WO2020143472A1

WO2020143472A1 - Method for correcting acoustic properties of a loudspeaker, an audio device and an electronics device

Info

Publication number: WO2020143472A1
Application number: PCT/CN2019/128807
Authority: WO
Inventors: Kim Therkelsen; Chistoforos KANAVAKIS
Original assignee: Goertek Inc.
Priority date: 2019-01-11
Filing date: 2019-12-26
Publication date: 2020-07-16

Abstract

A method for correcting acoustic properties of a loudspeaker, an audio device and an electronics device are disclosed. The method comprises: obtaining a volume velocity of a diaphragm of the loudspeaker; obtaining a sound pressure of the loudspeaker; determining an acoustic impedance and/or an acoustic resistance of the loudspeaker, wherein the acoustic impedance is given by the ratio of the sound pressure to the volume velocity; and correcting the acoustic properties of a loudspeaker by using the acoustic impedance and/or the acoustic resistance.

Description

METHOD FOR CORRECTING ACOUSTIC PROPERTIES OF A LOUDSPEAKER, AN AUDIO DEVICE AND AN ELECTRONICS DEVICE

FIELD OF THE INVENTION

The present disclosure relates to the technical field of a loudspeaker, and more specifically, to a method for correcting acoustic properties of a loudspeaker, an audio device and an electronics device.

BACKGROUND OF THE INVENTION

Radiation impedance estimation is used to correct the filter for a loudspeaker, in order to reduce acoustic distortion and improve the listening experience for a listener. Here, the loudspeaker include a driver to produce sound.

The article of “Adaptive Bass Control -The ABC Room Adaptation System” byPedersen, Jan A. proposes a system for adapting a loudspeaker to its position and to the acoustic properties of the listening room, which is hereby incorporated herein by reference.

US patent No. 9,992,595 B1 describes an acoustic change detection solution which uses a number of pairs of microphones, which is hereby incorporated herein by reference.

The article of “Adaptive Control of Loudspeaker Frequency Response at Low Frequencies” by G.J. Adams proposes a method for monitoring and adjusting the acoustic power-output/frequency response of a direct-radiator type loudspeaker system at low frequencies, which is hereby incorporated herein by reference.

The article of “Mechanical Fatigue and Load-Induced Aging of Loudspeaker Suspension” byWolfgang Klippel proposes a solution of determining the aging process of the mechanical suspension in electro-acoustical transducers, which is hereby incorporated herein by reference.

SUMMARY OF THE INVENTION

This disclosure provides a new solution for correcting acoustic properties of a loudspeaker.

According to a first aspect of the present invention, there is provided a method for correcting acoustic properties of a loudspeaker, comprising: obtaining a volume velocity of a diaphragm of the loudspeaker; obtaining a sound pressure of the loudspeaker; determining an acoustic impedance and/or an acoustic resistance of the loudspeaker, wherein the acoustic impedance is given by the ratio of the sound pressure to the volume velocity; and correcting the acoustic properties of a loudspeaker by using the acoustic impedance and/or the acoustic resistance.

According to a second aspect of the present invention, there is provided an audio device, comprising: a loudspeaker; a memory, storing instructions; and a processor, wherein when the instructions are executed by the processor, they cause the processor to perform the steps of method for correcting acoustic properties of a loudspeaker.

According to a third aspect of the present invention, there is provided an electronics device, which includes the audio device according to an embodiment of this disclosure.

According to various embodiment of this disclosure, a new solution for correcting acoustic properties of a loudspeaker is provided.

Further features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments according to the present invention with reference to the attached drawings.

BRIEF DISCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention.

Figure 1 shows a flow chart of a method for correcting acoustic properties of a loudspeaker according to an embodiment.

Figure 2 shows a schematic block diagram of an audio device according to an embodiment.

Figure 3 shows aschematic block diagram of an electronics device according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments of the present invention will now be described in detail with reference to the drawings. It should be noted that the relative arrangement of the components and steps, the numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention unless it is specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

Techniques, methods and apparatus as known by one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.

In all of the examples illustrated and discussed herein, any specific values should be interpreted to be illustrative only and non-limiting. Thus, other examples of the exemplary embodiments could have different values.

Notice that similar reference numerals and letters refer to similar items in the following figures, and thus once an item is defined in one figure, it is possible that it need not be further discussed for following figures.

