Driving of multi-channel speakers

1. A drive system for generating drive signals for audio drivers, the drive system comprising:

a splitter ( 107 ) for generating a first signal and a second signal from an input signal, wherein

the first signal comprises signal components of a first frequency interval of the input signal and the second signal comprises signal components of a second frequency interval of the input signal,

the first and second frequency intervals having a cross-over frequency and the first frequency interval corresponding to lower frequencies than the second frequency interval;

a first drive circuit ( 111 , 115 ) coupled to the splitter ( 107 ) and arranged to generate a first drive signal for a first audio driver ( 105 ) from the first signal;

a second drive circuit ( 117 , 119 ) coupled to the splitter ( 107 ) and arranged to generate a second drive signal for a second audio driver ( 101 ) from the second signal;

means ( 125 ) for determining a driver excursion indication for the second audio driver ( 101 );

means ( 117 ) for providing a bass frequency extension for the second audio driver ( 101 ) by applying low frequency boost to the second signal,

wherein the low frequency boost provides increased gain above an original maximum gain value for frequencies of the second signal within a first frequency band of the second frequency interval relative to frequencies of the second frequency band above the first frequency band; and

adjustment means ( 127 ) for performing a combined adjustment of the cross-over frequency and a characteristic of the low frequency boost in response to the driver excursion indication.

2. The drive system of claim 1 wherein the increased gain is at least 3 dB higher than an average gain for frequencies of the second signal within the second frequency interval and above the first frequency band.

3. The drive system of claim 1 wherein the adjustment means ( 127 ) is arranged to adjust the cross-over frequency within a frequency range and to provide increased gain for at least some frequencies above a current value of the cross-over frequency but within the frequency range.

4. The drive system of claim 1 wherein the adjustment means ( 127 ) is arranged to modify a frequency characteristic of the low frequency boost in response to the driver excursion indication.

5. The drive system of claim 4 wherein the adjustment means ( 127 ) is arranged to bias the cross-over frequency and a lower frequency for the low frequency boost towards lower frequencies for a reduced driver excursion.

6. The drive system of claim 1 wherein the adjustment means ( 127 ) is arranged to vary a frequency response for the second drive signal such that a gain in at least a first frequency band is higher than an average gain of the frequency response above the first frequency band and within the second frequency interval for at least one value of the cross-over frequency, and below the average gain for at least a second value of the cross-over frequency.

7. The drive system of claim 1 wherein the boost means ( 117 ) is arranged to provide the low frequency boost to compensate a sensitivity reduction for the second audio driver.

8. The drive system of claim 1 further comprising means ( 125 ) for determining the driver excursion indication in response to a volume setting for the drive system.

9. The drive system of claim 1 further comprising: means for measuring a signal level for the second signal at a point of the signal path for the second signal provided by the second drive circuit; and means for determining the driver excursion indication in response to the signal level.

10. The drive system of claim 1 further comprising: means for receiving a measurement signal from a driver excursion measuring device proximal to the second audio driver ( 101 ); and means for determining the driver excursion indication in response to the measurement signal.

11. The drive system of claim 1 further comprising: a further splitter ( 109 ) for generating a third signal and a fourth signal from a further input signal, wherein the third signal comprises signal components of the first frequency interval of the further input signal and the fourth signal comprises signal components of the second frequency interval of the further input signal; a third drive circuit ( 121 , 123 ) coupled to the further splitter ( 109 ) and arranged to generate a third drive signal for a third audio driver ( 103 ) from the fourth signal; and wherein the first drive circuit ( 111 , 115 ) is arranged to generate the first drive signal from a combination of the first signal and the third signal.

12. A surround sound speaker system comprising:

a driver system as claimed in claim 1 ;

the first audio driver ( 105 ) being a subwoofer; and

a plurality of speakers including the second audio driver ( 101 ).

13. A method of operation for a drive system, the method comprising:

generating a first signal and a second signal from an input signal, wherein

the first signal comprises signal components of a first frequency interval of the input signal and the second signal comprises signal components of a second frequency interval of the input signal,

the first and second frequency intervals having a cross-over frequency and the first frequency interval corresponding to lower frequencies than the second frequency interval;

generating a first drive signal for a first audio driver ( 105 ) from the first signal;

generating a second drive signal for a second audio driver ( 101 ) from the second signal;

determining a driver excursion indication for the second audio driver ( 101 );

providing a bass frequency extension for the second audio driver ( 101 ) by applying low frequency boost to the second signal

wherein the low frequency boost provides increased gain above an original maximum gain value for frequencies of the second signal within a first frequency band of the second frequency interval relative to frequencies of the second frequency band above the first frequency band; and

performing a combined adjustment of the cross-over frequency and a characteristic of the low frequency boost in response to the driver excursion indication.

14. The drive system of claim 1 , wherein the adjustment means ( 127 ) further performs a modification of a gain characteristic of the low frequency bass boost in response to the driver excursion indication.