[[email protected]]

I picked up one of these off fleabay with the plan to use the real
time analysis mode to set up equalization for my system. I've got an
8000 mic so I'm ok there. But I'm wondering about the location where
I need to add the equalizer in. I'm using a technics ac500d surround
sound processor as a input selector/pre-amp. The stereo lines from it
go into a dbx active crossover so I can bi-amp using a couple adcom
amps. The rest of the surround stuff goes out to another 3 channel
amp. I'm not concerned about the rest of the surround sound for
equalization purposes obviously. The easy place to put the 8024 is on
the stereo lines between the ac500d and the dbx active crossover. But
I'm wondering about the conversion back and forth to digital in the
8024 if I'm attenuating the signal before it gets to the 8024. Is
that going to be a problem for me at low levels? I have a couple
stereo sources going into the ac500d so moving the 8024 equalizer
upstream is not very practical. I took a look at the schematic for
the ac500d and it looks like they attenuate the signal right before it
gets output so I could theoretically add a set of input/output
connections there. But modifying the ac500d is sort of a last resort.

[Ethan Winer]

plan to use the real time analysis mode to set up equalization for my
system.

If your intent is to counter room acoustics problems using an equalizer,
you're barking up the wrong tree. It doesn't work very well. Even the really
expensive EQ systems don't work well. More he

http://www.realtraps.com/art_audyssey.htm

--Ethan

[jamesgangnc]

"Ethan Winer" ethanw at ethanwiner dot com wrote in message
...
plan to use the real time analysis mode to set up equalization for my
system.

If your intent is to counter room acoustics problems using an equalizer,
you're barking up the wrong tree. It doesn't work very well. Even the
really
expensive EQ systems don't work well. More he

http://www.realtraps.com/art_audyssey.htm

--Ethan

I don't have any specific room problem that I'm looking to correct.
Truthfully it's more for play that any particular expectation. I do have a
primary listening location where this audio system is setup. I occasionally
take the core system outside at a pool and I've thought about playing with
it there as well. I may use the results to tweak the speakers as well, they
are homemade. I may end up leaving the equalizer out of the system. Got it
for $100 off ebay so it's not like I'm spending a lot on this experiment.

You didn't answer my main question though, which is will I have a problem
using the attenuated signal from my processor as a source for this thing?

[Peter Larsen[_3_]]

wrote:

I picked up one of these off fleabay with the plan to use the real
time analysis mode to set up equalization for my system. I've got an
8000 mic so I'm ok there.

You CAN fix loudspeaker frequency response aberrations and you CAN fix bass
boost caused by the loudspeakers being too close to a wall or corner. What
you can NOT fix is room resonances, they will still resonate and if you try
the direct audio from the loudspeakers will sound wrong, so it will still
not be right, it is because of this that Ethan suggests fixing any room
issues by fixing the room.

But I'm wondering about the location where
I need to add the equalizer in. I'm using a technics ac500d surround
sound processor as a input selector/pre-amp. The stereo lines from it
go into a dbx active crossover so I can bi-amp using a couple adcom
amps.

Put it in just before the x-over, logically that is where it goes.

The rest of the surround stuff goes out to another 3 channel
amp. I'm not concerned about the rest of the surround sound for
equalization purposes obviously. The easy place to put the 8024 is on
the stereo lines between the ac500d and the dbx active crossover.

And it is where it should go.

But
I'm wondering about the conversion back and forth to digital in the
8024 if I'm attenuating the signal before it gets to the 8024. Is
that going to be a problem for me at low levels?

Nah, but you DO need to look into where you attenuate the signal, so as to
get optimum signal to noise ratio. Most "pre" stuff can deliver some 7 volts
output and many power amplifiers need only 1 volt input for max power out. I
don't know what comes out of your preamp, but it could be a good choice to
either turn the power amps some 12 to 15 dB down or to insert a fixed
attenuator in front of them.

I have a couple
stereo sources going into the ac500d so moving the 8024 equalizer
upstream is not very practical. I took a look at the schematic for
the ac500d and it looks like they attenuate the signal right before it
gets output so I could theoretically add a set of input/output
connections there. But modifying the ac500d is sort of a last
resort.

The above suggestion is simpler to implement and makes more sense in terms
of overall system optimization.

