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GIK Acoustics Presents
Acoustic Class Room
Nov, 2009 - Vol 10, Issue 10
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Dear Glenn,
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Welcome to GIK Acoustics classroom!
From time to time we'll be sending out
newsletters to all of you to keep you up to date on a variety of room
acoustics topics. Our hope for this
newsletter is that it will help you get a
better understanding of how
acoustics work and how you can benefit by
treating your rooms. If you have any questions about the information in this (also ideas for topics to cover)
or any other issue, please feel free to contact us. The more YOU understand
the better YOUR listening environment will be. Also we will be spot-lighting
a room in each newsletter, so if you'd like to show off your room to the
world please contact me at glenn.k@gikacoustics.com
Glenn Kuras
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Isolation
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Why
is isolation important? There are a
variety of reasons. The most commonly
recognized reason is to stop sound from bothering other people in the house or
other people outside the room and the house/building.
A
more important reason is to stop sound from getting INTO the room. Why is this important? In a recording live room setting, it's
critical to stop sound from contaminating what's being recorded. In the control/mixing room, home theater,
listening room, it's important to keep the noise floor down to a minimum so
it's not masking details and limiting the dynamic range of the room/equipment
"system."
Let's
look at an example:
Let's
say you have a home theater system which is capable of 100db peak output. In a normal room, the noise floor will
usually be say 50db. Things like HVAC
fans, dishwashers running, people walking, sound coming through windows, etc.
all contribute to this. In this case,
the maximum dynamic range the room/system can achieve is 50db (100db max minus
50db noise floor where sound will be masked by the noise).
Now,
if we build a room and pay attention to the isolation, we can hopefully get the
noise floor down to say 20-30db. If its
30db and we have the same equipment, we now have a maximum dynamic range o 70db
(100db max minus the 30db noise floor).
This results in more dynamic range, less need to turn things up as loud
to hear small details and harmonics, etc.
Sound
travels between rooms in 2 ways:
- Through the air
- Through the structure
Sound
travelling through the air is relatively easy to understand. Any holes you have in the room are sound
leaks. Outlets, switches, can lights,
gaps under doors, HVAC ducting, etc. are all excellent sound transmission
paths.
Sound
moving through the structure is much less understood. Sound vibrates your walls, your ceiling, your
floor, your tin ducting, etc. All of
those things are connected to other parts of the building. When they are caused to vibrate by the sound
in your room, the other side or what they're connected to also vibrate and
recreate that sound in other parts of the building. Even solid concrete basement floors are a
flanking path for sound to get to the rest of the structure. (Flanking is a
term used to describe a path by which sound 'goes around' the boundary of the
space.)
So,
how do we deal with these issues? The
answer is "It depends." It depends on
your budget, your situation, whether the room is already built or not, what
your required level of performance is, etc.
Let's look at a scenario:
Existing
room to be used for a listening room or home theater in a home. Bedrooms are not directly next to this room
but are close enough that sound transmission is an issue.
Level
1
- Insulate the walls. This is not expensive to do and will give a
nice performance gain. The walls now
become absorbers in the bass and also do not transmit mid and high frequencies
in either direction. The walls also now
do not ring like a big drum
- Replace the door to the room with a solid core
wood door and add seals to the door. The
door is usually the biggest sound leak in any room. Hollow core interior doors are horrid
blockers of bass energy.
- Remove the baseboards and use a 50 year
Latex caulk or acoustic caulk to caulk the gaps under the drywall (between the
drywall and floor) and also caulk the wall to the floor to stop air
penetration.
Level
2
- Level 1 plus
- Remove the existing outlets and switches
and build an MDF "backer box" behind each of them. Have a hole in the top of
the box only big enough for the Romex to enter and caulk that. Replace with old work boxes. Think about how many holes there are in your
room with switches and outlets. If you
can't take down the drywall to build the boxes, at a minimum, use putty pads on
the rear and sides of the plastic box to add some mass and seal it up tightly
- Repeat the above for any can lights in the
room. Make sure to use IC rated cans if
you're going to box around them.
- If you have access, replace any tin
ductwork with flex tubing and isolate in an MDF box with 90 degree bends in it.
This not only stops sound from getting out but also makes the room much
quieter. Consider larger vent diffusers.
HVAC is usually ignored but is extremely important. Remember, it goes all through the building
Level
3
- Levels 1 and 2 plus
- Add a second layer of drywall to the room
and use Green Glue between the layers.
This gives tremendous gains in isolation across the spectrum down into
the deep bass range. The additional mass
of the drywall stops a good amount of sound by itself. The Green Glue provides what's called a
'visco-elastic damping layer' between the sheets.
