LIVE ECHO CHAMBERS
Live chambers are out of style these days.
There are a number of reasons why they're not popular. Most of them are
well known and sound perfectly logical, but if there's somebody out there
who seriously thinks any artificial echo system sounds better than a live
chamber, I haven't met him.
The usual response to inquiries about live chambers is "Oh yeah, they
sound great, but......."
But; They take up too much room.
But; There's too much noise around here
But; They're not controllable like the....system.
Every one of those buts is valid.
But;
For some years, the best vocal chamber available to the mixers at United
Recorders on Sunset Avenue in Los Angeles was about seven miles away on
Fairfax Avenue.
Neat trick? Not really, just the same kind of 'phone lines that have been
used to carry the bulk of high quality audio around the country since
network radio was invented in the 20's. As a matter of fact they were so
pervasive that we still use Ma Bell's transmission line standards for
virtually all recording equipment.
They used to be called Class A Lines. The current term is Radio and TV
Broadcast Lines, and they're guaranteed out to 15 KHZ.
The cost of R/TV quality lines is wildly variable over long distances,
but for a run of a few miles two unbalanced stereo pairs would probably
double your phone bill. Not cheap, but it's a resource.
If you can get direct wiring, an old trick for monaural drive is to use
two balanced pairs, and hang the drive line on one leg of each balanced
pair. It's called a phantom line, and you get one free line for every
line you buy starting with two at the cost of a couple of transformers
per phantom. In other words 3 lines for 2 and 47 for 24.
Class A 'phone lines solve the problems of available space and noisy
environments at affordable cost even when nothing can be found in the
neighborhood, and since a live chamber is not intrinsically expensive,
the remote realie becomes a practical proposition.
The question of controlling the characteristics of a live chamber is
another matter. While the driving sound can be and usually is equalized
to produce an echo return sound that is brighter than that of the echoed
instrument(s), controlling anything much more than that is not only
cumbersome but largely a waste of effort.
The writer speaks from experience here. Bill Putnam once put a long,
thin (but very tall) vocal chamber at one side of a control room, and
hung the mike on a couple of clothesline pulleys, so he could vary the
echo attack delay. As with a set of variable acoustics mechanisms in
the studio room, the optimum setting was quickly determined, and the
variables were let alone after that.
As an aside, Bill just loved chambers, at least partly because he not
only recorded the first heavily echoed monster hit (Peg O My Heart with
the Harmonicats, still the 2nd best seller of all time) he owned it. It
was recorded on his Record Company Licence, Universal Records, and he
leased it out. Big bucks. Built a new studio with the bucks.
In another case, the writer ran up a small chamber which rang about six
seconds, and sounded wonderful on record work. Then we acquired some
jingle clients, and stuck a cheap rug in middle of the chamber which
we could unroll to pull the chamber time down to a couple of seconds
on the theory that the jingle people wouldn't be able to handle a six
second ringout at the end of a spot.
Turned out they absolutely loved the long echo, and we just downpotted
the ringout a little at the end of the spots.
Either of those mechanisms could be remoted, but proved useless in the
real world. In that same real world, the live chamber can't be varied
for much of anything else except funny eq for effect. Questionable.
Fortunately, it doesn't need much of anything else, as unlike every
synthetic system with which the writer has any experience, you can
feed anything into a live chamber and it'll come out sounding terrific.
A live chamber loves handclaps and claves, dotes on bass guitar and
timpani, probably sounds good on cannons, and damn sure sounds good on
everything else.
It's primary advantage is that since it's a real room, it sounds like
one in a way that nothing else can.
On the down side, it can't be made to sound like anything but a room,
and from that standpoint it's a specialized device.
In the case of a studio whose work involves extensive manipulation of
material to produce sound tailored to a specific purpose, a live chamber
may well be a waste of time and money.
But: For studios in the business of preserving the illusion of reality,
live chambers are indispensable. Motion picture work is a prime example
of that kind of thing, and the film/TV people are pretty hard nosed about
echo. Consider "ET" done on a spring chamber.
Preserving the illusion, or "getting a good picture" of the band is the
major part of music recording whether the material is extensively over-
dubbed or done as live as possible, and physical chambers contribute a
great deal to the illusion.
Oddly enough, they are very helpful in the case of overdubs, as their
uniquely uniform response to all instruments yields a consistent
acoustical environment to everything fed into them, with the result that
they tend to merge overdubs into the overall sound.
You'd never know the dubs weren't part of the original session, especially
if you put a trace of live echo on the tracks you're overdubbing.
In fact, a little live echo on a CD absolutly transforms the sound.