Kind regards

Peter Larsen

[Ethan Winer]

will I have a problem using the attenuated signal from my processor as a
source for this thing?

Probably not, but I guess it depends on how low the signal is.

--Ethan

[Chris Hornbeck]

On Sat, 30 Aug 2008 02:12:59 +0100, "Peter Larsen"
wrote:

You CAN fix loudspeaker frequency response aberrations and you CAN fix bass
boost caused by the loudspeakers being too close to a wall or corner. What
you can NOT fix is room resonances, they will still resonate and if you try
the direct audio from the loudspeakers will sound wrong, so it will still
not be right, it is because of this that Ethan suggests fixing any room
issues by fixing the room.

This leads into the question of where to place the measuring
microphone. Room effects are so huge that it can't be placed
too far from the speaker without hearing too much room.
Yet listening too close to the speaker will exaggerate small
variations in the summing of the drivers' separate outputs,
(normally heard from farther away, so less significant).

Rules of Thumb are tricky, but a distance of "several" times
interdriver distance is a common recipe. If EQ is to only be
applied in the range of a single driver, a *very* close mic
position is better.

Much thanks, as always,
Chris Hornbeck

[jamesgangnc]

"Peter Larsen" wrote in message
...
wrote:

Put it in just before the x-over, logically that is where it goes.

The rest of the surround stuff goes out to another 3 channel
amp. I'm not concerned about the rest of the surround sound for
equalization purposes obviously. The easy place to put the 8024 is on
the stereo lines between the ac500d and the dbx active crossover.

And it is where it should go.

But
I'm wondering about the conversion back and forth to digital in the
8024 if I'm attenuating the signal before it gets to the 8024. Is
that going to be a problem for me at low levels?

Nah, but you DO need to look into where you attenuate the signal, so as to
get optimum signal to noise ratio. Most "pre" stuff can deliver some 7
volts output and many power amplifiers need only 1 volt input for max
power out. I don't know what comes out of your preamp, but it could be a
good choice to either turn the power amps some 12 to 15 dB down or to
insert a fixed attenuator in front of them.

Not sure you're following me. I'm using adcoms for the amps after the
x-over. No level controls in them. The specifics are a 555 for the low
side and a 535 for the mid/high. The technics surround sound processor in
the front is also my source selector / preamp / level control. It doesn't
put out a signal outside typical range. No 7 volts. At the moment I run
the stereo front l+r from it to the active x-over. The logical place to put
the equalizer is between those two as you noted. But when the volume is low
the signal to the equalizer will be low. The question that concerns me is
if that will result in a loss of detail at low volume because of the digital
conversion? Or will the equalizer adjust to the lower signal? There's not
really any good way to get it into the signal path ahead of the surround
processor because I'm feeding it multiple digital sources.

I looked at the surround processor circuit and the attenuation appears to be
a tail end of the signal flow (which makes sense) so it looks like I could
enhance the circuit to inject the equalizer in/out before the attenuation
circuitry but it's far from something I want to do :-)

And for everyone, I'm not really looking to "fix" the room. I realize any
fixes for the room at spot A will has just as good a chance of making spot B
even more messed up. I'm more interested in flattening the speaker
response. Toward that end I was considering setting the speakers up outside
for measurements.

[Stéphane Guillard[_2_]]

Hi,

plan to use the real time analysis mode to set up equalization for my
system.

If your intent is to counter room acoustics problems using an equalizer,
you're barking up the wrong tree. It doesn't work very well.

Rather the opposite, EQ is the only way to tame primary room resonance modes
(as acoustic dampening would require materials as deep as 1/2th the size of
the room). This is simple physic, but not popular in the audiophile
community for sure.

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi,

plan to use the real time analysis mode to set up equalization for my
system.

If your intent is to counter room acoustics problems using an equalizer,
you're barking up the wrong tree. It doesn't work very well.

Rather the opposite, EQ is the only way to tame primary room resonance
modes (as acoustic dampening would require materials as deep as 1/2th
the size of the room). This is simple physic, but not popular in the
audiophile community for sure.

Regards,

Garbage. You cannot equalise a room - all you can equalise is a single,
specific path within the room.

