Piezoelectric Speaker

1 . A piezoelectric speaker, comprising:

a membrane;

an actuating layer comprising at least one a piezoelectric element mounted to said membrane, which at least one piezoelectric element is adapted to, when actuated, cause said membrane to vibrate in order to generate sound, and

variation means for varying the fraction of the actuating layer that is actuated depending on the sound frequency to be generated.

2 . A piezoelectric speaker according to claim 1 , wherein a reduced fraction of said actuating layer is actuated for higher sound frequencies.

3 . A piezoelectric speaker according to claim 1 , wherein said actuating layer comprises a single piezoelectric element.

4 . A piezoelectric speaker according to claim 3 , wherein said variation means is adapted to selectively actuate a number of different portions of said piezoelectric element by means of an electric input signal representative of the sound to be generated, wherein the number of actuated portions depends on the frequency of said input signal.

5 . A piezoelectric speaker according to claim 4 , wherein said variation means comprises a segmented electrode provided on one side of the piezoelectric element, said segmented electrode having individually activable segments corresponding to the portions of said piezoelectric element, whereby said portions can be individually actuated by supplying said input signal to a number of said electrode segments.

6 . A piezoelectric speaker according to claim 5 , wherein said segmented electrode is provided on one side of the piezoelectric element, while an unstructured electrode is provided on the opposite side of the piezoelectric element.

7 . A piezoelectric speaker according to claim 5 , wherein said variation means comprises a plurality of parallel frequency filters, each filter being adapted to receive said input signal and being connected to at least one of said electrode segments.

8 . A piezoelectric speaker according to claim 5 , wherein said variation means comprises a switch being connected to a frequency detector and having several output ports each connected to at least one of said electrode segments, wherein said switch is adapted to transfer said input signal to a number of said output ports depending on the frequency of said input signal as detected by said frequency detector.

9 . A piezoelectric speaker according to claim 1 , said speaker being a flat panel speaker.

10 . A method for driving a piezoelectric speaker having a membrane and an actuating layer comprising at least one piezoelectric element mounted to said membrane, which at least one piezoelectric element is adapted to, when actuated, cause said membrane to vibrate in order to generate sound, the method including the step of:

varying the fraction of the piezoelectric element that is actuated depending on the sound frequency to be generated.

11 . A piezoelectric speaker according to claim 2 , wherein said actuating layer comprises a single piezoelectric element.