contridiction in philosophy on control room design

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contridiction in philosophy on control room design

Postby Dan Nelson » Thu Jun 10, 2004 4:33 am

Subject: [acoustics] Re: RT-60 question
Date: Wed, 30 Apr 2003 15:10:48 -0000
From: jcgriggs23 <jcgriggs@xxxxxxxxxxx>

--- In, Rick Fitzpatrick <cadesignr@r...> wrote:

I'm obviously not Eric, but I hope you don't mind me piping in here
(like anyone could stop me 8^)

> Hello Eric and thank you. Ok, this probably is an assinine set of
> questions that does nothing but satisfy my curiosity and wastes peoples
> valuable time. Sorry. But there is a purpose. However stupid it may
> be. It comes from something I've been wondering about for a long time.
> I see contridiction in philosophy on control room design. So unless I
> trust one persons educated opinion over another, my only other option
> is to figure out why and what is the difference in philosophies. Does
> that make sense? Heres an example:
> LEDE design may be old and obsolete, but even here I see people
> mention using the principal. I read other opinions the flatly say IT

LEDE may be old, but it is by no means obsolete. I think the crux of
the problem is that many rooms that claim to be LEDE or look like LEDE
don't actually correctly implement all of the design criteria (for
instance, size is an important factor in LEDE - if the rear wall is
too close to the mix position, reflections arrive too soon.) Other
factors are that it is very difficult to compare rooms with different
sizes and different monitors to one another and that any such
comparison inevitably comes down to personal preference - some people
simply don't like the sound of LEDE, while others find
"non-environment" designs sound strange to their ears.

> Others say a non-envioronmental room is the way to go,
> what ever that is.

Non-environment design attempts to minimize all reflections from the
room surfaces by covering them all (except the front wall with the
speakers and the floor) with lots and lots of broadband absorbers.
The front wall and floor are kept reflective to provide "life" for
sounds from sources other than the speakers (i.e. people in the room
talking) and prevent the room from becoming overly dead and anechoic
(which can be very disconcerting.) The non-environment design is
generally associated with Tom Hidley and Phillip Newell, two well
known studio designers.

> And then again, I see pictures of studios all the
> time on the net which are totally oblivious to acoustics but produce
> great recordings. Ha! I mean, I don't think Les Paul was aware of any
> of this stuff, and his recordings sound great to me. Maybe not by
> current, but still great to my ears none the less.

I think this just goes to show that even a "less-than-perfect"
(whatever "perfect" is) space can be used to create great recordings
if you use your ears and are careful about microphone placement, etc.
Most people enjoy listening to music in their living rooms and cars,
despite the fact that most of these spaces are pretty awful
acoustically by the standards used for control rooms and recording spaces.

One the other hand, having a recording space with a great acoustic is
no guarantee of creating great recordings - it just means that you
don't have to work around the limitations of the space as much.
Although control rooms and other critical listening rooms have more
demanding criteria, it is still possible to arrange the source and
listening positions to minimize certain problems in the room.

> How about canted walls. There are two different camps. Both fully
> entrenched in their opinions, but who is to say whether canted walls do
> what some people say they are supposed to do.

I've never heard anybody say that canted walls don't do anything. As
far as I can see the debate hinges on two factors:

1) The amount of canting required to affect sound at low frequencies.
A wall must be canted on a fairly large angle to affect very low
frequencies since these waveforms are very long and don't interact
with features that are small in comparison.

2) The fact that it becomes very complicated to predict the behaviour
of a non-rectangular room. Some people feel that the reduction in
predictibility is not worth the effort, loss of useable space, etc.
required to cant walls.

> I just hate scientific
> ambiguity. Either it works or it doesn't. PERIOD. Thats all. I have
> no money or time to waste on bullshit anymore. I just want the truth.

I don't think there is that much scientific ambiguity here - just
complexity and the subjective nature of evaluating spaces for
recording music. It is hard to draw a line between the complicated
behaviour of sound in a (relatively) small enclosed space (which is
governed by the laws of physics) and the subjective evaluation of that
sound by an individual person in that room. Take a look at the
control of vibration in industrial settings or the design of spaces
for things like hearing tests (discussed here recently.) The
techniques used in these fields (where success or failure is much more
easily evaluated using objective measures) are much less controversial
and widely agreed upon. You'll also find more uniformity in approach
in studios used for sound for motion pictures (although less than in
industrial applications) where the end product will ultimately be used
in a fairly uniform environment (i.e. movie houses with audio systems
that comply to THX or Dolby or some other specification.)

> Who knows the truth? And if there isn't a truth, then ambiguity must
> rule. Which is arbitrary, so whats the point.

Who knows what is the best type of music? It seems to me that studio
design is the use of science (acoustical physics) to create a space
for making art (music.) Most of the debate and controversy is not
about the accuracy of the science, but about how well the results
serve the art and the artist.

