Mike, think of sound as if it were water. (It only "sort-of" behaves that way, so it's stretched analogy, but easy to understand.)
If you want to build an aquarium to keep your goldfish in, how many sides do you have to put glass on, to keep the water in? Answer: All of them! If you only put glass on three sides, then obviously that won't work: the water will just splash out all over. 4 sides won't work either, for the same reason: you have to do the bottom too. Even if you decide that you can't afford all that glass, but you have a piece of carpet that you could put in one side, some old newspapers stuffed in another side, and a bit of cardboard taped o with duct tape for the last side.... Well, you get the picture.
:!: :D
Such an aquarium ain't gonna hold water! And once the water spills out from one side, well, it's out and is now all over the place: it doesn't just carry on spilling out in one direction: it spreads out all around the aquarium, in a huge messy puddle (and your goldfish dies...). In order to keep the water in, you need glass and perfect seals on all sides.
Same with sound: to isolate your room, you need the SAME method for ALL walls. Doing one wall one way, and another wall a different way, is like putting glass on one side of the aquarium and carpet on the other: Just like the water takes the easiest path out, so does the sound. And once the sound is out, then it doesn't just carry on in only that direction, but spreads out all over, in a huge mess. (The only good part is that your goldfish doesn't die if the sound gets out of your room!
:) )
In other words, the isolation of your room is only as good as your weakest side. If you have a great concrete floor capable of 80 dB TL, and four really good staggered-stud walls rated at 50 dB TL each, and a cloth-and-rockwool ceiling rated at 20 dB, well then the isolation of your room is 20 dB. That's all you get. Basic physics.
Yes, sound travels through both paths: airborne and structure-borne. But to stop it getting out, you have to block BOTH paths. Just blocking one is no use. The average bedroom or living room in an average house does a pretty good job of blocking airborne sound if the doors and windows are closed, but is lousy at blocking structure-borne, and worse still, it converts airborne to structure-borne in the walls! The air-borne sound makes the wall and ceiling surfaces vibrate, that vibration is transmitted into the studs and joists, and from there to everywhere in the house. In order to stop that, you have to decouple the wall and ceiling surfaces from rest of the structure. Staggered studs is one way to do that. Resilient channel is another. Separate framing is a third. But you
have to decouple, one way or another, or the air-borne sound will become structure-borne. If you don't decouple, then you are limited by a principal of physics called "mass law", which isn't very encouraging.
Yes, a soft ceiling is a great idea, and highly recommendable, but that is
TREATMENT not
ISOLATION. They are two entirely different things. Your sound tech might be a great sound tech, but he suffers from the same misconceptions that most people do about acoustics: they think that absorbing sound can somehow stop it, but that simply isn't the case. You CANNOT stop sound with any reasonable amount of absorption.
Another water analogy: A sponge in the kitchen is a great tool for mopping up water that spilled some place where you didn't want it. But can you stop the water pouring out the tap by putting a sponge across the end? Obviously, no, you cannot! You need a cork. The cork is massive enough, rigid enough, and has a good enough seal that it will stop the water.
Likewise, acoustic absorption is a great tool for mopping up sound that spilled someplace you didn't want it, but can you stop sound getting out of the room by putting absorption on the walls or ceiling? No, you cannot, for the same reason that the sponge cannot stop the water flowing out the tap. To stop sound, you need a sound "cork". You need something ,massive enough, rigid enough, and with good enough seals around the edges to stop sound. Such as drywall, for example...
Your sound tech is mixing up the two concepts: isolation is one thing, and is accomplished only one way: mass. There are no other economical ways of stopping sound, no magical products or incantations. Just mass. And treatment is another thing entirely. Isolation needs mass, treatment needs absorption. Two different things. Corks and sponges. Not interchangeable.
Think of it this way: Isolation (mass) stops the sound getting out of your room. So if it can't get out, where does it go? Obviously, it stays
IN the room, bouncing around for a while before eventually dying out. While it is bouncing around, it is called "reverberation", and how long it takes to die down is called the "RT-60" time for your room, but that's another story that we wont go into yet.
So isolation keeps the sound in, and that makes your room sound BAD inside, due to the reverb. Not what you want! That's why you need treatment: to "mop up" the sound spilling around your room, and make the room sound good and clean again! THAT is the purpose of acoustic absorption. It does not stop sound getting out, any more than a sponge stops water, but it is damn useful for mopping up that sound splashing around, just like the sponge is damn useful for mopping up splashed water.
So that's the issue: If you want isolation, you need mass, all around, on all six sides, to the same level. If you want treatment, then you use absorption. If you need both isolation and treatment, then you need both mass and absorption.
I am fine mixing at lower volume and at agreeable times during the day if it means I can have good acoustics. That said what is your opinion of going this route?
Well, that gets back to the 64,000 dollar question! How much isolation do you NEED? You have to put a number on that: How many decibels of isolation is sufficient for you to be able to work at your normal mixing levels, and not disturb the rest of the house, or the neighbors.
That's the first and most basic question that you have to answer. Beg, borrow or buy a sound level meter, and use it to come up with that number. Based on that, you can look at the various options for attaining that level of isolation, and see which one fits your situation and your budget. Right now you are guessing, since you have no numbers, and I can't help you much either without those numbers.
So, get a meter, set up a loud, bass-heavy mix playing in that basement, just like it is right now, on your very best full range speakers. Play it at about 100 dB on the meter (that's LOUD! Use ear protection). Use "C" weighting and slow response on the meter. Now walk around the house, and your garden, carefully noting down the levels at each location, especially at the property lines to your neighbors. Find the loudest point on the list of places you went to, and get someone else to turn down the level gradually while you stand at that point, until you can no longer hear the music. Measure that level back inside the room, and at all other points, just in case.
Now you know how much isolation you need. (The above is one way to measure it: there are others). Now you have a number: it's the difference between "How loud am I?" and "How quiet do I need to be?", for the
worst case.
Now repeat that test starting from the NORMAL level that you mix at, which should be around 85 dB (that's the "standard" level) and measure those levels around your house, etc., in the same places again. Once again, subtract A from B. This gives you the absolute
minimum isolation that you need.
So now you know the minimum level of isolation that will work for you, and also the recommended level that you'll need for peaks.
(You also have other data hidden in those numbers, which is how much isolation you already have! That's another useful number to know....)
Maybe it turns out that you don't need to do much, but if that were the case then you wouldn't be here!
So, with your numbers in hand, we can then look at things like IR-761 and IR-169, and see what types of construction will get you that level of isolation. There's no need to guess: those documents show the results of huge numbers of tests on dozens of different types of walls and floors. So we just have to find one that hits your number and fits your budget and uses the least amount of headroom possible.
That's the smart way of approaching this!
:)
By the way, if you cant "beg" or "borrow" a meter, you can get them for for about US$ 50 to 100 on E-bay, Amazon, and places like that. Not expensive.
- Stuart -