Control of a loudspeaker output
View Patent ↗A method of controlling a loudspeaker output comprises deriving an admittance function over time from the voice coil voltage and current. In combination with a delta function, the force factor of the loudspeaker and the blocked electrical impedance, the input-voltage-to-excursion transfer function over time is obtained. This is used to control audio processing for the loudspeaker thereby to implement loudspeaker protection and/or acoustic signal processing; The invention provides a modelling and control approach which is not based on a parametric model. As a consequence, it does not require prior knowledge regarding the enclosure (e.g. closed or vented box) and can cope with complex designs of the enclosure.
1. A method of controlling a loudspeaker output, comprising:
measuring a voice coil voltage and a voice coil current over time,
deriving an admittance function over time;
combining the admittance function over time with a delta function, a force factor of a loudspeaker and a blocked electrical impedance; and
calculating an input-voltage-to-excursion transfer function over time from the admittance function, the blocked electrical impedance and the force factor; and
using the input-voltage-to-excursion transfer function over time to control audio processing for the loudspeaker thereby to implement at least one of loudspeaker protection and acoustic signal processing.
2. A method as claimed in claim 1 , wherein the discrete time input-voltage-to-excursion transfer function h vx [k] is calculated by:
h
vx
[
k
]
=
1
ϕ
(
δ
[
k
]
-
R
e
y
[
k
]
)
*
h
int
[
k
]
,
(
19
)
where φ is the force factor, δ[k] is a delta function, y[k] is the admittance function, Re is the blocked electrical resistance and h int [k] is an integrator function.
3. A method as claimed in claim 1 , wherein the admittance function is obtained using adaptive filtering with the voltage and current signals as inputs.
4. A method as claimed in claim 1 , further comprising deriving the acoustical output transfer function from the voltage-to-excursion transfer function.
5. A method as claimed in claim 1 , wherein the force factor is a constant value.
6. A loudspeaker control system, comprising:
a loudspeaker;
a sensor for measuring a voice coil voltage and a voice coil current; and
a processor,
wherein the processor is adapted to:
measure a voice coil voltage and a voice coil current over time and derive an admittance function over time;
combine the admittance function over time with a delta function, a force factor of the loudspeaker and a blocked electrical impedance; and
calculate an input-voltage-to-excursion transfer function over time from the admittance function, the blocked electrical impedance and the force factor; and
use the input-voltage-to-excursion transfer function over time to control audio processing for the loudspeaker thereby to implement at least one of loudspeaker protection and acoustic signal processing.
7. A system as claimed in claim 6 , wherein the processor is adapted to calculate the discrete time input-voltage-to-excursion transfer function h vx [k] based on:
h
vx
[
k
]
=
1
ϕ
(
δ
[
k
]
-
R
e
y
[
k
]
)
*
h
int
[
k
]
,
(
19
)
where φ is the force factor, δ[k] is the delta function, y[k] is the admittance function, R e is the blocked electrical resistance and h int [k] is an integrator function.
8. A system as claimed in claim 6 , wherein the processor is adapted to obtain the admittance function using adaptive filtering with the voltage and current signals as inputs.
9. A system as claimed in claim 6 , wherein the processor is adapted to derive the acoustical output transfer function from the voltage-to-excursion transfer function.
10. A computer-readable storage medium having non-transitory computer program code which performs the steps of claim 1 when said program is run on a computer.
11. A computer program as claimed in claim 10 embodied on a computer readable medium.