2.5 Testing sound levels

2.5.1 What do Acoustic Consultants do?

There are a large number of diverse companies that deal with noise reduction.

For example, The Owners Corporation of Australia has had a number of these present at to our members.

  • Soundblock Solutions offers a complete range of insulation and noise control products for domestic use.
  • Soundbarrier Systems provides sound insulation and soundproofing for the home or office.
  • Magnetite, which produces an ingenious secondary glazing window system.

An accredited acoustical engineer can be assessed and the right acoustic treatment can be recommended:

  • Engineering design advice relating to the control of sound and vibration
  • Behaviour of sound within rooms e.g. concert halls, theatres, etc
  • Transfer of sound between one place and another e.g. between apartments

An approximate guide of the cost for on-site testing and a written report is between $3,000 and $4,000 dollars.

2.5.2 Testing ambient noise transmission

A sound level meter is the instrument normally used to measure noise levels on the decibel scale. Several factors affect the noise level reading:

  • The distance between the meter and the source of the sound
  • The direction the noise source is facing, relative to the meter
  • Whether the measurement is taken outdoors (where noise can dissipate) or indoors (where noise can reverberate)

For a reported sound level value to be most useful, it is necessary to specify the conditions under which the reading was taken, especially the distance from the source. Acoustic measurements in relation to noise are usually only measured vertically, and not horizontally.

2.5.3 Testing walls and floors for sound transmission

Each building is different and therefore any acoustic treatment of floors in any building needs to be considered in relation to the structure, age and existing acoustic properties of the building.

Testing the sound levels involves determining the Impact Insulation Class (IIC) rating and  is usually done via ‘Tapping Testing’ Noise is generated by placing a standardised “tapping machine” on the floor and measuring the sound pressure levels are measured in the room under at several different frequencies.

A standard tapping machine with five–steel faced hammers strikes a test floor material, generating sounds between 125 Hz – 4000 Hz. The impact creates vibrations that travel through the flooring and produce sounds on the other side. Depending on the amount of impact sound that is lost during the transmission, the results from each tap are plotted on a graph. Depending where those points fall on the graph, they are compared to a reference and the IIC rating is determined. The sound levels are corrected to account for the acoustical properties of the receiving room.

The IIC rating can be tested in one of two different environments: Each floor covering product can be tested individually and given an IIC product rating based on that test, or can be tested as part of an entire floor/ceiling assembly. The latter can include not only the floor covering (carpet, hardwood, tile, etc.), but also the subfloor, underlayment, flooring joists, ceiling below, as well as adhesives and sealants that may be needed for installation. In addition, there are plenty of other sound–deadening materials that are used in floor/ceiling assemblies. For example, fiberglass insulation and resilient channels can be used to increase an IIC rating. In these tests, the entire floor/ceiling assembly works together to result in the structure's overall IIC rating.

The most appropriate and accurate way to measure the IIC of a home or building is to do so after installation. This way, all materials are taken into account for and given a total IIC value. Also, any air vents or other obstacles that sound can travel through are also accounted for with this method. This method is also known as the Field Impact Insulation Class (FIIC).

2.5.4 Flooring Joists and concrete subfloors

There is no easy way to accurately determine the projected IIC rating or a floor covering until it is installed and tested in the field. A large reason for this is the different types of subfloors – concrete or wood joist, which can have a large effect on the IIC rating of the floor covering. In addition, other sound deadening materials (an underlayment for example) can add to the IIC rating. To give you a better idea of the difference these factors make, the tables below show estimates of the excepted IIC ratings that you may achieve with the type of floor system shown. The first table shows floor coverings tested over concrete subfloors and the second table shows floor coverings rated over a basic floor joist system.

Approximate IIC ratings for a 150–mm–thick concrete slab with various kinds of toppings.

Diagram

Topping

IIC Rating

None, or ceramic or marble tile

28

Vinyl flooring

35–40

Hardwood flooring

30–35

9–mm–thick hardwood on 5–mm–thick resilient layer

45–50

16–mm plywood or OSB on 40– x 90–mm wood strapping on 25–mm mineral fibra board

50–55

35–mm concrete on 25–mm mineral fibra board

60–85

Carpet and underlay

75–85