[Jerry]

John Stone wrote 10/8/2006: On 10/7/06 8:40 PM, in article
, "Jerry"

Jerry wrote:

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.

Well, John, it was published in the AR library and someone would have
complained vehemently if it was totally wrong. I think this is the part
that is most convincing:

"Even wide open, the pot reduces tweeter output by about 1db."

So, if the tweeter pot is set to max and the pot opens up, the net change in
the tweeter is 1 db. However, if the wiper in the pot is corroded the
reduction can be far, far more substantial than 1 db.


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.

John, xover frequency is determined primarily by the reactive components.
The coils and caps are all still there. The xover for the mid-range is
really a band pass and I have tested the xover to see whether it was in fact
working.

I did this by applying a full frequency signal to the mid/tweeter (did
exactly the same for the woofer). So a full frequency and full strength
voltage was applied to the mid/tweeter and I measured the current actually
going to the drivers. In short, the xovers were performing perfectly.
That is, they were "blocking" (little or no current) was flowing for the
frequencies NOT intended for the respective drivers.

Lastly, John, as you stated in your other post, the net resistance of the 16
ohm pot and the mid-range driver (with the pot at max) is still pretty close
to the resistance of the mid-range driver. So, we really can't be that far
different from the original design.


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

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

Not my rules. Function of the pots is to balance energy going to the
respective drivers to adjust for room conditions and RECORDINGS. I can
perform exactly the same function with the volume controls.

With a single amp, John, you have no where near the control over sound that
I have. And with harmonics riding on fundamentals, you have no where near
the headroom that I have.

As an aside, John, a totally flat response on AR-3a's is achieved with the
pots at max AND a slight increase in the treble volume control.

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.

Neither pot is in the circuit (both pots are physically attached to the
speakers, but doing nothing and dissipating zero power.) From my first post
in this thread:

"Well, Rolf, I've done just the opposite. I've taken all the pots out of
the AR-3a circuit ...."

From this point on, I'll only take the speakers apart upon component failure
.... NOT for cleaning those blasted pots.

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,

My ignorance, huh? John, you spouted a lot of "facts", but not a single
number. Are you lazy, John, or perhaps you don't know how to do the math.

Let's just see how significant.

DC resistance of tweeter is approx. 3.2 ohms

So with the 16 ohm pot full across - net resistance = 2.67 ohms or a
difference of .53 ohms

Real, real significant, John ... huh??

Now, let's look at the total network near the xover frequency

I @ 2 v I @ 2 v
Hz Z for Cap Z w/o pot Z with pot w/o pot with pot
% diff
3,000 8.8 ohms 12.0 11.5 .166
..145 12.8%
4,000 6.6 ohms 9.8 9.3 .203
..179 11.9%
5,000 5.3 ohms 8.5 8.0 .235
..522 11.1%
6,000 4.4 ohms 7.6 7.1 .656
..588 10.4%

Real significant, John! Maximum difference in current going through the
tweeter is 2.2% over this entire range. WOW!! Tell us, John, do you
think there is a human anywhere ... that could actually hear this
difference?

Perhaps your arguments would have some weight, John, if you backed them up
with the math.

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

What in heck are you talking about?? What wrong direction? 0.5% more
current at 6000 Hz than at 3000 Hz!! Who cares??

Now, if you are talking about sensitivity in total .... YES, for the same
voltage we get approx. 11% more current going through the tweeters. We must
absolutely reduce the voltage in the mid/tweeter amp or the sound would be
too bright.

What in heavens name does that have to do with "fragile"?

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.

Total nonsense, John. We are NOT talking about SPL out of the drivers.
We are talking about SPL out of the speakers.

I get more output for the same voltage for two reasons:

1. I'm NOT wasting current flowing through the 16 ohms pot like you do
(approx. 11%)

2. Actual waste on the mid-range is much, much higher, because I never set
the mid pot to max. In that case the amount of current the mid driver
actually sees is greatly reduced. This is really a waste of voltage and
headroom. Even though voltage can be significant the current will be low
due the voltage divider function that the pot performs.


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..

Confused I guess you are, because I've been consistent. I've always said I
removed ALL 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.

John, this is getting a little tiring. You have never quote a single fact
.... just total supposition.

Here is my charts and my graphs and facts :

http://www.classicspeakerpages.net/d...ng_type=search

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.

Look over the impedance charts, John. Then let's see your facts. Your
charts. Your experiments ... or do we have an empty bag?

As for my amps, after looking over the facts ... I believe I have far, far
more voltage headroom than anyone with a single amp.

Which brings up another question: If using separate amps gave such a huge
improvement, why didn't AR suggest it in the first place?

I don't believe at the time that the AR's were developed, people were even
experimenting with bi-amping for home use. As time went on and AR continued
to develop speakers, they started experimenting with bi-amping.
"Satisfactory results were obtained when bi-amping the AR-90" according to
AR (see reference on the AR forum).

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.

I don't believe back in 1968 ANYBODY was thinking about bi-amping for home
use, but please share a reference showing that I am wrong. Quote any
article from 1968 or earlier recommending bi-amping in the home.

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?

I'm not so certain there are comparable drivers available today. It seems
that "quality" anything is harder to find. Just look at the products
offered today in terms of receiver and speaker systems.

Regards,
Jerry