"Scott Dorsey" wrote in message
...
Mike Rieves wrote:

But you don't use them for near field monitors, do you? :-) I could see
using Magnepans in a great room for far field or main monitors, but not
without a good pair of nearfields for the fine work. Maggies do have
awesome
midrange clarity.

No, I never really got the whole near-field thing. When near field
monitoring
started coming in, it came in with a huge amount of hype about eliminating
room problems and how you wouldn't have to treat the room any more.
Needless
to say this turned out to be false. But in the eighties I saw folks just
going berserk over the idea and I never felt like I ever liked working
thhat way.

I'll occasionally track on nearfields and I use them in the truck all
the time because there just isn't room for a decent monitoring system.
But for the most part I don't really like mixing on nearfields at all
if there is a good alternative.

Then again, I learned to mix on Altec 604s. Thank God that those days
are over.
--scott

My main monitors' location would qualify them as mid field and I've
treated the room appropriately, and I use them for the actual mixing and
imaging, but I do depend on my near fields for details and relative balance.
Doing all the mixing on near fields is as difficult as doing it all on mid
or far fields, but those with home studios often have no choice, the area is
often small and cramped and SPL levels can often be a problem since others
are living in the house or since it may be in an apartment, preventing the
use of larger monitor speakers located further away from the mixing
position.
In the final analysis, if you're getting good mixes, it doesn't matter
what you're getting them with. :-)

"Pooh Bear" wrote in message
...


David Nebenzahl wrote:

Pooh Bear spake thus:

CWCunningham wrote:

And while you're here, what's wrong with measuring into a resistive
load?
And if there's a qualitative reason that it's "not good" to measure
into a
resistive load, why do you do it that way?

Because it's the only possible standard. Once you get into xR +/- yj
you can have
multiple combinations of x and y and + or -. Not to mention the test
frequency too.

So I'm curious what you think of Arny Krueger's reactive dummy load:
http://www.pcabx.com/product/amplifiers/index.htm. Nobody has commented
on this yet.

It's just *an example* of what's possible.

It is one example of the millions of possible example and meaningless, for
that reason.

Here's a real-world example of just what I was proposing: a load that
combined resistance and reactance to mimic an (average) real-world load
(i.e., a speaker). With an admittedly arbitrarily-chosen topology, if
that's the right word; hey, you have to choose one.

All reactive loads will be arbitrary. Resistive ones aren't. Hence that's
why they're
used. Common playing field.

It clearly says "simulated" so it isn't even a real example. It certainly
isn't typical, because there is no typical speaker load simulator, if there
were, everyone would be using it.

"CWCunningham" charlesw-at-blackfoot.net wrote in message
...

Mike states,
"All of them rate their amps when driving purely resistive loads, and
those are the ratings they publish, they are the ratings listed in the
owners' manuals and in the advertisements for the product".

This is actually false.
Consider
http://www.soundstage.com/gettingtec...ical200503.htm

NAD says they rate their amp using a "difficult 4-ohm load", they don't say
it isn't a resistive load. So how is what I said false? Rating output power
into 4, 2 or even 1, ohm isn't unheard of, but they do use resistive loads.
NAD amps are rated with all channels driven and they do have very stiff
power supplies so the amps can drive difficult loads.
One the differences between really good studio amps and run of the mill hifi
amps is the stiffness of the power supply. A stiff supply will not drop on
voltage when driven hard, a soft one will, and many hifi amp makers use soft
supplies to cut costs while allowing them to keep power ratings high. Also
note that while requiring manufacturers to rate their amps a certain way to
conform with the FTC rule, it doesn't preclude them from using other methods
as well. You sometimes see amps rated at "XXX" watts music power, with the
actual FTC rating being further down the page and the FTC power rating may
be considerably lower than the "music power rating.


| It's called the 'amplifier rule' btw and was recently updated to take
account
of
| recent new product categories such as powered/active speakers.
| http://www.ftc.gov/opa/2000/12/amprule.htm
|
Note in the provided link how the engineers at NAD describe the
ammendments as a
loosening of the rules such that an amp will spec more powerful than it
could
under the original rules.

NAD does design their amps to drive loads with difficult impedances,
including reactance, but they still rate them using resistive loads, just as
I said. I agree with NAD, that the recent changes in the rule have made it
more difficult for the end user to assess an amp by its published specs, and
that is why I keep saying auditio the amp with speakers like the ones you'll
be using! :-)

Arny Krueger wrote:
"Les Cargill" wrote in message


Arny Krueger wrote:


"Pooh Bear"
wrote in message

snip


One simple reason for this is that reactance doesn't
dissipate energy so you couldn't use *watts* for the
spec. This is in fact an interesting point. It would in
fact be somewhat smarter to spec amplifers in terms of
*voltage* output but it would be a task and a half to
change decades of established practice.


Speccing amps in volt-amps would be even more to the
point.


???


Aren't volt-amps and watts purty near the same thing?


No, volt-amps and watts can be vastly different numbers. An ideal reactive
load dissipates no power, so the volt-amps delivered to a reactive load
could be lots while the watts could very small.



Well, of course. Even for sub-ideal inductors, the differences can
be significant. 8 ohm speakers often measure about 5 ohms
resistance - that's how my Dad first taught me about inductance.

So how far apart are they for typical audio amp - loudspeaker
interfaces, then? Assume you have a speaker that's 8 ohms, but
5 ohms resistance. Are you telling me that a power amp
putting out SQRT(12.5) volts of 1000 Hz sine wave into
that speaker is only actually dissipating 62.5 watts
instead of 100?

--
Les Cargill

Arny Krueger wrote:

"Les Cargill" wrote in message


Arny Krueger wrote:


"Pooh Bear"
wrote in message

snip


One simple reason for this is that reactance doesn't
dissipate energy so you couldn't use *watts* for the
spec. This is in fact an interesting point. It would in
fact be somewhat smarter to spec amplifers in terms of
*voltage* output but it would be a task and a half to
change decades of established practice.


Speccing amps in volt-amps would be even more to the
point.


???


