Acoustic+Vocabulary

[[image:waveforms1.jpg width="464" height="260" align="left"]] Background noise:
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.

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

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).

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.

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 strength (dB): **
 Measured in dB (deciBel). dB is measured at different frequencies. 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. dB(C) (or LpC ) particularly focuses on low frequencies and better reflects how a sound is perceived by people with impaired hearing.  

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.

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.