Glossary of Terms

Acoustics
Glossary of Terms
Direct Sound
Direct sound is a single path from source to receiver and it’s clarity is beneficial for speech intelligibility and music tone quality as it is unaffected by room surfaces.

Reflected Sound
Reflected sound is sound that is has reflected from one or more room surfaces. Reflected sound takes longer to reach the ear than direct sound because its path is longer, it is useful or problematic depending on the delay and overlap with direct sound. Reflected sound can be controlled by altering the surface absorbent or reflective qualities and Asona manufactures a wide range of ceiling and wall finishes to suit the many different applications.

Reverberation Time
This is the time in seconds that it takes for a sound to decay 60dB. Hard surfaces reflect sound and can lead to long reverberation times, porous surfaces absorb sound and help shorten reverberation times. For good speech intelligibility reverberation times of RT 0.4 to 0.8 seconds and a signal to noise ratio of 6dB are required.

Background Noise
This is any sound that is heard, it can be from air conditioning, traffic noise, noise from other people etc. Combined they add up to the back ground noise levels. Excessive back ground is a common problem in interiors.

NRC
Sound absorption of material finishes can be classified according to NRC (noise reduction co-efficient) as tested per ASTM C423 standard and is the average absorption of a material at 250, 500, 1000, 4000 Hz rounded to the nearest 5%
The NRC gives no information as to how absorptive a material is in the low and high frequencies, nor does it have anything to do with the material’s barrier effect (STC).

We strongly advise using full scale test data to assess individual frequency sound absorption data. NRC is superseded by ∂W per ISO 11654

∂W
Sound absorption of material finishes are classified according to ISO 11654 as tested to ISO 354 test method. It is the weighted average absorption of a material and is a good indicator of a product performance. ∂W numbers can have L M,H after the number as an indicator as to the shape of the absorption curve. L means the curve is higher at the low frequencies ( 125-250Hz) M means the curve is higher at the mid frequencies (500 – 1000 Hz) and H means the curve is higher at the high frequencies (2000 – 4000 Hz).

Satisfactory Design Sound Level
The level of noise that has found to be acceptable to most people for an environment question and also not to be intrusive. Reported in weighted average sound pressure rating dB(A)

Sound Transmission Coefficient ( STC)
STC) is a single-number rating of a material’s or assembly’s barrier effect. Higher STC values are more efficient for reducing sound transmission. The rating assesses the airborne sound transmission performance at a range of frequencies from 125 Hertz to 4000 Hertz. This range is consistent with the frequency range of speech. The STC rating does not assess the low frequency sound transfer. Special consideration must be given to spaces where the noise transfer concern is other than speech, such as mechanical equipment or music.

Flanking Sound
If you are disturbed by unwanted noise it can be caused by flanking sound.
Flanking sound can be air borne or structural borne and can seriously degrade room privacy ratings. 

Join our mailing list
Sign up to receive updates on new products & custom builds