Q: What would the best design for a production room that
would be most utilized for 5.1 surround applications productions? LEDE [Live
End/Dead End] just seems wrong. Not to mention the apparent creation of reflected
interference between the surround speakers and the main speakers? (981010)
A: The question, "What is the
best room design for 5.1 production?" is an excellent one, and a very hot topic in
this industry. I understand your misgivings regarding the realities of 5.1 surround
environments and what has simplistically come to be known as LEDE style control rooms. A
common misunderstanding -- that the LEDE concept is merely a room with an all absorptive
front and an all reflective rear -- has been propagated by those who know little to
nothing about acoustics and practical room design or construction.
Most of the basic tenets of modern acoustical design
for critical listening spaces have sprung from the criteria developed for the LEDE
listening room model. I think most designers and acousticians take these principles as a
"given." For example, one recommendation suggests that controlling short delayed
reflections from the source into the listening area will clean up frequency response and
imaging. Well, duh! What's to disagree with? The detrimental effect of
delayed reflections is common knowledge.
Another case in point is the recommendation to reduce, diffuse, and control late
reflections entering the listening area so that the reflected energy is low enough that it
will not convolute the monitor's direct response and will not be perceived as an echo. Duh,
again! These are only two examples. I think you would be hard pressed to disagree
with any of the principles purported in the LEDE design criteria.
But now we have to apply those principles to monitoring environments with more sources
than just a stereo pair. If you have trouble reconciling a 5.1 systems with a room whose
front is all absorptive and whose rear is all reflective, I'm not surprised. All of the
sources in the room must be addressed and accommodated acoustically. How this is best done
is still in flux and will be the topic of much debate.
If you haven't already, you will hear many opinions about the merits of one
configuration or device over another, and a whole slew of cookbook solutions and panaceas
spouted forth from all manner of self-appointed gurus and wannabes.
However, I am confident that, as in the past, science and good practice will merge with
art and aesthetic judgement, and will combine in a set of solutions that leave little room
for hearsay and conjecture.
Unfortunately, this may take a while. In the meantime, sit back and enjoy the show.  |
Q: What is the prevailing philosophy on reverberation
time for a "real-world" (not megabucks) radio announce studio? i.e.,
typically, problems arise from rooms being too lively, not too dead, so conventional
wisdom suggests that a rule of thumb approach is to deaden the snot out of it with
broadband absorbing material...(981010)
A: Since the sound of your studio establishes the character of your station's
"sound," you are right to be concerned about the room's ambient decay.
However, "reverberation time" or T60 is
not a good metric to describe how sound decays in a small room like a broadcast control
room, booth or small studio. This is not to say that sound doesn't decay or that there
isn't a reverberant tail in small rooms, just that there are basic constraints in the
technical definition of T60 and the way it must be measured that preclude it from use in
small rooms. (There is insufficient volume, you can't get the measurement microphone
beyond the room's critical distance or far enough from the room's boundaries, and you
cannot generate nor measure a statistically uniform sound field). In essence, the
measurements are meaningless.
The problem with making sense of sound in small
rooms, as compared with large rooms, is that you must pay more attention to surfaces that
are nearby the mic/listener/talker/performer. In fact, the energy that is returned from
locally reacting surfaces, which include virtually all the surfaces in a small room, has
the greatest effect on the sound and character of the room. Volume and shape are next in
importance.
So there is another way you might start thinking about how to effect change to the
character of sound in these rooms. But first you must apply the basics of good acoustical
practice: select good room ratios (a topic all by itself) and shape the room so as to
control potential flutter echo and to create a geometrically complex form that promotes
sound diffusion.
It should also go without saying that you will need some kind of sound absorptive
material for a small room and it should be of a sufficient thickness and configuration to
cover a wide range of frequencies. Distribute the absorption near the source to control
short specular reflections that can return to the mic. Allow surfaces that are more
distant from the mic to provide the diffuse energy that creates the character of sound you
are looking for in the room.
