concrete slab vs/ wood floor - pros and cons

Audiogoners, given the choice, with sound quality being a top priority, which choice is usually better?

I have been given the green light from my wife, bless her heart, to convert our stand-alone 1935-era garage into a dedicated music/theater room - woo hoo!! The fact that it's a separate structure will be ideal for playing loud movies whenever without bothering anyone in the house. The space is roughly 11.5 x 17' and I think it will make a terrific intimate theater. It's completely unfinished inside and has a sturdy stucco exterior. It's a very solid structure. However, the concrete floor has some large cracks lengthwise due to settling so it is pretty crowned in the middle. If I keep the concrete, I will need to build a floor over the slab and shim it quite a bit to level it out enough to install the underlayment. Headroom is limited as the walls are just over 7 feet, although the roofline peaks at just over 10' in the center, enough height to hang my projector.

If I removed the concrete, then I could dig down and build a normal floor over wood joists with a nice hollow space underneath. My house is built over a crawlspace with hardwood floors and I like the quality of bass and overall sound I get in our living room. The downside is that it would be more difficult to convert the garage back later to use for parking a car if we move. I was thinking it might be cool to design this type of floor and then have space below for insulation, wiring, etc. without sacrificing any height. Maybe the floor could even be designed as a sort of bass trap to help with the sound. Any thoughts? -thanks, -jz

Removing the concrete floor may cause you problems. Sounds like what you descibe is a floating slab construction where the entire weight of the garage is spead out over the 11 by 17 area. If you remove the slab what remains is the concrete under the wall. This may not be strong enough to support the walls or may shift under the weight of the structure or underground water which could cause everything to come down. Also, you don't know if the concrete has wire mesh or rebar which would make removal difficult. If you're really gung-ho about it, check with a civil engineer. I would also talk to contractors who do foundations - that floor may very well be capable of leveling without too much loss of headroom.
Yeah, stick with the slab and cover a large portion of it with thick carpet or rugs. It make a great base for speakers and turntables.

How about just pouring a little more concrete over the top...sufficient to add about 1" to the high spots and level the low spots?

Then you don't need to go adding a shimmed subfloor, maybe just plywood over the top, if desired.
Gs5556 has given you some good advice. I'd stay with the concrete floor; there are many products on the market for leveling your existing floor (Ardex feather-finish is one I've used alot, and is a great product). If you are'nt able to do this, then find a contractor who can. Then I would just go ahead and carpet/pad over the concrete. My sound room in my basement has this arrangement, and the sound is great.
The thought about later selling your home and needing to convert this room back to a garage should be a strong consideration to stay with the concrete.
No problems with concrete slab. Concrete slab and brick walls can be a bit much (excessively boomy) but (wood frame with thin stucco layer) should leak out enough bass energy that is does not matter. You should put thick carpet with underlay to deaden the highs and you are on your way!
I live on a slab. The audio is MUCH better then any other floor I've been on. Keep the cement. Place a good wall-to-wall or hardwood floor over it. You will never be happier.
After 60 years, the slab ain't goin' anywhere, but it most certainly wasn't waterproofed underneath (not in those days.) So what you want to do is cover the existing slab w/ construction grade polyethelyne sheet, the a layer of 2x2 or chicken wire mesh propped up on 4x4 squares if 3/4" thk plywood or fir, then call the concrete truck and tell them you need 2,5 yards of lightweight concrete topping layer (2" over the highest existing spot) and to notify you when they have extra from a job they're finishing. If you and the garage are ready when they call, you'll make out like a bandit because they hate having to dump that stuff!
Is this a joke? If not this is really a no brainer. In other words you would have to have no brain to consider digging up a slab, putting in joists etc. because you like the sound you get in your living room! Get real!
I don't see why you could not easily (especially with such a small room) simply go to the local hardware pickup a couple gallons of pre mixed concrete, take a big spackle type scrapper, pour some into your cracks smooth over, let it dry, simply go and get a really good (vapor barrier) type plastic foam that is used for underlayment for like the Cheap pergo flooring, than drop a thick carpet pad over that, and then carpet with a basic medium pile cheap carpet? I mean we are not really talking a very difficult thing here especially for the age of the building.

