Category: (((—Acoustics Engineering—))))

Sound can be focused like light, but in the case of sound the “optics”must be much larger because you are dealing with longer wavelengths.The effect is heard in some domed buildings such as the Capitol inWashington, and St Paul’s Cathedral in London providing noisebackground conditions permit. Large parabolic reflectors can be used very effectively to…

This is one of the most commonly asked questions of noise consultants. Firstly you should consider whether better insulation is reallyessential. The method of noise insulation will depend on the exactsituation, so the advice of a competent person should be sought at anearly stage. Sound insulation is most often asked for in order to keepout…

The measurement method depends on the particular situation. There arestandards for the measurement of the insulation of materials in thelaboratory, and for a number of different field circumstances. Usuallythe procedures involve generating a loud sound of a specified type andmonitoring the transmitted noise. It is very useful to have a single number to characterize theinsulation…

There is often confusion between sound insulation and sound absorption. Sound insulation is required in order to eliminate the sound path froma source to a receiver such as between apartments in a building, or toreduce unwanted external noise inside a concert hall. Heavy materialslike concrete tend to be the best materials for sound insulation –doubling…

The absorption coefficient of a material is ideally the fraction of therandomly incident sound power which is absorbed, or otherwise notreflected. It can be determined in two main ways, and there are oftenvariations in the results depending upon the method of measurementchosen. It is standard practice to measure the coefficient at thepreferred octave frequencies over…

Work on room acoustics was pioneered by Wallace Clement Sabine 1868-1919 (see his Collected Papers on Acoustics, 1922).The reverberation time, T, is defined as the time taken for soundenergy to decay in a room by a factor of one million (ie by 60 dB). Itis dependent on the room volume and its total absorption. In…

Vibration problems are solved by considering the system as a number ofsprings and masses with damping. It is sometimes possible to reduce theproblem to a single mass supported by a spring and a damper. If the vibration is produced by a motor inside a machine, it is usuallydesirable to ensure that the frequency of motor…

Vibration is monitored with an accelerometer. This is a device that issecurely attached by some means to the surface under investigation. Theaccelerometer produces a tiny electrical charge output, proportionalto the surface acceleration, which is then amplified by a chargeamplifier and recorded or observed with a meter. The frequencies ofinterest are generally lower than sound, and…

When something oscillates about a static position it can be said tovibrate. The vibration of a speaker diaphragm produces sound, butusually vibration is undesirable. Common examples of unwanted vibrationare the movement of a building near a railway line when a train passes,or the vibration of the floor caused by a washing machine or spindryer. Floor…

Loudness is the human impression of the strength of a sound. Theloudness of a noise does not necessarily correlate with its soundlevel. Loudness level of any sound, in phons, is the decibel level ofan equally loud 1kHz tone, heard binaurally by an otologically normallistener. Historically, it was with a little reluctance that a simplefrequency weighting…