- Consider building a plug for any windows in
the room. Make the front something that
has mass to it like MDF. Fill the rear
with insulation. If you have windows
recessed into a wall, make the plug small enough to fit in while using some ¾"
foam weatherstripping for a seal. If you
don't, then make a 2x2 frame around the window trim and slide the plug around
the outside.
Level
4
- Levels 1-3 plus
- Work on the floor. You can either float a floor using Dri-Cor or
you can use a specifically designed rubber dampening layer and then another
layer of subfloor. You can also add a 3rd layer of gypcrete between
the existing floor and the rubber matting.
Remember that the floor joists under you are likely shared with the rest
of the structure. Even with a concrete
floor, bass frequencies will transmit through to the other walls of the structure
and through the building.
- Add a separate HVAC system for the
room. Systems called Mini-Splits are
relatively cost effective ways to go.
The good ones have running noise levels of 25db.
- Consider adding a 3rd layer of
drywall
- If you're removing the drywall to
accomplish some of this, consider adding RSIC-1 isolation clips and hat channel
before replacing the drywall. This will
cost you a couple of inches in room size but will really ratchet up the isolation. Remember that the other side of those studs
is many times drywalled and in another room.
Even with all of our efforts, there will still be some movement. That entire wall acts like a big woofer.
Stay
tuned for our next newsletter where we'll look at how to build a dedicated
space from scratch as opposed to addressing an existing space.
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SPOTLIGHT: Massive Mastering - John Scrip
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MASSIVE Mastering bridges the wide gap between mastering
suites that can cost hundreds of dollars per hour and project &
demo recording studio mastering setups. The vision of former JEM Music
Complex chief engineer John Scrip, MASSIVE Mastering provides artists an affordable, yet professional quality dedicated digital audio mastering alternative. A clientele from across the USA and several countries around the world trust their CD premastering to MASSIVE Masterin g.
We sat down with John and ask him a few questions.
Q. So John what projects have you been working on lately?
It's coming
up on dance show season, so a big increase in editing and compilation. Other
than that, name it - Rock, pop,
classical, country, gospel - I've been working on spoken word projects from [ABC
Radio's] Paul Harvey, a constant stream of live tracking / mastering from the
Schaumburg Youth Orchestra - What a great bunch of kids and a great program that
Schaumburg [IL] put together. Not your typical "school" orchestra - Several
international tours, they're actually performing at [Chicago's] Orchestra
Hall this summer.
Lots of international work with the dollar flipped
around also, which is great. This - let's call it a "classic metal" project
from New Zealand stands out for some reason - Sonic Altar - If you get a chance
and you're into straight-up, fast-driving, Harley riding rock, you'll be hearing
from them soon I'm sure. Young "kids" for lack of a better term - but very
polished.
I'm seeing a trend here - Maybe the talent isn't really
getting younger but I'm just getting older... Lots of stuff from the smaller
indie labels too - The larger labels seem to be stepping very carefully with the
economy and the indies are going to take over if they don't watch out. But hey,
that's fine. Some of the cooler stuff I've worked on recently was on those
aggressive indie labels that really believe in what they're putting out - Stuff
that a lot of the majors wouldn't want to take a chance on.
Q. So
it's not just putting CD's together -
That's most of it, sure - But
editing and compiling [performance discs] for professional dance companies -
especially ones that have tried to do it themselves with less than wonderful
results - Vinyl transfers - I just started with that last year. Neat stuff
sometimes when you get this record in that's the last known remaining unopened
copy and the master tapes were lost decades ago or what not. Tape transfers
too. Sometimes they just want a flat transfer to digital from tape.
Typical mastering makes up the bulk, but those "related" projects break
up the monotony nicely.
Q. What equipment do
you find is "most important" for today's mastering engineer.
Same as
it's always been - Monitoring and acoustic control. I know a lot of people are
fond of the old "There are no rules in audio" adage, but either they have no
idea or they have wonderful monitoring in a great space. There are *two* rules
I can think of right off the top of my head -- One is that you will only ever
hear as well as your monitoring chain allows you to. The other is that your
monitoring chain will only ever be as accurate and consistent as your room
allows them to be. Put the guy with the greatest hearing in the world in front
of cheesy speakers and he's not going to be able to do much... Put him in a
bad room and he's going to be taking a best guess. An educated guess - but a
guess nonetheless. That sounds like Dr. Seuss...
But the stuff with
the knobs on it - "today's mastering engineer" has to be really picky. The
demands are so high and the budgets aren't what they used to be - but the gear
hasn't come down in price. So you have to make sure the gear you choose is
going to work well with almost anything. I have several pieces that I use for
"this" sound or "that" sound - When you need a [Manley] Vari-Mu, there's no
substitute. When you want that SSL mix-buss sound, you need that sound. But
you need a "bread and butter" chain that will take on anything you throw at it.