Personally, I don't like an overly "dead" room. I like to hear some character
returned from the talker. This late arriving energy provides the listener with a sense of
space, place, and containment that puts the talker/performer in context. I do not care for
the "disembodied voice," a sound character that is evident in many commercial
stations' program material. For music, late returning energy is a must and oftentimes may
be supplemented by electronic means. A more natural room sound, not overly dead or live,
helps in-studio guests and talent to feel more comfortable. |
Q:We have some leakage between two adjacent control
rooms -- they were originally intended to be a studio and it's control room, but
now are both combo rooms with the smaller one used for simple production. The building is
scheduled to be renovated soon, so we don't want to spend a lot of money. Is there a cost
effective short term solution?
I'm not certain where the main leakage is coming from. It might be through the windows, or
through wiring troughs, or through the ceiling.(981010)
A: Obtaining adequate sound isolation from one sound sensitive room to
another is a common problem that is usually straightforward to accommodate during the
design and construction process, but can be very difficult and sometimes expensive to
remedy in existing construction.
Tracking down sound leakage and identifying the path
of transmission can be challenging. It might be as simple as someone talking on the other
side of a door and listening on the other side, or it might involve rigging up enormous
loudspeaker systems as a source and measuring sound transmission with sensitive and
enormously expensive test gear. It depends on the source, the path/partition
configuration, and the listener expectations.
When you are trying to improve sound transmission loss from one space to another, you
must identify and quantify the noise source, determine the path of the sound transmission,
differentiate the source from the background noise, and quantify the amount and type of
sound that is being transferred.
Then you must address a variety of questions: How will this space be used?
- How does the intended use affect noise levels?
- What kind of noise levels can I live with?
- What is the frequency bandwidth and character (tonal,impulsive, explosive, periodic,
constant, audible, tactile, etc.) of the noise intrusion that I am dealing with?
- Is the existing construction already providing all the sound isolation performance that
can be expected?
In other words, even if I take heroic acoustical measures to gain performance, can I
really expect any significant improvements? Are there other alternatives to a
less-than-ideal fix, like changes to scheduling (no simultaneous booking of adjacent
studios), procedures (change the production values), or methods (different mic
techniques)?
In all of this, however, there is one almost universal truth: the lower the frequency
of disturbance, the more costly the fix. Regardless of the nature of the problem, someone
with special experience with noise control can help you find cost effective solutions. In
the long run, it will save you time, dollars, and headaches. |
Q:Can anybody tell me, specifically, you build floating
floors for a studio? I know everybody does it, but how is it done? How expensive
is it? A: Some factors to consider in building a floating floor:
1) Select an isolator that will actually do some good at the frequencies where you need
it. From what I've seen in other do-it-yourself projects,the "rubber pads"
others have mentioned don't provide any benefit below about 400 Hz. Keep in mind, too,
that near the resonant frequency of the isolation system, you can actually make the
problem worse.
2) Unless you put enough mass on an isolator, it won't do
any good. A single layer of plywood on sleepers is too flimsy to provide much isolation at
low frequencies, and will be resonant as well. Commercial floating floors typically impose
between 12 and 50 lb./sq.ft.
3) The materials you select are critical, but how you put
them together is just as important. Make sure that you've addressed other "flanking
paths." If your walls are already supported from a common structural slab or
load-bearing framing, a floating floor by itself may not improve your sound isolation.
4) Make sure that a floating floor will make a real
difference. "Balanced construction" is the goal - getting all the components to
provide similar performance. There's no point in building a floating floor if the weak
link in sound isolation will still be the doors, or if there's so much HVAC noise that you
can't hear the difference. A floating floor is not an acoustical silver bullet.
5) Remember that in most cases a floating floor will be
elevated above the floor in adjacent rooms. Local codes and accessibility requirements
(e.g. ADA) dictate the location, length, and construction of ramps necessary to make the
transition.
Floating floors are often essential to getting
adequate isolation, particularly for upper-floor construction, but I've seen many stations
waste money by putting together floor systems that don't work at the frequencies of
interest or are defeated by other shortcomings in the acoustical design. -Richard
Schrag |
Reverberation Time for "real-world" facilities