Acoustics_Vocabulary

 **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 absorbers** 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.  **Sound absorption** 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.  **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** 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.  **Sound pressure level (dB) ** 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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Sound strength (dB)** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">Measured in dB (deciBel). dB is measured at different frequencies. <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">dB(A) (or L pA ) 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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">dB(C) (or L pC ) particularly focuses on low frequencies and better reflects how a sound is perceived by people with impaired hearing. <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">** Speech intelligibility ** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Speech Transmission Index (STI)** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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. <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Noise** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">Unwanted sound. Noise can often be the individual perception of a particular sound, e.g. a background noise. <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Noise Reduction Coefficient (NRC)** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">** Privacy ** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">Acoustic privacy between working places in open plan offices is expressed with the Articulation Class (AC). <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Rapid Speech Transmission Index (RASTI)** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Reverberation time, (T or RT)** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;"> **Sabine** <span style="background-color: #ffffff; color: #444444; font-family: 'Segoe UI','Lucida Grande',Arial; vertical-align: baseline;">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).