And damping can be quite thin. You don't need to make the room anechoic,
just knock 10% off the reflections that cause modes and the job is done.
The physics is indeed simple, but you have not grasped it.

d

[Stéphane Guillard[_2_]]

Hi,

a écrit dans le message de
...
I picked up one of these off fleabay with the plan to use the real
time analysis mode to set up equalization for my system. I've got an
8000 mic so I'm ok there. But I'm wondering about the location where
I need to add the equalizer in.

Several (first hand experience-derived) suggestions :

- forget the 8024 RTA to define the parametric filters, it does not work
because it is (by far) not accurate enough. Download the freely available
Room Eq Wizard application, purchase a cheap mic preamp (with a phantom
power supply, this is crucial) to connect the ECM8000 to your PC's line
level sound input, also purchase a cheap Radio Shack sound pressure level
meter in order to calibrate "what is 75 dB" on your PC, use Room Eq Wizard
in sine sweep mode to plot your room response curve, and start entering
filters in the 8024

- the only place where a digital equalizer makes sense is the digital domain
(and before volume calculation otherwise the digital filter EQ calculation
process takes place on too few bits and generates audible distorsion. Thus
the only place where to insert your 8024 is between your CD player's digital
output and your amp's either digital or analog input, before volume (again).
It makes no sense at all to insert the EQ in the analog signal path (because
the EQ will A/D, calc and then D/A, which ends up in unnecessary A/D/A)

- this poses the problem of the stock 8024 having no digital I/O. This is an
option, you can purchase the extra module online, it is named AES8024.

This is why people in the know usually opt for the more recent DEQ2492,
which has builtin digital I/O (and excellent D/A on output but don't say
that in an audiophile circle or you might get burnt or hung).

Regards,
--
Stéphane

[Stéphane Guillard[_2_]]

Hi,

plan to use the real time analysis mode to set up equalization for my
system.
If your intent is to counter room acoustics problems using an equalizer,
you're barking up the wrong tree. It doesn't work very well.

Rather the opposite, EQ is the only way to tame primary room resonance
modes (as acoustic dampening would require materials as deep as 1/2th the
size of the room). This is simple physic, but not popular in the
audiophile community for sure.

Garbage. You cannot equalise a room - all you can equalise is a single,
specific path within the room.
And damping can be quite thin. You don't need to make the room anechoic,
just knock 10% off the reflections that cause modes and the job is done.
The physics is indeed simple, but you have not grasped it.

Are you a manufacturer or seller of those "real traps" or similar snake oil
products ?

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi,

plan to use the real time analysis mode to set up equalization for my
system.
If your intent is to counter room acoustics problems using an
equalizer,
you're barking up the wrong tree. It doesn't work very well.

Rather the opposite, EQ is the only way to tame primary room
resonance modes (as acoustic dampening would require materials as
deep as 1/2th the size of the room). This is simple physic, but not
popular in the audiophile community for sure.

Garbage. You cannot equalise a room - all you can equalise is a
single, specific path within the room.
And damping can be quite thin. You don't need to make the room
anechoic, just knock 10% off the reflections that cause modes and the
job is done. The physics is indeed simple, but you have not grasped it.

Are you a manufacturer or seller of those "real traps" or similar snake
oil products ?

No, and they are not snake oil; they work. Do the modal maths for
yourself if you don't believe me. I have done acoustics work on several
studios and maybe a dozen venues, and am currently engaged on the
technical content of a book on the architecture of concert halls around
the world.

d

[Stéphane Guillard[_2_]]

Hi,

Are you a manufacturer or seller of those "real traps" or similar snake
oil products ?

No, and they are not snake oil; they work. Do the modal maths for yourself
if you don't believe me. I have done acoustics work on several studios and
maybe a dozen venues, and am currently engaged on the technical content of
a book on the architecture of concert halls around the world.

Wonderful, I'm honoured. And you don't use EQ's to tame primary room modes ?

Below 200 Hz, there's not much you can do without EQ. Now I'd be delighted
that you prove me wrong with some math, let it flow !

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi,

Are you a manufacturer or seller of those "real traps" or similar
snake oil products ?

No, and they are not snake oil; they work. Do the modal maths for
yourself if you don't believe me. I have done acoustics work on
several studios and maybe a dozen venues, and am currently engaged on
the technical content of a book on the architecture of concert halls
around the world.

