TECH TERMS

Room noise

Noise in a closed room which has already been reflected several times by the time it reaches the place where it is heard or measured.

Reverberation time

The reverberation time is how long it takes for the sound pressure level in a room to fall by 60 decibels after the sound source is turned off. For practical reasons, it is usual to measure the time taken for a drop of only 30 decibels.

Sound transmission (STC)

Is an integer rating of how well a building partition attenuates airborne sound and is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations.

free-field noise

The terms “free field” or “direct field” refer to a situation in which sound is not reflected at all. Free-field conditions are only found in nature for example where new snow prevents sound from being reflected from the ground. Free-field conditions can be created artificially in non-reverberating rooms. They play an important role in acoustic measurements and hearing tests, because the results in a free-field environment are only influenced by sound from the noise source and not by reflections from the room.

Stc ratings

STC 30
Loud speech can be understood fairly well, normal speech heard but not understood
STC 35
Loud speech audible but not intelligible
STC 40
Onset of "privacy"
STC 45
Loud speech not audible; 90% of statistical population not annoyed
STC 50
Very loud sounds such as musical instruments or a stereo can be faintly heard; 99% of population not annoyed
STC 60+
Superior soundproofing; most sounds inaudible

sound absorption

We speak of sound absorption when a sound wave meets a soft, elastic or porous body and is wholly or partially absorbed. When this happens, sound energy is converted into heat. When a sound wave hits a hard object and is thrown back, the result is a sound reflection.

impact insulation (IIC)

Tests the ability to block impact sound by measuring the resistance to transmission of impact noise or structure-borne noise (simulating footfalls, objects dropped on the floor, etc).

IIC Ratings

IIC 43
Footfall clearly audible
IIC 50
The least amount of impact sound transmission reduction considered effective
IIC 60
Considered a medium level of impact sound transmission reduction
IIC 65
Considered a high level of impact sound transmission reduction that would satisfy most occupants
IIC 74+
Footfall inaudible

sound pressure level

A sound field can be quantitatively described through measurements. The sound pressure level is the characteristic most often measured in practice. It describes the ratio of the sound pressure of an acoustic event to a reference value which roughly corresponds to the threshold of human hearing. Where the sound is able to propagate freely, the sound pressure level decreases with increasing distance from the sound source. However, if it occurs inside a room, beyond a certain distance it is more or less independent of location. This is due to reflections and inter-reflections on the room surfaces which create a diffuse sound field. How high the sound pressure level is depends on whether reflections occur.

CHANGE IN SPL

3dB
Just perceptible
5dB
Clearly noticeable
10 dB
Twice as loud (or 1/2)
15 dB
Three times as loud (or 1/3)
20 dB
Four times as loud (or 1/4)

acoustic quality

Acoustic quality means the suitability of a room for particular types of sound. The acoustic quality of a room refers in particular to the communication of speech and musical performances to those parts of the room which are intended to be occupied by people.

wall soundproofing

Typical party walls rate STC 30-40. Adding insulation, additional layers of drywall, and damping compounds can net STC ratings in the low to mid 50's. Decoupling can net ratings of STC 60+.

ceiling soundproofing

Impact sound (footfall) is a common complaint and can be reduced with decoupling measures applied to either the offending floor or the ceiling below. Existing ceilings typically rate IIC 35-45.

speech intelligibility

Basic criterion of acoustic quality in speech performance rooms. The subjective intelligibility of speech may be determined based on the percentage of correctly recognized syllables, words or sentences.

Frequency

This means the number of air vibrations per second of an acoustic event. The sound propagation corresponds to an air pressure fluctuation. Low frequencies involve a small number of slow vibrations; high frequencies on the other hand involve a lot of rapid vibrations.