EP3476135A1 - Method for simulating total harmonic distortion of a loudspeaker - Google Patents
Method for simulating total harmonic distortion of a loudspeakerInfo
- Publication number
- EP3476135A1 EP3476135A1 EP17733433.1A EP17733433A EP3476135A1 EP 3476135 A1 EP3476135 A1 EP 3476135A1 EP 17733433 A EP17733433 A EP 17733433A EP 3476135 A1 EP3476135 A1 EP 3476135A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- linear
- displacement
- input voltage
- element model
- lumped element
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R29/00—Monitoring arrangements; Testing arrangements
- H04R29/001—Monitoring arrangements; Testing arrangements for loudspeakers
Definitions
- a loudspeaker is generally an electromechanical transducer that produces sound in response to an electronic input signal.
- a loudspeaker may include a front side and a back side that is opposite the front side. The front side of the loudspeaker may communicate with a first volume of air, and the backside may communicate with a second volume of air.
- the loudspeaker may be mounted to an infinite baffle such that soundwaves from the backside of the loudspeaker do not interfere with soundwaves from the front side of the loudspeaker.
- a loudspeaker may be housed within a closed box or a vented enclosure and may include a speaker cone and a voice coil centered therein. The vented enclosure may include a port.
- Harmonic distortion adds overtones that are whole number multiples of a sound wave's frequencies. Nonlinearities that give rise to amplitude distortion in audio systems are most often measured in terms of the harmonics (overtones) added to a pure sinewave fed to the system. Harmonic distortion may be expressed in terms of the relative strength of individual components, in decibels, or the root mean square of all harmonic components (total harmonic distortion), as a percentage. Total harmonic distortion may be determined in different ways.
- the total harmonic distortion may be determined using a lumped parameter model (LPM), for example.
- LPM lumped parameter model
- any enclosure configuration closed box, vented pass band with passive radiators, etc.
- a vented box (linear) simulation it may be assumed that the front side of the loudspeaker and the back side of the loudspeaker via the port radiate to the listener.
- Using a non-linear LPM generally only allows to simulate closed box configurations where the front side of the loudspeaker radiates to the listener.
- the front side of the loudspeaker radiates to the listener, while the port does not radiate to the listener. This means that, as in the closed box configuration, only the front side of the loudspeaker is radiating to the listener. Loudspeaker displacements are usually not the same for a closed box or for a vented configuration.
- a method for simulating the total harmonic distortion of a loudspeaker comprises, performing a linear simulation or measurement to determine a real speaker displacement, performing a linear or non-linear lumped element model prediction, wherein the resulting speaker displacement of the lumped element model is adapted to correspond to the real speaker displacement by tuning an input voltage of the lumped element model, and performing a non- linear lumped element model prediction using the tuned voltage as an input voltage, thereby simulating the total harmonic distortion.
- a software is configured to execute the method steps of, performing a linear simulation or measurement to determine a real speaker displacement, performing a linear or non-linear lumped element model prediction, wherein the resulting speaker displacement of the lumped element model is adapted to correspond to the real speaker displacement by tuning an input voltage of the lumped element model, and performing a non-linear lumped element model prediction.
- Figure 1 is a diagram illustrating a fundamental and its harmonics.
- Figure 2 is a schematic diagram of a loudspeaker.
- Figure 3 illustrates an equivalent circuit for the loudspeaker of Figure 2.
- Harmonic distortion is a measure of the amount of power contained in the harmonics of a fundamental signal and can be divided into two main categories, namely linear distortion and non-linear distortion.
- Linear distortion is the time and frequency dependent characteristic of the amplitude and phase response of the transfer function. This occurs with no changes in the frequency content of the input signal such that one frequency at the input results in only one frequency at the output.
- Non-linear distortion causes changes in the frequency content of the input signal such that energy is transferred from one frequency at the input to more than one frequency at the output.
- Total harmonic distortion may be expressed in terms of the relative strength of individual components, in decibel (see Figure 1), or as a percentage of the power sum of all the harmonics to the power sum of all the harmonics plus the fundamental:
- HN is the harmonic response of the Nth harmonic and F is the fundamental response.
- anechoic chamber For valid results at low frequencies, a very large anechoic chamber is needed, with large absorbent wedges on all sides. However, most anechoic chambers are not designed for accurate measurement down to 20Hz. Further possibilities are to perform measurements outdoor, to perform half-space measurements or to perform room measurements.