Wonderful, I'm honoured. And you don't use EQ's to tame primary room
modes ?

Below 200 Hz, there's not much you can do without EQ. Now I'd be
delighted that you prove me wrong with some math, let it flow !

Regards,

You have made the preposterous assertion - that room modes can be tamed
with eq. You'd better show how that happens. Bear in mind that moving a
mic by even an inch or so will result in signal level changing by 20 to
30dB when you are close to a node.

So we have a studio set up with perhaps a dozen mics, all in different
locations. Over to you.

Oh and don't forget that people move around in studios. That changes the
modal behaviour significantly too.

d

[Stéphane Guillard[_2_]]

Hi Don,


Are you a manufacturer or seller of those "real traps" or similar snake
oil products ?

No, and they are not snake oil; they work. Do the modal maths for
yourself if you don't believe me. I have done acoustics work on several
studios and maybe a dozen venues, and am currently engaged on the
technical content of a book on the architecture of concert halls around
the world.

Wonderful, I'm honoured. And you don't use EQ's to tame primary room
modes ?
Below 200 Hz, there's not much you can do without EQ. Now I'd be
delighted that you prove me wrong with some math, let it flow !

You have made the preposterous assertion - that room modes can be tamed
with eq. You'd better show how that happens. Bear in mind that moving a
mic by even an inch or so will result in signal level changing by 20 to
30dB when you are close to a node.

So that's all the math you have to serve me ? Where is the Q factor of a
primary mode ? Where is the modal analysis ?

I'm very disappointed, and will ask again, prove me wrong with some math,
let it flow ! I want to see equations !

Of course, Linkwitz cannot be considered a scientist, thus we will not
consider his statement at http://www.linkwitzlab.com/rooms.htm : "Attempts
to treat the room with absorbers will make only marginal differences unless
very many absorbers or large absorbing surfaces are used"...

(which is obvious from a theoretical point of view on air resonance in a
bounded box, but that takes math... quarter wavelength... who will want 5
feet of foam on the wall in a 20 ft room)

Regards,
--
Stéphane

[Chris Hornbeck]

On Mon, 1 Sep 2008 18:50:14 +0200, Stéphane Guillard
wrote:

And you don't use EQ's to tame primary room modes ?

Below 200 Hz, there's not much you can do without EQ. Now I'd be delighted
that you prove me wrong with some math, let it flow !

This was a common misconception in the 1970's and into
the 1980's. We've since moved on to a better understanding.

There are two parallel ways to tackle the issue:

One is to say that EQ operates in the frequency domain
and room modes operate in the time domain, but many
folks will find that too obscure.

The other way to say it is that EQ is possible from *one
and only one* point in space to *one and only one* other
point in space. It is wrong for every other combination
of points.

Does that help? All good fortune,
Chris Hornbeck

[Don Pearce]

Stéphane Guillard wrote:
Hi Don,


Are you a manufacturer or seller of those "real traps" or similar snake
oil products ?

No, and they are not snake oil; they work. Do the modal maths for
yourself if you don't believe me. I have done acoustics work on several
studios and maybe a dozen venues, and am currently engaged on the
technical content of a book on the architecture of concert halls around
the world.

Wonderful, I'm honoured. And you don't use EQ's to tame primary room
modes ?
Below 200 Hz, there's not much you can do without EQ. Now I'd be
delighted that you prove me wrong with some math, let it flow !

You have made the preposterous assertion - that room modes can be tamed
with eq. You'd better show how that happens. Bear in mind that moving a
mic by even an inch or so will result in signal level changing by 20 to
30dB when you are close to a node.

So that's all the math you have to serve me ? Where is the Q factor of a
primary mode ? Where is the modal analysis ?

I'm very disappointed, and will ask again, prove me wrong with some math,
let it flow ! I want to see equations !


No deal. If I show you some maths that fails to equalise a room, you
will simply say my maths is not good enough. You show me the maths that
does it, and I will have no choice but to retract - which I will instantly.

Of course, Linkwitz cannot be considered a scientist, thus we will not
consider his statement at http://www.linkwitzlab.com/rooms.htm : "Attempts
to treat the room with absorbers will make only marginal differences unless
very many absorbers or large absorbing surfaces are used"...

