John Stone wrote on 10/7/2006:
I thought all your bi-amping adventures were done with the purpose of not
altering the original design of your AR3a's. Well, now that you're in
there
changing things around, I'm wondering if you did anything to compensate
for
the removal of those pots from the circuit. They place a 16 ohm load
across
the mid and tweeter crossover circuits, and that load forms part of the
filter network. Did you put a fixed 16 ohm resistor in the circuit in
their
place? If not, you've certainly altered the crossover responses and
consequently, the speaker response. (I can't wait to see whether you're
going to agree with this). I'm also trying to figure out how you got such
a
huge gain in sensitivity by removing the pots. Turned all the way up, the
mid and tweeter are directly connected to the crossover outputs, so the
pot
is out of the circuit other than presenting a parallel 16 ohm load. Unless
those were the world's most defective pots-and you would have easily been
able to tell from the intermittent operation-then I don't see where you're
picking up all the sensitivity from.
No, John! No pots and no fixed resistors. Pots are removed from the
circuit.
The real purpose of the pots was to balance the energy going to the more
sensitive drivers (mid and tweeters) in relationship to the energy going to
the woofers. In short, they were "padding" to bring all the drivers in
balance, plus they allowed some minor tweaking.
Now most folks have long set the tweeter pot to max as is recommended
everywhere. Further, removing the tweeter pot was even suggested by Chuck
McShane. See:
http://www.classicspeakerpages.net/ar/ar-9/3and9.txt
So, John, this leaves just the mid pot and it has a dramatic impact on the
balance of music ... no question about it. Any adjustments to this pot
dramatically impact the balance of high vs low frequencies. I don't think
anyone would argue this as a simple test of moving the pot form end to end
results in dramatically different sound.
Your question is how can I remove this pot and still maintain the proper
balance.
Well, for me, John, the pot is redundant. I still have total control over
the balance of energy going to the woofers vs the energy going to the
mids/tweeters ... only instead of pots, I use volume controls. Yes, the
volume controls on the amps that independently power each half of the
speaker.
I think you'll agree, John, that over time it's far, far easier to maintain
low power volume controls than it is to maintain the high power pots in the
speakers.
As for the improvement in sensitivity, all I can say it's significant and
very noticable. That 16 ohms still draws current that produces no sound.
If we assume that the impedance of the driver over it's frequency range
averages 4 ohms. Then if the pot is set to max increase, approx 25% of the
current going through the driver is also flowing through the pot and ...
producing zero sound.
On top of this, I never had the mid pot set to max. That would be way too
"bright" and in my room would NOT be balanced. So when I removed the pots
the padding that was going on, is no longer happening. So to balance the
speakers, I send significantly less power to the mids and tweeters and my
guess is the actual current flowing through them is very similar to what it
was when the pots were in the circuits.
John, when I removed the pots, I never claimed any change in sound with the
minor exception that my left speaker no longer loses mid-range completely
any more.
I'm also amazed at how much work you've gone through to deviate from the
original design intent of the AR3a's. If it was me, I would put them back
to
stock and sell them. They still bring decent money. Then I would invest in
some real DIY loudspeaker building using the much more robust and better
performing loudspeaker components that are available today. You could then
tweak to your heart's desire without the worry of blowing fragile drivers
that are no longer available. You seem like the type that loves to
experiment. Why limit yourself to such old technology that will never
reach
today's performance levels no matter what you do?
John, I don't believe that I have changed the intent of the AR3a's. I think
they sound terrific and I believe that any amp will drive them better with
the complex xover network split.
Further these drivers are somewhat unusual. AR made both the mid and
tweeter because they could NOT find drivers of comparable quality. The
woofer they purchased, but they specified all parameters so that it matched
the closed cabinet.
Regards,
Jerry