Reducing Impact Noise

Hi All, First time posting, so I will do my best. I have been mixing out of a commercial building for artists for about a year and my landlord/contractor recently gutted and renovated one floor of an old warehouse down the street. Before doing so we talked a bit and he decided to try to build and isolated room as an experiment. I can get you more details about the construction if it is necessary, but it was his attempt at a 'room in room' build-out. CONSTRUCTION DETAILS (may not be necessary): The original floor is is concrete (probably 3 feet deep), and the original walls are cinder blocks. The initial walls were covered in rockwool and two layers of 2" gypsum board with a 6" air gap to the inner room. The walls of the inner room sit on the faux-floated floor which was made with 2x4's and rubber stoppers. I believe the inner walls are then another 4" of gypsum board glued with green glue, and with a thin rubber mat pasted to the sides. There is a "floating" ceiling atop the walls. The first door into the place leads into a vestibule, then another door for the outer wall (up a step), then another door for the inner wall. There is a main room and a side room with a door which was initially going to be a machine room but we decided to make into a vocal booth. The dimensions of the rooms are (13' high ceilings): square footage of big room: 13'4.5" L x 14'5.5" W -or- [ 13.375 ft x 14.458 ft ] = 193.12 square feet square footage of vocal booth: 7'.25" L x 4'5" W -or- [ 7.02 ft x 4.416 ft ] = 31.01 square feet PROBLEMS: So it isn't perfect but it's quieter than our current space and a very good price for the area; so we want to make it work. It will mostly be a mixing room, but want to offer overdub recording of voice, solo strings, guitar, upright bass (no drums). We can hear footsteps, and doors closing from the outside possibly loud enough to get into the recording (sorry no dB meter yet...in the mail). My hunch is that the floor is too light and transmitting a majority of the vibrations. The room is also very reverberant and I'm not sure if the impact sounds will be quieter or louder once we put in our bass traps/absorption. MAIN QUESTION: Is there anything we can do internally to minimize the impact vibrations? Does it make sense to get some heavy overlay to weigh down the top level of plywood on the floor, or will most products not be heavy enough? Will a bunch of rockwool with plywood atop help? Rubber mats are probably a no-go, right? We're looking to improve the situation for $1000 or under...not hoping for miracles, just an improvement. I know the design wasn't proper so there won't be a cure-all solution. Thank you in advance for any advice.

Hi there " onyx000000", and welcome!

The original floor is is concrete (probably 3 feet deep), and the original walls are cinder blocks.

That was a really good starting point, but some things weren't done ideally from there on. Some of that can be fixed (hopefully!).

The initial walls were covered in rockwool and two layers of 2" gypsum board with a 6" air gap to the inner room. ... I believe the inner walls are then another 4" of gypsum board glued with green glue,

That sounds like a 3-leaf system: If I understand you correctly, there is a an outer-leaf consisting of cinder blocks, then a "middle leaf" which is this 2" gypsum board, then beyond that an "inner-leaf" which is 4" of gypsum board. Is that correct? My first reaction is to raise several eyebrows: TWO INCHES of gypsum board? And FOUR INCHES of gypsum board??? :shock: As in one solid slab? :!: I didn't even know yo could get 2" thick drywall!!! The thickest I ever heard of is 3/4".... Or was that 4" slab built up from eight layers of 1/2" drywall? 6 layers of 5/8" drywall plus one layer of 1/2"? I'm really not sure how you would manage to make four inches of solid gypsum board, or why you would even want to do that! Or maybe I'm just misunderstanding your description. Perhaps you could make a sketch of how each leaf was actually built? Next, I'm not sure what you mean by " 4" of gypsum board glued with green glue ". despite the name, Green Glue is not glue at all, and cannot be used to glue layers of drywall together. Green Glue is a visco-elastic polymer that acts as a constrained layer damping material between layers of drywall, but it is NOT an adhesive, and CANNOT be used as such. Please can you provide more info on how this "glueing" was done. Finally, a question: when you say that there is a 6" gap between the cinder block and the 2" gypsum board, what does that really mean? Does it mean that there is 6" framing that is attached to both the cinder block and the drywall, or does it mean that there is 2x4 framing located 2-1/2" inches away from the cinder block, or does it means something else? The issue here is that you say you can hear noises from outside getting into the room, and badly enough that you are concerned about it getting into mics, which should be totally impossible, based on the isolation system you describe. So there is something major wrong with the way that was built. That's what I'm trying to figure out with the above questions. There should be pretty darn good isolation there, but clearly there isn't, so the task is to figure out why, and see if it can be fixed.

he inner walls are then another 4" of gypsum board glued with green glue, and with a thin rubber mat pasted to the sides.

