John Sayers' Recording Studio Design Forum Archive

This may be worthless to you, but FWIW here's a success story of someone cutting their slab to reduce flanking.

http://www.recording.org/ftopict-23578- ... l+concrete

Sorry I can't offer more technical help as you're probably more knowledgable and definitely more cautious (and law-abiding) than I. Only moral support I can offer is to remember that what you build will be much, much better than what you have now. I'd also recommend being friendly with your neighbors if you haven't already. The best way to avoid BRAs with dB meters is to have no one complaining. Some people are actually quite tolerant of bands practicing if it's at a reasonable hour, especially if they're your friends.

Best of luck,
Marc

Thanks for jumping in, Marc! Worthless? Hardly. Even if it were a bad idea, it would give others an opportunity to learn.

I had been considering cutting the floor -- and based on this success story, I will definitely consider it even more. I realize it's not as good as a well designed floating floor, but it may be a good alternative for me.

Anyone have any thoughts about this approach?

A concern that I do have is floating my 8,000 pound walls (which also bear the weight of the ceiling) on the edge of a cut slab. I'm also concerned about the likelihood of settling, especially if it is uneven. I wouldn't want my music room to be like a freight elevator! ("Going down?")

As for my neighbors, yes, I have met them and they all seem very nice. I'm pretty extroverted, so I tend to strike up conversations with them any opportunity I get. However, in my quest to not piss anyone off, I may have set a very high standard: I have not played my drums at all in this house. In fact, I've been fairly tight-lipped about this whole plan, since I don't want any of my neighbors to get nervous about the mere possibility that they'll be disturbed. I'll inform everyone before construction actually begins though -- I want them to see all the details of the plans to have an appreciation of what I'm doing for them.

Unfortunately, the houses are packed in pretty tightly in my neighborhood -- the fence line evenly divides a 10 foot separation. Back yards are not very deep either -- setbacks are (I believe) 15 feet minimum.

Thanks again, Marc.

I wrote to Paul Woodlock recently about my project, as I was curious what his thoughts would be. (What? You don't recognize his name? Well, brew yourself a double shot of expresso, then dive face-first into this monstrosity!)

Once upon a time, in an e-mail to Sir Woodlock, I wrote:With Steve's one-on-one consultation and forum help, the recommendation is:

Inner leaf: 3 layers of 5/8" on walls and ceiling, 6" of concrete, floated on some kind of elastomer. I had purchased a cut sheet of EPDM to cut into pucks, enough for close to 200 of them, and I had a machine shop do some compression tests to see how much weight they can hold. 1 3/4" solid core door. Room will be approximately 9' x 14' when finished.

Outer leaf: add two layers of 5/8" sheet rock to existing walls between studs. Add one layer of 5/8" sheet rock to ceiling. Newly constructed outer leaf walls will have 3 layers of 5/8" sheet rock. 1 3/4" solid core door.

The air gap between inner and outer walls will be nearly 12". The air gap between inner and outer ceilings will be at least 9". I'm not sure about the air gap between floors yet. I'm fortunate to have 10 foot (plus a couple of inches) ceilings in my garage.

I have estimated the inner ceiling to be about 2,000 pounds, and the inner walls are about 6,000 pounds. The 6" concrete floor would be about 11,000 pounds. That's 19,000 pounds, empty -- about the weight of eight compact cars -- sitting on a floor that is meant for a single car.

The existing concrete floor is supposedly 4" with a 6" x 6" wire mesh, no rebar.

I'm now weighing (no pun intended) the pros/cons of using a lighter floor and increasing the air gap to attempt to make up for the some of the inferior TL. I'm also mindful that there comes a point when floating an inferior floor would possibly do more harm than good, so if there's a way I could not float the floor at all and still achieve very good TL, I'm all for it.

If there is absolutely no other alternative but to jackhammer (a portion of) my garage floor and then replace it with a rebar reinforced 6" (or thicker?) structural slab, then I'm willing to accept that.

Lately I'm contemplating cutting the slab and not floating a floor, but I'm concerned about settling and/or major cracks in the slab.

Keep in mind that this is not for recording -- it's for rock band rehearsal in a residential neighborhood with strict noise regulations.

Then, after a long sip of lager, Paul wrote:I guess the only way to be sure if your original floor will take the weight is to consult a structural engineer. I broke up my original garage floor and dug down to pour a new subfloor. I had to do this for two reasons. 1] ceiling height was limited, and 2] the original floor sloped for drainage purposes (standard in the UK ).

The new subfloor was 6" thick overall but had 12" thick edges to add a bit of beef for the walls. I didn't use any steel in this floor.

To be honest unless you uprate your inner walls and ceiling (more drywall layers) I'm not sure a floating concrete floor is worth it, and you'll probably be better served by cutting the slab. if your original slab has steel mesh as you suspect, I would think the weight on it wouldn't be a problem. But again double check with a structural engineer first.