Aren't volt-amps and watts purty near the same thing?


No, volt-amps and watts can be vastly different numbers. An ideal reactive
load dissipates no power, so the volt-amps delivered to a reactive load
could be lots while the watts could very small.



Ah, scratch my other post. You said re*act*anc,e not
re*luct*ance. Ne'er mind...

Amp-speaker interfaces are generally not very reactive, yes?

--
Les Cargill

Mike Rieves wrote:

Also remember that there are different rating methods currently in use,
making it even more confusing. I've seen amps rated as: "RMS continuous
power ", "RMS music power", "RMS peak power", "peak power", and others, none
of which have much in common. With so many rating methods now in use, adding
more will only increase the confusion, not clarify anything.

FTC requires power to be rated as continuous average power ( the same as what's
typically called 'rms power' ).

Graham

Pooh Bear wrote:
Mike Rieves wrote:

Also remember that there are different rating methods currently in use,
making it even more confusing. I've seen amps rated as: "RMS continuous
power ", "RMS music power", "RMS peak power", "peak power", and others, none
of which have much in common. With so many rating methods now in use, adding
more will only increase the confusion, not clarify anything.

FTC requires power to be rated as continuous average power ( the same as what's
typically called 'rms power' ).

Note that the FTC regulations only apply to advertisements of home stereo gear
in the US.

The car stereo people and boom box people and (the very worst) computer
people can still advertise ONE MILLION WATTS PEAK MUSIC POWER OUTPUT.

Pro audio gear usually follows FTC guidelines but doesn't always, and you
will occasionally see some goofy numbers here and there.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

"Pooh Bear" wrote in message
...


Mike Rieves wrote:

Also remember that there are different rating methods currently in
use,
making it even more confusing. I've seen amps rated as: "RMS continuous
power ", "RMS music power", "RMS peak power", "peak power", and others,
none
of which have much in common. With so many rating methods now in use,
adding
more will only increase the confusion, not clarify anything.

FTC requires power to be rated as continuous average power ( the same as
what's
typically called 'rms power' ).

Graham

You're right, but as long as the FTC rated power is displayed somewhere in
the specs, they're free to use other ratings as well. You see it all the
time on car amps, boomboxes and home theater systems.

Mike Rieves wrote:

Since this discussion is primarily about studio monotors and studio
control rooms (especially home studio control rooms) are often quite small,
there can enough room effect on the cone dynamics to make a measureable
difference, enough to cause an audible difference in the speaker's sound.

Citation please?


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein

Scott Dorsey wrote:

Pooh Bear wrote:
Mike Rieves wrote:

Also remember that there are different rating methods currently in use,
making it even more confusing. I've seen amps rated as: "RMS continuous
power ", "RMS music power", "RMS peak power", "peak power", and others, none
of which have much in common. With so many rating methods now in use, adding
more will only increase the confusion, not clarify anything.

FTC requires power to be rated as continuous average power ( the same as what's
typically called 'rms power' ).

Note that the FTC regulations only apply to advertisements of home stereo gear
in the US.

The car stereo people and boom box people and (the very worst) computer
people can still advertise ONE MILLION WATTS PEAK MUSIC POWER OUTPUT.

For the life of me I can't understand why they still allow this.

Pro audio gear usually follows FTC guidelines but doesn't always, and you
will occasionally see some goofy numbers here and there.

I can't say I have myself. Do you have any examples ?

Graham

"Mike Rieves" wrote in message


David, old boy, what did you not understand about:
"That's easy, in simple terms, the air in the room acts
as a spring (the smaller the room, the more powerful the
spring) which acts on the speaker cone's motion, which in
turn has an effect on the voice coil movement, which has
an effect on the electromotive mechanism. This is
reflected back to the amp output as an impedance change.
Standing waves in the room may also have an affect as
well. This isn't something made up for this news group,
that fact that the room affects a speaker's overall
reactance has been known for many years. Anyone who knows
anything about speakers knows that the enclosure the
speaker is installed in has a major effect on a speaker's
characteristics, including impedance, but some may not
realize that the room is actually another enclosure on
the other side of the speaker, and it has an effect as
well. Typically, the back of the speaker cone is loading
into the enclosure and the front of the cone is loading
into the room."

How is that nebulous?

It lacks quantification.

If you were technically competent Mike, you'd have already tried to measure
it, and you'd know that it is a nit.

"Les Cargill" wrote in message

Arny Krueger wrote:
"Les Cargill" wrote in message


Arny Krueger wrote:


"Pooh Bear"
wrote in message

snip


One simple reason for this is that reactance doesn't
dissipate energy so you couldn't use *watts* for the
spec. This is in fact an interesting point. It would
in fact be somewhat smarter to spec amplifers in
terms of *voltage* output but it would be a task and
a half to change decades of established practice.


Speccing amps in volt-amps would be even more to the
point.


???


Aren't volt-amps and watts purty near the same thing?

No, volt-amps and watts can be vastly different numbers.
An ideal reactive load dissipates no power, so the
volt-amps delivered to a reactive load could be lots
while the watts could very small.

Well, of course. Even for sub-ideal inductors, the
differences can be significant. 8 ohm speakers often
measure about 5 ohms resistance - that's how my Dad first
taught me about inductance.
So how far apart are they for typical audio amp -
loudspeaker interfaces, then? Assume you have a speaker
that's 8 ohms, but 5 ohms resistance.

That is unrealistically simple for a speaker.

The magnitude of the impedance of a speaker can easily range from 0.75 of
rated impedance to 10 times rated impedance and back again, maybe several
times over the regular audio band.

It is not unusual for the impedance of a speaker to have a phase angle of
45-60 degrees at some frequencies.

I studied this out once, and built a circuit that behaved like a reasonable
worst case loudspeaker. Here are the impdeance magnitude and phase angle
curves:

http://www.pcavtech.com/techtalk/wir...mulator-mag-hi

http://www.pcavtech.com/techtalk/wir...imulator-phase


Are you telling me that a power amp putting out SQRT(12.5) volts of
1000 Hz sine wave into
that speaker is only actually dissipating 62.5 watts instead of 100?