As shown in Figure 1, at step S12, a volume velocity of a diaphragm of the loudspeaker is obtained.

For example, the volume velocity is obtained by at least one of the following approaches.

In a first approaches, the volume velocity is obtained by estimating the volume velocity by measuring the impulse response of the driver velocity.

We can take the assumption here that the loudspeaker diaphragm volume velocity almost remains constant irrespective its position in a listening environment, for example a listening room. Therefore, the volume velocity can be considered a linear time-invariant system and can be modelled by an impulse response.

For example, the impulse response of the driver velocity is measured by using a laser doppler vibrometer.

When measuring the impulse response of the diaphragm velocity, the driver of the loudspeaker shall be within its linear range.

In a second approaches, the volume velocity is obtained by estimating the volume velocity based on a model for the diaphragm.

The model for the diaphragm is not limited to linear static models. The model can be linear or non-linear. The model can be time-variant or time-invariant. The model can be statistical or deterministic. The model may be static or adaptive. The model can e.g. be based on differential equations describing the behavior of the driverof the loudspeaker.

In an example, the model for the diaphragm is a lumped parameter model using Thiele-Small parameters of the driver of the loudspeaker. For example, the lumped parameter model uses the Thiele-Small parameters of the driver of the loudspeaker in free-air along with parameters of an enclosure assembly of the loudspeaker or in a final enclosure assembly of the loudspeaker.

In a specific example, the velocity transfer function U _Dcan then be described by the following formula,

where Bl denotes a force factor for the loudspeaker, C _ms denotes a mechanical compliance of a system for the loudspeaker, e _g denotes a driving voltage for the loudspeaker, R _e denotes a DC resistance of a voice coil of the loudspeaker, omega ω _s denotes a resonance angular frequency for the loudspeaker, Q _TS denotes a total quality factor of the whole system for the loudspeaker, and ω denotes an angular frequency for the loudspeaker.

In a third approaches, the volume velocity is obtained by estimating the volume velocity from a measurement by a microphone using a smoothing and/or dereverberation technique, wherein the microphone is placed near to the loudspeaker.

We have some prior knowledgefor predicting the diaphragm velocity directly from microphone measurement. First, in an anechoic room, the magnitude of the diaphragm acceleration and the microphone pressure will be very similar. Second, in a listening room, peaks and dips are introduced because of room modes. Each peak and dip introduce corresponding phase changes. It is the phase change between the pressure and velocity that is the primary parameter when determining the acoustic resistance. Third, to some degree, the diaphragm acceleration can be considered “minimum phase” .

So, the accelerometer signal can be predicted from the recorded microphone signal, by using various smoothing and dereverberation (blind deconvolution) techniques.

Therefore, the volume velocity can be estimated from a measurement by a microphone by using the following approaches:

estimating the volume velocity from a model; and/or

estimating the volume velocity by using a smoothing and/or dereverberation technique on the microphone measurement; and/or

estimating the volume velocity phase from the estimated volume velocity magnitude by assuming the response is minimum phase.

Heating up the voice coil will causethe driver characteristics to change significantly. So, the impulse response shall be measured or estimated when the temperature of the voice coil of the loudspeaker is in a given temperature range.

For example, the temperature of the voice coil is determined as a function of time, and/or is sensed by a temperature sensor mounted in the loudspeaker, and/or is obtained through a voltage and/or current sensing. In an example, the temperature of the voice coil is determined as a function of time in combination with the PCM signal before the DAC, the DAC voltage gain, the power amplifier voltage gain and the heat dissipation of the voice coil for the loudspeaker.

Another but much simpler way of dealing with the heat problem is to only monitor the device digital “volume setting” and the output PCM signal power. Based on simple statistics some reasonable thresholds can be determined without knowing the actual temperature of the voice coil. For instance, if the “volume setting” has not exceeded a certain threshold for two minutes, it is safe to predict the diaphragm velocity. Or similarly, if the “volume setting” times the output PCM signal power has not exceeded a certain threshold for a period of time. As such, whether the temperature of the voice coil of the loudspeaker is in a given temperature range can be determined by monitoring the device digital volume setting for the loudspeaker and/or the output PCM signal power for the loudspeaker. If the volume setting has not exceeded a first certain threshold for a first preset time, it is determined that the temperature of the voice coil of the loudspeaker is in a given temperature range. If the volume setting has exceeded a first certain threshold for a first preset time but the output PCM signal power has not exceeded a second certain threshold for a second preset time, it is determined that the temperature of the voice coil of the loudspeaker is in a given temperature range.