However not sure if you have any seeping or whatever under the garage walls that you will not end up with a soaked carpet acting as a sponge from the outer edges of your foundation.. In any case it would probably not cost much more than a few hundred bucks to do what I just listed..
Oh and yes it will sound Pretty Good!

I would put up some cheap absorbtion and diffusion products on the walls as well, it sounds like you might not even have drywall up yet, or if you do thats fine and just treat with some good bass traps or other foam products for studios possibly..

Other thing to remember is the garaged door, if its metal it will have some sound echo probably.

Are you putting in a Heating / cooling unit? If your gonna put any good gear out there, and furniture for that matter I would have a decent environmental control over the weather.. A projector, DVD player, whatever else will probably not like any extreme temps. Hot or cold.

If the floor is really un-level It will not cause you any sonic issues, however might not be good if it traps moisture or something.
The older concrete gets, the harder it gets -- and I mean jackhammer hard!! You have two problems: levelling, and (potential) moisture. So far, you haven't said if your garage floor ever gets damp or even floods. So is moisture a problem or not? If not (the garage is on high ground?) then you could just level the floor with a fine sand bed and sand-set pavers (brick, stone, terrazo, slate) to make a very beautiful floor, with a really nice oriental rug on top. And if it's cold where you live (where was that?) you could lay some radiant heating elements in the sand bed. The 7' wall height shouldn't be a problem if the roof ridge is at 10', but there are probably cross members at 7'. There is a solution for this too: knee braces at the walls and cross braces near the peak.
Home depot sells a sub floor board which is easy to install. It comes in 2'x2'sheets and could be leveled out for any irregularities in the floor it will give you a nice warm floor and it helps out with acoustics you can put any kind of flooring over it you want rug wood or easy to install laminate. it adds approximately, a inch to hight even after you add flooring this is the ideal thing to do for leveling comfort and acoustics.I have a article on acoustic property's if I can find it.each Pallet covers 70sq foot you wood need approximately, 3 link OVRX 35 Pk. 2 Ft x 2 Ft Sanded OSB Insulated Sub Flooring Tile

Model H2424OVRX

John, Garages have been built the same way for a very long time, with a floating slab. This means that, yes you can tear out the old slab and the stem walls will remain. Forever... Ever wonder why the floor is cracked and not the stems? Two different pours. My guess (not really) is that the garage was first built with a dirt floor. That is how it was done in '35. The conc floor was probably "homeowner" done in the recent past. Tear it up. It will likely be simple cause it was done on the cheap, and is not 4 inches thick, nor does it have any baserock. Or rebar. Dig down another 4 inches, compact A/B, then barrier that, throw a little steel in there, run some conduit for your surround wires/cables and you have a floor that will increase resale value. Hang 5/8 board on the walls and you will realize how bad the bass is that you think you like now. Your Welcome. Z
John, tell Z you'd like to pay him to "tear out" the old slab for you. The laughs alone will justify the cost!! Just remember to invite us ;-) The driveway and garage floor of my little 1928 house in Hollywood, was poured at the time of construction, and jackhammering it out would have brought down the garage as well as the house, ha, ha!!
John, Tell NS to input only if he has some clue about the topic. Yes, the driveway and garage floor (in HW) were done at the same time, AS I describe. NOT the foundation. I will be bringing a wet saw, so there won't be too many laughs, just a VERY RED face! How about if the structure remains standing, NSGump pays? Two hours with the saw, two more with the Bobcat. Can MR. 837 answers afford that? John, please consider the source here, ever see anyone else with speakers four feet apart, who knew what they were talking about? ha,ha!! Z.
OH Yeah, and John, tell the city NSGump has a wet stamp for the redesign to the "peak". Most engineers would call it a ridge. Better to have NS there to smooth everything out with them... NOT! ha ha!! Z.
Zzzzzzzz -- I have far more than a 'clue' about both subjects, and more than enough experience to refute your bombastic assertions; many of the nice folks on Audiogon are already quite aware of my credentials and background, so troll away, you won't be here long ;-)
Gump, So I guess this means you are turning down my offer to help the member with the floor? Keeping you behind the monitor will likely be the safest for us after all. The nice members here USED to know your "credentials". They are beginning to wonder now, how much of the other stuff you have been spewing comes from your rather fertile imagination, rather than education or experience. How is that soundstage anyway! Gump is reinventing the mono revolution? ha,ha!! Z.
Hey all, thank you for some great feedback! I honestly did not intend this thread as a joke. What might seem obvious to someone with a background in construction or engineering is a fair question for someone like myself who works in an office cubicle all day.. I had no idea what a floating slab floor was or how they work to hold up a building, LOL!

