Acoustic_Vocabulary



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

Acoustics “Acoustics” is the term for the study of sound and how sound is experienced. The field of acoustics is divided into several specialist areas. The word acoustics comes from the Greek akoustikos (“to do with hearing”) and akouo (“to hear”).

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. Background Noise (dB) For example, speech, scraping chairs, humming ventilation, traffic, machinery and equipment, sound from corridors, adjoining rooms, playgrounds. Increased background noise can have long-term negative effects, such as illness, fatigue, decreased productivity and efficiency. Therefore it is not recommended to attempt to obtain better daily speech privacy by increasing the ventilation noise, or use other sound masking systems. Another thing to bear in mind is that people are differently sensitive to sound and noise in general. Privacy and seclusion in open plan spaces can only be solved satisfactory by creating separate rooms for confidential discussions and work tasks needing higher concentration.

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. Dn,f,w (dB) 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.

Flutter echo Occurs when noise bounces between parallel surfaces in a room.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Noise <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Unwanted sound. Noise can often be the individual perception of a particular sound, e.g. a background noise. <span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Noise Reduction Coefficient (NRC) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Single value for sound absorption according to ASTM C 423, derived as the mean value of 4 frequencies in the range 250-2000 Hz.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Privacy <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Acoustic privacy between working places in open plan offices is expressed with the Articulation Class (AC).

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Rapid Speech Transmission Index (RASTI) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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).

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Reverberation time, (T or RT) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sabine <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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). <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">(image): (Sabine's formula)

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Signal to noise ratio (S/N) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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. <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;"> 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.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound absorbers <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Materials and structures with the ability to take up sound energy and convert it into other forms of energy. They improve room acoustics by removing sound reflections, thus reducing the noise and the reverberation time. <span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound Absorption <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Means that sound energy is converted into mechanical vibration energy and/or heat energy. Sound absorption is expressed as the sound absorption coefficient α or the sound absorption class (A-E) according to EN ISO 11654 or NRC/SAA according to ASTM C 423.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound Absorption Average (SAA) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Single value for the sound absorption according to ASTM C 423, including the third octaves in the frequency range 200-2500 Hz.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound Absorption Class <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Classification of sound absorbers into Sound Absorption Classes A-E, according to EN ISO 11654, including frequencies 200-5000 Hz.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound insulation <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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, Dn,f,w, Rw or R'w. Impact sound insulation is expressed by a single value Ln,w or L' n,w. <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound pressure level (dB) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Sound strength (dB) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Measured in dB (deciBel). dB is measured at different frequencies. <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">dB(A) (or LpA) is a single-figure value used to describe the total sound strength for all frequencies in a way similar to the sensitivity of the ear. <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">dB(C) (or LpC) particularly focuses on low frequencies and better reflects how a sound is perceived by people with impaired hearing.

<span style="color: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Speech intelligibility <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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: #ff7600; font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">Speech Transmission Index (STI) <span style="font-family: 'Arial Black',Gadget,sans-serif; font-size: 110%;">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.