As an example, all of the control room design philosophies that I know
of (LEDE, Reflection Free Zone, Controlled Image Design,
Non-Environment Room, Early Sound Scattering) all deal with the
management of early reflections from the room surfaces to the
listening position. Everyone agrees that this is an important
criteria, but they disagree about which method of dealing with it
"sounds best" and allows the user to create mixes that best translate
to other spaces. LEDE, RFZ and CID all try to direct early
reflections away from the listening position and to only allow later
reflections to get there. Non-Environment design tries to eliminate
these reflections as completely as possible by absorbing them. Early
Sound Scattering takes the approach of randomizing and diffusing these
reflections rather than absorbing them or directing them away from the
listening position. All the approaches deal with the same criteria
(Initial Time Delay Gap), but in different ways. I don't think it is
possible to say one is better or worse then the other (assuming the
design is correctly implemented), only that a given person prefers the
sound of one or the other for a given type of music. They also have
different basic requirements - you need a certain amount of distance
from the listening position to the rear boundary for LEDE, RFZ and
CID, you need room for a lot of absorption on the room surfaces for
Non-environment - so the space you are building in may also be a
factor in selecting a design approach.

> How about diffusers on the back wall? I just saw pictures of a studio
> that is a reversed LEDE with diffusers around the monitors on the front
> wall and absorbers on the rear wall.

This sounds like an Early Sound Scattering design to me.

> And how about absorbers
> themselves. There are a myrad of OPINION here and else where. Tested
> or not.

What opinion? I've seen discussion of the complexity of making
meaningful measurements (given the difference between the lab
environment where measurements are made and any "practical", "real
world" space.)

> Please do not take me wrong here Eric. I'm a black and white type
> person, and without being educated in this field, all I can do is ask
> questions and read to satisfy my curiosity. Some times my curiosity gets
> me in trouble and makes me look stupid.

I don't think it makes you look stupid at all!! As long as recording
is an art as well as a science there will always be certain aspects
that are matters of opinion and thus impossible to put into black and
white terms. It frustrating sometimes (I also like cut and dried
truths, myself) but it is a fact of life.

> So be it.
> Heres the crux of my question. If the outdoors or a window is the
> perfect absorber, what is the perfect reflector.

A perfect reflector would reflect 100% of the sound energy that
impinges on it. A perfect absorber would reflect 0%. I don't think
either exists (in practical terms) in the real world.

> In other words, I'm
> trying to understand what does what? And why?
> Is it safe to say, to correctly monitor what the mics are picking up
> in the studio, the direct sound field from the monitors to the
> engineers ears must be isolated from reflected sound in the control
> room environment, to keep the reflections from altering his perception
> of what he thinks he is hearing as direct sound?

It is generally accepted that early reflections (reflections occurring
between 0 to about 80 msec after the direct sound and at a significant
level - less than 20 dB or so below the level of the direct sound)
affect your perception of the location and timbre of a sound and the
size and qualities of the space you are listening in. The
disagreement revolves around how best to manage these reflections to
create a musically pleasing but relatively neutral space. Since the
timing, level and coherence of these reflections relative to the
direct sound all play a role in how they affect perception, there are
various ways of dealing with them, each with their own requirements
(which must be implemented properly) and each producing different
sounding environments.

> And the
> walls/floor/ceiling must not allow sound transmission from the studio
> to the control room, or that too will alter the perception, correct?

This one is fairly straight forward: to judge the mix coming out of
the speakers you want to hear that sound and only that sound. If
there is low bass leaking through the walls, you won't be getting a
true picture of the amount of signal at those frequencies coming from
the speakers. When you play this mix back without the extra bass due
to leakage it will likely not have enough signal in that frequency range.

You can adjust for this by knowing that you need more bass than you
think and mixing accordingly, but most people would agree that it is
easier if you can trust the signal you are hearing to be a true
representation of what is coming out of the speakers.

> Then why should a control room have any reflections at all? Why
> shouldn't it be anachoic? Seems to me, ANY reflections alter your
> perception.

This is what Non-Environment designs try to do. Anyone who has been
in a true anechoic environment will tell you that they are very wierd
and disconcerting spaces to listen in. N-E design tries to eliminate
this wierdness with the reflective front wall and floor to provide
reflective support for sounds not coming from the speakers (like
people talking in the room.)

> Unless they are delayed enough to perceive it. Isn't that
> what a Time Delay Gap is? Which by your interpretation, is an echo,
> correct? And from what I understand, the engineer is SUPPOSED to hear
> it, correct?

Your brain relies on early reflections to locate sound sources and the
space in which they occur. Removing these reflections entirely
results in the wierd "having your ears sucked out" effect you get in
anechoic environments. Very few (if any) people listen to music in
environments that provide any control over these early reflections.
Given that these reflections affect the perception of sound and that
music will ultimately be listened to in a variety of "less than
perfect" spaces, the design of any space for critical evaluation of
musical mixes has to take into consideration how to bridge the gap
between the controlled space used for evaluation and the uncontrolled
spaces where it will ultimately be enjoyed. The debate is not so much
about which method of dealing with early reflections (redirecting them
ala LEDE, RFZ or CID, absorbing them ala N-E or randomizing them ala
ESS) works best in a scientific, physical sense, but which one
subjectively bridges the gap between the controlled space and the
majority of other listening spaces best.

> Hmmmmm, my mind is reeling :(
> Well, I better stop now :) More later. Oh, the difference was the
> ceramic tile. I was under the impression this was a perfect reflector.

The whole construction of the wall, not just it's surface covering,
will affect it's efficiency as a reflector or absorber. A wood stud
and drywall wall will absorb more bass (by flexing) than a heavier,
stiffer masonary wall with the same surface.

Hope this helps!!

Dan Nelson
Posts: 629
Joined: Sat Jan 31, 2004 2:52 am

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