How ACOUSTIC COMFORT
Find out more about the ways that human beings identify and react to different sound levels...
THE PHYSIOLOGICAL ASPECT
The human ear is comprised of three parts – the outer (1), middle (2) and inner ears (3) – which respectively receive, transmit and detect sound.
Sound pressures set the eardrum in vibration, and this movement is transmitted to the inner ear, where nerves are stimulated. Hearing is the only human sense that fully functions while we sleep.
The difference in scale of the pressure changes. The unit of quantity is the bel, but common practice uses the decibel (dB), which is one tenth of a bel. To give an idea of their values, our day-to-day experiences might include the following:
- Bedroom at night time: 30dB
- Normal conversation 1 meter away: 60dB
- Car traffic 10 meters away: 80dB
- Peak levels in a night club: 110dB
- Jet plane take-off: 120dB
- Threshold of pain: 130dB
A healthy human ear is sensitive to a very wide range of frequencies. These are measured in hertz (Hz), and range from around 20Hz to 20,000Hz. In general, low frequency sound – vibrations at 20-125Hz – is perceived as very annoying (air conditioning units, for example), while the ear is most sensitive to frequencies of between 3,000-5,000Hz.
It’s interesting to note that in human speech, it’s the high-frequency component – consonants – that provides most of the intelligibility, even though consonants represent only 25% of the sound energy.
This explains why the chances of non-native pupils succeeding in school are largely determined by the level of acoustic comfort in their classroom. If the reverberation time in the room is more than 0.5 seconds, children seated beyond the first rows of seats will not be able to distinguish consonants and therefore will not be able to learn properly.
THE PHYSICAL ASPECT
The quality of sound in an indoor space is initially determined by the source:
These noises can either be transmitted through the air or through the building fabric itself – from the outside in (through the envelope), vertically (from floor to floor), or laterally (through internal partitions).
The way sound behaves within the space will depend on levels of reverberation and absorption within the building – somewhere between the booming reverberation of a Gothic cathedral and the insulated absorption of a padded cell is the comfortable space.
The acceptance of any given sound depends on many factors that vary according to the type of building, the type of activity being performed, and the social and cultural habits of the occupants.
The effect of noise on our overall sense of wellbeing is based on our individual psychological response to a sound. Parameters include the predictability and familiarity of sound, the controllability of sound, personal attitude and sensitivities, information on the contents of sound, and the necessity of sound.
It seems that we’re always more tolerant of noise from well-liked neighbors than from neighbors we’re not so fond of, for example!