英语翻译Examples of periodic sources and broadband sources are,r

英语翻译
Examples of periodic sources and broadband sources are,respectively,rotating machinery such as turbines,fans,etc.,and aerodynamic noise associated with jets or flow past a solid surface.In fact,the two types often occur together with a series of pure tone peaks above a broadband spectrum.An example is where a large machine with several random sources has a strong periodic mode of operation.For more specific detail on the frequency spectra and appropriate analysis required for different kinds of sources see section 3.3.3.
图2.4及其说明
2.1.3 Wavelength
A wavelength is defined as the distance between analogous points on successive waves of a pure tone signal; it is most easily assessed by measuring the distance between adjacent maxima or minima on the pressure spatial distribution (see figure 2.3a,above).Wavelength is denoted by the symbol X and is numerically equal to the ratio of the speed of sound in a medium to the frequency:
公式
where c is the speed of sound,m/s
f is the frequency,Hz.
2.1.4 Speed
For very high amplitude waves,which occur either when the ambient speed of sound is exceeded (see section 7.1.1) or with strong source radiation as in certain severe impact situations,shock formation occurs,and the waveform is distorted into nonlinear behavior.Essentially,this means that sounds of different frequencies propagate at different speeds through the transmitting medium.However,for most commonplace situations in industry this will not be so,and the speed of sound can be regarded as being the same for all frequencies.
For propagation in a gas,the general expression for the velocity of sound waves,c,is given by
c = _fTrT m/s
where
λ is the ratio of specific heat of gas at constant pressure to that at constant volume
r is the constant dependent on gas involved and equal to the ratio of the gas constant and molecular weight of the gas,J/kg.K
T is the absolute temperature,K.
The velocity is directly proportional to the square root of the absolute temperature,the other terms being constant.Pressure changes and nonuniformity of gas composition are of much less significance in affecting the velocity.For air at atmospheric pressure,the relationship simplifies to
公式：c = 20.05x/T m/s
More complex relationships exist for liquids and solids 1:
Liquids:公式
Solids:公式
(large cross section)
Solids公式
(small cross section)
where
Bbt is the isothermal bulk modulus,N/m 2
0o is the density,kg/m 3