(which is obvious from a theoretical point of view on air resonance in a
bounded box, but that takes math... quarter wavelength... who will want 5
feet of foam on the wall in a 20 ft room)


Explain why you think you need a quarter wave thickness of foam, please?
Do you seriously believe you have to eliminate 100% of reflected energy
- an anechoic chamber in other words?

d

[Stéphane Guillard[_2_]]

Hi Don,

You have made the preposterous assertion - that room modes can be tamed
with eq. You'd better show how that happens. Bear in mind that moving a
mic by even an inch or so will result in signal level changing by 20 to
30dB when you are close to a node.

So that's all the math you have to serve me ? Where is the Q factor of a
primary mode ? Where is the modal analysis ?

I'm very disappointed, and will ask again, prove me wrong with some math,
let it flow ! I want to see equations !


No deal. If I show you some maths that fails to equalise a room, you will
simply say my maths is not good enough. You show me the maths that does
it, and I will have no choice but to retract - which I will instantly.

I am sorry but assessing "I have a studio with 12 mics" does not compute
here. You said you master "modal math" that would apply to LF room EQ and I
am seriously disputing this, so I want to see the math.

You also said that you are engaged in a book on that matter, I can't wait to
read your demonstrations.

Anyway, nevermind. You also said that

moving a mic by even an inch or so
will result in signal level changing by 20 to 30dB when you are close to a
node

which demonstrates that you haven't understood the difference between LF
room modes taming (what I was originally talking about, read my OP again and
search for "primary room resonance modes"), and HF comb filtering, so I'll
stop at that.

Explain why you think you need a quarter wave thickness of foam, please?

Well, do yourself the favor of googling for wave absorption, you may figure
out.

I may resume the conversation once you post here the math behind "modal
analysis" which demonstrate how you can tame a 25 Hz +30 dB room mode with
toilet paper roll shaped foamies. I am eager to see that, as this may pave
the way for new acoustic theories.

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi Don,

You have made the preposterous assertion - that room modes can be
tamed with eq. You'd better show how that happens. Bear in mind that
moving a mic by even an inch or so will result in signal level
changing by 20 to 30dB when you are close to a node.

So that's all the math you have to serve me ? Where is the Q factor
of a primary mode ? Where is the modal analysis ?

I'm very disappointed, and will ask again, prove me wrong with some
math, let it flow ! I want to see equations !


No deal. If I show you some maths that fails to equalise a room, you
will simply say my maths is not good enough. You show me the maths
that does it, and I will have no choice but to retract - which I will
instantly.

I am sorry but assessing "I have a studio with 12 mics" does not compute
here. You said you master "modal math" that would apply to LF room EQ and I
am seriously disputing this, so I want to see the math.


No, you fail to understand. There is no mathematics that will apply LF
room eq. It is an impossible task because every point in the room
relative to every other point in the room requires a different solution.
That means that even if you tried to equalise a mic it would only work
from a single point. Since all musical instruments are distributed, not
point sources, the equalisation would fail even that one instrument, let
alone all the others it was receiving.

You also said that you are engaged in a book on that matter, I can't
wait to
read your demonstrations.

Anyway, nevermind. You also said that

moving a mic by even an inch or so
will result in signal level changing by 20 to 30dB when you are close
to a node

which demonstrates that you haven't understood the difference between LF
room modes taming (what I was originally talking about, read my OP again
and
search for "primary room resonance modes"), and HF comb filtering, so I'll
stop at that.


I know exactly what I was writing about. And I stand by what I wrote.
Try it yourself with a quick and dirty test. Find a frequency that
produces a strong mode and play it continuously. Then move about slowly
and carefully until you find the null points. Even the tiniest movement
of your head causes the sound to come leaping out of the silence. You
will need to block one ear, because there is no chance of your finding a
location that nulls both simultaneously.

Explain why you think you need a quarter wave thickness of foam, please?

Well, do yourself the favor of googling for wave absorption, you may figure
out.


You are still failing to explain why you believe you need to absorb so
much of the wave to kill a mode.

I may resume the conversation once you post here the math behind "modal
analysis" which demonstrate how you can tame a 25 Hz +30 dB room mode with
toilet paper roll shaped foamies. I am eager to see that, as this may pave
the way for new acoustic theories.


