Building Acoustics

38 Building acoustics

Table 2.1 Impedance and mobility of the simple elements mass, spring and viscous damper. F – force, v –
velocity, a – acceleration, k – spring stiffness, c – damping coefficient.

Element Symbol Calculation Impedance Mobility

Mass

F

m

d

j

d

v

F ma m mv

t

=⋅= =ω

jω m

1 /jω m

Spring

F k

dj

k

F kx k vt v

ω

=⋅=∫ =−

j

k

ω

−

j

k

ω

Damper

(viscous)

F c

F=cv⋅

c

1/c

10 20 50 100 200 500 1000 2000 5000

Frequency (Hz)

0

20

40

60

80

100

Modulus of impedance (dB

re 1Ns/m)

Mass Stiffness

0.1 kg

1 kg

10 kg

105 N/m

106 N/m

107 N/m

Figure 2.5 Modulus of impedance for the components mass and spring, given as a function of frequency. Mass
weight and spring stiffness are indicated on the curves.