Depends on what the impedance of the speaker is at 1 KHz.

I found that a reasoanble worst-case 4 ohm 2-way speaker might have an
impedance of about 12 ohms at 1 KHz.

Letsee if my 40 year-old recollections of EE classes are any good:

The phase angle of the impedance of my reasonble-worst-case speaker at that
point was about 37 degrees. The real (resistive) component of the impedance
at that frequency would be about 9.5 ohms. The imaginary (reactive)
component of the impedance at that frequency would be about 7.2 ohms. If
you applied 12 volts across this speaker, the speaker would draw about an
amp over-all, but there would be a out-of-phase current drain that would be
more like 1.7 amps. The power amp would therefore be required to provide
more like 20 volt-amps.

Bob Cain wrote:
Mike Rieves wrote:

Since this discussion is primarily about studio monotors and studio
control rooms (especially home studio control rooms) are often quite small,
there can enough room effect on the cone dynamics to make a measureable
difference, enough to cause an audible difference in the speaker's sound.

Citation please?

I don't think it should be significant, but it just so happens that I have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Pooh Bear wrote:
Scott Dorsey wrote:
The car stereo people and boom box people and (the very worst) computer
people can still advertise ONE MILLION WATTS PEAK MUSIC POWER OUTPUT.

For the life of me I can't understand why they still allow this.

I find it less offensive than the magnets that are advertised as improving
your gas mileage or the copper bracelets advertised as helping arthritis.

Pro audio gear usually follows FTC guidelines but doesn't always, and you
will occasionally see some goofy numbers here and there.

I can't say I have myself. Do you have any examples ?

Well, on the GOOD side you'll see folks like QSC which list power ratings
on the data sheet with both FTC and EIA methods.

On the BAD side you'll see American DJ.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article , (Scott Dorsey) wrote:
Bob Cain wrote:
Mike Rieves wrote:

Since this discussion is primarily about studio monotors and studio
control rooms (especially home studio control rooms) are often quite small,
there can enough room effect on the cone dynamics to make a measureable
difference, enough to cause an audible difference in the speaker's sound.

Citation please?

I don't think it should be significant, but it just so happens that I have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.

The main change would be at woofer resonance I imagine. The amplifier
will nullify the variation, or try to, but this in itself would not make
large differences in sound, but levels matter trying to do things at low power
is much different at high power.

greg

In article , (Scott Dorsey) wrote:
Pooh Bear wrote:
Scott Dorsey wrote:
The car stereo people and boom box people and (the very worst) computer
people can still advertise ONE MILLION WATTS PEAK MUSIC POWER OUTPUT.

For the life of me I can't understand why they still allow this.

I find it less offensive than the magnets that are advertised as improving
your gas mileage or the copper bracelets advertised as helping arthritis.

Also magnets for arthritis. And how can bracelets be polarized with a solid
piece of metal?

I like to see graph of watts, ohms, and distortion. I also like a peak power @ seconds
rating. There are those amps that delelop more peak power due to different
methods as used in NAD, Hitachi, and Souncraftsman amps.
When ever I get a chance to fix it, I have what Julian Hirsch said
was the worlds most powrfull receiver. That NAD with something like
100 WPC and 400 watts peak.

greg

Pro audio gear usually follows FTC guidelines but doesn't always, and you
will occasionally see some goofy numbers here and there.

I can't say I have myself. Do you have any examples ?

Well, on the GOOD side you'll see folks like QSC which list power ratings
on the data sheet with both FTC and EIA methods.

On the BAD side you'll see American DJ.
--scott

Scott Dorsey wrote:

I don't think it should be significant, but it just so happens that I have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.

Very cool, Scott! Placement in the room would also be an interesting
variable.


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein

On Fri, 02 Jun 2006 14:04:41 -0700, Bob Cain
wrote:

Scott Dorsey wrote:

I don't think it should be significant, but it just so happens that I have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.

Very cool, Scott! Placement in the room would also be an interesting
variable.


Bob

There might be a tiny change around the LF resonance points, but I
wouldn't expect anything elsewhere.

d

--
Pearce Consulting
http://www.pearce.uk.com

Scott Dorsey wrote:

I don't think it should be significant, but it just so happens that I
have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.

See? There is an up side to moving.

Peace,
Paul

"GregS" wrote in message
...
In article , (Scott
Dorsey) wrote:
Bob Cain wrote:
Mike Rieves wrote:

Since this discussion is primarily about studio monotors and studio
control rooms (especially home studio control rooms) are often quite
small,
there can enough room effect on the cone dynamics to make a measureable
difference, enough to cause an audible difference in the speaker's
sound.

Citation please?

I don't think it should be significant, but it just so happens that I have
speakers set up in an empty room and an impedance bridge. Let me do a
plot on them, and see how it changes when the rugs and furniture are in
and the room is less live. I doubt it'll be as much as 1%, but it'll
be interesting to see and minimal effort to measure.

The main change would be at woofer resonance I imagine. The amplifier
will nullify the variation, or try to, but this in itself would not make
large differences in sound, but levels matter trying to do things at low
power
is much different at high power.


I would think that the room volume would be the primary factor affecting
the speaker impedance. I don't think that furnishings will have an
appreciable effect unless they happen to affect standing waves at the
speaker locations.

Mike Rieves wrote:
"David Nebenzahl" wrote in message
.com...

First, let me say that I come to this argument late, as a long-
overdue vacation to Wales and Ireland stood betwixt myself and
the regrettably common rec.audio techno-babble..

Mr Rieves makes very specific technical assertions regarding the
electrical behavior of loudspeakers in rooms.

Any assertions that the impedance/reactance changes appreciably due to
change in the "sonic environment" (whatever the ****** that is) are just
audiophool pixie-dust fantasies. Like maybe small changes in barometric
pressure? Relative humidity?

Come on; this ought to be good. Explain away. Get specific.

That's easy, in simple terms,

Good, then we shall evaluate as you suggest..

the air in the room acts as a spring (the
smaller the room, the more powerful the spring) which acts
on the speaker cone's motion, which in turn has an effect
on the voice coil movement, which has an effect on the
electromotive mechanism. This is reflected back to the
amp output as an impedance change.

