Categories
Science

How are architectural acoustics developed

In any auditorium the whole audience must be able to hear clearly the performer or musician on the stage, without undue echoes. For some types of music, notably choral and organ music, a degree of echo or reverberation actually makes the sound more pleasant, but to hear speech clearly this reverberation must be kept to a minimum. The reverberation time (RT) of a concert hall – the time taken for an initial burst of sound to fall to half of its original level – depends on its shape and the materials of which it is made. Auditoria designed for large scale orchestral works are generally oblong-shaped, so there are plenty of reflections from the sides of the hall into the audience. This reverberant field combines with the directly radiated sound from the musicians and lends a pleasing air of ambiance to the music. For speech, the reverberation time of a hall should be less than one second; for chamber music around one to two seconds and for full orchestras over two seconds.

Rock concerts provide a great problem for many concert halls. The sound energy is enormous and usually has artificial reverberation components added electronically. The reverberation field in some parts of conventional auditoria can easily swamp the detail in the music. The best type of hall for this sort of music is a fan-shaped arrangement, like the old movie theaters. The rock band can then concentrate their output into direct beams covering parts of the hall without much reflection from the side walls which create reverberation.

How-are-architectural-acoustics-developed-photo

Even in conventional halls the RT can be controlled by movable absorbers and reflectors. Some venues can even alter their acoustics by recycling the original sound through arrays of loudspeakers placed strategically throughout the auditorium.

In the flying laboratories of the Space Shuttle sound waves are being used to suspend research materials without visible means of support. Acoustic levitation uses the radiation pressure of intense acoustic waves to balance out gravity so that the experimental object floats in one position.

Acoustic detection is used to guide acoustical torpedoes onto their targets. Sounds from the engine, propeller, and other attributes of the target are picked up, or else the detector emits sonar pulses. Once in the target area, the detector controls the torpedo servomechanisms.

Nondestructive testing, which employs high-frequency sound waves along with powerful microcomputers, helps engineers to monitor invisible pipe-line welds, the condition of pressure vessels inside nuclear reactors, and hidden faults deep inside metal components.