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[email protected] dpierce@cartchunk.org is offline
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Default AR3a/AS103a speakers and the Heathkit AR1500 receiver

Jerry wrote:
John Stone wrote on 10/11/2006:


John, xover frequency is determined primarily by the reactive

components.

Any filter network's turnover frequency is calculated through
the values of source impedance, the value of reactive
components, and the impedance of the
load. Don't believe me? Then substitute a 100 ohm resistor
for the tweeter and run a sweep of the crossover. I'm sure
you'll you'll see a pretty huge change.


OK, but in this case (16 ohms across 3.2 ohms) the xover frequency is
primarily determined by the reactive components.


False. Completely false, for several reasons.

First, especially in the case of the high-pass function for
the tweeter crossover and the low-pass function for the
midrange crossover, these are first-order networks, and
the crossover frequency is an equal function of BOTH
the series reactance AND the driver impedance.

Second, you keep making a simplifying assumption
that the drivers are essentially equivalent to these
3.2 ohm resistors, and the most assuredly ARE NOT.
Take, for instance, the fact that the tweeter impedance
shows a significant rise above it's DC resistance at the
fundamental mechanical resonance, which is around
2500 Hz. The impedance reaches, IIR, a high of about
9-10 ohms at that frequency. Under this circumstance,
the presence or absence of that 16 ohm shunt resistance
makes a SUBSTANTIAL difference in the response of
the crossover output below cutoff, and that has an
equally substantial effect on the amount of signal fed to
the tweeter below cutoff. This changes the frequency
response of the speaker as a whole, increases the
distortion output of the tweeter and reduces its overall
power handling.

More specifically, the impedance presented to the tweeter
crossover at about 2.5 kHz with and without the shunt
resistance of the pot is 6 ohms vs about 9.5 ohms.

Thirdly, you keep focusing on one VERY narrow aspect
of the crossover response, the "crossover frequency" while
ignoring totally the much BIGGER issue of the overall
crossover transfer function. IN just the case of the tweeter,
not only is the crosover frequency changed rather substantially
(assuming the "crossover frequency, you mean the -3dB re
passband level frequency, which is moved DOWN by a third
of an octave), but you have also substantially changed the
shape of the crossover response. Among other things, you
have introduced a substantial hump in the response around
2.5 kHz, leading to the problems outlined above.

No you can't. You pulled out 2 pots and substituted them with 1 amplifier
gain control, driving the entire mid/tweeter section. You have removed one
of the pots' key functions, which was to allow shelving of the mid and
tweeter levels individually.


True, accept I always set the tweeter pot to max increase. Actually to
achieve a totally FLAT response both pots should be set to MAX and there
should be a slight increase in treble control.

So for me the only real control was over the mid range (which I set fairly
close to max as well). I still have control over the tweeter using my
treble tone control. If I need more I simply turn it up. If I need less, I
turn it down.

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.

I have no idea what this means.

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.


Anybody who has actually measured AR3a's as opposed to just reading the AR
literature will tell you this isn't true. Here's an actual real world
measurement of the 3a's:

http://murphyblaster.com/content.php?f=AR3a.html

These measurements are backed up in a post on 8/7 by Dick Pierce to you
regarding the frequency response of the AR3a:


We have asbolutley no idea how the pots were set in this dude's experiments.
Nor do we know how well or what he did when he "restored" his AR-3a's. I
can't believe anyone takes this guy's stuff seriously.

And on top of all that, he mentions a problem in the mid-highs that the pots
would actually help correct.

I much prefer the folks at AR who really knew how to test speakers.
Further, I don't consider this advertising literatu

http://www.classicspeakerpages.net/a...ember_1968.jpg

"No, the reason for this is that Roy Allison and Ed Villchur at AR
decided on a balance that resulted in an overall downward trend
in the speaker's response toward the high end. That was their
choice, for whatever reasons.