First, Mr. Rieve4s makes several very specific technical
assertions. Let's deal with each of those in turn.

"the air in the room acts as a spring (the smaller the room,
the more powerful the spring)"

Well, in a technically inaccurate, viceral sort of way, maybe.
Springs, however, aren't "powerful." Springs, mechanical
reactances, don't have power any more than masses or
capacitances or inductances do. Springs have, not surprisingly
stiffness. That stiffness can be shown, as any reasonable text
on acoustics will show (check Beranek, Kinsler and Frey,
Blackenstock, etc.), to be a reciprocal function of the volume.
And that is the basis of our analysis of Mr. Rieves' assertions.

He further asserts:

"Anyone who knows anything about speakers knows that the
enclosure the speaker is installed in has a major effect on a
speaker's characteristics, including impedance, but some may
not realize that the room is actually another enclosure on the
other side of the speaker, and it has an effect as well.
Typically, the back of the speaker cone is loading into the
enclosure and the front of the cone is loading into the room."

Mr. Rieves has conveniently provided us with the means of
evaluating his own assertion. Let's do just exactly that.

As we have already stated, the stiffness of an enclosure is
proprotional to the reciprocal of its volume. Using this well-
established principle, we can evaluate directly the effect of
the room on. To do so, let's make some assumptions, chosen, in
fact, to support Mr. Rieves' assertions as much as possible.
Those assertions include:

1. A sealed box acoustic-suspension loudspeaker whose internal
volume is 1.5 cubic feet. We chose this configuration to
directly support Mr. Rieves' assertion, and it represents a
typical value for high-performance systems of this type. In
such a system, the enclosure stiffness dominates the
suspension's mechanical stiffness and is the determining
factor in the system stiffness.

2. We will assume a listening room whose dimensions are 8 feet
high, 12 feet wide and 15 feet long, whose internal volume is
approximately 1500 cubic feet. We will assume this room has
absolutely rock-solid, totally reflective walls, there is no
absorbtion in the room at all, and that the room is tightly
sealed, with no doors, windows, vents or other means by which
air can enter or escape. The same can be said for any
uccupants as well.

3. We will compare the performance in the room to the
performance in absolute free air.

So, since the acoustical stiffness is proportional to the
reciprocal of the volume, we have a direct means of comapring
the effect of each, according to Mr. Rieves. The total stiffness
felt by the cone is, in fact, simply the linear sum of all
stiffnesses. And since the room has a volume that 1/1000 that of
the enclosure, we can reasonably deduce that it's stiffness is
1/1000 that of the enclosure. Thus the total system stiffness of
the entire system, including the room, has been changed by
1+1/1000 or 1.001 times that of the speaker in a totally free
environment.

Let's examine some the consequences of that

1. Change to system resonance

This is, in fact, the ONLY substantive change that can
happen, for a couple of reasons. First, Despite Mr. Rieves'
assertions to the contrary, stiffness will only have an
effect at and below fundamental resonance, as the system is
mass controlled above resonance, This is why, for example,
changing the enclosure size for a given driver has NO impact
on reference efficiency. Second, changing the total system
stiffness WILL affect both the resonant frequency AND the
system Q at resonance (due to the increased reactance
provided by the additional stuffness).

The resonance of the system goes as:

F = 1/(2 pi) * 1/sqrt(M/K)

where M is the effective moving mass, and K is the total
stiffness. We'll assume that the stiffness is determined
solely by the acoustic stiffness of the enclosure and the
room (as any additional stiffnessses, such as the suspension,
will simply diminish the effects of the room stiffness).

Given that, we can directly evaluate how much the resonance
changes:

F' = 1/(2 pi) * 1/sqrt(M/1.001)

Since we are looking simply at the effect of changing one
parameter, K, M can be considered a constant and f' will
simply be the ratio of the change in resonant frequency. The
result of evaluating this relation is that the room will
change the resonant frequency by 0.05%. And since damping
goesd as the resonant frequency, the system Q will change by
a similar 0.05%.

Thse figures are substantially smaller than can be reliably
measured using the best current methods.

For comparison, let's put that same speaker in a room that's
half the total volume, say 8 feet tall by 8 feet wide by 11
feet long. Now the resonance will change by a whopping 0.1%.

2. Confounding factors

The enclosure and room acoustical stiffness are NOT the conly
contributing factors. We purposely ignored the mechanical
stiffness to maximize the potential effects of the room. We
can't ignore the mechanical stiffness simply because it is SO
much larger than that provided by the room. In a typical
acoustic suspension system, the mechanical stiffness of the
suspension is usually no more than 1/4-1/3 that of the
enclosure (this larger ratio is what defines "acoustic
suspension"). Thus, that stiffness is on the order of 250
times that of the room.

More importantly is the fact that the mechanical stiffness of
the suspension is one of the hardest mechanical parameters to
control during manufacturing, and variations in the parameter
of 20% are not uncommon. Indeed, 20% is considered quite
good. Since the suspension stiffness is on the order of 1/4
the total stiffness, changes in that stiffness can be
considered to contrinute 1/4 the total cariation in system
stiffness. Thus, variations of +-20% in mechanical stiffness
result in changes of +-5% in total system stiffness.

This means that the simple manufacturing tolerances in the
suspension have an effect that's 100 times GREATER than the
effect of the room on total system stiffness.

Using Mr. Rieves own technical basis for his assertions, it's
safe to say that his assertions are shown to be, in essence,
bunkum.

Standing waves in the room may also have an affect as well.

This can alos be evaluated. Any of the above cited texts will
show that the total impedance of a loudspeaker is the result, in
order of the magnitude of the contribution, to be the electrical
portion, the mechanical proportion and the acoustical
proportion. Further, it can be shown that the acoustical
contribution is, by far, the smallest of all three, and is
essentially a function of, at its greatest, the reference
efficiency of the system. Seldom does the efficiency of a direct
radiator loudspeaker exceed 1%, so one can reasonably expect the
effects of standing waves to never influence the impedance in
excess of the total contribution of its change in radiation
impedance to total system impedance.

