Audio Engineering

Loudspeakers 689

The conical diaphragm also has radial or “ bell ” modes of fl exure. These are similar
to the resonances in a bell and occur when the circumference is an integral number of
wavelengths [see Figure 23.10(b) ].

Obviously, both modes occur simultaneously, and at some frequencies reinforce each
other and at others tend to cancel. Their main effects on performance are the “ wiggles ”
on the response curve and transient and delay distortions. It is instructive to apply a
short “ tone burst ” ; it will be seen that at particular frequencies during the duration of the
input signal the diaphragm is stationary and on cessation of the pulse it will burst into
oscillation at some frequency unrelated to the driving current.

The art of diaphragm design is to minimize these deleterious effects. One method is to
introduce concentric corrugations; the effect is to increase the stiffness seen by the bell

A

B

A

B

C

(a)

Figure 23.10 : (a) Concentric and (b) bell modes.

A

AB

C

B

















Rim flexure





 



 







 



(b)