As commonly defined, Noise is a sound that is loud or unpleasant or that causes disturbance. Sound is measured in a unit called the 'decibel' (dB). Our hearing range starts at 10 decibels (dB) and is considered safe up to 70 dB. Any prolonged exposure of sound of around 90 dB will lead to permanent damage to human ears. Extensive destruction and pain to the auditory nerves occurs at 140 dB. and destruction and
persistent ringing in ears will occur immediately at 150-160 dB.
There are two types noise control in buildings.
Air Born Sound - sound coming from air when the sound is produced directly to the air, like speech, sound from radio, TV, airplane.
Structure born are the sounds created when someone walks on a floor close to the flat, objects falling on the floor, house hold appliances etc.
Reverberation time is the time taken for the sound pressure level to drop by 60 dB after the generated noise has been stopped.
Areas with a long reverberation time are referred to as being 'live', e.g. cathedrals and churches. Those with a short reverberation time are referred to as being 'dead', e.g. offices with thick carpets and absorbent ceilings.
A reduction of 60 dB in the sound pressure level is equivalent to the reduction of acoustic energy by a factor of one million. As a rough guide, the reverberation time of a room is approximately equal to the time it takes for loud clapping to become inaudible.
STC (Sound Transmission Class) value is a single number rating to specify the reduction in sound levels that the partition provides. The sound transmission loss performance of a partition is measured using ASTM E 90 "Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements" and calculated according to ASTM E 413 "Classification for Rating Sound Insulation." As a general rule, the higher the STC rating, the better the partition's acoustical performance.
Ceiling Attenuation Class (CAC) ratings are used to determine the sound transmission loss through an acoustical or dropped ceiling. A CAC rating is determined by ASTM test method E 1414 "Standard Test Method for Airborne Sound Attenuation Between Rooms Sharing a Common Ceiling Plenum" and provides a value that is equivalent to an STC value
An IIC (Impact Isolation Class) rating describes the impact noise that is transmitted through a floor/ceiling assembly. The rating is determined by ASTM E 492 "Standard Test Method for Laboratory Measurement of Impact Sound transmission Through Floor-Ceiling Assemblies Using the Tapping Machine." High ratings indicate that impact noise is reduced substantially.
Resilient channels are strips of metal with an offset that spaces the drywall approximately ½" away from the framing. They are typically installed 24 inches on center perpendicular to the studs. The use of resilient channels dramatically reduces the amount of sound that is conducted though the structure.
Q: Are there advantages to using steel studs over wood studs?
Twenty five gauge steel studs provide superior sound control performance to wood studs with the same dimensions. The flexibility of the studs allows the partition to provide performance equivalent to a wood stud construction with resilient channels.