This is simply born out by the many thousands of impednace
curves I have measured of speakers in and out of rooms that
show, effectively NO such changes Mr. Rieves asserts must exist
that cannot be fully explained by any number of confounding
factors, only 1 of which is mentioned above.

This isn't something made up for this news group,

Well, it would appear that, in fact, it is, since the effect is
not documented as Mr. Rieves claims in any of the professional
literature.

that fact that the room affects a speaker's overall reactance
has been known for many years.

Known by whom? Would Mr. Rieves be so kind as to cite the
specifric references he seems to be alluding to?

Now, one of the problems associated with actually proving or
disproving Mr. Rieves assertions by measurements is the simple
fact that the measurement techniques alone can lead to
varations in the data that well exceed the kinds of effects his
assertions would suggest exist. For example, simply measuring
the same loudspeaker under identical conditions two times n a
row will almost certainly lead to detectable differences due to
such effects as small changes in voice coil temperature,
flexations and changes in suspension due to mechanical
hysteresis and relaxation effects, and so on. Attempting to
allow such parameters to stabilize over time means that we now
must deal with inevitable changes in environment (temperature,
prissure, humidity) which can have greater effects thah that of
the room.

What it seems we have here, yet again, is the application of
common intuition aided by a lack of technical expertise in a
topic to draw a conclusion that, while, within a very bnarrow
context, may seem intuitivgely correcdt, is simply at odds with
physical fact. Not an uncommon occurance in audio, to be sure.

wrote in message
oups.com...

What it seems we have here, yet again, is the application of
common intuition aided by a lack of technical expertise in a
topic to draw a conclusion that, while, within a very bnarrow
context, may seem intuitivgely correcdt, is simply at odds with
physical fact. Not an uncommon occurance in audio, to be sure.

But it's not at odds with physical fact. The effects are there. They're
simply too tiny to make any real-world audible difference.

Peace,
Paul

Paul Stamler spake thus:

wrote in message
oups.com...

What it seems we have here, yet again, is the application of
common intuition aided by a lack of technical expertise in a
topic to draw a conclusion that, while, within a very bnarrow
context, may seem intuitivgely correcdt, is simply at odds with
physical fact. Not an uncommon occurance in audio, to be sure.

But it's not at odds with physical fact. The effects are there. They're
simply too tiny to make any real-world audible difference.

Which is what I was saying all along in this thread: effects, yes, but
inconsequential.

Apparently, though, some audio-fools have to be beaten over the head
repeatedly by a 50 lb. doctoral thesis before it sinks in.


--
Any system of knowledge that is capable of listing films in order
of use of the word "****" is incapable of writing a good summary
and analysis of the Philippine-American War. And vice-versa.
This is an inviolable rule.

- Matthew White, referring to Wikipedia on his WikiWatch site
(http://users.erols.com/mwhite28/wikiwoo.htm)

wrote in message
oups.com...

Mike Rieves wrote:
"David Nebenzahl" wrote in message
.com...

First, let me say that I come to this argument late, as a long-
overdue vacation to Wales and Ireland stood betwixt myself and
the regrettably common rec.audio techno-babble..

Mr Rieves makes very specific technical assertions regarding the
electrical behavior of loudspeakers in rooms.

Any assertions that the impedance/reactance changes appreciably due to
change in the "sonic environment" (whatever the ****** that is) are
just
audiophool pixie-dust fantasies. Like maybe small changes in barometric
pressure? Relative humidity?

Come on; this ought to be good. Explain away. Get specific.

That's easy, in simple terms,

Good, then we shall evaluate as you suggest..

the air in the room acts as a spring (the
smaller the room, the more powerful the spring) which acts
on the speaker cone's motion, which in turn has an effect
on the voice coil movement, which has an effect on the
electromotive mechanism. This is reflected back to the
amp output as an impedance change.

First, Mr. Rieve4s makes several very specific technical
assertions. Let's deal with each of those in turn.

"the air in the room acts as a spring (the smaller the room,
the more powerful the spring)"

Well, in a technically inaccurate, viceral sort of way, maybe.
Springs, however, aren't "powerful." Springs, mechanical
reactances, don't have power any more than masses or
capacitances or inductances do. Springs have, not surprisingly
stiffness. That stiffness can be shown, as any reasonable text
on acoustics will show (check Beranek, Kinsler and Frey,
Blackenstock, etc.), to be a reciprocal function of the volume.
And that is the basis of our analysis of Mr. Rieves' assertions.

He further asserts:

"Anyone who knows anything about speakers knows that the
enclosure the speaker is installed in has a major effect on a
speaker's characteristics, including impedance, but some may
not realize that the room is actually another enclosure on the
other side of the speaker, and it has an effect as well.
Typically, the back of the speaker cone is loading into the
enclosure and the front of the cone is loading into the room."

Mr. Rieves has conveniently provided us with the means of
evaluating his own assertion. Let's do just exactly that.

As we have already stated, the stiffness of an enclosure is
proprotional to the reciprocal of its volume. Using this well-
established principle, we can evaluate directly the effect of
the room on. To do so, let's make some assumptions, chosen, in
fact, to support Mr. Rieves' assertions as much as possible.
Those assertions include:

1. A sealed box acoustic-suspension loudspeaker whose internal
volume is 1.5 cubic feet. We chose this configuration to
directly support Mr. Rieves' assertion, and it represents a
typical value for high-performance systems of this type. In
such a system, the enclosure stiffness dominates the
suspension's mechanical stiffness and is the determining
factor in the system stiffness.

2. We will assume a listening room whose dimensions are 8 feet
high, 12 feet wide and 15 feet long, whose internal volume is
approximately 1500 cubic feet. We will assume this room has
absolutely rock-solid, totally reflective walls, there is no
absorbtion in the room at all, and that the room is tightly
sealed, with no doors, windows, vents or other means by which
air can enter or escape. The same can be said for any
uccupants as well.

