The first thing you should do however is check with your buildings strata (if there is one). Quite often there are rules in place that govern the method of hardwood flooring installation and type of sound insulation used.
Lets start with the floating floor method of installation.
The term 'floating hardwood floor' refers to the method of installation. A floating floor rests on underlay and is not fixed to the substrate or sub-floor. Essentially, gravity holds the floor down.
1. Less expensive than the glue down alternative due to less installation time and minimal adhesive cost.
2. Easier to install especially for the 'do-it-yourselfer'
3. Quieter for your neighbors below. The two air pockets between the flooring and underlay and between the underlay and the concrete break down sound transference between you and your neighbors.
4. A finished floating floor deflects or 'gives' sightly when walked on. This makes living on the floor easier on your legs and back. Don't worry, the movement in the floor is to be expected because the floor rests on a soft underlay however the amount of deflection must not be excessive. 1/8" is acceptable. Your concrete sub-floor should be flattened properly before your flooring contractor. This work is considered a billable extra. You should have no sudden drops or ridges in the concrete before you begin installation. Inadequate or poor flattening will leave excessive soft spots in the finished floor which can cause movement and lead to problems later on.
5. Sound-barrier. There are many sound-rated underlays on the market, each with their own pros and cons.
Look for the IIC rating on the product (Impact Insulation Class) and the test parameters. Your situation must mimic the test scenario if you are to get the sound rating advertised. These ratings measure the amount of sound generated by an impact (foot falling, object dropping) transferring through the concrete sub-floor to the space below in a test setting. The higher the IIC number the less sound transference. The other rating number is STC (Sound Transmission Class) which measures ambient, resinating sound, such as voices or noise from a TV. There are many company's that offer such products with STC and IIC ratings that claim numbers between 54 and 73. Underlays can only achieve such high acoustical ratings when tested in conjunction with the sub-floor and substrate. Follow this link for a list of BCFCA distributor members who could help answer questions.
Glue down floors
1. With this method of installation, the finished floor feels stronger and more solid underfoot. This is because the floor design doesn't allow for movement or slight deflection.
2. Noise. Imagine the sound of a foot step on a glue down floor to be a 'dull thud' as opposed to a brighter 'clack' sound that comes with the floating floor design. The sound of the floor is generally quieter to live with because less noise is reflected back into the room you are in.
3. Expense. Glue down floors are more labour-intensive to install. The adhesive alone will add significant cost. If a sound barrier is required, then it will need to be glued to the concrete first, adding yet another cost per square foot for the adhesive PLUS labour to install.
4. Removing a glue down floor is a tough job. The adhesive is very strong and designed not to let go.