:shock: :?: So the inner surface of the room is rubber, all the way around? In other words, as you stand inside the room, what you see on all sides is rubber? :shock: :!:

There is a "floating" ceiling atop the walls.

How is that built? In what way is it "floating"?

The first door into the place leads into a vestibule, then another door for the outer wall (up a step), then another door for the inner wall. There is a main room and a side room with a door which was initially going to be a machine room but we decided to make into a vocal booth.

I'm getting confused by all those doors and leaves! It would really help if you could make an accurate diagram in SketchUp, and post it here so we can understand what you are dealing with. Photos would help greatly too!

My hunch is that the floor is too light and transmitting a majority of the vibrations.

Very likely! :!:

The walls of the inner room sit on the faux-floated floor which was made with 2x4's and rubber stoppers.

Big mistake. That is very, very probably the cause of your problems. It appears that someone tried to float a floor but didn't have a clue about how to do it right, and made the usual, very common mistakes seen so often all over YouTube. Well-meaning folks continue to perpetuate the myth that studio floors can be floated on rubber pucks with light weight framing and light weight decks: they cannot. It does not work like that. Even worse, the vast majority of studio floors do NOT need to be floated anyway! And most certainly not if you have a 3 foot concrete slab under you! That is about the most perfect studio floor you could ever hope for, right there! Nothing else needed doing to that, unless perhaps it is shared by something else that makes a lot of noise. Here's a thread about the right way to float a floor, and also about the myths surrounding the concept: viewtopic.php?f=2&t=8173 So most likely, the source of your ailment is the floor. Or perhaps the ceiling. Or perhaps the HVAC system. Or perhaps the electrical system. Or perhaps the door seals. There are many possibilities here, so it would be good to try to eliminate them one by one. Diagrams and photos would go a long way to helping with that.

Is there anything we can do internally to minimize the impact vibrations?

Probably the best you can do is to take out the "floated" floor and either re-float it properly (an expensive proposition) or don't float it at all, and rather just use the original 3-foot concrete floor, perhaps treated in another way.

Does it make sense to get some heavy overlay to weigh down the top level of plywood on the floor, or will most products not be heavy enough?

Yes, it does make sense, but it MUST be done correctly: Acoustics is a science, not guesswork, and there are equations for calculating how much mass you need on the floor in order to make it float correctly, depending on the resilience of the rubber pucks, the size of the air gap, and other factors. Getting the numbers wrong is even worse than not floating the floor: if you get the numbers wrong, then instead of ending up with a floated floor, you end up with a membrane floor deck stretched over a resonant cavity: in other words, a drum.

Will a bunch of rockwool with plywood atop help?

Nope, unfortunately not.

Rubber mats are probably a no-go, right?

Right!

We're looking to improve the situation for $1000 or under

I don't want to sound harsh here, but that is totally unrealistic, and out by one (or maybe two) orders of magnitude. You have over 220 square feet of floor to fix, so a budget of US$ 1000 works out to less than $ 5 per square foot. Four dollars and fifty four cents, to be exact. That wouldn't even be enough to buy carpet! (Not that carpet is any use in a studio, but just to illustrate that the budget is unrealistic). If you wanted to float your floor properly, then multiply your budget by at least five (and probably more like ten), then you'll be in the ball park. Even taking out the wrongly floated floor would probably cost you more than a grand, since you say that the inner-leaf walls are built on top of that floor, and the inner-leaf ceiling rests on the inner-leaf walls... Having said all that, the solution might not be that expensive at all, depending on what the problem actually is! So, before you do ANYTHING, I'd suggest first going through all the possible sources of this gross lack of isolation to try to identify which one is the culprit, and THEN based on that, decide what to do about it. In order of probability, I would guess (most probably to least probable): 1) The "floated" floor 2) The ceiling 3) The doors (probably the seals) 4) The HVAC system 5) The walls 6) The electrical system 7) Something else Please provide as much detailed information as you can about how this place is built, with several photos, and an accurate SketchUp model. Based on that we can help you figure out what is wrong, then help you figure out how to fix it. - Stuart -