 ). 

Digital crossovers are expensive compared to active analog crossovers.

Digital attenuation is not a problem with 24 bit processors processing 24 bit recordings. Quantization errors, the only ones specific to digital filters, are not audible when this is the case. Even 16 bit processors can attenuate up to 8 bits without audible 'rounding' errors. 

In terms of dynamics, 6 dB of digital attenuation equals roughly a 1 bit loss of resolution and a 50% reduction of dynamic range. This also applies to analog attenuation . The solution is to use a crossover - digital or analog - with high voltage output. ( Sensitive systems like horn speakers must use amps with low input sensitivity, or you can use voltage splitters. I use voltage splitters. ) You get decreasing Sound to Noise ratios with lower voltage signals whether you use analog or digital filters.

Finally, if the DAC chips in a digital crossover are limited to a SNR of 120 dB, as they usually are, a 24 bit processor ( w/ a dynamic range of 144 dB ) loses 24 dB of dynamic range. In this case the DAC chips themselves add noise to the signal. So an analog crossover can sound better than a digital one if attenuation ranges greater than 24 dB must be achieved. If the range of attenuation is less than 24 dB, a 24 dB processor should give more than satisfactory results with 24/96 files.

Kerry

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