[Jerry]

Peter Wieck wrote on 10/12/2006:

Jerry:

On a purely techical level, I also question your contention that by
simply turning down the Volume Control (and therefore reducing the
potential for clipping), you are increasing headroom to the mid/tweet.
You are increasing both the simple resistance across the voice-coil and
the overall impedance (of course). This means that you will require
_more_ energy out of the amplifier to make the same voltage at the
speakers (watts drop as nominal load increases for most solid-state
devices).

Peter, it's a little confusing (actually it can be a LOT confusing), even
though the impedance without the pots goes UP, the actual current flowing
through the driver goes UP. Please remember that the pots "steal current"
yet produce no sound.

So for exactly the same voltage (with and without pots), there is more
current flowing through the driver when the pots are completely removed.
Since Watts = I * I * R Power consumed in the driver is approx 25%
higher and it follows with more power we get more SPL.

So for the same voltage, we get approx 25% more SPL and this would make the
sound far, far too bright. So we must reduce the voltage coming out of the
amp by turning down the volume.

Lower voltage for the same sound gets us further away from the rail voltages
..... hence more headroom.

So what you gain at one end, you lose at the other.

There is NO losss only a gain in sensitivity of the speakers (the
sensitivity of the raw drivers, of course, remains unchanged).

However in this case, the speaker VCs are now acting as the system fuse...
Pre
Ferro-Fluid AR domes are not so good at that... allow me to rephrase:
they are very good at being fuses, and blowing.

Ok, for the same voltage we have approximately 25% more power dissipated in
the voice coil. Over driving is easier ... admittley, but that's why I use
a quality, low power amp (approx. 30 -35 watts). This amp has no where
near the power of the AR1500, but even at 30 watts, it could still easily
fry the mid and the tweeter. However to achieve that kind of power
requires the volume control to be way, way over on the right hand side. I
rarely advance beyond 9 o'clock.

Energy Dissipation: You may think that the most energy going into a
speaker goes into the woofer. Not really. Take a simple operatic piece,
one of my favorites: Handel's "Let the Bright Seraphim" and the
test-piece I used for my biamping experiments. Although there is _some_
bass on that piece (kettledrums, and so forth), even those elements are
mostly above the crossover point to the woofer. The P/A on that piece
is well over 10dB, approaching 20dB. So at some of the loudest
passages, at least 70% (probably more) of the total energy delivered to
the speakers is above the crossover point to the woofers.

Peter, I seriously doubt your numbers. It's more complicated than just the
ratio of frequencies. The low frequencies require far, far more power to
reproduce, so even though you don't hear much low frequency, what you do
hear requires plenty of power.

Peter, the only way to understand this better is to watch the current
flowing to the respective halves. You'd be surprised by how much current
goes to woofer ... even for instruments we consider "altos".

I am not
saying that you are going to clip, but I am saying that you are sending
a bunch of energy (heat) into those speakers with all the designed-in
protections removed, such as they were.

The pots really aren't protection, Peter. Yes, they siphon off 25% of the
current, but you can still over drive. Their real function is "padding" to
bring the SPL from the various drivers somewhat "in line".

Bi-amped or otherwise. Not that
I am arguing with your scope and other instruments, but just do a
simple band-pass reading of the amp(s) output and see where the
frequencies (and associated energy levels) are.

I have and the vast majority of energy goes to the woofer ... by a lot!

Just some thoughts. What you have done seems to work for you, but as
much as you have urged me to try things, I also urge you to do the
same. I also really hope you have fused your speakers, the AR factory
had quite a bit of literature on fusing, and specified quite-expensive
low-loss fuses, not the little glass-bits that most use.

Peter Wieck
Wyncote, PA

My amp has fuses, however, I doubt they'd protect the drivers. The AR
literature is OK, except I would have to reduce everything by approx. 12%.

Regards,
Jerry