Room Problem Improvement Question: Over a Garage

My current listening space is a second story room located over a 3 car garage and about 18-20'x30' that is a 2x4 stick construction supported by 2 microlam beams that run over the garage, parallel to the cars parked below, supporting the joists and 3/4inch subfloor beneath it. The surface is thin pile carpet with a thin pad under that.

The previous owners finished the space themselves and as such did not insulate at all between the floor joists to the uninsulated concrete garage underneath. The Garage ceiling below is about 10 ft and has blueboard with plaster over it.

Acoustically speaking, this is not a bad space, with ceilings being around 8' and is actually one of the better listening spaces I've had in my last 3 houses, even though on the left wall is a 45degree slant coming out around 3 feet running a good part of the length of the long wall next to my left speaker. I get great depth and fairly decent imaging and tonal balance, but I have floors which leak a considerable amount of bass and are INCREDIBLY SPRINGY! I can be walking softly on the other side of the room and my lead and sand filled Billy Bags rack cannot stop my needle from bouncing on a record! Also, I'm concerned about room nodes and overwhelming the space with all the sympathetic vibrations/resonances going on all at once, and even some of the reverberation from sound leaking down, bouncing off concrete then coming back up.

I am getting some very full range very dynamic and very heavy loudspeakers delivered in August and am concerned about this enough to begin getting quotes from builders for some kind of fix before their arrival.

Some of the ideas I've been given include:

-Spraying Icynene foam between the floor joists from the garage below to fill the spaces that are uninsulated

-Placing another layer of subflooring with a product called Advantech, which is a type of OSB that is far heavier than 3/4" subfloor then resurfacing with either:

a) Hardwood or
b) Another carpet or the same one if it can be salvaged.

- Just placing hardwood over the 3/4 inch subfloor and call it a day.

- Move the party to the 3car garage below which would entail getting HVAC systems,carpeting as well as walling off my garage doors and dealing with my wife having to park outside during the cold snowy winters and rain.

Any ideas on what to do in this type of a space? Has anyone had a similar problem with a room over the garage? The span is so long (23 ft) that I think it may be a lost cause and that adding subflooring ($2k) plus carpeting ($3k) may not even do the trick since it may be the floor joists below that are causing the problems.

My question is if anyone out there has done this type of project, what were the results and should I give it a try or just wait and see what happens when the new speakers arrive in August? It may be impossible to move them once they are in place. I'm also concerned that if I use wood flooring the room may become too bright sounding by not having the wall to wall carpeting currently in the space.
Is the garage ceiling finished? If not you might consider adding some more joists and support beams to beef up the 'music' room's floor. Without doing that I doubt you'd get much benefit from just putting in a new hardwood floor. If your ceiling joists were about 12" apart with support beams about 24' apart you could probably do most anything. But if you are spanned at 24 to 48 inches, which conforms to code in a lot of places, you'll always have a spongy floor no matter what you put on top of it. What the effect of this floor will be on bass response is another issue intirely. Have you done any analysis on the actual in room bass response yet which supports that you are in fact loosing bass thru the flexing floor?

Just some things to think about. I'm sure others will have great suggestions.

Unfortunately the ceiling in the garage is finished blueboard with plaster over it. I'm actually contemplating what you recommend as far as increasing the density/number of the floor joists but would have to do so by tearing up the carpet then the subfloor to get at it from the listening room.

Have had a RTA in here and things were fairly flat but bass output turned out to be slightly low even with a powered subwoofer. We had to crank up the sub to it's peak capability to get a flat response, where a colleague who has the exact same sub actually had to reduce it's level as much as the sub would allow. This in part due to room size and perhaps partially the floor. I guess I should have mentioned another primary concern is my equipment vibrating somewhat when I have significant volume level, although I'm using Walker Valid POints which do help drastically and the rack sits on spikes which then sit on drilled platforms of Corian solid surface material.
Dumb question time. When you did you RTA measurements were you also searching out the nodes and nulls. Could it be as simple as finding the best nodes for speakers and listening positions? Regarding equipment vibration casued by floor movement, can you beef up the floor under the equipment by using piers under the floor extending down to the garage floor, even if set at an angle. If thats possible, then you can put down a layer of vibration absorbant materiel between your floor surface and the base of your equipment to minimize vibrations. BTW re footfalls and bouncing stylus, do you by any chance have a suspended table? If so, consider that contrary to common perception suspended tables don't like foot falls. A good isolation platform and an unsuspended table can be much better.

What a bummer, having a great space for a dedicated room, great equipment, and a lousy floor. :-(
Owl, I have a similar room over a 2 car garage. The floor was somewhat spongy and was driven into a strong resonance at 31 hz. This was solved by building a beam out of 2x6s in the shape of a "T" and lag bolting the top of the "T" to each joist across the center of the garage ceiling. The "T" beam can be broken into pieces if necessary to avoid any obsticals. This beam resists flexing and ties the joists into a much tighter network. This improved the situation greatly, and might be enough for you.

