## The iannoyance factor

Loudness is not the only factor that affects our tolerance of sound waves.

Which do you find more annoying?

(c) Someone scraping their fingernails over a blackboard at 55 dB?

(d) Handel's Water Music at 58 dB?

The amount of annoyance created by a noise should not be measured simply in terms of decibels. Nobody can tell us that we are not annoyed by some sound simply because the decibel reading indicates that we should not be annoyed. This is very relevant, because laws governing the level of noise may well be based only on the decibel level of the sound and not our perception.

### 7.5 Other sensations 7.5.1 Pitch

The pitch of a sound is our perception of its frequency. It depends, to some extent, on the intensity and harmonic content of the sound. Pitch increases with increasing frequency. A 'pure' tone is a sine wave and has a definite pitch. The vast majority of sounds are combinations of different tones and do not give a single value of pitch. Complex tones produced by musical instruments give the sensation of a single pitch, related to the frequency of the fundamental.

Pythagoras did the earliest acoustical experiments. A woodcut, dated 1492, in the Theorica Musice in Naples, shows him establishing the relationship between mathematical frequency ratios and harmonious musical sounds.

A musical interval is the difference in pitch between pairs of tones. It is related to the ratio of the frequencies of the tones

and not to the frequencies themselves (for example, the interval between tones of 200 Hz and 400 Hz is the same as between tones of 2000 Hz and 4000 Hz). Harmonious tones have intervals with small integer ratios such as 2:1 or 3:2 and form the basis of all music. Pairs of tones with equal intervals sound similar when played together. For example, a pair of tones at 440 Hz and 660 Hz sounds similar to a pair at 330 Hz and 495 Hz (both intervals are 3:2).

Frequency ratios 2:1 and 3:2.

Frequency ratios 2:1 and 3:2.

The most important interval is the octave. If notes an octave apart are played simultaneously, the difference in their tones is barely noticeable. A musical scale is a set of tones which are used to make music. The octave is normally the interval of repetition. (In the diatonic major scale do-re-mi-fa-sol-la-ti-do', the interval between do and do' is one octave). The ear recognizes notes in a scale as being related to one another

### Ancient Irish pipes

A set of six prehistoric pipes was discovered in 2004, during archaeological work on a Bronze Age site in County Wicklow, on the east coast of Ireland. The site was being surveyed to comply with planning regulations, prior to the construction of a residential development. Six pipes made from yew wood were

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Ancient Pipes. Courtesy of Margaret Gowan & Co. www.mglarc.com.

found at the bottom of a wood-lined trough, and radiocarbon dating has established that a wooden peg used in the construction of the lining dates back to somewhere between 2120 BC and 2085 BC. The pipes are not perforated but there is evidence to suggest that they originally formed a set. The photograph shows the pipes, together with a marker graduated in centimetres.

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