Anyhow, my goal is to plan this project from the get-go and ask a few questions on this forum before construction to help me avoid costly mistakes and choose the best compromises in building out my new space. A few years back Russ Herschelman wrote a series of articles in Stereophile magazine which pointed out a whole bunch of mistakes in a home theater design that had been built in someone's basement and suggestions on how to fix them. He brought up several issues that many DIY people might not even consider that have a big impact on the final result. (I wish I could find those again!) The concrete floor is one of the "big questions" that I had about what to do, pros and cons, so thanks again for your feedback.

BTW, I live in the S.F. Bay Area, so the climate is fairly mild. The floor stays dry even during the rainy months, but it has some HUGE oil stains soaked into it that look very old so the garage has that faint repair-shop smell which I hope to get rid of. It's getting a new roof (badly needed) and upgraded electrical, too. Insulation and sheetrock (probably QuietRock?) for the walls and ceiling. I plan to include an air conditioner and heater to control the climate, possibly radiant heat in floor but still looking into cost/benefit. I like that radiant heat is silent but it would only be needed for a few weeks a year out here in sunny California.

Yes, there are three 2x4's that span across to reinforce the roof(?) I was wondering if they can be modified or removed to give me more headroom in there. The garage door is a wooden one-piece swing-up design which I plan to keep and frame a new wall behind it so the garage will still look the same from the outside - stealth. Oh boy, this is gonna be fun! -jz

John, you can move the cross ties closer to the peak (a lay term for ridge) so you get better headroom (they're there to keep the walls from splaying outward under the weight of the roof ;-) Make sure you do it to every pair of rafters to be safe. Placing 18" diagonal knee braces nailed near the bottom of each rafter and the top of the corresponding wall stud (put an xtra stud in if there's not one near the rafter) will keep the building from racking. You should also put in diagonal metal bracing (two metal straps nailed across the wall studs in a big "X" on each sidewall of the garage) to insure earthquake resistance.