3. We will compare the performance in the room to the
performance in absolute free air.

So, since the acoustical stiffness is proportional to the
reciprocal of the volume, we have a direct means of comapring
the effect of each, according to Mr. Rieves. The total stiffness
felt by the cone is, in fact, simply the linear sum of all
stiffnesses. And since the room has a volume that 1/1000 that of
the enclosure, we can reasonably deduce that it's stiffness is
1/1000 that of the enclosure. Thus the total system stiffness of
the entire system, including the room, has been changed by
1+1/1000 or 1.001 times that of the speaker in a totally free
environment.

Let's examine some the consequences of that

1. Change to system resonance

This is, in fact, the ONLY substantive change that can
happen, for a couple of reasons. First, Despite Mr. Rieves'
assertions to the contrary, stiffness will only have an
effect at and below fundamental resonance, as the system is
mass controlled above resonance, This is why, for example,
changing the enclosure size for a given driver has NO impact
on reference efficiency. Second, changing the total system
stiffness WILL affect both the resonant frequency AND the
system Q at resonance (due to the increased reactance
provided by the additional stuffness).

The resonance of the system goes as:

F = 1/(2 pi) * 1/sqrt(M/K)

where M is the effective moving mass, and K is the total
stiffness. We'll assume that the stiffness is determined
solely by the acoustic stiffness of the enclosure and the
room (as any additional stiffnessses, such as the suspension,
will simply diminish the effects of the room stiffness).

Given that, we can directly evaluate how much the resonance
changes:

F' = 1/(2 pi) * 1/sqrt(M/1.001)

Since we are looking simply at the effect of changing one
parameter, K, M can be considered a constant and f' will
simply be the ratio of the change in resonant frequency. The
result of evaluating this relation is that the room will
change the resonant frequency by 0.05%. And since damping
goesd as the resonant frequency, the system Q will change by
a similar 0.05%.

Thse figures are substantially smaller than can be reliably
measured using the best current methods.

For comparison, let's put that same speaker in a room that's
half the total volume, say 8 feet tall by 8 feet wide by 11
feet long. Now the resonance will change by a whopping 0.1%.

2. Confounding factors

The enclosure and room acoustical stiffness are NOT the conly
contributing factors. We purposely ignored the mechanical
stiffness to maximize the potential effects of the room. We
can't ignore the mechanical stiffness simply because it is SO
much larger than that provided by the room. In a typical
acoustic suspension system, the mechanical stiffness of the
suspension is usually no more than 1/4-1/3 that of the
enclosure (this larger ratio is what defines "acoustic
suspension"). Thus, that stiffness is on the order of 250
times that of the room.

More importantly is the fact that the mechanical stiffness of
the suspension is one of the hardest mechanical parameters to
control during manufacturing, and variations in the parameter
of 20% are not uncommon. Indeed, 20% is considered quite
good. Since the suspension stiffness is on the order of 1/4
the total stiffness, changes in that stiffness can be
considered to contrinute 1/4 the total cariation in system
stiffness. Thus, variations of +-20% in mechanical stiffness
result in changes of +-5% in total system stiffness.

This means that the simple manufacturing tolerances in the
suspension have an effect that's 100 times GREATER than the
effect of the room on total system stiffness.

Using Mr. Rieves own technical basis for his assertions, it's
safe to say that his assertions are shown to be, in essence,
bunkum.

Standing waves in the room may also have an affect as well.

This can alos be evaluated. Any of the above cited texts will
show that the total impedance of a loudspeaker is the result, in
order of the magnitude of the contribution, to be the electrical
portion, the mechanical proportion and the acoustical
proportion. Further, it can be shown that the acoustical
contribution is, by far, the smallest of all three, and is
essentially a function of, at its greatest, the reference
efficiency of the system. Seldom does the efficiency of a direct
radiator loudspeaker exceed 1%, so one can reasonably expect the
effects of standing waves to never influence the impedance in
excess of the total contribution of its change in radiation
impedance to total system impedance.

This is simply born out by the many thousands of impednace
curves I have measured of speakers in and out of rooms that
show, effectively NO such changes Mr. Rieves asserts must exist
that cannot be fully explained by any number of confounding
factors, only 1 of which is mentioned above.

This isn't something made up for this news group,

Well, it would appear that, in fact, it is, since the effect is
not documented as Mr. Rieves claims in any of the professional
literature.

that fact that the room affects a speaker's overall reactance
has been known for many years.

Known by whom? Would Mr. Rieves be so kind as to cite the
specifric references he seems to be alluding to?

Now, one of the problems associated with actually proving or
disproving Mr. Rieves assertions by measurements is the simple
fact that the measurement techniques alone can lead to
varations in the data that well exceed the kinds of effects his
assertions would suggest exist. For example, simply measuring
the same loudspeaker under identical conditions two times n a
row will almost certainly lead to detectable differences due to
such effects as small changes in voice coil temperature,
flexations and changes in suspension due to mechanical
hysteresis and relaxation effects, and so on. Attempting to
allow such parameters to stabilize over time means that we now
must deal with inevitable changes in environment (temperature,
prissure, humidity) which can have greater effects thah that of
the room.

What it seems we have here, yet again, is the application of
common intuition aided by a lack of technical expertise in a
topic to draw a conclusion that, while, within a very bnarrow
context, may seem intuitivgely correcdt, is simply at odds with
physical fact. Not an uncommon occurance in audio, to be sure.


Since this was one small part of a discussion of much larger scope, having
to do with why manufacturers rate their amplifiers instead of some mythical
"typical speaker" reactive dummy load, it's validity has little to do with
the overall argument. I will concede that the room's effect is very small
compared to other factors, and it may indeed be inconsequential from a
practical standpoint, but that does not alter one whit the fact that there
is no way to calculate a "typical speaker" reactive load for rating amps.
The current method may be a nominal method, but does give some common
factors to compare when evaluating amplifiers. As I said here more than
once, when buying a new amplifier, you should evaluate the amps with the
same speakers you're going to be using. Or don't, whatever strikes your
fancy.
I got into this discussion because it was cross-posted to
alt.music.home-studio, and my comments were in response to a a post asking
"Why don't manufacturers use a reactive dummy load typical of a real
speaker?" My point was and is that there is no "typical" speaker, and I
stand by that.