If you do float a floor then use at least 2" Elastomer blocks and air gap under it. Anything less wont give a you a resonant freqeuncy low enough to make the floating floor worth it.

hope that helps

Interesting stuff, eh?

keith,

along the lines of what paul said, i'm starting to think about doing FIVE 5/8 layers per wall leaf instead of three. that's what i think i'll need to "compete" with my THREE 5/8 layer MDF floating floor (9" gap).

3 layers isn't going to cut it, i don't think. resonance freq is TOO HIGH.

i could be wrong tho.

dan

Hello Kieth and Dan. Gents, I've been following this subject(about a mile back ) and it brings up many questions. But personally, I've only got a few right now. This resonant low frequency. Resonance only appears WHEN you excite it, no. What instruments are you playing that has frequencys this low that could excite it? I believe Dan is aiming at 12hz or so, correct. Why? No one hears below 20hz? Even if they do, even at high SPL levels, don't the the ears roll it off? Perhaps bass drums will go this low, and in that case I understand, but I didn't think so.
fitZ

ah, my fellow Fitz!

good question, and one i need to find out more about.

i don't know how low a bass amp or a drumkit will go to be honest. one of the many holes in my knowledge on this stuff. i'm kind of going on the assumption that even if the primary frequencies are X, there are harmonics that may go well below X.

also, i'm not sure you need to excite a system with its specific resonance frequency for it to resonate at that frequency. a sheet of drywall will resonate at a specific frequency if you whack it with a hammer one time, for example.

here's what i'm understanding so far: a wall with, say, a 12hz frequency will perform WORST at that frequency. it will actually perform WORSE than a single-leaf wall with equal mass. so, all the effort of building the double stud wall is for nothing, at exactly the most troublesome frequencies.

because higher frequencies are relatively easy to stop, you might just as well build a single leaf wall and save yourself the trouble if you don't keep the resonance frequency down very low. and i believe that the wall will always perform AT BEST as a single leaf wall "down-frequency" from the resonance. so if your frequency is high you really are wasting effort doing a double stud wall.

it will only become AS GOOD as the single-leaf wall at a frequency 1.4 times the resonance frequency or in this case 16.8 hz. that leaves only a precious few herz "up-frequency" for the wall's optimal 2-leaf performance to start kicking in, hopefully giving some decent TL at about 20hz.

if anyone thinks this is wrong or misinformed or has an alternate POV, don't hesitate to shoot me down. i am still slowly learning this stuff, and i don't even know all of the stuff i don't know.

EDIT: maybe i am worried about frequencies that are too low here. anyone have any insight on this? frankly, my knowledge of music ain't that much better than that of soundproofing

EDIT AGAIN: i think even if you can't hear those low freqencies, you (or your neighbors/family) can feel them, and they could excite exterior walls to create noise at audible frequencies. so you should try to stop them for that reason too, i guess.

dan

This resonant low frequency. Resonance only appears WHEN you excite it, no. What instruments are you playing that has frequencys this low that could excite it? I believe Dan is aiming at 12hz or so, correct. Why? No one hears below 20hz? Even if they do, even at high SPL levels, don't the the ears roll it off?

You are getting into a hole new ball game here. At teh resonance frequncies, the displacement is amplified. Trucks, cars, trains, etc can all excite those frequencies. At those frequencies, it becomes significant what the body feels. This is the frequency range used for infrasonic weapons. If ylu don't hear or feel it, it can still afect eh recording chain. Overload, im distiortion etc.

Andre

Of course, context is important -- my goal is keeping my neighbors and wife happy. I don't intend to do any recording in the space.

Also figure that heavy drums will be a near constant when the room is in use.

Recall my city's "objective" noise ordinances which call for music being no louder than 55 dbA from 7 AM to 10 PM, and 50 dbA from 10 PM to 7 AM. Also, recall that my city's "subjective" noise ordinances incorporates touchy-feely language, such as "it is unlawful for any person to make or continue or cause to be made or continued any loud, unnecessary or unusual noise which disturbs the peace and quiet of any neighborhood or which causes discomfort or annoyance to any reasonable person of normal sensitiveness residing in the area."

The point is, I need to comply with both standards, and I believe the more I comply with the "objective" rules, the less likely I am going to be accused of breaking the "subjective" rules -- and the more likely I'd be able to defend myself in the (hopefully) unlikely event that happens.

FYI, I don't believe that my city is especially strict. I believe these ordinances are commonplace.

Hey guys,

I just read that floating a floor on elastomers CAN make the overall mass-air-mass frequency go up. (Actually Brian Dayton warned me about that and i didn't listen.)

Anyway it's also spelled out pretty well in NRCC-44692 ... they're talking about RC, but I think the principles are the same.

I don't know how to figure the numbers tho. Thought I should say something since I been shooting my mouth off on this.

Dan

You're always welcome to shoot your mouth off on this thread, Dan. You're like another chunk of my brain on this f^%*ing thing.