And ever since my first piece of Crane Song gear [the STC-8M compressor], I've
added Crane Song to every part of the chain - I have their compressor, the IBIS
[Stereo EQ], the HEDD 192 [AD/DA converter] and the Avocet [monitoring DA and
controller] calling the shots on the whole thing. I'm convinced that they can
just do no wrong, sonically speaking. I even had a Flamingo [stereo mic preamp]
here for a time - I won't bore you with the details, but I'll tell you - If that
thing had stepped controls and line-level inputs, I'd be running mixes through
it right now. True story - I was running mixes through a Flamingo to see what
it could do - And don't think I didn't have a long discussion with Dave [Hill]
about modifying one at some point. Great, great stuff though - If I suddenly
had to get rid of everything in the chain that didn't say "Crane Song" on it, I
wouldn't really find it a compromise.
In any case, Crane Song, Manley,
API, BelCanto, the hot-rodded SSL 4000 clone - It's all ridiculously clean, very
quiet stuff with gobs of headroom. And with the demand for volume at this point
in time - as much as I wish it weren't the case - without a lot of headroom, you
might as well just throw it away.
Q. What is the biggest problem you
come across these days with mixes being submitted to you?
Too much.
Too much going on, too many effects, too hot on the way in - Too much volume.
A lot of "less seasoned" engineers are convinced that if they don't make
everything as loud as possible right off the bat, then the finished product
isn't going to be loud. Loudness aside, it's the perfect way to make sure that
it won't have the potential to *be* loud when it's done. So they track too hot
and overdrive the input chain right off the bat and it just goes downhill from
there. If people would pretend that -12 [dBFS] was as hot as anything should go
during tracking, their recordings would sound so much better. And at the
mastering stage, they could actually get that volume they want while still
retaining some clarity and dynamics.
That and the trend to "fix it" at
the mastering stage. Some will send in mixes that they're not happy with hoping
that I can "fix" them here and it just doesn't work that way. Ask any mastering
engineer - We'd much rather "enhance" a great recording than try to make a bad
recording "less bad" - If it's even possible in some cases.
The funny
part of that whole situation is the experience of the engineers in some cases -
I'll get in these great sounding projects that are obviously "safe" but very
decent sounding from hobbyists that have been at it for less than a year. I'll
get great sounding projects in from engineers who have been full-time industry
pros for a decade or more. But the most problematic projects tend to come in
the middle - It's like the "rookies" haven't learned enough to screw anything
up, the pros have learned how to get out of the way. But a lot guys in the
middle are the ones with enough rope to hang themselves with. You know how you
learn something new and then you have to do it all the time? Or you get that
new piece of gear that's suddenly never turned off? Turn it off once in a
while. Get back to the basics - Get the core sounds sounding as amazing as you
can, then just get out of their way. Track at "normal" levels - not "as hot as
you can without clipping." Go ahead and record 5 vocal tracks but you don't
have to use them all if the mix doesn't need it. Use reverb, but once you
actually notice it, you're probably using too much. You can always add more
later if you actually need it.
Q. So tell us a little about your ro om?
How are you set up and what kind of acoustics do you have?
I was
limited by the existing space quite a bit so took parts of two different rooms
and made this one. It's relatively small, so I knew it was going to need a lot
of broadband trapping right off the bat. I think I started out with 18 traps
from you guys then added some custom units and fortified the corners [with GIK
Tri-Traps] - I think I'm up to 29 or 30 traps in here now including the clouds.
The floor is floating above concrete except for the front of the room where
there's a concrete slab right under the wood flooring where the speakers are.
The walls are doubled-up with compressed insulation and 1-1/2" of plaster on
both sides so transmission isn't a problem.
The last time I had the
room shot, we noticed a little comb-filtering from the desk to the ceiling
above, so I decided to add a couple [GIK D1] diffusors overhead - I know that's
not exactly what they were designed for, but it really made the difference -
Opened the high end right up and tweaked the imaging above the [desk] rail
better than I would've expected. So it's really well-controlled, but it's not
dead - I hate dead rooms.
CONTACT INFO:
MASSIVE Mastering
P.O. Box 68143
Schaumburg, IL 60168
USA
Owner / Engineer: John Scrip
Office Manager / Booking Coordinator: Bridget Shepley
Phone (direct studio line): 1.630.237.4393
Fax (office/studio fax):1.630.233.8310
http://www.massivemastering.com
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