Acoustic+Glossary

Absorption Class Classification of sound absorbers into Sound Absorption Classes A-E, according to EN ISO 11654, including frequencies 200-5000 Hz.

Articulation Class (AC) A classification of suspended ceilings according to their ability to contribute to the acoustic privacy between work stations. AC is calculated from the Interzone Attenuation according to ASTM E-1110. The Articulation Class (AC) can be calculated from the interzone attenuation. This can then be used as a tool to classify and compare acoustic ceiling systems. The higher the AC the better the speech privacy in an open plan situation. We recommend that you use a suspended ceiling with minimum Articulation class 180 in order to achieve acceptable speech privacy. A high Articulation Class gives some privacy, a lower Articulation Class means lower privacy. Confidential conversation and work tasks demanding concentration need good privacy.

Articulation Loss of CONSonants (%-Alcons) One method of objectively measuring speech intelligibility is Articulation Loss of CONSonants (%-Alcons), showing the number of consonants being missed as a percentage. Consonants play a much more significant role in speech intelligibility than vowels. If the consonants are heard clearly, the speech can be understood more easily.

Ceiling Attenuation Class (CAC) Single value for the laboratory sound attenuation of a suspended ceiling between two rooms according to ASTM E 1414. This measurement takes only into account the sound transmission through the suspended ceiling. Single value, according to EN ISO 717-1, for the laboratory sound insulation of a suspended ceiling between two rooms, measured according to ISO 10848-2. This measurement takes only into account the sound transmission through the suspended ceiling.

Noise Reduction Coefficient (NRC) Single value for sound absorption according to ASTM C 423, derived as the mean value of 4 frequencies in the range 250-2000 Hz.

Privacy Acoustic privacy between working places in open plan offices is expressed with the Articulation Class (AC).

Rapid Speech Transmission Index (RASTI) RASTI is an objective way of measuring speech intelligibility. It is measured at two frequencies, 500 and 2000 Hz, by placing a loudspeaker, which transmits sound from the location of the person speaking, and a microphone where the listeners are situated. (See also STI).

Reverberation time, (T or RT) The time it takes for the sound pressure level to fall by 60 dB after the sound has been turned off. Measuring the reverberation time allows us to calculate the total sound absorption. The reverberation time varies according to the frequency.

Sabine The physicist Wallace Clement Sabine (1869-1919) created in Riverbank, west of Chicago, the well known Sabine formula (T=0,16V/A), showing the relationship between reverberation time (T s), room volume (V m³) and the amount of absorption (A m²). (image): (Sabine's formula)

Signal to noise ratio (S/N)  Another important parameter influencing speech intelligibility is the background noise level or, more specifically, the signal to noise ratio (S/N). This is the ratio between signal (e.g. speech) and background noise (e.g. ventilation noise). To achieve good speech intelligibility a signal is considered to be at least 15 dB above noise level. For hearing- impaired people the need is even greater; a ratio of at least 20 dB is often referred to. On the other hand, if the signal to noise ratio is much less, or if the signal is lower than the noise, the signal will be partly masked. Thus some privacy can be achieved.

Sound Absorption Average (SAA) Single value for the sound absorption according to ASTM C 423, including the third octaves in the frequency range 200-2500 Hz.

Sound Absorption Class Classification of sound absorbers into Sound Absorption Classes A-E, according to EN ISO 11654, including frequencies 200-5000 Hz.

Sound insulation <span style="display: block; font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 10pt;"> The ability of a building element or building structure to reduce the sound transmission through it. The sound insulation is measured at different frequencies, normally 100-3150 Hz. Airborne sound insulation is expressed by a single value, //D//<span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">n,f,w, //R//<span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">w or //R'//<span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">w. Impact sound insulation is expressed by a single value //L//<span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">n ,<span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">w or //L'// <span class="Subscript" style="font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 6pt; vertical-align: sub;">n,w.

<span class="Heading1" style="color: #404040; font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 15pt;">Sound pressure level (dB) <span style="color: #404040; font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 10pt;">The pressure variations caused by sound waves in air are called sound pressure. The lowest sound pressure level which can be heard is 0 dB, known as the hearing threshold. The highest level which can be tolerated is called the pain threshold and is around 120 dB.

<span style="color: #404040; font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 15pt;">Speech intelligibility Speech intelligibility is directly dependent on the level of background noise, reverberation time and the shape of the room. Different methods are used to evaluate speech intelligibility, the most common ones are RASTI, STI and %-Alcons.

<span style="color: #404040; font-family: Arial,Verdana,Tahoma,Helvetica; font-size: 15pt;">Speech Transmission Index (STI) Similar to the RASTI method but a more complete form of measuring speech intelligibility by measuring all octave bands in the frequency range 125-8000 Hz.