 |
Damping |
| The internal property of a material which reduces the vibration in the material after the forced vibration has been removed. Materials with low damping ring for a long time (a bell), and materials with a high damping have a short vibration time. |
 |
|
Decibel addition |
| The total of a series of discrete levels obtained by taking the sum of the anti-logs of one-tenth of the levels and taking 10 times the logarithm of the result. This sum is used for sound levels, sound pressure levels and sound power levels. |
|
|
Decibel (dB) |
| The label used for levels in acoustics. It is 10 times the logarithm of the ratio of the acoustical properties which are being described. The properties must be proportional to power. |
|
|
Directivity |
| The radiation of sound in a preferred direction |
|
|
Displacement level (dB re 10' m[in.]) |
| The level of a vibration displacement on a logaritmic scale. The displacement and reference quantities can be either rms or peak values. |
|
|
Displacement (vibration) (m[ft] or cm[in.]) |
| The distance that a surface moves during vibration. Displacement may be in terms of the rms (effective) motion of the surface or the peak-to-peak motion. |
|
|
Day-night sound level (Ldn, dB) |
| The equivalent A-weighted sound level calculated for a 24-hourfor the increased sensitivity of people to sound during nighttime hours (2200 hrs to 0700 hrs). |
|
|
Doppler effect (shift) |
| The apparent change in frequency of a sound caed by the motion of the sound source toward or away from the receiver. The faster the sound source (or the observer) is moving the greater the apparent change in frequency. |
|
|
Double wall resonance (fo, Hz) |
| The resonance created when two surfaces on either side of an air cavity, which acts as a spring connecting the two surfaces, are excited by a sound. This resonance can be computed from the surface weights of the two surfaces and the depth of the air space. It is also a function of the angle at which the sound impinges on the surface. |
|
|