However, as a extra measure, I then added a steel post in the center by jacking up the beam slightly and sliding it between the beam and the concrete floor. The post was centered between the two car parking slots.

Did it work? The 31 hz resonance is much reduced (some is still in the walls) and you can now go into the listening room and jump up and down as hard as you wish and the turntable (unsuspended on a mass loaded stand) is unaffected.

This solution is very inexpensive and totally unabtrusive to the listening room. You do have to tolerate the beam, but if you place it just ahead of the car doors (near the rear view mirror), it really doesn't get in the way. My total cost was well under $100.
Do what Zargon says - it works. You can even paint the steel jackpost bright orange so it's more noticeable when parking in the garage.

The nice thing about Zargon's suggestion is that the fix works, but is not permanent. Permanent structural modifications to a house are risky (especially if you DIY outside of code). Not necessarily risky to life/limb, but risky in the sense that you may end up with a non-saleable house.

Along those lines, don't modify your garage into a listening room. It's tempting, but it can have severe negative effects on resale value. Most people who buy a house with a garage want to use the garage as a garage. If it's been turned into living space, it's no longer a garage. Also, if you live in an area with property taxation, your remodeling project will force a reassessment (upwards) of your home's tax value.
Zargon gave you good advice. I do wonder about an uninsulated garage joined to your living area. I think your idea of Icynene might be worth doing dependent on the price as you get the side benefit of enegy savings and better resale value. IMHO
The orginal post states 2x4 stick construction.
The floor joists (garage rafters) are 2x4's as well? Not 2x6's?
If the floor joists really are 2x4's they are then most likely on 18 or 24 inch centers.
If so... splurge and hire a structural engineer (or competent "truly" professional carpenter) to come in and assess the situation.
Is the center ridge in the garage still straight?
If the previous owners totally ignored sound construction practices in their effort to save some $$$ in this DIY room there might be bigger issues than what you know.
Hbarrell - the floor joists are 10inches, 16 inches on center.

Yes resale and taxes are important in this project, all good advice.
If you have 2x10's (16" centers) that are allowing the floor to bounce I'm going to guess there is no "X" bracing between the joists.
The sub floor must have a minimum of nails and no PL400.

Personally, I think the cheapest fix would be to tear the garage ceiling out and fix things correctly. Insulate, cross brace, run any required wiring and HVAC...
Drywall is relatively inexpensive and besides it is the garage. Plus if additional support columns (or sisters) are required they can then be properly installed.

Had a very good contractor over this morning who had previously done a wonderful job building out a home theater for me in my last house, and he actually came up with the same suggestion: to place some x crossbracing materials between the floor joists, and to add another layer of subfloor ontop of the existing one. He says the x braces are metal, however, and this concerns me as it may be attracting stray RF and act as a giant antenna possibly?

He also unfortunately indicated that he'd have to go in from the top as well as the bottom to properly mount the x braces. He also wants to reinforce the spans with microlam and the materials are around $1k alone for that, so it's starting to add up to a fairly expensive project, more so if I decide to take out the carpet and replace it with hardwood.

The good news is that we found some insulation was there, however it is very thin, and even though it says R13 was only a couple of inches thick (?)

He is giving me the day to let me consider what I want to do
Don't concern yourself with the metal cross braces and them creating any electronic issues. That's a non-issue.

Wow. I'm surprised at the need to go in from both sides to install cross bracing. I'd really question that requirement.
Although in the end it might make the job easy to perform and allow the guy to get in and out in an orderly fashion.
i.e. cheaper in the end

I have a funny feeling he feels that the bottomline fix is sistering the microlam to the existing joists.
Based strictly from what you've written I'll agree. However do question him as to the need to sister every joist or if every other one will do or every third, etc.

Make sure that when the 3/4" sub-floor goes back down it truly ties together the span. Staggered joints, screwed and glued.
He's really have to do some serious selling to get me to agree to another sub-floor on top of the one that just got glued and screwed. Especially if it's 3/4" underlayment.

Remember the five P's; Proper planning prevents poor perfomance.
Or the seven P's; Proper prior planning prevents piss poor perfomance. :)

Just buy some commercial grade low nap office carpeting ($15 a yd with pad/installed) and enjoy your new room.
Great comments. Why aren't you liking the idea of adding a second layer of subflooring? Wouldn't greater mass of the floor be a positive thing?
It might be a positive thing. The question how posiitve. Personally I don't think any gains would be worth the additional expense.
Spend that money on running a dedicated line or two.