>>> Interesting, how do they do that?
>>
>> You think *I* know?
> 
> It used to be that more efficient speakers in general had more unwanted 
> resonances and lumps in their frequency responses: IOW poorer fidelity.  
> I don't particularly know why but that's how it was.  Obviously the 
> designers would have overcome that if they could have, but some chose 
> low efficiency in return for better sound quality.  I don't know how 
> well they are doing now with that trade-off, it's been some years since 
> I last read any reviews.

That sounds about right.

>>> Hard to see how you could deliberately make the system less efficient 
>>> without just plonking a huge 50W resistor in series (which would 
>>> totally screw up the quality of the sound).
>>
>> And why would that be?
> 
> The answers lie in the way passive networks of electronic components 
> work and in speaker mechanics.
> 
> 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.
> 
> So if you plonk a great big resistor in series with all that, the amp 
> can't damp unwanted speaker motion, the crossover detunes, the frequency 
> response goes lumpy, the sound goes muddy, and you think "bleccch!"  :-)

I'm sure that would be the case.

Now, what if that resistance was part of the design right from the 
beginning?

By the way... The documentation for my mum's amplifier claims that it 
contains special circuitry to cancel out the electric signals generated 
by the speakers themselves. (I have no idea whether this is special or 
whether it's something all modern amps do and they just wrote about it 
to make themselves sound cleaver...)

>>>> Hmm, I think my amplifier (nothing special) is rated at 60 W per 
>>>> channel. (IIRC, into 8 ohms at 1 kHz.)
> 
> For listening at home, the real reason for high-powered amps is not to 
> make louder noise, but for fidelity.

Hmm, isn't that what *I* said several posts ago? ;-)

>> (It's like all toasters 
>> have a special setting that transforms bread into charcole. We don't 
>> know why, but they all have it.)
> 
> <Ahem>  Just because you didn't figure it out, doesn't automatically 
> make the manufacturers into idiots.  The high setting on toasters is 
> needed to get even a _little_ colour into *crumpets*.  But, as you 
> apparently haven't toasted a crumpet before, they obviously don't exist 
> and every manufacturer out there is stupid for gratuitously making 
> toasters with a nuclear setting.
>  :-P

Wait... Surely to toast a crumpet you want a *lower* heat? (Since it's 
thicker and hence nearer to the heat source - and also you want to cook 
it slower so it cooks through completely.)

>> (I once tried connecting a line-level output to the phono input. Big 
>> mistake...)
> 
> Ow.  :-(

Sounded a bit like a metal guitar. Also made the sound come out on *all* 
input selections. o_O

-- 
http://blog.orphi.me.uk/

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