? If a tree fell in a wood and there was no-one there to hear it – would it make a sound?

SOUND What is Sound? “Is a form of vibrational energy which can pass through air, liquids and solids”

“Sound that is unwanted by the recipient.” What is Noise? “Sound that is unwanted by the recipient.”

In Decibels using a sound meter How do we measure it? In Decibels using a sound meter

ACOUSTICS

Reflections can result in unwanted echoes Reflections can result in unwanted echoes. An echo will be heard if the time difference between hearing the direct sound and the reflected sound is 50ms or greater then we will perceive this as an echo. Room geometry may also result in standing or resonant sound waves. Non-uniform sound levels throughout a room will be a problem.

The rate of decay of reverberation has an impact on sound quality The rate of decay of reverberation has an impact on sound quality. The reverberation time is defined as the time taken for a sound to decay by 60dB. Speech 0.5 to 1 s Music 1-2s The time will depend on sound frequency, room dimensions, room surfaces - materials and areas

We can apply one of two simple formulae to predict the reverberation time of a space Sabine’s formula, used when absorption is not high and decay is continuous

Sound absorption is defined as the reduction in sound energy reflected from a surface. The absorption coefficient is the ratio of the absorbed sound energy to the incident sound energy.

We can combine our surface absorption information with that for the contents of a space to decide if it is necessary to adjust the absorption qualities of the space. In addition to use of say soft finishes, such as curtains, specific absorbers can be installed.

Optimum room times can be calculated using Stephens and Bates formula: The calculated time can be compared with published recommendations.

EXERCISE Calculate the total absorption (that is the total amount of absorbent material necessary) at 500Hz in a 250 seat hall, of volume 2500m3, containing the following surface finishes:

EXERCISE Calculate the total absorption (that is the total amount of absorbent material necessary) at 500Hz in a 250 seat hall, of volume 2500m3, containing the following surface finishes: Area (m2) Coefficient m2 Plaster on brickwork 265m2 0.02 5.3 3mm glass window 43m2 0.1 Stage, boards on joist 70m2 25mm wood-wool slabs 60m2 0.4 Plate-glass screen 96m2 0.04 Ceiling plaster 310m2 Wood block floor 300m2 0.05 – 40% Audience – will reduce floor absorption by 40% 250 0.43/ person Total absorption