Sound transmissibility within a condominium building.

The proppagation of sound is affected by the density of material. Since the whole structure is made of wood, the sound will not only travel from one condo to another easily, it will reverberate. If the space between the I joists and the framing is empty, the sound will accumulate in strength as it travels the length of the void space.

The shapes of rooms also will contribute to echoes.

There are a number of ways to improve this.

There is acoustic gyproc for the walls that deaden the sound. (higher density) Even a second layer of regular gyproc will help.

Since I assume the owner does not want to rip up the hardwood floor, and install a proper sound absorbing layer, the next best option would be to add insulation in the ceiling of any lower apartments.

If the apartments are all on the same level, I would question if the fire protection between the condos are up to code. Again insulation is required.

The addition of any soft material will help, curtains, rugs, plants in the corners.

How certain are you that the sound transmission can be attenuated with fiberglass batts between the floors? The ceilings are fastened to the bottom of the floor joists. Therefore, if the vibrations are transmitted via the structure wouldn't they bypass the batts, passing through the joists to be propagated by the ceiling system below?

If I am correct in my suspicions then it would seem that dampening the floor system with added mass or other method of modifying the natural frequency would be necessary.

On the question of diagnostics: I was hoping that there might be some suggestions such as using surface mounted transducers to locate (maybe confirm) where the vibrations are most significant. Any thoughts?

True, Any sound travelling through the solid part of the structure would not be affected, however the sound would be restricted to a certain band of frequencies. The major problem is the void space, where, as sound travels the length of a void space, it actually increases in strength the same way a blast wave is actually stronger than the initial explosion... or sound in a long tube such as a tail pipe or gun barrel increases in power. Any baffeling or different density material will reduce this effect. This is the same reason a car muffler was invented.

Dappening the floor is best done with a different density of material (other than wood). this will tend to cause the sound to refract or change the direction of the sound path. Adding mass just lowers the resonant frequency.

Add plush deep pile carpeting and heavy drapes. Plenty of soft furnishings. Earplugs?

Problem: Neighbors knees don't bend resulting in much stomping. Unfortunately, soundproofing is a very difficult thing. Modifying an existing structure would require practically tearing it down. Best solution: MOVE! Anyway that is what worked best for me.

I agree with the comment that to corect an existing structure with passive means is very difficult.

In such a case it is possible that an active noise cancellation system could bring more. I know there are such systems working but I do not knom how efficient they are and if it is possible to use them in big structures. The principle is to generate a counter wave to, at least, reduce the amplitude of the incoming vibration. Due to limited reaction speed there is always a phase shift so that a full cancelation is not possible at higher frequencies.

Realistically, the only active system that will work is for example a set of Bose noise canceling headphones. To generate a sound field of the complexity required over a large area is impossible at this time and may never be in the foreseeable future. However, the Bose headphones do a pretty good job because they are circumaural and isolate what's outside from what's in. That greatly simplifies the task, to control a very small area, which is isolated. Even so it uses a DSP processor and requires quite sophisticated algorithms.

I would not assume that the structure is any more light and flexible than that of any other structure, and probably more rigid than most if built to code. Code requires main rooms must be at 40 psf and bedrooms at 30 psf, notwithstanding how long the span is. Plus beams are more rigid than regular lumber and they didn't use to glue down subfloors like they do now, with the result that your struture is probably much stiffer than one built only 10-20 years ago. I bet you don't feel a bounce in the floor like in my century-old house.

You're not telling us where the sound is coming from,ceiling? walls? another unit? No matter, you've got good advice here-it will be expensive no matter what; maybe better to move. Quick and dirty advice: if the sound comes from a side wall, build a completely separate 2x3 interior wall just inside of the existing side wall, and also be sure to isolate it from the I-joists. Somebody mentioned this soundproofing sheet rock that's out there and it is GOOD and costs 100 bucks a sheet. Tear off the existing ceiling, mount rubber isolator clips to the I joists, clip in steel "sound channel" into the isolator clips (they are made to work together) and re-sheet rock the ceiling with the sondproof sheetrock. Oops, forgot, put in 3.5 inch fiberglass in all cavities. Using more than 3 1/2 fiberglass will NOT help appreciably and cost more money. I got this method from a scientific study I ran accross on the internet and it works. Ray

If the structure was built to code, and this hasn't been verified yet, then it must conform to a 40 psf LL in most spaces and 30 psf LL in bedrooms. Further the deflection under LL or DL cannot exceed L/360 or L/240 for a combination of both.

However, Wood I-Joists and LVL beams actually allow us to construct structures that span wider spaces with less mass in the structure than ever before. Therefore, sound transmissibility can be more of a problem than ever before.

The part of the question that I most need assistance with is diagnostics. Can anyone direct me toward the best procedures or equipment or people that can assist me in determining what part of the structure is the most problematic (floors, walls, ....). I would like to use diagnostics to prioritize remediation efforts, assuming that something reasonable can be devised.

Ray noted that I had not reported where the noise is coming from. It is from other units, but as described above - I do not know whether the floors or the walls are the most problematic - but I do strongly suspect that the lightness of the floor system is at the core of the issue - we are about to begin invasive inspections and I don't expect to find any type of isolation.

Diagnostics are a complex procedure involving measuring the sound levels and beam patterns using specific test equipment and complex mathematics. There are companies that specialize in this. You would have to find one in your area that specialize in buildings.

Thanks for the link - I intend to contact these folks and see where it leads me. This is the sort of thing I'd hoped for.

Have you worked with them before?

No... we have our own specialists in the Navy

Bob, sounds like you found the best solution with a professional company to do that for you, especially if you're working on a multi-condo project which means big money. You might think about identifyling a few acoustical analysis companies and getting the condo owner to pick and contract the company on his own, so you can avoid potential exposure or responsibility, and just do the soundproofing work (which you are professional at) based on their recommendations.

You mentioned procedures and equipment in your question also, and although I wouldn't recommend this for your large project, the following might be feasible for a smaller project that doesn't justify the expense of a full blown acoustical analysis contractor.

An engineer friend of mine is a stickler, and he was able to track down the sources of "generalized" noise in his new home using an ingenious, cheap and effective method. With electronics going for next to nothing these days, he bought himself a parabolic dish microphone; not a 40 buck toy but one similar to what birdwatchers use, although I don't believe he spent much over 100 bucks. With full, padded headphones, he heard virtually nothing at all until locating a sound source. Apparently, these things are so directional that you can use them as a "stethescope" for the home. Ray

Bob, I had a single family home project which had the identical floor framing system and noise problem. The T-joists were long spans on the second floor. The floor resonated like a bass drum as people walked about. My solution was to stiffen the floor framing with retrofit joists "sistered" to the T-joists. For your high-end condos you are wise to get "quantifiable" information before trying to fix the problem. As suggested by others, an acoustical engineer can do this kind of analysis and recommend the appropriate design solution. I normally design hotels so sound control is critical. The engineers have always solved my problems. xdesign@pacbell.net