See Privacy.
In order to categorise the absorptive effects of different elements (such as ceiling tiles), classes from A to E were derived, as per BS EN ISO 11654:1997. A class ‘A’ absorber would be very acoustically absorptive, a Class ‘E’ absorber would be less absorptive and more reflective. A product that is highly reflective may not be classified.
A value usually between 0 and 1 assigned to a material to indicate how acoustically absorptive it is. 0 indicates a material is entirely reflective (and therefore not absorptive), and 1 indicates a material is entirely absorptive (and therefore not reflective). Absorption coefficients are usually given for each octave band between 125 Hz and 4 kHz, or as an overall ‘practical’ coefficient.
Sound transmitted through air.
Department of Transport document ‘Calculation of Road Traffic Noise’ (CRTN), published in 1988. The memorandum was prepared to enable entitlement under the Noise Insulation Regulations 1975 to be determined, but it is stated in the document that the guidance is equally appropriate to the calculation of traffic noise for land use planning purposes.
The CRTN shortened measurement method involves taking traffic noise measurements (LA10) over representative time periods within any three consecutive hours between 10:00 and 17:00. By using the LA10,3hour, as the arithmetic mean of the measured LA10 values, the LA10,18hour value can then be calculated; CRTN states that ‘LA10,18hour = LA10,3hour, – 1dB(A)’. The LA10,18hour values can then been converted into the equivalent LAeq,16hour values by subtracting 2.2 dB from the LA10,18hour for use in the subsequent assessment.
Literally meaning ‘a tenth of a bel’, the bel being a unit devised by the Bell Laboratory and named after Alexander Graham Bell. A logarithmically based descriptor to compare a level to a reference level. Decibel arithmetic is not linear, due to the logarithmic base. For example:
30 dB + 30 dB does not equal 60 dB
30 dB + 30 dB = 33 dB
Measured in Hertz (after Heinrich Hertz), and represents the number of cycles per second of a sound or tone.
Re-radiated sound as a result of impact(s) on a solid medium, such as footfalls on floors.
Different metrics are used to describe the level of impact noise measured in a space.
Very low level frequencies below the accepted range of human hearing, located between 1 Hz and 20 Hz.
Unwanted sound.
Noise Criterion (NC) level, an octave band dependent system of rating noise levels similar to the Noise Rating system.
Pascals, the Systeme International (SI) I unit to describe pressure, after physicist Blaise Pascal.
Privacy is the addition of the level of sound insulation between two rooms and the background noise within a receiving room. It can be used to assess the level of privacy afforded in the ‘receiving room’ for speech from the ‘source room’.
The ‘privacy factor’ is a value that is the combination of the average ‘A’ weighted background noise level in the receiving room dB and the weighted sound level difference (Dw) of the separating structure in dB.
The ‘speech privacy potential‘ is another measure of privacy, and this is the combination of the D‘w of the separating structure in dB and the Noise Rating (NR) level in the receiving room.
The table below details the privacy factor ratings and associated descriptions.
| Privacy Factor | Resulting privacy assuming normal speech |
|---|---|
| < 70 | Clearly audible and intelligible |
| 70 – 75 | Audible but not intrusive |
| 75 – 80 | Audible but not intelligible |
| > 80 | Inaudible |
The sound level difference between two internal spaces, or between internal and external spaces. The ‘D’ value is used to denote the differences at each third octave or octave band, with a single figure ‘weighted’ value to describe an overall performance. Note that the ‘D’ value will always describe an in-situ or on-site acoustic performance. All values are described using the decibel.
Single figure weighted sound level difference, simply the measured source noise level minus receiver noise level, not adjusted to reference conditions
Weighted normalised sound level difference – a single, weighted sound insulation value, normalised to a reference reverberation time using the measured reverberation time in the receive room
As above, with a spectral adaptation term applied to account for the effects of low frequency noise, and based on urban traffic noise
Overall flanking normalised level difference – A parameter that defines the flanking transmission of sound from room to room where a dividing partition or floor construction abuts a flanking building element common to both rooms, such as the building façade or ceiling
Weighted single figure sound reduction index
As above, with a spectral adaptation term applied to account for the effects of low frequency noise, and based on urban traffic noise
The ‘apparent sound reduction index’, a field measurement to obtain the sound reduction index of a material or element, with all effects of site installation accepted.
| Privacy Rating | Speech Privacy Potential (SPP) | Description of Privacy |
|---|---|---|
| Total Privacy | 85 | Shouting is barely audible |
| Confidential | 80 | Normal voice levels not audible. Raised voices barely audible but not intelligible. |
| Excellent | 75 | Normal voice levels barely audible. Raised voices audible, but mostly unintelligible. |
| Good | 70 | Normal voices are audible but unintelligible most of the time. Raised voices are partially intelligible |
| Fair | 65 | Normal voices audible and intelligible some of the time. Raised voices are intelligible. |
| Poor | 60 | Normal voices audible and intelligible most of the time. |
| None | < 60 | No speech privacy |
Tones are prominent frequencies (or octaves, or third-octaves) that are ‘proud’ of the immediately adjacent frequency bands such that they are distinguishable, for example, as a ‘hum’, ‘whine’ or ‘whistle’.
Very high level frequencies above the accepted range of human hearing, located above 20 kHz.
Watts, the Systeme International (SI) unit to describe power, after engineer James Watt.
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Company number 11008703
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