I have no idea what you are talking about. (Hint here - room modes are
never greater than about +6dB. -30dB, on the other hand is very common).
Please go and do some reading, you are clearly very confused about how
this works.

d

[Stéphane Guillard[_2_]]

Hi Don,

No, you fail to understand. There is no mathematics that will apply LF
room eq. It is an impossible task because every point in the room relative
to every other point in the room requires a different solution. That means
that even if you tried to equalise a mic it would only work from a single
point. Since all musical instruments are distributed, not point sources,
the equalisation would fail even that one instrument, let alone all the
others it was receiving.

.... and ...

I know exactly what I was writing about. And I stand by what I wrote. Try
it yourself with a quick and dirty test. Find a frequency that produces a
strong mode and play it continuously. Then move about slowly and carefully
until you find the null points. Even the tiniest movement of your head
causes the sound to come leaping out of the silence. You will need to
block one ear, because there is no chance of your finding a location that
nulls both simultaneously.

This is total nonsense. Primary LF room modes have a wavelength which is in
the order of the room dimensions, which means you'll have to move a LOT to
go from a boom to a suckout. You clearly totally mix HF comb nodes (which
anyone can indeed observe by doing your experiment above, at say 2 KHz) and
LF modes (200 Hz, again).

Please go and do some reading, you are clearly very confused about how
this works.

Rather the opposite, I'm afraid.

Still no math, just blabla...

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi Don,

No, you fail to understand. There is no mathematics that will apply LF
room eq. It is an impossible task because every point in the room
relative to every other point in the room requires a different
solution. That means that even if you tried to equalise a mic it would
only work from a single point. Since all musical instruments are
distributed, not point sources, the equalisation would fail even that
one instrument, let alone all the others it was receiving.

... and ...

I know exactly what I was writing about. And I stand by what I wrote.
Try it yourself with a quick and dirty test. Find a frequency that
produces a strong mode and play it continuously. Then move about
slowly and carefully until you find the null points. Even the tiniest
movement of your head causes the sound to come leaping out of the
silence. You will need to block one ear, because there is no chance of
your finding a location that nulls both simultaneously.

This is total nonsense. Primary LF room modes have a wavelength which is
in the order of the room dimensions, which means you'll have to move a
LOT to go from a boom to a suckout. You clearly totally mix HF comb
nodes (which anyone can indeed observe by doing your experiment above,
at say 2 KHz) and LF modes (200 Hz, again).


You are failing to understand yet again. You don't need to move from the
suckout to the centre of the boom. Just move even marginally away from
the suckout and the amplitude increases sharply.

Please go and do some reading, you are clearly very confused about how
this works.

Rather the opposite, I'm afraid.

Still no math, just blabla...


So I notice - kindly get writing. You have yet to demonstrate a way to
equalise a room. If you can do it you will be the first person in
history and a fortune awaits you. I believe you will be able to cite
your demonstration here as primary claim for your patent.

d

[Stéphane Guillard[_2_]]

Hi,

Still no math, just blabla...

So I notice - kindly get writing. You have yet to demonstrate a way to
equalise a room. If you can do it you will be the first person in history
and a fortune awaits you. I believe you will be able to cite your
demonstration here as primary claim for your patent.

I'll leave the obviously skilled troll where I should have left it in the
first place : in the killfile.

Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi,

Still no math, just blabla...

So I notice - kindly get writing. You have yet to demonstrate a way to
equalise a room. If you can do it you will be the first person in
history and a fortune awaits you. I believe you will be able to cite
your demonstration here as primary claim for your patent.

I'll leave the obviously skilled troll where I should have left it in
the first place : in the killfile.

Stéphane


And thus he runs and hides...

d

[Ethan Winer]

"Chris Hornbeck" wrote in message
...

This was a common misconception in the 1970's and into the 1980's. We've
since moved on to a better understanding.

Yes, and my Audyssey article I linked originally:

http://www.realtraps.com/art_audyssey.htm

explains the issues in detail. This next article takes a different approach
and provides further proof:

http://www.ethanwiner.com/believe.html

I'm amused that Stéphane is so hung up on math proof, because empirical
evidence trumps his incorrect theory every time. No math is needed, just
look at the test results shown in my Believe article above.