Urban legend. Simply not true. Per Ken Kantor:

"Quantifying the high frequency response of a speaker, any speaker, is a
much more complex subject than (almost) anyone wants to think about. Short
sounds can evoke a perceptually different response than longer tones.
Distance from the speaker can have a profound effect, as can placement,
listening position and room acoustics. Even more subtly, the whole idea that
there is one uniquely "correct" frequency response is unjustifiable, as
comforting as it may be. (I believe it to be a residue of the Logical
Positivism that arose in the 1960's as an over-reaction to the magical
thinking of 1950's High End subjectivism. Kind of like now...)

To this day, there is little agreement even between very experienced
professionals about how to properly characterize what "flat" response is. AR
had their methods, (which evolved over the years.) Within the limitations of
those methodologies, AR always tried to make accurate speakers, at least
near the top of their line. "


Nowhere in this quote does Mr. Kantor in any way refute what
I said, nor does Mr. Kantor sdtate or even infer that the AR3a's
had anechoically flat response. Indeed, the AR3a literature to
which you refer show clearly THEY DID NOT HAVE ANECHOICALLY
flat response and never did they claim that it did.

Further, if you read the other reference, you can see that AR
recommended that folks set the pots at mid point to correct
for what the record companies were doing in 1968.


The midrange efficiency is about
2 db less than the woofer, and the tweeter is another 2-3 dB
less efficient than that. That's what the people of AR designed
it to be." (end quote)

A "slight increase" in the treble control will not achieve a totally flat
response as is clear from the actual response measurements.


So you are saying that the pots should be at flat and we need a more than a
slight increase in treble?? OK, so?

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


Sorry Jerry, but yes, your ignorance, or perhaps just lack of attention to
detail, as again demonstrated above. DC resistance is utterly meaningless

to
this discussion, as the last time I checked, tweeters required AC to

produce
sound. Yet you use resistance interchangeably with impedance as if they

were
one and the same. The "nominal" impedance of a tweeter with 3.2ohm dcr is

4
ohms.


Yep, the reactive component combined with the resistive componet yields an
"effective" Z. Z= 3.2 +jwL

But the resistance components will respond exactly as I stated. There is no
reactive component in the pot.


You utterly and completely failed or igored what he said.
The simply point is that the drivers DO NOT present a resistive
load equal to the DC resistance of the voice coils to the
crossover, and any conclusion based on this assumption
are simply incorrect.

With the pots out, naturally LESS current flows ... all of the time. So
what?? The end result of that is the speakers have increased in
sensitivity.


False, the SENSITIVITY, as defined by the loudspeaker industry
IS THE SAME.

Your issue was that we have significantly altered the xover
frequency.


No, his issues, and your problem, is that you have changed
THE CROSSOVER RESPONSE. The crossover frequency is
merely one aspect of that repsonse. You have chosen, at your
peril, to ignore the bigger issue.

is, taking the pots out causes current to flow MORE at
some frequencies than
at others. That is we have a frequency altering impact.


If you want to play in the realm of loudspeaker engineering,
how about using the proper terminology and concepts, please?

You HAVE change the transfer function of the network by what you
did. You HAVE altered the frequency response as a result. This
is true whether you want to admit it or know it or not.

Yes, the speakers (not drivers) are more sensitive and it is significant.
The change in xover frequency is INSIGNIFICANT!


THE CROSSOVER FREQUENCY IS NOT THE ISSUE! YOU HAVE
CHANGED THE OVERALL REPONSE OF THE CROSSOVER, EVEN
IF THE CROSSOVER FREQUENCY REMAINS THE SAME.

Minimum shift in what? Current doesn't change by 20%. From my table
there is 14.7% more current at 3000 Hz and 11.6% more current flowing at
6,000 for the same applied voltage. Over the frequency range of where the
tweeter operates, my guess is the average increase in current through the
driver will be around 10%.


STOP LOOKING AT THE NARROW ISSUE OF CURRENT AND
CROSSOVER FREQUENCY.

Try this: Jerry, youy're staring at a single tree. Are you aware
there's a bug forest that you have igored?