At step S14, a sound pressure of the loudspeaker is obtained.

For example, the sound pressure can be obtained through a microphone placed close to the diaphragm of the loudspeaker. Specifically, the microphone may be placed in front of the diaphragm. The sound pressure is recorded by the microphone.

Here, the microphone for determining the sound pressure can be a single microphone that is in a fixed position with respect to the loudspeaker.

At step S16, an acoustic impedance and/or an acoustic resistance of the loudspeaker is determined. The acoustic impedanceis given by the ratio of the sound pressure to the volume velocity, which means the acoustic impedance can be determined based on the sound pressure and the volume velocity.

In a simple example, the acoustic impedance is Z, the sound pressure is p and the volume velocity is U. So, the acoustic impedance (Z) is calculated as below:

The acoustic resistance is the real part of the acoustic impedance Z. The acoustic impedance can be frequency dependent.

At step S18, the acoustic properties of a loudspeaker by using the acoustic impedance and/or the acoustic resistance is corrected.

For example, a filter for correcting the acoustic properties is adjusted based on comparison of the current acoustic impedance and/or acoustic resistance with a reference acoustic impedance and/or acoustic resistance for the position where the loudspeaker was originally tuned.

In an example, the magnitude of the equalization filter EQ _dB (f) is calculated as:

EQ _dB (f) =0.5· (20·log10 (Rs _Ref (f) ) -20·log10 (Rs _Cur (f) ) )

Where f is frequency, Rs _Ref (f) is the acoustic resistance at the reference position and the Rs _Cur (f) is the acoustic resistance at the current position. For example, the acoustic resistance is estimated directly from the pressure measure by a microphone and the magnitude of the acceleration is given directly.

In another example, he magnitude of the equalization filter EQ _dB (f) is calculated as:

EQ _dB (f) =0.5· (20·log10 (Rs _Ref, Norm (f) ) -20·log10 (Rs _Cur, Norm (f) ) )

Where f is frequency, Rs _Ref, Norm (f) is the normalized acoustic resistance at the reference position and the Rs _Cur, Norm (f) is the normalized acoustic resistance at the current position. For example, the acoustic resistance is calculated from the impulse response of the driver of the loudspeaker and/or modelled from the system parameters, and the magnitude of the acceleration is not known.

In another example, a minimum phase equalization filter is used for correcting, for example, an IIR (infinite impulse response) filter.

The acoustic properties of a loudspeaker will be corrected so that the low frequency response of the loudspeaker is adapted to its current position in any listening environment. A filter for correcting the acoustic properties can be inserted into the signal path before the power amplifier of the loudspeaker.

The correcting the acoustic properties is performed (1) when the loudspeaker is moved; and/or (2) in a predefined time interval; and/or (3) by being manually triggered by a user.

In this regard, a sensor, such as an accelerometer or a mechanical contact, can be mounted in the loudspeaker and/or near the loudspeaker to determine that the loudspeaker is moved.

Alternatively, a timer can be set in the loudspeaker or be coupled to the loudspeaker to determine the predefined time interval.

Alternatively, correcting the acoustic properties is performed when the filter for correcting the acoustic properties creates an audible difference to a user and/or the filter for correcting the acoustic properties is stable.

Correcting the acoustic properties is performed in a smooth manner. For example, the correcting the acoustic properties is performed in a smooth manner by creating at least one intermediate update for the filter for correcting the acoustic properties.

In this disclosure, a system for adapting the low frequency response of a loudspeaker to the acoustic properties of its position when placed in any listening environment is proposed.

We use the sound pressure in combination with diaphragm volume velocity to determine the acoustic impedance of the loudspeaker, which can simplify the arrangement of the audio system which can correct the acoustic properties to be adapted to different listening environments.

The sound pressure can be recorded with a closely placed microphone, which may be placed in front of the loudspeaker. The position of the microphone can be fixed and a single microphone could be sufficient although some designer would like to use multiple microphones with similar functions to enhance the performance, which is also feasible.

A digital correction filter can be constructed from the real part of the acoustic impedance. The digital correction filter can be inserted into the signal path before the power amplifier. As such, the overall performance of the audio device can be improved.