- FIG. 2 illustrates a cross-sectional view of a loudspeaker.
- the loudspeaker includes a magnet 210, a back plate 285, a top plate 290, a pole piece 225, and a voice coil 230.
- a magnetic gap may be defined between the top plate 290 and the pole piece 225.
- the voice coil 230 may be arranged in this magnetic gap.
- the top plate 290, back plate 285, and pole piece 225 may direct the magnetic field of the permanent magnet 210, thus generating a radial magnetic field in the magnetic gap.
- the voice coil 230 may include a wire such as an insulated copper wire wound on a coil former with the two ends of the wire forming the electrical leads of the voice coil 230.
- the voice coil 230 may be centered within the magnetic gap.
- the two ends of the voice coil wire may be configured to receive a signal from an amplifier (not illustrated). This signal may create an electrical current within the voice coil 230.
- the magnetic field in the magnetic gap may interact with the current carrying voice coil 230, thereby generating a force.
- the resulting force my cause the voice coil 230 to move back and forth and consequently displace the cone (or membrane) 250 from its rest position.
- the motion of the cone 250 moves the air in front of the loudspeaker, creating sound waves, thus acoustically reproducing the electrical signal.
- the cone 250 extends radially outward from the voice coil 230, thereby creating a conical or dome-like shape.
- the cone 250 may be produced from a variety of materials, including but not limited to plastic, metal, paper, composite material, and any combination thereof.
- An opening may be defined at the center of the cone 250 and a dust cap 245 may create a dome-like cover at the opening.
- the outer edge of the cone 250 may be attached to the frame 255 by a surround 260.
- the center of the cone 250 near the voice coil 230 may be held in place by a spider 275.
- the spider 275 and surround 260 together generally allow only for axial movement of the cone 250.
- the frame 255 may be a conical casing that holds the cone 250 in a fixed position.
- the frame 255 may surround the cone 250 and may include a more rigid material to help maintain the shape and placement of the cone 250 during operation.
- the voice coil 230 may move laterally along the pole piece 225. This movement of the voice coil 230 may in turn cause movement of the cone 250.
- This cone excursion or displacement in general, is the distance that the cone 250 moves from a rest position. The distance from the rest position varies as the magnitude of the electric signal supplied to the voice coil 230 changes.
- the voice coil 230 upon receiving an electronic signal with a large voltage, may cause the voice coil 230 to move out of or further into the magnetic gap.
- the cone 250 may be displaced from its rest position.
- a large voltage may result in a large cone excursion which in turn causes the non-linearities inherent in the loudspeaker to become dominant.
- the loudspeaker can be split into three different domains, namely an electrical domain, a mechanical domain, and an acoustical domain.
- the electrical domain is characterized by the voice coil with a given DC resistance R E and self-inductance L e .
- the electrical signal is converted to a mechanical motion.
- the strength of this coupling from the electrical to the mechanical domain is related to the force factor Bl, which is the product of the magnetic field strength B of the static magnet in the voice coil gap, and the length 1 of the voice coil in the static magnetic field.
- the mechanical domain is characterized by the mass MMD of the diaphragm, the compliance CMS of the suspension and a mechanical damping RMS.
- the mass, the compliance and the damper will introduce a resonant frequency fs with a given quality factor QMS (mechanical Q-factor).
- QMS quality factor
- the electrical domain is also characterized by a Q-factor QES which is dependent on the force factor Bl, the DC resistance R E , the mass MMD, and the compliance CMS. Combining the mechanical and electrical Q-factors results in a total Q-factor known as QTS.
- the mechanical motion is converted to acoustical sound through the cone and the strength of this coupling is related to the area of the cone SD.
- the voice coil can be approximated as a voice coil resistance R2 in series with a voice coil inductance LI .
- the voice coil and magnet convert current to force.
- voltage is related to the velocity.
- the relationship between the electrical side and the mechanical side can be modeled by a first transformer Tl .
- a moving coil loudspeaker may be thought of as a mass-spring system where the cone and the voice coil constitute the mass and the spider and surround constitute the spring element. Losses in the suspension can be modeled as a suspension resistance R3.
- the suspension compliance may be modeled as a suspension inductance L2 and the moving mass (voice coil and cone) can be modeled as a capacitance CI .
- the suspension resistance R3, the suspension inductance L2 and the capacitance CI are coupled in parallel.
