Tri-amp output powers
 

On Mon, 8 Nov 2004 22:15:31 -0000, "Wally"
wrote:

What's the deal with choosing output powers when tri-amping? If my 3-way
speakers are rated at 50W, and I want to double the number of bass drivers,
what o/p power should I choose for each amp?

At the moment, I'm thinking of 100W low bass, and 50W each for bass/mid and
treble. Won't my T27s freak out if there's a 50W amp dedicated to them? In
the present 3-way setup, how would the power from a single 50W amp split up
in terms of which driver gets what power?

In spite of being unsure of this, I'm presently thinking that an easy way to
do this is a stack of three Cyrus Two amps. That way, I can adjust the
volumes to balance the level to each driver, with overall output determined
by the capability of the low bass section. I could also compensate for the
somewhat recessed mid that becomes apparent at times.

From what I've read, the Cyrus Two is very good at detail, but a little
light on bass. I like the idea of good detail. I'm after bass which is
tight, solid, and very low. It doesn't have to be mega-loud. Maybe the light
bass (be there such) can be compensated for by adjusting the volume of the
low bass amp, or using some sort of filter at the pre-amp.

Am I on a concievably-sensible track with this Cyrus Two idea?

Not sure where you got the idea about the Cyrus II being light on
bass. I just measured mine and it ruler flat down to 10Hz. I think it
hits -3dB somewhere around 1Hz.

So no, isn't in the least light on bass.

As far as I can tell, pretty much all the detail that goes in the
input comes out of the output, so you are right there.

d
Pearce Consulting
http://www.pearce.uk.com

Tri-amp output powers
 

In article , Wally
wrote:
Jim Lesurf wrote:

Can you say how you intend to "double the number of bass drivers"? Any
anwer will depend upon how you are thinking of doing this. i.e. how
are you going to wire them up, mount them in the same or different
cabinets, crossover/filter arrangements, etc.

Isobaric subs using B139s, wired in parallel, infinite baffle cab of
60-80 litres, active low-pass filter before the power amp.

OK. The point to bear in mind here is to assess how these conditions of use
compare with those 'assumed' by the speaker unit maker when they quoted a
value for its power handling.

The problem is that isobarik tends to mean each unit is being 'driven'
acoustically by the other. This alters the effective impedance of each
unit. Thus the situation is different to when using one unit in a box.

Wiring in parallel probably means the amp will see a lower impedance as
well, so needs to be able to work happily into the resulting load.

The problem is that the power ratings for speakers are quoted on an
entirely different basis than that quoted for amplifiers. The
speaker's ability to handle a given power also depends upon other
factors as well.

Something to do with losses in the crossover of a conventional speaker,
and the fact that the speaker's rating is for the full three-driver
setup with crossover?

The main problem is that amp powers tend to be quoted in terms of the
maximum sustainable sinewave power level into 8 Ohm resistors. Whereas the
speaker 'power handling' tends to be a more nebulous value.

Allegedly, the speaker ratings tend to indicate the typical levels you can
use for moderate periods of 'music'. Since the power level and spectrum of
music is very variable, this ends up being a fairly vague statistical
value. Perhaps obtained by playing band-shaped noise into the speaker for a
period of time. Or by various other methods that might end up giving
different values.

Am I on a concievably-sensible track with this Cyrus Two idea?

In principle, it may well be OK. But you have not provided enough
detail to be sure.

Subs as above, B110 bass/mid, T27 tweeter. I figure that, if a Cyrus Two
can drive the 4 ohm isobaric subs to a volume that I'm happy with, then
the B110 and T27 should be fine. I'm looking into an active crossover
for all frequency bands, before the power amps.

You will *probably* be OK, but this assumes you will be doing what most
people actually do - i.e. buy systems rated at XX watts, then use them at
mean levels of XX/20 or less. :-)

Music tends to have mean powers that sit around 20dB or more below the peak
levels. Hence if you are using 100W amps, the chances are that you are
actually using mean powers somewhat below 10W. The snag is such comments
are simple 'typical' or 'likely' so don't represent a guarantee or a figure
that is completely reliable in your individual case.

Slainte,

Jim

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