Acoustical Testing - Frequently Asked Questions

Below are answers to commonly asked questions about Acoustical Testing:

What is Acoustics and what is acoustical testing used for?
Acoustics is the study of sound, noise, and vibration. Understanding the acoustical performance of your product is important because windows, doors, and walls in a house need to diminish the transfer of unwanted sound into living areas. Acoustical testing helps diminish high levels of noise from traffic, neighbors, and other sources. Acoustical testing helps product manufacturers determine these values.

What is sound power, and what’s the difference between sound power and sound pressure?
Sound Power is the calculated acoustic output of an object in watts without respect to distance from the source. The difference between sound power and sound pressure can be analyzed by looking at the units of each. Sound pressure is a measurable value in Pascal’s that is used for other calculations or for the calculation of sound power. Sound pressure changes with respect to distance and room conditions. Sound power is expressed in power units of watts and is independent of room conditions and distance. The advantage of sound power level is that it can be to calculate sound pressure levels at given distances and room conditions. Both values lack directional characteristics and therefore are only scalar values.

Where does Intertek conduct acoustical testing?
Intertek’s acoustical testing is conducted at a facility located in Cortland, NY, USA. The Cortland lab is the only Intertek site that can make any lab-based sound measurements, including: ASTM C423, E90, E492, E477, ANSI S12.31, S12.32, S12.52, and many others. We also can provide field testing if an item is too large to ship or is already installed.

What is an STC and/or an IIC rating?
STC stands for sound transmission class. It is defined as an integer-number rating of how well a building element reduces airborne sound. It is a calculation based on transmission loss values through an element. Transmission loss is the measurement of the noise reduction in individual frequency bands from a source room containing noise to a receiving room containing a microphone. The transmission loss values are also corrected for room absorption on the receiving side.

IIC stands for Impact Insulation Class. It is defined as a single number rating derived from the normalized impact sound pressure levels through a floor ceiling assembly. The sound source is a standard tapping machine through which sound pressure levels radiate off the bottom of the assembly into a receiving room and are then normalized for the rating calculation. There are nearly unlimited systems this testing can be performed on. Intertek offers three standard systems and can build nearly any system requested.

What can I do to improve the STC rating of my product, both before and after testing?
The major thing to remember during an STC test is that “limp mass,” i.e., lead or vinyl can help improve STC values. Another method to improve values is isolation and air spaces so that the airborne sound does not have a direct path to radiate off of.

Which floor system achieves the highest IIC rating?The floor system at Intertek that achieves the highest IIC rating is the 6” concrete with a ceiling plenum. Every floor and underlayment combination will achieve different results. It is very difficult to predict what results a particular floor will get. Typical results for the system range from the mid 50s to the low 60s in IIC rating. Typically carpets will get much higher ratings.

Can you do field evaluations / testing, and if "Yes," then to what standards?
Yes, we can perform field testing and field evaluations. The amount of standards we test to in the field is nearly limitless and the best way to find out if your product can be tested in the field or in the lab is to contact Intertek. 

What is a dB?
A dB is an abbreviation for decibel meaning 10 Bels. A Bel is an imaginary unit with a logarithmic scale used to make measurement results easier to understand. A decibel value or a Bel value has to be referenced to a number with a unit; this reference describes what kind of decibel or Bel is being used. For example, a typical measurement would give a result of 60 decibels with a reference to 20 micro-Pascal’s. 60 decibels is the same as a sound pressure with a measurement of 20 Pascal’s. At 200000 Pascal’s the decibel level only increases to 100 dB. The dB scale is easier to understand than directly using the units in the reference.

What is the difference between a Hemi-Anechoic and a Semi-Anechoic Room?
A hemi-anechoic room has a concrete floor and can be used for testing in an essentially free field over a reflecting plane. A semi-anechoic room has a carpet floor and is used for various other tests. 

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