- a loudspeaker's cone may be thought of as a piston that pushes and pulls on the air facing it, converting mechanical force and velocity into acoustic pressure and volume velocity.
- the input voltage provided by the voltage source VI may be a pure sine wave or a more sophisticated signal such as the sum of two different sine waves, for example.
- a linear lumped element model does not allow to predict the harmonics of a loudspeaker, because the force factor, the suspension stiffness and the voice coil inductance are constant (in relation to the voice coil position).
- Non- linear lumped element models are known, which combine the lumped element model with differential equations, and in which the force factor, the suspension stiffness and the voice coil inductance are non-constant (in relation to the voice coil position).
- Such non-linear lumped element models allow to predict the fundamental and the harmonics in the sound pressure.
- the amplitude of the fundamental and the harmonics of the sound pressure can be predicted using a non-linear lumped element model and a constant input voltage at the speaker terminals.
- a non-linear lumped element model approach using a constant voltage (sine wave with constant amplitude) as an input voltage cannot be used to determine the real speaker displacement, as has already been described above. Therefore, according to one example of the present invention a measurement or a subsystem simulation is performed first to determine the real speaker displacement. Based on this real speaker displacement, the input voltage at the speaker terminals of a non-linear LPM (lumped parameter model) approach is then tuned (adapted) until the same speaker displacement is received as in the measurement or in the FEM/BEM prediction. In other words, the speaker displacement of the non-linear LPM approach is the same as the real speaker displacement.
- a linear LPM model does not allow to predict the harmonics because the force factor, the suspension stiffness and the voice coil inductance are constant (constant versus the voice coil position).
- the use of a non-linear LPM model where the force factor, the suspension stiffness and the voice coil inductance are non-constant (versus the voice coil position) allows to predict the fundamental and the harmonics in the sound pressure.
- no (neither linear nor non-linear) LPM approach considers the geometry of the speaker enclosure. In LPM approaches, the speaker enclosure usually is only defined by the volume of the air in the enclosure.
- the voltage at the speaker terminals is a concatenation of pure sine waves at different frequency values (the same voltage amplitude for all frequency values).
- a non-constant voltage is used in combination with a non-linear speaker lumped element model.
- this tuned voltage allows to control the fundamental of the speaker displacement.
- the amplitude of the tuned voltage is computed to reach the same speaker fundamental displacement as delivered by a measurement or simulation method, which both include the interaction between the speaker membrane and the air in the speaker enclosure.
- every harmonic amplitude delivered by the non-linear LPM simulation may be updated.
- the harmonic magnitude update is based on the use of the transfer function between the fundamental speaker displacement delivered by the non-linear LPM and the linear speaker displacement delivered by the simulation or measurement methods.
- the ratio used to increase or decrease the harmonic level is computed by checking the relative amplitude of the speaker displacement at the fundamental and the harmonic frequencies.
- a measurement or a subsystem simulation may first be performed to determine the real speaker displacement.
- the real speaker displacement is also called first speaker displacement in the following.
- the simulation may include a finite element method (FEM) or a boundary element method (BEM), for example. If a first (constant) input voltage is used as an input voltage of a lumped element model prediction, this results in a second speaker displacement, which is usually different from the first speaker displacement. This means, that performing a non-linear LPM method with a first (constant) input voltage, this does not result in the real speaker displacement, but in a second speaker displacement which differs from the real speaker displacement.
- FEM finite element method
- BEM boundary element method
- third speaker displacement first (real) speaker displacement
- the transfer function between the tuned voltage (after adapting the voltage) and the non-tuned (constant) voltage (before adapting the voltage) is equal to the transfer function between the real speaker displacement and the displacement predicted by the LPM model using the constant voltage at the speaker terminals.
- This tuned voltage which results in the real speaker displacement, is then used in a simulation tool combining a LPM model and differential equations to simulate the amplitude of the fundamental and the harmonics in the sound pressure.
- the membrane displacement may be determined by means of a (linear or non-linear) lumped element model of the loudspeaker (step 402).
- a first (constant) voltage as an input voltage for the lumped element model results in a (second) speaker displacement which may differ from the first (real) speaker displacement that has been determined by means of a measurement or simulation at the first voltage.
- This second membrane displacement may be determined for a case in which the air resonance in the enclosure does not correspond to the frequency working range of the loudspeaker, for example.
