DocID025705 Rev 1

11/19

AN4427

Acoustic gasket and sealing guidelines

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Figure 8. MP34DT01 frequency response vs. complex geometry

Basically the goal of the above simulations is to understand the effect of the addition of

different volumes in terms of radius and length with respect to a fixed geometry. The first

simulation is a simple geometry, Figure 7 (a), while the next geometries [Figure 7 (b), (c),

(d), (e)] increase the complexity of the previous one, adding different radius and length

volumes. For example, the second geometry includes a volume with a doubled radius close

to the microphone sound inlet, the third one reaches a radius of 1 mm, the fourth geometry

interposes a doubled radius volume at the middle of the original tube and the last one

increases the entire volume except a 1 mm length section close to the microphone sound

inlet. The geometries of the Figure 7 (f) and (g) are a little bit different. The purpose of the

last two simulations is to check if the resonance frequency depends on the inclination of the

tube or not.

The simulations done, the observations given below are helpful to understand how the

resonance frequency of a simple geometry moves in the frequency domain due to the

addition of different volumes. The next consideration must be read as a comparison with

respect to the first geometry. Checking the results of the simulations in Figure 8, the

following observations can be asserted:

1.

The introduction of a bigger volume geometry, in the side close to the sound inlet,

forces the resonance peak to lower frequencies (Figure 7 (b), blue trace in Figure 8)

2.

The resonance peak moves to a lower frequency in proportion to the increase of the

diameter of the geometry close to the sound inlet (Figure 7 (c), violet trace in Figure 8)

3.

The resonance peak moves to higher frequencies when the bigger geometry moves

away from the sound inlet of the microphone. (Figure 7 (d) (e), green and red traces in

Figure 8)

4.

The resonance peak depends on the geometry, length and width, only. The peak

position is independent of geometry inclination. The geometry in Figure 7 (f) represents

the same structure of the Figure 7 (a) but rotated 90 degrees, the two respective

simulation results are almost the same (yellow and orange traces in Figure 8).

The last simulation, geometry represented in Figure 7 (g), has been performed to double

check the previous statement. The geometry is similar to that of Figure 7 (b) and the

simulation results are almost the same (blue and cyan traces in Figure 8)

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(a): L=4mm ; R=300u

(b): L=4mm ; R1=300u ; R2= 600u

(c): L=4mm ; R1=300u ; R2= 1mm

(d): L=4mm ; R1=300u ; R2= 600u; R3= 300u

(e): L=4mm ; R1=600u ; R2= 300u

(f): Tank L=4mm ; R=300u

(g): Tank L=4mm ; R=300u ; W= 600u