Some good news: Since my last post we've signed a contract giving us a steady income from doing live productions
That sure is good news, and welcome back!
:)
The bad news is we can't make use of all that extra space after all. We can't raise the ceiling nearly enough at this point to make it usable.
Is there any chance you can go the other way? Dig down?
There are also some techniques that you can use to minimize the loss of height from your inner-leaf ceiling. Do you have Rod's book? HE shows how to do that.
First suggestion
It looks like you are using Johns "Small 3D studio" as the basis for your design, but you seem to have misinterpreted it. The angled panel on the right side of the control room in that design is NOT a wall! It is a bass trap: You seem to have assumed it was a wall, an incorporated that into your design. The room should be as symmetrical as possible, so there should be no angled wall like that at the back.
The ceiling is also gone above the entire large room, and we're currently working on a frame for the new ceiling.
Are you talking about the outer-leaf ceiling, or the inner-leaf ceiling? The framing for the final inner-leaf ceiling must rest ONLY on the new inner-leaf walls, but since you don't have those in place yet, there's no way you can build the inner-leaf ceiling yet! So your comment that you are "currently working on a frame for the new ceiling" is a bit confusing...
:shock:
Our plan is to get the ceiling height to 2700mm (inside height), as we can get great deals on 2700mm length 15mm fire rated plasterboard. Is this sufficient? We can go higher if necessary.
If that is going to be your live room, then go as high as you can, but do make sure that the inner-leaf ceiling and walls are full decoupled from the outer-leaf that is visible at present in the photos you posted.
2. The floor is not build directly on the ground; however, the slab is about 30 cm thick. Will this be a problem? There's plenty of support from below, so no problem there. This used to house cows and horses, plus heavy farming equipment. I'm thinking more in terms of resonance.
What is underneath it? Just an empty space, open to the outside world? Or an empty space that is fully enclosed with walls? How big is that space?
Would it be a good idea to combine those two rooms into one control room and keep the big room "as-is"? That would allow for a booth in the big room as well. The issue here is that the control room would be a it on the narrow side. Maybe not enough to make it feel too small? Would it be better to just turn them into another recording room/booth and keep the proposed rooms the way they are?
Have you checked the room ratios for each possibility using one of the mode calculators, to see which one gives you the best possibilities?
4. Isolation measurements: In progress, will try to have it done tonight. What is the best way to do this? Is a stereo system playing at around 100 dB good enough, or do we need a full band to get the full frequency spectrum and volume?
You need full-range speakers that can produce at least 115 dB, and louder would be better: Don't forget to wear hearing protection when you do the tests!
Assuming the dB decline is linear across the full volume range,
It isn't! It is logarithmic, usually. So the assumption is not correct.
it shouldn't matter if we test this at a lower volume than full blast, as long as it's loud enough for the meter to get a good reading. Is this correct?
No, unfortunately. You really do need to do tests at levels similar to what you expect to have inside the room, for many reasons: For example, there may be resonant issues in the existing building structure that are only triggered at those levels, not at lower levels.
We'll be measuring inside, right outside the wall, and close to the neighbors. We'll figure out much sound we can allow to escape while doing the tests.
Do all your measurements using a good quality, calibrated sound level meter (not an iPhone!!!
:shock: ), set to "C" weighting and "slow" response: You can also do additional tests on "A" weighting if you want, to have a complete record and check legal compliance, but "C" is what you need for accurate acoustic results, since that is what most closely models the way humans perceive loud noise.
5. Windows: We want to seal them. Do we use brick, concrete, plasterboard, ..? Our outer leaf is only part concrete, which means we won't get the full isolation properties of the concrete even if we fill up the window cavities.
Brick. The density if brick is fairly close to that of concrete, so if you want to close off windows or doors, then do it with brick. Take care that the hole is fully sealed, all around, and for extra isolation you can render the brick (plaster) on one side, or better still on both sides.
6. Two/three leaf system? The (simplified) sketch below shows the existing outer wall and the proposed new ceiling frame. The rooms would be built inside as new boxes. Would this make part of our wall a three leaf system? If that's the case, should we attach the ceiling frame to the outer wall instead?
The outer-leaf ceiling (or roof) should be attached ONLY to the outer leaf walls, and should have ONLY one leaf of sheathing on it, either above the joists or below the joists, but not both. In the same way, inner-leaf ceiling is attached only to the inner-leaf walls. There are no connections at all between the inner-leaf and the outer-leaf.
Your diagram also shows drywall attached to the surface of the concrete outer-leaf: you don't need that drywall. It won't do anything at all to helps your isolation, since it is extremely thin and extremely light, when compared to the concrete wall.
7. The current design suggestion: I just noticed two of the LR walls are almost equally long. Will this cause increased modal problems?
It probably doesn't matter, since that is the live room, not the control room. It is also fairly large, so the modal issues will only be right down at the bottom of the spectrum, and as you can say you can test the finished room then install treatment to damp that, if there are unpleasant modal issues.
- Stuart -