Aktyvines ir pasyvines GAS plačiai apžvelgė Philip Newell ir Keith Holland Loudspeakers For Music Recording and Reproduction knygos Active versus passive crossovers skyriuje.
Kviečiu perskaityti ką parašė britų Akustikos instituto bendradarbis, Audio Inžinierių Organizacijos narys, daugelio knygų autorius kartu P. N ir jo kolega – Garso ir Vibracijų tyrinėjimų instituto lektorius, profesorius K. H. Bus tiksliau, jei įkelsiu knygos kalboje.
The list of advantages in favour of active crossovers and multi-amplification is impressive:
1) Loudspeaker drive units of different sensitivities may be used in one system without the need for lossy resistive networks or transformers. This can be advantageous because drive units of sonic compatibility may be electronically incompatible in passive systems.
2) Distortions due to overload in any one band are captive within that band, and cannot affect any of the other drivers.
3) Occasional low frequency overloads do not pass distortion products into the high-frequency drivers, and instead of being objectionable may, if slight, be inaudible.
4) Amplifier power and distortion characteristics can be optimally matched to the drive unit sensitivities and frequency ranges.
5) Driver protection, if required, can be precisely tailored to the needs of each driver.
6) Complex frequency response curves can easily be realised in the electronics to deliver flat (or as required) acoustic responses in front of the loudspeakers. Driver irregularities can, except if too sharp, be easily regularised.
7) There are no complex load impedances as found in passive crossovers, making amplifier performance (and the whole system performance) more dynamically predictable.
8) System intermodulation distortion can be significantly reduced.
9) Cable problems can be dramatically reduced.
10) If mild low frequency clipping or limiting can be tolerated, much higher SPLs can be generated from the same drive units (vis-α-vis their use in passive systems) without subjective quality impairment. (See 2) and 3) above.)
11) Modelling of thermal time constants can be incorporated into the drive amplifiers, helping to compensate for thermal compression in the drive units, although they cannot totally eliminate its effects.
12) Low source impedances at the amplifier outputs can damp out-of band resonances in drive units, which otherwise may be uncontrolled due to the passive crossover effectively buffering them away from the amplifier.
13) Drive units are essentially voltage-controlled, which means that when coupled directly to a power amplifier, (most of which act like voltage sources) they can be more optimally driven than when impedances are placed between the source and load, such as by passive crossover components. When ‘seen’ from the point of view of a voice coil, the crossover components represent an irregularity in the amplifier output impedance.
14) 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.
15) Higher order filter slopes can easily be achieved without loss of system efficiency.
16) Low frequency cabinet/driver alignments can be made possible which, by passive means, would be more or less out of the question.
17) Drive unit production tolerances can easily be trimmed out.
18) Driver ageing drift can easily be trimmed out.
19) Subjectively, clarity and dynamic range are generally considered to be better on an active system compared to the passive equivalent (i.e. same box, same drive units).
20) Out of band filters can easily be accommodated, if required.
21) Amplifier design may be able to be simplified, sometimes to sonic benefit.
22) 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.
23) Problems of inductor siting (to minimise interaction with drive unit voice coils at high current levels) do not occur.
24) Active systems have the potential for the relatively simple application of motional feedback, which may come more into vogue as time passes.
Paminėti ir pasyvinių sistemų privalumai, bet jie su išlygomis.
Conversely, the list of benefits for the use of passive, high level crossovers for studio monitors would typically consist of:
1) Reduced cost? Not necessarily, because several limited bandwidth amplifiers may be cheaper to produce than one large amplifier capable of driving complex loads. What is more, the passive crossovers for the 1000 watt Kinoshita studio monitors cost over 3000 euros each.
2) Passive crossovers are less prone to being misadjusted by misinformed users, who think that crossovers are some sort of ‘adjust to taste’ tone controls. On the other hand, passive systems have a tendency to misadjust themselves with age.
3) Simplicity? Not really, because very high quality, passive, high level crossovers can be hellishly complicated to implement, not to mention the amplifiers which are needed to drive them.
4) Ruggedness? No, because the electrolytic capacitors (necessary for the large values) are notorious for ageing, and gradually changing their values.
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