Appologies for my redundant questions. I'm just trying to see these new concepts from every angle. Added mass, good thing. Got it.The reason for not floating is that the structure cannot support the additional weight. In order to compile enough density you would wind up placing an enormous amount of stress on the building. The thing is, all things should be equal. So if the best you can do is two sheets of 5/8 inch rock on the wall, having two sheets of MDF on the floor is a near match. It's not perfect, but it's not something to loose your shirt over. So, yes, adding mass to the floor directly is a good idea. Andre agreed with this already.
read the rules, read the book, got some plans... Help.
Originally posted at johnlsayers.com, topic 11524.
Yep. Like Brien said, extra mass in the floor is the way to go. Since you can't decouple it very easily due to being above another room, you kind of have to do the best you can and live with the results. Although it is probably feasible to decouple it very effectively, the cost of doing so would be very high. It would involve ripping out the entire floor, and replacing it with something else that is both massive and isolated from the rest of the structure. Doable? Yes. Cheap? No. Now, what you CAN do for the ceiling of the room downstairs, directly below your studio, is to take off the existing sheetrock, install resilient channel, and hang a couple of layers of sheetrock with GG in between, and fill the cavity with rock wool. That would help. But like Brien said, it makes no sense to build a better floor than your walls, or vice-versa. Build it all to roughly the level of the weakest link. If you build a fantastic STC 65 wall but you only put an STC 35 door in it, then you wasted a LOT of money on your walls! Sound takes the easiest path out. Ditto the floor: If you can only get STC 45 in the floor (for example) then it doesn't make sense to build STC 55 walls. Just match and balance your construction so that it is roughly the same all around. You haven't posted your sound level numbers yet, so it's hard to say what will work for your case, and what wont, or if these numbers are anywhere near what you need, in terms of isolation. Do you have a sound level meter? About your roof vent issue:Would it make sense to add mass DIRECTLY to the current floor, thus retaining a two-leaf? How about adding layers of Green Glue and 1/4 plywood? (original floor, GG, 1/4, GG, 1/2, corkboard, Finishing Floor) Flanking would be an issue but the floor should have a higher TL value and lower resonance frequency. (I'm guessing)
Looking through the great research paper that Andre just posted a link to, it seems that your ridge vents will cost you around 6 dB of isolation, maybe more, depending on the size of the vents (I think! Still working may way through the paper, but at first glance this seems to be the case). The good news is that the reduction in TL will be at higher frequencies more than at lower frequencies. In fact, it doesn't seem to affect the bottom end at all, but it DOES effect the top end. Curious. (Or maybe I'm reading it wrong....) Once again, you haven't posted your sound level numbers yet, so it's hard to say if a 6dB drop in isolation is an issue or not (or 10 dB, or 3dB, or 15 dB...) - Stuart -The bottom line, I have two soffit vents where the roof trusses meet the walls that feed up through the roof's ridge vent
I've got a meter but haven't taken measurements. What would be a good base line test?
I've thought about playing some white noise at 85db A-weighted, then measuring the db from several points outside the room; right outside the door, in rooms directly underneath, outside the house, etc.
Correct, as was all your post. I did not quote it avoid screen clutter. AndreHmmmm... I may be wrong on this, but I believe that "solid" doesn't matter, to a certain extent, depending on your definition of "solid". It's the mass that matters. For example, a heavy sheet of thick rubber hung inside your wall, with an air gap on both sides, would still be a leaf. Andre? Is that correct?
Congratulations. How long have you been studying acoustics and how many hours a week? I am asking to get a timeline of how many hours a person with a good mathematics background has to study it before becoming knowledgeable. AndreIt's all making more and more sense, as the days go by...
I bought MHoA about two years ago, plus a couple of other books on building studios around the same time. Read them all, maybe 20 hours just reading, to get me started. Basic principles. Another few hours for Rod's book this year. Then I started researching on-line around the same time. For the first year, that added up to maybe 2 or 3 hours per weak, on average. Then when I seriously got the urge to build, in the first half of Year #2, it was about 5 hours per week. And since I found this place, I'd say more like 20 - 25 hours per week for the last 20 weeks or so. That's average. Sometimes I'm here ten hours a day. Sometimes a week passes with zilch. So call it a total of around 700 hours, so far. And I'm still not there. Still learning. OK, that big number also includes time learning SketchUp, and LOTS of time on the design for my room, plus various sidetracks into equipment, construction techniques, tools, materials, etc. Maybe half of that total is actual time dedicated to pure research and learning about acoustics. Call it 200 to 300 hours, roughly. But prior to that is 30 years of experience running live sound, with at least a couple of gigs each month on average, which kind of includes a whole cart load of empirical learning and understanding of acoustics in large rooms of all shapes and sizes, without worrying too much about the math and theory behind it: For example, I figured out the 38% rule (except I called it the "two-thirds rule") many years ago, because I discovered from years of trial and error that roughly 1/3 or 2/3 back in the venue is the best place for my console, away from walls (bass build up) not under balconies (resonance), in the middle (side to side) for symmetry. etc. Ditto for speaker placement. Etc. So a lot of this stuff I already "knew", but know I'm understanding WHY I knew it, and how it actually works, and I think my mixes are getting better, thanks to that. Add to that time spent teaching live sound seminars (including basic acoustics!), plus time recording live events, tracking in studios, mixing, and.... Oh damn!! Just call it "a hell of a lot of time" and you wont be far off! Maybe someone smarter than me could learn it much faster, but I'm having a ball doing it my way! Thanks mostly to you and the other guys here! You don't know how much I appreciate it; Andre. - Stuart -Congratulations. How long have you been studying acoustics and how many hours a week? I am asking to get a timeline of how many hours a person with a good mathematics background has to study it before becoming knowledgeable.
I may have a potential problem. The floor on which I had planned to build doesn't seem to be a typical floor; no bracing. After removing some insulation and looking underneath, I think I've discovered that the "second floor bonus room" is just 1" OSB nailed on top of 2x10 boards which has sheetrock nailed to the bottom. Closer to an attic space than a to a second floor room.
I still plan to call a structural engineer but, based on this info, do you think the project is in danger of exceeding weight restrictions? I have detailed measurements if it would help.
You should get the engineer in there to give you the final say-so. 2x10 joists should be able to do the trick depending on the span. Putting in bracing is not that big a deal in the overall scheme. You definitely need it to prevent rolling of the joists under a load. The engineering consult should not set you back that much. I hired a retired guy who was very helpful and each visit was only $75. Talk to your local code guys (city inspectors?) and ask them for a recommendation.
Good luck!
-ashley