Removing the existing slab is an unnecessary expense, if you don't have moisture problems. A level sand bed over an electric radiant heating pad with sand set pavers on top would make an easy and attractive floor.
John, If you would like to become intimately familiar with the term "Red Tag" and your city's Building Dept., follow Gumps advice. Roof trusses are an engineered product, leave them as they are. Since I am also in the SF Bay Area, please call me over when the plumbers tape diagonal bracing is looked at. The City may take photos for their "wall of shame". My definition of an "unnecessary expense" would be The City's requirement that you demo this now non-complying structure and rebuild to current code from approved drawings. Figure about 85 bucks a foot by following Gump off the cliff. My suggestion might burn up 2500 and add twice that in equity. Tough choice... Z.
You might be better off demolishing the garage and start from scratch.
As a construction professional and an amateur audiophile my advice would be to tread very lightly with the advice regarding concrete repairs on Audiogon.
Jaffe, I could not agree more. Good thing we are only getting incorrect input for a 200sq.ft. detatched structure! I am afraid I have to add that most of the audio advice is in the same league. Wasn't always this way here... "Those who can, do, those who can't, teach", fits these forum sitters. All one has to do, however is look at the profile and see if the advisor is a member with all the answers and no questions, as well as the extent of trading feedback. Thanks for the help! Z.
I find the advice regarding our hobby very helpful here on Audiogon. It has helped me immensely in building my system. IMO advise/comments regarding how different building materials/methods may affect the sound of one’s stereo or home theater is very appropriate here on A’gon. The point of my previous post was only to infer that IMO it is not appropriate to give advice regarding repairing or modifying the structure of one’s home without first physically inspecting the structure and then only if you are qualified to do so.
Jaffe, "qualified to do so" is/was my point as well. Plumbers tape for shear is just one example. Clearly, an unqualified bit of advice, that if followed, would have led to a bit of pain, had the OP followed it. I'm sure you cringed as well. The forums are now somewhat populated by "professional" posters. IMposters if you ask me. How this or that worked for me, or how this or that "might" work for you, is more appropriate, as you stated. I agree. Thanks. Z.
The point of my previous post was only to infer that IMO it is not appropriate to give advice regarding repairing or modifying the structure of one’s home without first physically inspecting the structure and then only if you are qualified to do so.

I cannot agree more.
Well! Now that makes three of us! Do I see a trend here! Gump, you gettin all this? Troll away was it? Ha ha!! Z.
I’ll make one last point and then I’ll shut up. I find the bantering on many A’gon threads to be distasteful. It certainly was not my intention to end up in the middle of this one. And John z my apologies for hijacking your thread. I’m sure that you have the savvy not to be ripping up concrete or modifying the structure of your home without seeking the advice of professionals.
Jaffe, Don't leave! We construction professionals can provide valuable suggestions, (including advice to seek local professionals) as well as nip the bad advice in the bud. As to the bantering (what a polite term!) I have seen a huge increase in pure pontification. Is this bantering distasteful? Sure. Curative? I certainly hope so... Z.
Yes, I am planning on calling my local contractor, who did a very nice job remodeling our kitchen two years ago (I'm reminded of him every time the HELOC payment is due. LOL!) But I wanted some input from the "Gon before calling him for a bid. The more clearly I can define my wants, the better he'll be able to plan out an accurate bid and avoid "surprises" once building begins. I may have to show him some posts here regarding isolated ground electrical and other A/V-related stuff to avoid issues with the system. During our kitchen project, I caught him running Romex right next to my surround speaker wire/coax antenna drops that I had previously fished in-wall. It was easier for him and he did not realize it could cause hum or other problems in my A/V, (or didn't care).. Luckily I caught it and he was able to re-route the romex prior to the sheetrock going up. Regarding construction and safety, I'll definately use his guidance regarding our local codes and permitting that may be required..

I wanted to point out that I never meant this thread to veer into actual contruction issues, just which material sounded better/different given a choice. Lord knows I don't want to create an unsafe situation. But this is a rare case where I could take it either way, starting from a clean slate, as it were. If it were feasible to do a suspended floor on joists to really improve sound, (IF that's the case, not saying it is..) then I think it's a reasonable consideration. I'll be spending a lot of time in there once it's done! Besides,almost every home theater project you read about in the A/V magazines have some pretty big compromises due to pre-existing structure/layout/huge windows/you-name-it issues that they have to design around. Luckily, my garage has no windows, every dimension is non-divisible (which hopefully will tame most standing waves) and the only door will be a solid-core heavy duty outside type near the back corner with total isolation from other parts of the house. I think/hope this room's gonna ROCK!

Thank you all again for some great input and guidance. I'll try to create a "virtual system" post once I get started with some pics to show the progress. Regards, -jz