Figure 2 shows a schematic block diagram of an audio device according to an embodiment. As shown in Figure 2, the audio device 20 receives audio input and produces sound. The audio device 20 comprises a loudspeaker 23, a memory 22 storing instructions and a processor 21. When the instructions are executed by the processor, they cause the processor 21 to perform the steps of the method as above so as to correct acoustic properties of the loudspeaker 23.

The processor 21 may be a DSP (Digital Signal Processor) . In such a situation, the memory 22 may be integrated into the DSP.

As shown in Figure 2, the audio device 20 further comprises: an amplifier 24 for the loudspeaker 23. The processor 21 is placed in front of the amplifier 24 in the signal link from the audio input to the loudspeaker 23.

The audio device 20 further comprises: adigital-to-analog converter 25, which is placed between the amplifier 24 and the processor 21.

The audio device 20 further comprises: amicrophone 26 for determining the sound pressure. The microphone 26 is connected to a microphone power 27 and transfers obtained information to the processor 21.

The microphone 26 is placed close to the diaphragm of the loudspeaker 23. For example, the microphone 26 is placed in front of the diaphragm. The sound pressure is recorded by the microphone 26.

The microphone 26 for determining the sound pressure is a single microphone that is in a fixed position with respect to the loudspeaker 23.

Unit 28 may comprise a sensor, such as an accelerometer or a mechanical contact, mounted in the loudspeaker and/or near the loudspeaker to determine that the loudspeaker is moved; and/or a timer set in the loudspeaker or coupled to the loudspeaker to determine the predefined time interval.

The audio device 20 may also comprise a correction filter 29. The correction filter 29 can be constructed from the real part of the acoustic impedance. Alternatively, the correction filter 29 may be incorporated into the processor 21.

As shown in Figure 3, the electronics device 30 includes the audio device 20 as described above. The electronics apparatus 30 may be a TV, a smart speaker, and so on.

Although some specific embodiments of the present invention have been demonstrated in detail with examples, it should be understood bya personskilled in the art that the above examples are only intended to be illustrative but not to limit the scope of the present invention.

Claims

A method for correcting acoustic properties of a loudspeaker, comprising:

obtaining a volume velocity of a diaphragm of the loudspeaker;

obtaining a sound pressure of the loudspeaker;

determining an acoustic impedance and/or an acoustic resistance of the loudspeaker, wherein the acoustic impedance is given by the ratio of the sound pressure to the volume velocity; and

correcting the acoustic properties of a loudspeaker by using the acoustic impedance and/or the acoustic resistance.
The method according to claim 1, wherein the volume velocity is obtained by at least one of the following approaches:

- estimating the volume velocity by measuring animpulse response of the driver velocity;

- estimating the volume velocity based on a model for the diaphragm;

- estimating the volume velocity from a measurement by a microphone using a smoothing and/or dereverberation technique, wherein the microphone is placed near to the loudspeaker.
The method according toclaim 2, wherein estimating the volume velocity from a measurement by a microphone further comprising:

estimating the volume velocity from a model; and/or

estimating the volume velocity by using a smoothing and/or dereverberation technique on the microphone measurement; and/or

estimating the volume velocity phase from the estimated volume velocity magnitude by assuming the response is minimum phase.
The method according to claim 2, wherein the impulse response is measured or estimated when the temperature of the voice coil of the loudspeaker is in a given temperature range.
The method according to claim 1, wherein the sound pressure is obtained through a microphone placed close to the diaphragm.
The method according to claim 5, wherein the microphone for determining the sound pressure is a single microphone that is in a fixed position with respect to the loudspeaker.
The method according to claim 1, wherein a filter for correcting the acoustic properties is adjusted based on comparison of the current acoustic impedance and/or acoustic resistance with a reference acoustic impedance and/or acoustic resistance for the position where the loudspeaker was originally tuned.
The method according to claim 1, wherein the correcting the acoustic properties is performed (1) when the loudspeaker is moved; and/or (2) in a predefined time interval; and/or (3) by being manually triggered by a user.
An audio device, comprising:

a loudspeaker;

a memory, storing instructions; and

a processor,

wherein when the instructions are executed by the processor, they cause the processor to perform the steps of any of claims 1-8.
An electronics device, which includes the audio device according to claims 9.