--Ethan

[Peter Larsen[_3_]]

Stéphane Guillard wrote:

This is total nonsense. Primary LF room modes have a wavelength which
is in the order of the room dimensions, which means you'll have to
move a LOT to go from a boom to a suckout. You clearly totally mix HF
comb nodes (which anyone can indeed observe by doing your experiment
above, at say 2 KHz) and LF modes (200 Hz, again).

Have you tried actually meauring at different locations in a room?

Still no math, just blabla...

And still quite arrogant and negligent of simple psychoacoustics or failing
to allow yourself the time to read what people actually write. IF you
equalize steady state frequency response in a room THEN the initial
wavefront from the loudspeaker gets incorrect, and the sense of hearing is
very good at discriminating between room response and direct signal, so it
will sound plain wrong.

What you can fix with an equalizer is construction and radiation angle
dependent frequency response errors, which is to say that you can fix the
loudspeaker, including compensating for placing it too close to a room
boundary. What you can not fix with an equalizer is the reverb in the room,
to fix that you need acoustic resistance properly positioned in the air
volume of the room or membrane absorbers combined with acoustic resistance.

To the loudspeaker that which is of the loudspeaker and to the room that
which is of the room ... O;-)

Regards,

Kind regards

Peter Larsen

[Stéphane Guillard[_2_]]

Hi,

What you can fix with an equalizer is construction and radiation angle
dependent frequency response errors, which is to say that you can fix the
loudspeaker, including compensating for placing it too close to a room
boundary. What you can not fix with an equalizer is the reverb in the
room, to fix that you need acoustic resistance properly positioned in the
air volume of the room or membrane absorbers combined with acoustic
resistance.

Are you too (as in: like Don) mixing up primary room modes and room reverb ?

Primary room modes will be in the 25 to 100 Hz range (more often 25 than 100
for practical rooms), and for those, a suitable acoustic resistance would
fill a good part of the room, which is to say, impossible to implement.
There, EQ can remove the adequate level of excitation before it arrives at
the loudspeaker, and the overall output will be (more or less) linearized,
thus reducing the distorsion brought in by the room nonlinearities. Note
that I don't (and never did) speak about filling in the suckouts, as this is
just impossible (it would saturate amps and loudspeakers).

Above 200 Hz, EQ is useless (and I don't debate that, it is even an horrible
source of timbral distorsion because of phase rotation, which is not
relevant in LF with modern digital filters). Taming reverberation and
standing waves is perfectly doable with furniture, Schroeder diffusers, and
maybe some complimentary room treatment, but these are not room modes.

I sense from the discussion that both Don & you are not talking about the
same thing as me. Don says "moving the mike by a small amount brings you
from a node to a suckout" (commonly called room comb filtering, in sci terms
that would rather be interference fringes which dimensions are in the order
of the wavelength, thus definately not in the order of magnitude of the room
dimensions), and you speak about "reverberation", both cases are high
frequency concerns ( 200 Hz, maybe 1 KHz even), and I am talking about
the suitability of EQ for primary room modes taming, which is totally not
the same frequency range.

Addressing reverberation and standing waves with furnitures is doable... for
the very same reason as addressing primary room modes with furnitures or
other absorption material is not : the thickness of the absorption material
is related to the frequency in an 1/X manner, thus it only takes a few
millimeters of carpet or whatever to dampen 500 Hz, where it would take 2
to 5 m to dampen 25 to 30 Hz...

As to the "arrogance", I hate when I show that, but if you look back into
that thread, you will find that :

- all my posts start with "hello" or "hi", and end with "regards", and try
to remain polite in the wording (even though English is not my native
language at all),

- Don's very first post in that thread, an answer to one of mine, starts
without greeting, the first word being "Garbage."

- In same post, Don claims "The physics is indeed simple, but you have not
grasped it.", and in his next post he states "Do the modal maths" along with
his experience and knowledge in that matter. So from here on I ask for the
math which would show how to tame primary room modes with anything other
than EQ or non-practical huge absorbers. Those math never came. A shame, I
am Sc.D and would definately prefer debating equations rather than opinions,
but I guess said "math" and "modal analysis" might not expand further than
the will to argue and troll... as the rest of the discussion showed.