So there's a case to be made for a live chamber, and there's a way to
get it off the premises.
The next logical step involves construction and setup.
To the surprise of absolutely nobody, a live chamber is a very live room.
Actually, it's a totally live room, which makes construction a little
different than for normal rooms.
What's required is walls that neither absorb sound nor drumhead when
driven by sound. In short, masonry.
Don't panic. Masonry's cheap. Specifically, concrete block walls are cheap.
The ideal venue for a chamber is a nice quiet basement with a poured
concrete floor slab and a concrete ceiling. Concerning the ceiling, fat
chance, but it's not essential.
A chamber needs about 10 feet to handle low frequencies, but only in two
dimensions, so ceiling height is not critical. 10 x 12 x 8 to 9 feet works
nicely. A little bigger is a little better, but it's best not to get
carried away. While chambers get longer as they get bigger, even small
rooms will yield several seconds of echo time, and very large ones tend
to go somewhat muddy because of air absorption at high frequencies. It
comes down to a matter of volume, and 800 to 1600 cubic feet appears to
be optimum.
Since it is the function of a chamber is to generate standing waves, the
normal rules of acoustics don't apply. For that reason the actual shape
of the room is immaterial. I recall one that was built into the space left
under a staircase. It was short, but the sound was first rate. Square,
cubical, triangular and round rooms all work equally well, except for
placing equipment. Assuming stereo, that could get pretty weird in a
triangular space.
If a concrete ceiling is not available, 1 inch Lamiboard (a heavy form of
particle board at 200 pounds a sheet) will do, as will sandbagged solid
2 x 4's on edge. The primary thing is to prevent vibration, which eats
energy and therefore cuts down the chamber time.
Concrete floor slabs wick up moisture from the ground, so the floor slab
must be waterproofed or the chamber will be damp forever. If there's a
question of ground moisture and/or wicking, lay a couple of sheets of
plastic food wrap on the slab for a day and see how much moisture
accumulates on the underside. You might be surprised.
A proper door in a chamber is hellish expensive, and not really needed.
A more practical approach is a 3 foot square hatch with a door made of
2 inches of particle board. Glue up two sheets of one inch board and use
bolts to mount the hardware. Forget screws. They won't hold. The hatch
should be airtight to keep outside sound out of the chamber unless it's
in a dead quiet area. If it's really tight, you can get away with an
amazing amount of outside noise. This is, after all, a soundproof room
with the mikes normally sloped off below 200 HZ. The only time I've had
noise problems with a chamber was an oversized item that sat about 100
yards off lake Michigan. Storms caused enough ground vibration so that
we had to mount the thing up on bridge pads.
With walls and ceiling in place, waterproof the inside with one of the
various masonry waterproofing paints to force the masonry to dry to the
outside, and finish the inside with Portland plaster.
That's the stuff used in bathrooms you can't drive a nail into, because
it's not really plaster. If it were, the shower steam would take it out.
Portland plaster is actually fine grained concrete, and it's hard as rock.
It is also the equivalent of terrazzo or marble, with virtually no sound
absorption at all.
Given this construction and finish, the chamber should come up at ten to
twelve seconds inside, yielding about half that on record. Keeping in mind
that it's easy to shorten an existing room but very difficult to lengthen
one, go the whole nine yards and get the maximum ring for starters.
Equipment; Neither speakers nor mikes are critical for a chamber, although
the mike amplifiers had better be as quiet as possible since the mikes are
working at levels down to no sound at all. The speakers and amps should be
capable of handling 100 watts or more, partly because of the top end
equalization normally set into the driver line, and partly because the
chamber's signal to noise ratio depends on your being able to drive it to
fairly high levels. If you can put 110 Db SPL in the chamber you're not
likely to hear anything anything with no signal, as the undriven room will
be at 35 Db or so and that's a 75 Db S/N ratio. NoNoise is about 72.
One very special bit of equipment is a 100 watt light bulb with a diode
button under it. Keeps the chamber warm and dry.
Setup; Nothing complicated here. Stick a speaker in each corner, and hang
a mike about 7 feet off each one.
If you want a more solid stereo center (and the chamber will supply one)
put the speaker-mike pairs closer together rather than increasing the
speaker to mike distances. Seven to eight feet is optimum.
In use, crossing the returns (left sent to right return) improves
instrumental clarity a bit, and makes the overall sound even better.
Finally, a live chamber will do a lot for the sound of most studios,
doesn't cost as much as might be thought, and if there's no room on or
near the premises, can be remoted to any reasonably quiet space available
using high quality telephone lines. The competitive advantage is
undeniable, and the project is worth consideration.
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