Control of a loudspeaker output
View Patent ↗A method of modeling the frequency-dependent input-voltage-to-excursion transfer function of a loudspeaker, comprises, for a plurality of measurement frequencies, measuring a voltage and current and deriving an impedance at the measurement frequency. A frequency-dependent impedance function is derived. By additionally using the blocked electrical impedance and a force factor for the loudspeaker, a frequency-dependent input-voltage-to-excursion transfer function can be calculated. The invention provides a modeling approach which is not based on a parametric model, but computes the transfer functions for a set of frequencies separately. 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:
modelling a frequency-dependent input-voltage-to-excursion transfer function of a loudspeaker, by:
for a plurality of measurement frequencies, measuring a voltage and a current and deriving an impedance at the measurement frequency, and from the plurality of impedance values deriving a frequency-dependent impedance function;
one of estimating, measuring and obtaining the blocked electrical impedance and a force factor for the loudspeaker;
calculating the frequency-dependent input-voltage-to-excursion transfer function from the impedance function, blocked electrical impedance and force factor; and
using the frequency-dependent input-voltage-to-excursion transfer function to control audio processing for the loudspeaker.
2. A method as claimed in claim 1 , further comprising deriving a mechanical impedance from the blocked electrical impedance, the force factor and the frequency-dependent impedance function, and wherein the frequency-dependent input-voltage-to-excursion transfer function is calculated from the impedance function and the mechanical impedance function.
3. A method as claimed in claim 2 , wherein the mechanical impedance is derived from an equation:
Z
m
(
s
)
=
ϕ
2
Z
(
s
)
-
Z
e
(
s
)
wherein φ is the force factor, Z(s) is the impedance function and Ze(s) is the blocked electrical impedance.
4. A method as claimed in claim 3 , wherein the frequency-dependent input-voltage-to-excursion transfer function is calculated by:
h
vx
(
j
ω
)
=
ϕ
j
ω
Z
m
(
j
ω
)
Z
(
j
ω
)
wherein Zm(jω) is a frequency-dependent mechanical impedance function and Z(jω) is the frequency-dependent impedance function.
5. A method as claimed in claim 1 , further comprising deriving an frequency-dependent acoustic output transfer function from the frequency-dependent input-voltage-to-excursion transfer function.
6. A method as claimed in claim 1 , wherein the force factor is a constant value.
7. A method as in claim 1 , wherein the audio processing implements at least one of loudspeaker protection and acoustic signal processing.
8. A loudspeaker control system, comprising:
a loudspeaker;
a sensor for measuring a voltage and a current for a plurality of measurement frequencies; and
a processor,
wherein the processor is configure to:
derive an impedance at each measurement frequency, and from the plurality of impedance values derive a frequency-dependent impedance function;
calculate a frequency-dependent input-voltage-to-excursion transfer function from the impedance function and from a blocked electrical impedance and a force factor for the loudspeaker; and
use the frequency-dependent input-voltage-to-excursion transfer function to control audio processing for the loudspeaker.
9. A system as claimed in claim 8 , wherein the processor is further configured to:
derive a mechanical impedance from the blocked electrical impedance, the force factor and the frequency-dependent impedance function, wherein the processor is configured to calculate the frequency-dependent input-voltage-to-excursion transfer function from the impedance function and the mechanical impedance function.
10. A system as claimed in claim 9 , wherein the processor is configured to derive the mechanical impedance from an equation:
Z
m
(
s
)
=
ϕ
2
Z
(
s
)
-
Z
e
(
s
)
wherein Φ is the force factor, Z(s) is the impedance function and Z e (s) is the blocked electrical impedance.
11. A system as claimed in claim 10 , wherein the processor is further adapted to calculate the frequency-dependent input-voltage-to-excursion transfer function by:
h
vx
(
j
ω
)
=
ϕ
j
ω
Z
m
(
j
ω
)
Z
(
j
ω
)
wherein Z m (jω) is a frequency-dependent mechanical impedance function and Z(jω) is the frequency-dependent impedance function.
12. A system as claimed in claim 8 , wherein the processor is further configured to derive the frequency-dependent acoustic output transfer function from the frequency-dependent input-voltage-to-excursion transfer function.
13. A system as in claim 8 , wherein the audio processing implements at least one of loudspeaker protection and acoustic signal processing.
14. A non-transitory computer-readable storage medium having a computer program comprising computer program code configured to perform an operation, the operation includes:
modelling a frequency-dependent input-voltage-to-excursion transfer function of a loudspeaker, by:
for a plurality of measurement frequencies, measuring a voltage and a current and deriving an impedance at the measurement frequency, and from the plurality of impedance values deriving a frequency-dependent impedance function;
one of estimating, measuring and obtaining the blocked electrical impedance and a force factor for the loudspeaker;
calculating the frequency-dependent input-voltage-to-excursion transfer function from the impedance function, blocked electrical impedance and force factor; and
using the frequency-dependent input-voltage-to-excursion transfer function to control audio processing for the loudspeaker.