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John Stone John Stone is offline
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Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

On 10/7/06 8:40 PM, in article , "Jerry"
wrote:

John Stone wrote on 10/7/2006:
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.


No, John! No pots and no fixed resistors. Pots are removed from the
circuit.


Oh boy!

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
Yes, I read that. It wasn't Chuck McShane that wrote this, it was his nephew
writing what he BELIEVES Chuck McShane said. Hardly authoritative. The
context of this post is totally missing, and the meaning of the word
"remove" is misleading at best. He could easily have meant removing the L
pad aspect of the pots as opposed to removing the pots completely. I find it
hard to believe Chuck McShane would have recommended just pulling them out.


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.


No, my question is NOT how you can remove the pot and still maintain the
proper balance. It's how you can remove the pot and still maintain the
proper crossover frequency.


Well, for me, John, the pot is redundant.

Obviously. You do like to make up your own rules, independent of facts or
reality.

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 fully understand what you are doing here. It doesn't take rocket science
to figure it out.

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.


But you say you've left the midrange pots in, so you still have to maintain
those. So you really haven't solved the maintenance problem at all. The big
issue with the pots is having to take apart the speakers to get to them.
Once you're in there, cleaning them is no big deal. All you've done is
eliminate the need to clean one of them, which you could have done anyway
just by jumpering the wiper to the high side of the pot.

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.


Jerry, your ignorance of even basic loudspeaker design principles is
appalling. If I didn't know better, I'd swear you were joking. The tweeter
network in the AR3a consists of a single series element; i.e., a 6uf cap
feeding a load consisting of a tweeter and a 16 ohm tapped resistor. For all
intents and purposes, when you run the tweeter pot at full, you simply have
a tweeter and a 16 ohm resistor in parallel. The crossover frequency is
determined by the value of the series cap AND the impedance of the load.
Removing that 16 ohm resistor alters the load (increases the impedance),
which in turn alters the crossover frequency, moving it downward. I'm quite
sure what you've done IS significant, just as I am quite sure what you have
done has completely changed the intended tonal balance of your speakers.
What I'm not sure of is how much you've increased the risk of blowing your
tweeters. But let's just say that those are quite fragile and you've
definitely moved things in the wrong direction regarding the chances of
surviving your "improvement". If you still don't get this, here's a link
that demonstrates, in simple terms, the relationship between load impedance
and crossover frequency:

http://www.carstereo.com/help/Articles.cfm?id=1

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.


Well the only part of this statement I agree with is that you are guessing.
How do you dissipate less power through the drivers while keeping the
current flow the same? Sorry Jerry, but you cannot change the relationship
between SPL and power dissipation through the drivers. If you are getting
more output from a driver, it is simply because you are putting more signal
into it. End of story.


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.

Now I'm really confused. I thought you said you didn't remove the midrange
pots..

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.


There's that belief system again. Never let the facts get in the way of what
you believe. You have come to the conclusion that ANY amp will drive them
better with split x-over based on what? Using what even you admit is a
pretty marginal amp for those speakers? Many here have told you from their
own experience that using a single amp of adequate power and stability for
these speakers will get as much out of them as they are capable of giving.

Which brings up another question: If using separate amps gave such a huge
improvement, why didn't AR suggest it in the first place? The same exact
thing you have done could have been done back in 1968
when they were introduced. Yet nowhere in the owner's manual or the
literature is any such arrangement suggested. Why not? Are you saying that
the designers never thought of it, or were totally unaware of the
capabilities of their own speakers? Strange that they could be so
brilliant in designing the speakers, yet so ignorant of their true
capabilities.

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.

Yes, and all of that happened back in 1968. What does any of this have to do
with my suggestion of looking at what is going on today in DIY using
up-to-date driver technology?