In reality, the tweeter (and
midrange) impedance curve is nowhere near flat, and deviates considerably
with frequency. Given that these drivers use no ferrofluid they will

exhibit
a fairly high Q at mechanical resonance ( which I'd estimate around 300Hz
for the mid and 3kHz for the tweeter), yielding an impedance peak at
resonance perhaps double the nominal value. The driver impedance also

rises
gradually with increased frequency, due to the voice coil inductance. So

the
pots were there for 2 reasons: provide level adjustment, and to provide a
measure of impedance stabilization for the crossover. By removing them,

you
have changed things a whole bunch.


John, I don't agree with your conclusion at all. I even calculated the
current flow through the tweeter at 3000Hz both ways. At 3000 Hz there is a
14.7% difference .... @ 4000 hz the difference is 13.5% .... @ 5000 hz the
difference is 12.5% ... @ 6000 hz 11.6%


Once again, you ignored what he said, and you ignored the physical
reality of what's going on with the drivers.

You failed completely to address his point:

"In reality, the tweeter (and midrange) impedance curve is
nowhere near flat, and deviates considerably with
frequency. Given that these drivers use no ferrofluid they will
exhibit a fairly high Q at mechanical resonance ( which I'd
estimate around 300Hz for the mid and 3kHz for the tweeter),
yielding an impedance peak at resonance perhaps double
the nominal value. The driver impedance also rises gradually
with increased frequency, due to the voice coil inductance.

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


He did. You chose, perhaps conveniently, to ignore it.

It's possible that no such amplifier exists.


They do. They're quite common and affrodable. The Heath AR1500
most assuredly isn't one of them.

Some could better than others,


And almost all are better than what you're using, with all due
respect, but you've reduced your experiment to one based
on the lowest common denominator of 30 years ago. You
have an obvious problem with your am,plifier, and you've
done absolutely everything EXCEPT fix the problem: the
amplifier.

but the AR-3a has a very complex impedance map.


No, it most assuredly does not. It's impedance is low,
to be sure, but it is largely resistive in nature. Above its
low-frequency resonance of about 43 Hz, the impedance
is, in fact, quite tame.

The fact that YOU have decided to stick with an amplifier
that seems to be uniquely incapable of handling one of the
more common speakers of the era is no reason to assume
that the faults and warts or your AR1500 is generally applicable.

I don't know if any
amplifier can perform over the entire range


You should get out a lot more. THere are literally hundreds of
such that will do what you are trying to do with your ancient
AR1500 MUCH better than the AR1500 ever good on its best
day.

Further, the amp driving the mid/tweeter is operating at a completely
different level in terms of both voltage and current. In addition, it isn't
burdened at all with fundamentals. Whenever we mix fundamentals with
harmonics we create the opportunity for IM distortion.


When you mix fundamentals with harmonics AND they generate
intermodulation products, those products ARE AT THE SAME
FREQUENCIES AS THE FUNDAMENTAL AND HARMONICS.

When these
frequencies are NOT mixed that opportunity is greatly reduced.


But, even in your scheme, they are, because you have completely
failed to priovide a sufficiently sharp crossover to eliminate one
from the other. Further, the largest producer of distortion products
is the woofer, and it will produce them whether or not you've multi
amped or not.

Virtually all competent
amplifiers act as voltage sources, and within the limit of their power
output capability, perform largely independent of the load they see.


I don't believe that for a minute. One requires enormous "faith" to assume
the simply because an amp can produce a nice wave form open loop, it will
perform the same when driving a dynamic speaker system.


Uh, no. An audio amplifier without a load IS NOT 'OPEN LOOP."

Please learn what the terminology measn before you bandy it about
so.

I believe that much
is going on inside an amp under continually varying loads and very complex
music signals. I believe they are anything, but pure voltage sources.


My, god, Jerry, do you really NOT have any idea what "pure
voltage source" means. Are you at all familiar with the
concept of Thevenin equivalents?

Mr. Stone is talking about fundamental concepts of electrical
engineering which you are twisting into so much gobbledygook.

The impedance seen by two amps is much, much more stable.


No, the impedance is NOT more or less "stable." Please
define what "stable impedance" mean, in your view.

In an single map with widely varying impedance by
frequency, we'll see widely fluctuating current flows over the frequency
range ... at the same voltage. This "instability" just has to have
ramifications.