I hope asking questions isn't considered bad form here Keith. And I wasn't infering ANYTHING, other than what I asked. I too would like the answer to this seeminglu unending conundrum. If you float, then your raise resonance frequency, therefore add mass, but when you do you stiffen, and when you stiffen you raise the frequency, therefore you deepen the gap, but when you do...??? And all the while home studios are being built with NONE of this in mind and do perfectly well...to a point. Hmmmm.

I'm glad I'm on a hill in the country in Oregon. The only thing that I hardly ever hear is a train horn, a boat horn, and some kind of unidentified jet aircraft that comes over this area and STAYS for an hour. One night there were THREE all circling my house, but we couldn't see a damn thing. Hey Keith, ever hear the rockets out at Aerojet? I used to live 3 miles from the test bed for the Saturn rocket motors. LOUD doesn't even begin to describe the SPL. I even moved to Citrus Heights, which was 7 miles away and they were STILL louder than..you know what. Well, these unidentified jets were LOUDER than the Saturn rockets. I called the local TV station 4 times and no one would even call me back. They circled the whole area so I know other people must have heard them. I thought my windows would break. The house sure shook. Next time I'll call the FAA. Haven't got a clue what these could be Even Erics Galaxy studio probably wouldn't keep the noise out...unbelievably loud. Anybody know what weghting for an SPL meter to use? Next time I'll measure it and record it. I recorded the longest RT-60 and echos of the train horns here I've ever heard too. Man does it sound cool. Maybe I'll blast my Strat out into the valley and see what I get. Talk about an echo chamber.
fitZ

Geez, you didn't happen to lose 9 minutes while the "planes" were overhead, did you?

For the weighting, it doesn't really matter, as long as you know which weighting your at. C is more flat (-/+3dB between 30Hz and 8kHz) and expressed in dBC and A is basically inverse of the fletcher-munson curve and expressed in dBA. So if you want a more scientific example, probably C would be the way to go. A lot of gear manufacturers rate their gear in dBA because it hides nasty stuff going on in the low end of their gear.

btw, you ever heard a Harrier hover in one spot? It's pretty loud. The good news is that most UFO sightings in Oregon usually include the words "it was completely silent, just sitting in the air."

btw, you ever heard a Harrier hover in one spot? It's pretty loud. The good news is that most UFO sightings in Oregon usually include the words "it was completely silent, just sitting in the air."

Thanks for the info Sword. As a matter of fact, I had 2 witnesses on all occasions. We were all amazed. The first time it happened was at night, and it or they actually hovered for 5 to 7 minutes. The house began shaking when it approached. We went outside and listened for almost an hour. Sometimes it sounded like one object, but then it would start to move and then sounded like two and then three different objects. I am very familiar with UFO reports around here. I live right on the Southern Oregon coast. Many many reports come out of here, and you are right about them being reported as silent. This is NOT silent
The first time we heard it, I called the local TV station while we were listening to see if anyone else was reporting it. Since this is a very small town, there was no answer at the news dept., but I left a message. Since then, I have contacted them 3 other times with NO return call. Pisses me off.
The ONLY airport around is in Northbend, about 5 miles away. Very small commercial jets fly in and out about once per day, and the Coast Gaurd has some turbine powered helicopters. I've seen and heard these craft directly over my head and they are NOTHING like this sound we have heard. I never see large commercial jets or military jets over here. Actually, this area is pretty isolated and there is no reason for any low flying large jets. All I know is this thing is so loud we had to put our hands over our ears. We could actually feel low frequency waves in our body. Pretty weird to say the least. Not one single report on radio, tv or newspapers. I guess I'll have to get proof or something before anyone will listen to me here. Maybe the FAA will if I do.get it.
Sorry for interjecting this in your thread Keith. It wont happen again.
fitZ

And now, back to our regularly scheduled "to float or not to float" crap.

Last weekend I submitted a request on ServiceMagic. I got one match: Works General Engineering, Inc. I spoke with the proprietor Friday evening on my drive home from work for about 40 minutes. His name is Bill and he's a semi-retired civil engineer with a lot of building experience.

He has worked on a couple of acoustical projects in the past (isolating noisy equipment mostly) and is familiar with at least the basics of mass-air-mass -- although I told him that's not the area I need his expertise. What I need to determine is what kind of weight my existing floor can take on, and if insufficient, what kind of retrofitting is in order.

He offers free phone consultation to get things going initially, mainly to ensure that he can be of help. He also seems to be interested in learning more about acoustics projects, so this could be a unique opportunity for him as well.

Overall, it was a good first conversation. I'll talk with him again later in the coming week after he has (hopefully) checked out this thread. (I warned him it's long, so he may just skim it.)

In other news, I had a really cool phone conversation with a really cool Mike Klooster this week.

Wish me luck, guys!

And now, back to our regularly scheduled "to float or not to float" crap. Wink

Wear waterwings. Good luck!