|
|
Brian Elliott wrote:
> Firstly, the crossover network divides the signal from the amplifier to
> the woofer and the tweeter drivers. It must be tuned to the right
> frequency and shape the frequency falloff curves and phase so that the
> sound levels from both drivers are balanced without dips or humps or
> comb-filtering at the crossover band where both drivers transmit part of
> the signal. It is also supposed to keep the signal phase true between
> the two drivers over the frequency range so they operate in a unison
> making the sound wavefront from both drivers combine and arrive at your
> ear together. That is fekking difficult to design, because...
>
> Crossovers are passive networks of resistors, capacitors and inductors.
> Networks behave much more complicatedly than isolated components because
> everything interacts with everything else, not just its immediate
> neighbours. Speaker drivers are *also* R-L-C networks, so crossovers
> must be designed with that driver's electrical properties being integral
> to it.
>
> In short, the whole thing is interbalanced, so if one resistor,
> capacitor or inductor changes, everything goes out of whack -- crossover
> frequency, frequency response, phase response, impedance response,
> resonances and ringing -- and the speaker sounds like crap.
>
> For predictability, a speaker and its crossover also rely on the
> amplifier's output stage being very low impedance. Signal-wise, the
> amplifier is near to a short-circuit, regardless of the voltage swings
> it generates. A speaker is a motor and when moving, it generates
> back-EMF through its crossover. It has mechanical inertia and wants to
> overshoot. It also has natural resonances from driver suspension
> springiness, cabinet air volume, acoustic transmission line length,
> tuned acoustic port, etc. That colouration is NOT part of the original
> signal. If the amplifier doesn't soak up that energy (absorb the
> current), to damp the unwanted motion (overshoot and ringing) it will
> reflect back into the network and colour the sound you hear.
I read about this kind of thing in a DSP book. Damn, IIR filters sound
so complicated! Fascinating, but... I wouldn't want to design them for a
living.
--
http://blog.orphi.me.uk/
Post a reply to this message
|
|