No, it does not. Your fundamental premise is highly flawed.

Each amp in a bi-amp of the AR-3a's just has a much, much easier job to do
and in my opinion, will always out perform a single amp.


That's your opinion, and you're entitled to it. But no matter
how strongly held, your opinion is still opinion and not
fact.

There have been a number of people involved in this
conversation, any one of whom has DECADES more
professionial experiuence than you have, yet you have
chosen to simply plow forward, ignoring facts, ignoring
reality, and stating your opinions as fact.

I
believe the AR-3a benefits greatly from bi-amping because of the very
difficult frequency dependent load it presents to any single amp.


NO, IT PRESENTS A DIFFICULT LOAD TO YOUR AR1500, WHICH
CAN'T GET OUT OF ITS OWN WAY.

If your amp is BUSTED, which you have provided ample evidence
that it is, the solution is to REPLACE THE AMP.

I've demonstrated that enormous headroom can be gained in the mid-tweeter
amp. Then others have argued that even if clipping occurs in the woofer
amp, the "harmful" harmonics are totally isolated from the mid-range and
tweeter.


No, you have misread, misconstrued, mirunderstood and
misrepresented that they are "totally" isolate. They most
assuredly ARE NOT, and your particular "solution" is about
as far from what you are claiming as one could imagine.

I know what you believe. Now, please explain the basis of this belief.

Let's
see your experiments or charts showing your "biamp" configuration with
ancient low powered amplifiers of dubious quality having far more headroom
than a single 250 watt/ch amplifier with total stability down to 2 ohms.
Your claim, your proof.


First of all, I don't believe any claims of stable down to 2 ohms. I have
some pretty large 2 ohm resistors.


The wide disparity between your beliefs and opinions and physical
reality have been noted a plenty elsewhere.

Wanna burn out your amp?


Bring it on. I have amplifiers here that are UNDCONDITIONALLY
stable into ANY load, resistive or reactive. ANY load.

Your AR1500 seems to have problems driving one of the more
common speakers of its era. Sorry about that, but the world has
LONG since moved on. Maybe you should, too.

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.

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.


Having lived during that era, I can assure you that biamping was indeed
being done in home systems well before 1968. Ever hear of the Marantz 3?
It's an electronic crossover from the '50s. In fact, even Heathkit offered
one called the XO-1 which also dates back well before 1968. There were
others.


I never heard of any of this and was a Heathkit customer, so I can't imagine
it was very popular.


So, once again, YOUR opinon is the same as reality?

What about the Marantz 3, which was sold a decade before
your time frame? What about the Heat XO-1? What about
products from DeCoursey, Crown and others.

What about the AR1-W? which was late '50's/early '60's which
was SPECIFICALLY designed for multi-amped systems? A
VERY common high-end setup at the time was KLH-9's
with AR1W's using the McIntosh electronic crossovers.

The fact that you never heard of them doesn't mean they didn't
exist.

You are either unaware of or have deliberately chosen to
ignore an enormous body of act that contradicts your world
view. Unfortunately, no matter how much you might ignore
or be unaware of, the real worls is still out there, and your
continued tilting against it has done little but squander
any credibility you might have enjoyed.

I mean no insult by this, none whatseoevere, and only use it
necause it is a convenient metaphor, but Mr. Stone (who has
been in the loudspeaker business for a LONG time) myself
(who also enhoys a long and successful career in the business)
and other have been egaging in an excercise akin to teaching
a pig to sing: It's a long, frustrating and fruitless endeavor, and
it only serves to **** off the pig.

There is SO much to learn and know and enjoy about how
loudspeakers work, and you have done yourself a huge
disservice by staking out such a narrowly constructed,
poorly supported and largely technically incorrect position.
The facts and realities of loudspeaker physics are so much
more varied and nuanced and powerful than what your opinions
and what you are unaware of aloow you to experience.

If that satisfies you, then, well, fine, have at it. But while you are
sitting there with your AR1500 and your VERY narrowly limited
experience and view, the rest of the world has moved on. Decades
ago.