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Acoustic glossary...

Absorption class

Classification of sound absorbers in absorption class A-E according to the international standard EN ISO 11654 applicable in the frequency range 250-4000 Hz.

Acoustics

The science of sound. Colloquially thought how sound is perceived in a room.

Articulation Class (AC)

Classification of suspended ceilings according to their ability to contribute to the acoustic.
Privacy in offices.
AC is calculated from the ceiling ability to reduce the sound between areas (the interzone attenuation) according to ASTM E-1110.

Articulation Loss of Consonants (%-Alcons)

A method of objectively measuring of speech perception. %(Percentage) Alcons show the number of lost consonants expressed in percentage. The consonants play a more important role in speech perception than vowels. If you hear the consonants properly, then you understand the speech well.

Background Noise (dB)

For example speech, rattling with chairs, whirring ventilation, traffic noise, noise from machines and equipment, noise from corridors, adjoining rooms and school yards.

Dn,c,w (dB)

Single value, according to EN ISO 717-1, for the sound insulation between two rooms with suspended ceilings is measured according to ISO 140-9. These measurements deal only with the sound transmission through the suspended ceiling.

Flutter Echo

An Echo, which occurs, when the sound is reflected between parallel surfaces in a room.

Frequency (f)

Indicated in Hz (Hertz). The higher value the lighter tone (treble).
The frequency range for speech is mainly between 125-8.000 Hz, while audible sound is between 20-20.000 Hz.

Noise

Unwanted sound. Noise can often be an individual experience of a special sound for instance a background noise.

Noise Reduction Coefficient (NRC)

Single value for sound absorption according to
ASTM C 423, derived as the mean of four frequencies in the frequency range 250-2000 Hz.

Privacy (speech privacy)

Acoustic privacy in open offices is expressed through Articulation Class (AC).

Rapid Speech Transmission Index (RASTI)

RASTI is an objective method of measuring speech perception. By placing a speaker on the speaker's place sending out sounds and a microphone on the listener's place, you can measure the speech perception in two frequencies: 500 and 2000 Hz. (See also STI).

Reverberation (RT60)​

The time it takes for a sound level to fall by 60 dB, after "the sound has stopped" (in practice the time it takes the sound to die out). By measuring the reverberation, you can calculate the total sound absorption of the room. The reverberation varies with the frequency.

Sabine

The physicist Wallace Clement Sabine (1869-1919) deduced in Riverbank, West of Chicago, the well-known Sabine reverberation equation(T=0,16*V/A), that show the context between the reverberation (RT), the volume of the room (V m³) and the absorption quantity (A m²).

Sound Absorbers

Materials and constructions with the ability to "absorb" sound energy and transform this to another type of energy. Sound absorbers improve the room acoustics by removing sound reflects, which lower the noise level and shortens the reverberation.


Sound Absorption

Means that sound energy is transformed into mechanical vibration energy and/or thermal energy.

Sound absorption is expressed through the sound absorption coefficient α or the sound absorption classes A-E according to EN ISO 11654 or NRC/SAA according to ASTM C 423.


Sound Absorption class

Classification of sound absorbers in the absorption classes A-E according to the international standard EN ISO 11654 in the frequency range 200-5000 Hz.


Sound Insulation

The ability of a building to prevent sound energy to pass from one room to another. Sound insulation is measured at different frequencies, normally at 100-3150 Hz. Airborne sound insulation is expressed as a single value Dn,c,w , Rw or R'w.

Impact sound insulation is expressed as a single value Ln,w or L' n,w .


Sound pressure/Sound pressure level (dB)

The variations, that sound waves creates in air, are called sound pressure. The lowest sound pressure level, which you can perceive, is 0 dB and is called the hearing threshold. The highest level, which you can endure, is called the pain threshold and is about 120 dB.


Volume (dB)

Is measured in dB (deciBel). dB is measured by different frequencies. dB(A) (now also LpA) is a single value, which is used to describe the total volume for al frequencies in a way, that mimics the ear's sensitivity. dB(C) (now also LpC) gives special consideration to low frequencies and reflects better, how a hearing injured person perceives sound.


Speech Perception

The speech perception is directly dependent on the level of the background noise, the reverberation, and the type of space. There are different methods of how to measure the speech perception. The most common ones are RASTI, STI and %-Alcons.


Speech Transmission Index (STI)

Similar to the RASTI-method, but it is a more complete kind of measurement of the speech perception by measuring al the octaves in the frequency range 125-8.000 Hz.

Contact us

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