- Constant input voltage in this context means that the signal, i.e. a sine wave or a more complex signal, has a constant amplitude which does not change over time.
- the input voltage may have a certain frequency and a certain voltage (amplitude).
- the first (constant) input voltage may then be altered until the resulting (third) membrane displacement equals the first (real) speaker displacement (step 403).
- the resulting (third) membrane displacement and also the harmonics change as well.
- the resulting (third) speaker displacement and the first (real) speaker displacement are the same when a second (tuned) input voltage is used as an input for the lumped element model. Amending the input voltage allows to control the fundamental of the speaker displacement.
- the input voltage is adapted for each frequency separately.
- the second (tuned) input voltage may then be used to simulate the amplitude of the fundamental and the harmonics of the sound pressure (step 404).
- the simulation may be based on a non-linear lumped element model that allows to predict the amplitude of the fundamental, the harmonics of the sound pressure and the total harmonic distortion.
- the same method as has been described above, may be used if the input voltage at the speaker terminals is a multitoned signal which is generally used to predict sound pressure intermodulation.
- Input parameters for the lumped element model in step 402 may include the force factor Bl, the self inductance of the voice coil L e , and the suspension compliance CMS while the voice coil is in its rest position for the linear lumped element model and for all voice coil positions for the non- linear lumped element model.
- Input parameters for the lumped element model in step 403 may include the force factor Bl, the self inductance of the voice coil L e , and the suspension compliance CMS for all voice coil positions.
- the method may further comprise determining of at least one of the amplitude of the fundamental, the harmonics of the sound pressure, and the sound pressure intermodulation.
- the speaker displacement may be the displacement of a membrane of the loudspeaker from its rest position.
- a software may be configured to execute the steps of determining a first speaker displacement of a loudspeaker at a first loudspeaker input voltage, by using a measurement or a simulation, determining a second speaker displacement at the first loudspeaker input voltage, by using a lumped element model, adapting the first loudspeaker input voltage resulting in a third speaker displacement and determining a second loudspeaker input voltage at which the third speaker displacement equals the first speaker displacement, by using a linear lumped element model, and determining the total harmonic distortion of the
- the computer readable medium may be a computer readable signal medium or a computer readable storage medium.
- a computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.
- a computer readable storage medium may be any tangible medium that can contain, or store a software or program for use by or in connection with an instruction execution system, apparatus, or device.
- each block in the flowchart may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s).
- the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.
- each block of the flowchart illustration, and combinations of blocks in the flowchart illustration can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
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- Health & Medical Sciences (AREA)
- General Health & Medical Sciences (AREA)
- Otolaryngology (AREA)
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
Abstract
Description
Claims
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP16176205 | 2016-06-24 | ||
PCT/EP2017/065686 WO2017220816A1 (en) | 2016-06-24 | 2017-06-26 | Method for simulating total harmonic distortion of a loudspeaker |
Publications (1)
Publication Number | Publication Date |
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EP3476135A1 true EP3476135A1 (en) | 2019-05-01 |
Family
ID=56235716
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP17733433.1A Ceased EP3476135A1 (en) | 2016-06-24 | 2017-06-26 | Method for simulating total harmonic distortion of a loudspeaker |
Country Status (2)
Country | Link |
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EP (1) | EP3476135A1 (en) |
WO (1) | WO2017220816A1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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WO2021226515A1 (en) | 2020-05-08 | 2021-11-11 | Nuance Communications, Inc. | System and method for data augmentation for multi-microphone signal processing |
Family Cites Families (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6269318B1 (en) * | 1997-04-30 | 2001-07-31 | Earl R. Geddes | Method for determining transducer linear operational parameters |
EP2453669A1 (en) * | 2010-11-16 | 2012-05-16 | Nxp B.V. | Control of a loudspeaker output |
EP2901711B1 (en) * | 2012-09-24 | 2021-04-07 | Cirrus Logic International Semiconductor Limited | Control and protection of loudspeakers |
CN102970647B (en) * | 2012-11-16 | 2015-04-01 | 嘉善恩益迪电声技术服务有限公司 | Simulating calculation method for nonlinear characteristics in loudspeaker vibration |
-
2017
- 2017-06-26 EP EP17733433.1A patent/EP3476135A1/en not_active Ceased
- 2017-06-26 WO PCT/EP2017/065686 patent/WO2017220816A1/en unknown
Also Published As
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WO2017220816A1 (en) | 2017-12-28 |
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