Piezo acoustic system Cup A
To design a useful housing for a car horn, an acoustic system that amplifies a few low frequencies to
a high amplitude will give a typical warm warning sound.
The red line in figure one shows the pink noise response * of a high quality piezo cup system that
results in a first peak around 400Hz. A square wave is analysed (figure 2) and tuned on the
amplification peaks of the piezo vibrating system.
dB SPL (A)
120.0
110.0
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
1800.00 Hz 3550.00 Hz
0.0
30 50 70 100 200 300 500 700 1k 2k 3k 5k 7k 10k 20k Wide
Frequency (Hz)
Figure 1: pink noise graph (red) and total SPL (blue)
The total sound pressure level is shown in the right table of figure one (blue line) and reaches
96dB(A) at 2m. The character of the sound is mainly formed by three sine waves at 374Hz (f ), 748Hz
(2f ) and 1122Hz (3f ).
dB SPL (A)
120.0
110.0
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
*definitions see sound considerations in addendum
1800.00 Hz 3550.00 Hz
0.0
30 50 70 100 200 300 500 700 1k 2k 3k 5k 7k 10k 20k Wide
Frequency (Hz)
Figure 2: Fourier analyse square wave 374 Hz
120.0
110.0
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
120.0
110.0
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
96 dB(A)
72
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