Regards,
--
Stéphane

[Don Pearce]

Stéphane Guillard wrote:
Hi,

What you can fix with an equalizer is construction and radiation angle
dependent frequency response errors, which is to say that you can fix
the loudspeaker, including compensating for placing it too close to a
room boundary. What you can not fix with an equalizer is the reverb in
the room, to fix that you need acoustic resistance properly positioned
in the air volume of the room or membrane absorbers combined with
acoustic resistance.

Are you too (as in: like Don) mixing up primary room modes and room
reverb ?


No, he isn't.

Primary room modes will be in the 25 to 100 Hz range (more often 25 than
100 for practical rooms), and for those, a suitable acoustic resistance
would fill a good part of the room, which is to say, impossible to
implement. There, EQ can remove the adequate level of excitation before
it arrives at the loudspeaker, and the overall output will be (more or
less) linearized, thus reducing the distorsion brought in by the room
nonlinearities. Note that I don't (and never did) speak about filling in
the suckouts, as this is just impossible (it would saturate amps and
loudspeakers).

More nonsense. The suckouts change sound level at various locations. A
suckout at location A becomes a peak at nearby location B. Reducing the
level in the amplifier by filtering off the offending frequency merely
means that you don't hear it at all. And there are no room
non-linearities that cause distortion (other than perhaps glass
ornaments that tinkle). Th effect of moding is linear - it doesn't
matter what level of sound you excite them with, they still exist, and
have exactly the same depth.

Above 200 Hz, EQ is useless (and I don't debate that, it is even an
horrible source of timbral distorsion because of phase rotation, which
is not relevant in LF with modern digital filters). Taming reverberation
and standing waves is perfectly doable with furniture, Schroeder
diffusers, and maybe some complimentary room treatment, but these are
not room modes.


Phase rotation causes no timbral distortion. It is an essentially
inaudible phenomenon. And of course standing waves are precisely what
room modes are.

I sense from the discussion that both Don & you are not talking about
the same thing as me. Don says "moving the mike by a small amount brings
you from a node to a suckout" (commonly called room comb filtering, in
sci terms that would rather be interference fringes which dimensions are
in the order of the wavelength, thus definately not in the order of
magnitude of the room dimensions), and you speak about "reverberation",
both cases are high frequency concerns ( 200 Hz, maybe 1 KHz even),
and I am talking about the suitability of EQ for primary room modes
taming, which is totally not the same frequency range.


A node IS a suckout, so clearly I said no such thing. And comb filtering
is merely the same interference phenomenon as a standing wave, but with
the wavefronts not arriving aligned from opposite directions. The maths
of what happens is just the same.

Addressing reverberation and standing waves with furnitures is doable...
for the very same reason as addressing primary room modes with
furnitures or other absorption material is not : the thickness of the
absorption material is related to the frequency in an 1/X manner, thus
it only takes a few millimeters of carpet or whatever to dampen 500
Hz, where it would take 2 to 5 m to dampen 25 to 30 Hz...


Who's talking about carpet? Glass fibre panel mounted a few inches off a
wlll do a fabulous job down to well below 100Hz.

As to the "arrogance", I hate when I show that, but if you look back
into that thread, you will find that :

- all my posts start with "hello" or "hi", and end with "regards", and
try to remain polite in the wording (even though English is not my
native language at all),


Your salutation contributes nothing to the discussio.

- Don's very first post in that thread, an answer to one of mine, starts
without greeting, the first word being "Garbage."


That's right. And the garbage has continued.

- In same post, Don claims "The physics is indeed simple, but you have
not grasped it.", and in his next post he states "Do the modal maths"
along with his experience and knowledge in that matter. So from here on
I ask for the math which would show how to tame primary room modes with
anything other than EQ or non-practical huge absorbers. Those math never
came. A shame, I am Sc.D and would definately prefer debating equations
rather than opinions, but I guess said "math" and "modal analysis" might
not expand further than the will to argue and troll... as the rest of
the discussion showed.


You claim to be able to tame room modes with eq - something which
everybody else here who knows anything about the subject agrees to be
impossible. It is your job to demonstrate the truth of your
extraordinary claim. Now back it up with the maths or go away.

d