Mike Rieves wrote:
Since this was one small part of a discussion of much larger scope, having
to do with why manufacturers rate their amplifiers instead of some mythical
"typical speaker" reactive dummy load, it's validity has little to do with
the overall argument.

Well, no. Whether or not the particular set of assertions you made
is applicable to another topic does absolve them of their inherent
technical incorrectness.

You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

I will concede that the room's effect is very small
compared to other factors, and it may indeed be inconsequential from a
practical standpoint, but that does not alter one whit the fact that there
is no way to calculate a "typical speaker" reactive load for rating amps.

Actually, there most assuredly is, and your attempts to suggest
otherwise by cobbling up assertion that the room is an important
factor by appealing to some unknown and unheard-of authority
simply weakens you position further.

As I mentioned, I have personally performed many thousands
of impedance (and other) measurements on loudspeakers
over the last 30+ years. From that massive amount of data,
supported by many ore measurements that are available, it
most assuredly IS possible to come up with no more than
maybe a half-dozen impedance models which cover the vast
majority of loads encountered by typical amplifiers.

First of all, it's possible, given the relative size of the market
segments, to eliminate a number of "pathological" speaker
loads. For example, pure electrostatics and hybrids can
effectively eliminated from evaluation simply because their
penetration into the market is far to small to have any
consequence, and they can be dealt with as special cases.
The same can be said of most planar speakers and conjugate-
compensated speakers, which behave like resistors in any case.

By pruning these rare and patholigical cases, we can reduce the
problem set to essentially a two-dimensial matrix. One dimension
is two-way vs three-way systems, the other dimension is simply
moderate nominal impedance (6-8 ohms) vs low impedance
(3-5 ohms).

All the other variations, such as sealed box vs reflex , crossover
frequencies and order, fundamental resonant frequancy and
such, while they may lead to a different LOOKING impedance
curve, do not lead to any models which result in measurably
different performance.

Once you have covered these two crucial dimensions and
the gross variations in each of those, the departure you have
made from simple resitive loading is FAR greater than ANY
individual variations due to system tuning, configuration and
topology.

The current method may be a nominal method, but does give
some common factors to compare when evaluating amplifiers.

None of which, it can be argued have any relevance to actual
in-situ behavior.

What you are, in essence, arguing is that since you can't
think of any "typical" load, you've decided to pick the most
non-typical one imaginable.

and my comments were in response to a a post asking
"Why don't manufacturers use a reactive dummy load
typical of a real speaker?" My point was and is that there
is no "typical" speaker, and I stand by that.

Stand as you wish, but your point is not technically supportable.
I have constructed 4 such impedance models, based precisely
on the pruning model I discussed above, but have further
performed measurements on a much wider variety of loads
driven by a wide variety of amplifiers. These measurement data
all clearly support the assertion that the largets differences is
between puerely resistive loading and nearly ANY "typical"
speaker impedance, i.e., one that reasonably emulates a
two-way or three-way system of moderate of low impedance.
Chaning parameters such as moving the systems fundamental
resonance from, say, 30 to 50 Hz, or changing it from a sealed
box with one impedance peak to a reflex with two and such
does nOT substantially change how the amplifier behaves.

The exception, of course, being the outlyinh pathological
cases, such as amplifiers with extremely high output
impedance, and more.

But as to the assertion that there can be now "typcial" load?
No.

wrote:

Mike Rieves wrote:
Since this was one small part of a discussion of much larger scope, having
to do with why manufacturers rate their amplifiers instead of some mythical
"typical speaker" reactive dummy load, it's validity has little to do with
the overall argument.

Well, no. Whether or not the particular set of assertions you made
is applicable to another topic does absolve them of their inherent
technical incorrectness.

You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet influences the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat rather
smaller effect. Just because it can be normally ignored doesn't mean it doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there at a
minute level.

Graham

"Pooh Bear" wrote in message
...
You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet
influences the
impedance curve is there ? By analogy, clearly the room ( in effect
another
cabinet in front of the speaker cone ) must have a similar if somewhat
rather
smaller effect. Just because it can be normally ignored doesn't mean it
doesn't
exist.

In practice of course it's not an issue but the effect must clearly be
there at a
minute level.


But since it *IS* a MINUTE factor, and can be safely ignored in all cases,
bringing it up in the thread as something that needs to considered (or at
all), would be well and truly classified as a "red herring", or maybe a
"straw man", wouldn't you agree?

MrT.

"Mr.T" wrote:

"Pooh Bear" wrote in message
...
You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet influences
the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat
rather
smaller effect. Just because it can be normally ignored doesn't mean it
doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there
at a
minute level.

But since it *IS* a MINUTE factor, and can be safely ignored in all cases,
bringing it up in the thread as something that needs to considered (or at
all), would be well and truly classified as a "red herring", or maybe a
"straw man", wouldn't you agree?

Depends on context. Since there clearly must be *some* effect, I think it's
unreasonable to dismiss it out of hand.

Graham

On Fri, 09 Jun 2006 05:08:43 +0100, Pooh Bear
wrote:



"Mr.T" wrote:

"Pooh Bear" wrote in message
...
You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet influences
the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat
rather
smaller effect. Just because it can be normally ignored doesn't mean it
doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there
at a
minute level.

But since it *IS* a MINUTE factor, and can be safely ignored in all cases,
bringing it up in the thread as something that needs to considered (or at
all), would be well and truly classified as a "red herring", or maybe a
"straw man", wouldn't you agree?

Depends on context. Since there clearly must be *some* effect, I think it's
unreasonable to dismiss it out of hand.

