Archived from groups: rec.audio.tech (More info?)
"Thomas A" <Thomas_Akerlund@hotmail.com> wrote in message
news:9a6b3d08.0404270255.3fa0ff6d@posting.google.com...
> much snipped...
>
>
> > >
> > >This is what I've heard (I run active filters myself):
> > >
> > >Active - positive:
> > >
> > >- Less power needed, simpler power amps, less possibility of clipping
> > >artefacts
> > >- Stable impedance seen by the filter
> > >- Less impact of voice coil temperature and filters - bigger advantage
> > >if complex filters
> > >- Often adjustable levels of tweet/midrange. Good if cross-over is set
> > >properly. Can be used to adjust for some room acoustics (bright/dull
> > >room)
> > >
> > >Active - negative:
> > >
> > >- More power amps = more expensive
> > >- Often less protection of tweeters (DC)
> > >- Lower distortion possible with passive filters, often with tweeters
> > >(impedance matching). Can be done actively also, but needs
> > >impedance-matched outputs of power amp. Sometimes a resistor in series
> > >with the tweet may reduce impedance-related distortion, but will also
> > >change fr resp. Colloms says something about this in his loudspeaker
> > >book. Have too little knowledge to say how much it will affect.
> > >
> > >T
> >
> > All agreed, but while "often less protection of tweeters (DC)" is true,
there's
> > more to it. Even with an active xover it's a good idea to isolate the
tweeter by
> > a cap to protect it against DC amp faults. And all tweeters need
protective
> > devices anyway (polyswitch, PTC, lamp, etc). But at least with an active
xover
> > you can size the power amps reasonably (eg 1kW for sub, 500+500 for
mid-bass,
> > 100+100 for horns), whereas with a passive xover even a 1000+1000W amp
won't
> > give the same output or clarity, and someone waving a mic in front of
the FOH
> > can take out the horn drivers very quickly.
> >
> > I'll have to follow up on the reduction of distortion by impedance
matching -
> > I've never heard that before, and it sounds counter-intuitive.
>
> There is a chapter which I read in the Colloms "High Performance
> Loudspeakers" book, and I've been talking to some other people about
> this. It is possible to reduce distorsion by some kind of impedance
> matched output (going from voltage to more current drive?). I'm sure
> there are people here that can explain it better than me.
>
I think you're on to Zobel networks there.
Look it up and see if it's what you're looking for.
cb
"Thomas A" <Thomas_Akerlund@hotmail.com> wrote in message
news:9a6b3d08.0404270255.3fa0ff6d@posting.google.com...
> much snipped...
>
>
> > >
> > >This is what I've heard (I run active filters myself):
> > >
> > >Active - positive:
> > >
> > >- Less power needed, simpler power amps, less possibility of clipping
> > >artefacts
> > >- Stable impedance seen by the filter
> > >- Less impact of voice coil temperature and filters - bigger advantage
> > >if complex filters
> > >- Often adjustable levels of tweet/midrange. Good if cross-over is set
> > >properly. Can be used to adjust for some room acoustics (bright/dull
> > >room)
> > >
> > >Active - negative:
> > >
> > >- More power amps = more expensive
> > >- Often less protection of tweeters (DC)
> > >- Lower distortion possible with passive filters, often with tweeters
> > >(impedance matching). Can be done actively also, but needs
> > >impedance-matched outputs of power amp. Sometimes a resistor in series
> > >with the tweet may reduce impedance-related distortion, but will also
> > >change fr resp. Colloms says something about this in his loudspeaker
> > >book. Have too little knowledge to say how much it will affect.
> > >
> > >T
> >
> > All agreed, but while "often less protection of tweeters (DC)" is true,
there's
> > more to it. Even with an active xover it's a good idea to isolate the
tweeter by
> > a cap to protect it against DC amp faults. And all tweeters need
protective
> > devices anyway (polyswitch, PTC, lamp, etc). But at least with an active
xover
> > you can size the power amps reasonably (eg 1kW for sub, 500+500 for
mid-bass,
> > 100+100 for horns), whereas with a passive xover even a 1000+1000W amp
won't
> > give the same output or clarity, and someone waving a mic in front of
the FOH
> > can take out the horn drivers very quickly.
> >
> > I'll have to follow up on the reduction of distortion by impedance
matching -
> > I've never heard that before, and it sounds counter-intuitive.
>
> There is a chapter which I read in the Colloms "High Performance
> Loudspeakers" book, and I've been talking to some other people about
> this. It is possible to reduce distorsion by some kind of impedance
> matched output (going from voltage to more current drive?). I'm sure
> there are people here that can explain it better than me.
>
I think you're on to Zobel networks there.
Look it up and see if it's what you're looking for.
cb
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