Since it's effect has been calculated to be less than 0.1% of the only
factor (fundamental resonance) that will show any demonstrable effect
at all, and since the two drivers in a pair of speakers are unlikely
to have their fundamental resonances matched to better than a couple
of percent, I think it's *entirely* reasonable to dismiss it out of
hand. If you disagree, then we'll have to move on to the equally if
not in many cases more significant matters of room temperature and
humidity, not to mention altitude and its dramatic effect on air
density.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

"Stewart Pinkerton" wrote in message
...
On Fri, 09 Jun 2006 05:08:43 +0100, Pooh Bear
wrote:



"Mr.T" wrote:

"Pooh Bear" wrote in message
...
You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet
influences
the
impedance curve is there ? By analogy, clearly the room ( in effect
another
cabinet in front of the speaker cone ) must have a similar if
somewhat
rather
smaller effect. Just because it can be normally ignored doesn't mean
it
doesn't
exist.

In practice of course it's not an issue but the effect must clearly
be there
at a
minute level.

But since it *IS* a MINUTE factor, and can be safely ignored in all
cases,
bringing it up in the thread as something that needs to considered (or
at
all), would be well and truly classified as a "red herring", or maybe a
"straw man", wouldn't you agree?

Depends on context. Since there clearly must be *some* effect, I think
it's
unreasonable to dismiss it out of hand.

Since it's effect has been calculated to be less than 0.1% of the only
factor (fundamental resonance) that will show any demonstrable effect
at all, and since the two drivers in a pair of speakers are unlikely
to have their fundamental resonances matched to better than a couple
of percent, I think it's *entirely* reasonable to dismiss it out of
hand. If you disagree, then we'll have to move on to the equally if
not in many cases more significant matters of room temperature and
humidity, not to mention altitude and its dramatic effect on air
density.

There's one case, and only one, where the room volume *may* have an effect,
and that's the case of the automobile. And only when the windows are closed.

As for "typical" speaker impedances, I think Don has nailed it: you can't
design a single dummy load that represents everything, but you can design a
few that represent almost everything, and that's good enough for practical
purposes. It's like the (male) mathematician who told the (male) engineer
that it was mathematically impossible for him to actually come into contact
with the luscious (female) graduate student across the room. "No," replied
the engineer, "but I can get arbitrarily close, and from a practical point
of view that's good enough for me."

Peace,
Paul

Pooh Bear wrote:

"Mr.T" wrote:

"Pooh Bear" wrote in message
...
You further stated, clearly, that:

"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"
Well...... I don't think there's any doubt that a speaker cabinet influences
the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat
rather
smaller effect. Just because it can be normally ignored doesn't mean it
doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there
at a
minute level.
But since it *IS* a MINUTE factor, and can be safely ignored in all cases,
bringing it up in the thread as something that needs to considered (or at
all), would be well and truly classified as a "red herring", or maybe a
"straw man", wouldn't you agree?

Depends on context. Since there clearly must be *some* effect, I think it's
unreasonable to dismiss it out of hand.

Error bars, man. Think error bars. :-)


Bob
--

"Things should be described as simply as possible, but no simpler."

A. Einstein

Pooh Bear wrote:
wrote:

Again, I ask, "known by whom?"

Dick, I am very glad to see you here in rec.audio.pro again.

Well...... I don't think there's any doubt that a speaker cabinet influences the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat rather
smaller effect. Just because it can be normally ignored doesn't mean it doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there at a
minute level.

I actually did do a plot on the NHT A-20 speakers in my new editing room,
with the room empty and very live and with the room dead. I could see
no difference in the curve that I did at octave intervals with a
military ZM-35 bridge good down to 0.1 ohm and a 200CD signal generator,
on both the woofer and tweeter. (With the A-20, the crossover is in the
amp so it was easier to do the drivers directly). What can I say, I was
bored and looking for any excuse to avoid moving more boxes of tapes.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Pooh Bear wrote:
wrote:

Mike Rieves wrote:
"that the room affects a speaker's overall reactance
has been known for many years."

Again, I ask, "known by whom?"

Well...... I don't think there's any doubt that a speaker cabinet
influences the impedance curve is there ? By analogy, clearly
the room ( in effect another cabinet in front of the speaker cone )
must have a similar if somewhat rather smaller effect.

Excuse me, but a factor of 1,000 is NOT a "somewhat rather
smaller effect."

Just because it can be normally ignored doesn't mean it doesn't
exist.

No, it's not that "it can be normally ignored." Given that there are
many confounding variables that have at least an order of
magnitude greater effect, and no one to date has supplied
a single shred of repeatable data to support your assertion,
It's reasonable to state that it can be totally ignored.

In practice of course it's not an issue but the effect must clearly
be there at a minute level.

It is most assuredly NOT clearly visible. There are any number of
confounding variables, temperature of the spaker components,
changes in humidity, driver-to-driver variations, mechanical
hysteresis in the surround and spider, so on and so forth, all
of which have effects that are AT LEAST and order of magnitude
greater.

Given all those variations, how could you possible claim that
"the effect must clearly be there ate a minute level?"

You nor anyone else has presented any actual data to suggest
otherwise.

And there are any number of effects that are there on a minute
level. How many people are concerned with the Hall effect of
the charge carriers in the voice coil winding, for example. The
effect is "there," it's just that's its not there.

Scott Dorsey wrote:

Pooh Bear wrote:
wrote:

Again, I ask, "known by whom?"

Dick, I am very glad to see you here in rec.audio.pro again.

Well...... I don't think there's any doubt that a speaker cabinet influences the
impedance curve is there ? By analogy, clearly the room ( in effect another
cabinet in front of the speaker cone ) must have a similar if somewhat rather
smaller effect. Just because it can be normally ignored doesn't mean it doesn't
exist.

In practice of course it's not an issue but the effect must clearly be there at a
minute level.

I actually did do a plot on the NHT A-20 speakers in my new editing room,
with the room empty and very live and with the room dead. I could see
no difference in the curve that I did at octave intervals with a
military ZM-35 bridge good down to 0.1 ohm and a 200CD signal generator,
on both the woofer and tweeter. (With the A-20, the crossover is in the
amp so it was easier to do the drivers directly). What can I say, I was
bored and looking for any excuse to avoid moving more boxes of tapes.

Fair enough. You've proved the point. I was just nitpicking really.

Graham