WO2024254820A1

WO2024254820A1 - Method for designing constant sound field speaker

Info

Publication number: WO2024254820A1
Application number: PCT/CN2023/100411
Authority: WO
Inventors: Guochao LU; Cheng JIANG; Yu Jiang; Jianwen ZHENG
Original assignee: Harman International Industries Inc
Current assignee: Harman International Industries Inc
Priority date: 2023-06-15
Filing date: 2023-06-15
Publication date: 2024-12-19
Anticipated expiration: 2025-12-15
Also published as: EP4728755A1; CN121312153A

Abstract

A method for reproducing a constant field speaker is provided, which includes the steps of reproducing low-frequency audio with left and right channel inputs below a first crossover point through a woofer. This method also includes the steps of reproducing high-frequency audio above the first crossover point in all directions with constant frequency responses through a tweeter unit. The tweeter unit can be configured by using a CSF algorithm with DSP above the first crossover point and below a second crossover point. And the unit can be configured by using the CSF algorithm with acoustic processing combined with the DSP, to reproduce the constant sound field. A speaker apparatus for reproducing the constant sound field using this method is also provided.

Description

METHOD FOR DESIGNING CONSTANT SOUND FIELD SPEAKER

TECHNICAL FIELD

The inventive subject matter generally relates to signal processing. More particularly, the inventive subject matter relates to a method for reproducing a constant sound field and a speaker apparatus therefor.

BACKGROUND

An audio signal is a carrier of regular sound wave frequency and amplitude change information. Regular audio may be represented by a sound wave or a sine wave. The sine wave includes three important parameters: frequency, amplitude, and phase, which also characterize the audio signal. Taking music as an example, people’s perception of sound frequency is expressed as pitch. A higher pitch corresponds to a higher frequency. The amplitude reflects the energy magnitude of a signal. A high-amplitude waveform signal has a larger volume, and a low-amplitude waveform has a quieter sound.

Dual-channel stereo can simulate the binaural effect to include directional information in the audio signal, and simulate the different gains and delays of a sound source from different positions to the left and right ears, enabling people to distinguish the sound source from different directions, thus obtaining a sense of presence. And audio signals are converted into sound through speakers. The speaker converts the audio power signal within a certain range into audible sound with low distortion and enough sound pressure level through energy conversion, thus attempting to reproduce the sound field. For a long time, people have typically used axial frequency response curves to depict speakers. However, the off-axis performance of speakers can have an impact on sound quality and subjective listening experience. Based on this, when using a mono speaker to reproduce stereo sound, a sweet spot can be limited on axis. When using a stereo speaker in one chamber or with dedicated chambers to reproduce stereo sound, a small sweet spot may be limited around an axis, while a comb filtering issue caused by coherence between the left and right channels of the stereo exists when off axis.

Therefore, it is desirable to design a speaker apparatus that may create a constant sound field with uniform frequency responses both on axis and off axis.

SUMMARY OF THE INVENTIVE SUBJECT MATTER

In one aspect, by using a constant sound field (CSF) algorithm in a tweeter unit for digital signal processing (DSP) and acoustic processing, a method for reproducing a constant sound field is provided. The method comprises a step of reproducing, via a woofer, low-frequency audio below a first crossover point from a left channel input and a right channel input. The method further comprises a step of reproducing, via a tweeter unit, high-frequency audio above the first crossover point with constant frequency responses in all directions. In the method, the tweeter unit may be configured to reproduce a constant sound field using a constant sound field algorithm with digital signal processing (DSP) in a frequency range above the first crossover point and below a second crossover point as well as with acoustic processing combined with the DSP in the frequency range above the second crossover point.

In another aspect, a speaker apparatus for reproducing a constant sound field is provided. The speaker apparatus comprises a woofer configured to reproduce low-frequency audio below a first crossover point from a left channel input and a right channel input. The speaker apparatus further comprises a tweeter unit configured to reproduce high-frequency audio with constant frequency responses in all directions. In the speaker apparatus, the tweeter unit may be configured to reproduce a constant sound field using a constant sound field algorithm with digital signal processing (DSP) in a frequency range above the first crossover point and below a second crossover point as well as with acoustic processing combined with the DSP in the frequency range above the second crossover point.

BRIEF DESCRIPTION OF THE DRAWINGS

The present inventive subject matter may be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings. In the FIG. s, like reference numeral designates corresponding parts, wherein below:

FIG. 1 illustrates an exemplary flowchart of the method for reproducing a constant sound field (CSF) according to one or more embodiments of the inventive subject matter;

FIG. 2A illustrates a front view of a speaker apparatus for reproducing a constant sound field, in accordance with the one or more embodiments of the inventive subject matter;

FIG. 2B illustrates the top view of the speaker apparatus of FIG. 2A for reproducing a constant sound field, in accordance with the one or more embodiments of the inventive subject matter;

FIG. 3 shows a block diagram with audio chains using a CSF algorithm to achieve a constant sound field reproduction through DSP and acoustic processing, in accordance with the one or more embodiments of the inventive subject matter;

FIG. 4 illustrates an exemplary energy distribution map of the speaker apparatus for reproducing a constant sound field, optimized for interference by a three-horn combination structure in the high-frequency range, in accordance with the one or more embodiments of the inventive subject matter;

FIG. 5A illustrates an exemplary directivity comparison diagram for reproducing the frequency response of a sound field in speaker devices of different design tweeter combination structures, in accordance with the one or more embodiments of the inventive subject matter;

FIG. 5B illustrates an exemplary directivity comparison diagram for reproducing the frequency response of a sound field in speaker devices of different design tweeter combination structures using the CSF algorithm, in accordance with the one or more embodiments of the inventive subject matter; and

FIG. s6A and 6B illustrate exemplary comparison diagrams of the normalized audio frequency responses at various angles and directions in the sound field reproduced by the mono speaker and a CSF feature speaker, respectively, including the comparison data of the CSF speaker to the similar dimension of the mono speaker, in accordance with the one or more embodiments of the inventive subject matter.

DETAILED DESCRIPTION

The detailed description of the one or more embodiments of the inventive subject matter is disclosed hereinafter; however, it is understood that the disclosed embodiments are merely exemplary of the inventive subject matter that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and function details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present inventive subject matter.

The directivity of a speaker system refers to the spatial distribution of the sound pressure it radiates. At low frequencies, a dimension of its radiation surface is much smaller than the wavelength of the radiated sound wave, and the speaker system can be regarded as a point source, with its radiation being directionless. But as the frequency increases, the wavelength of sound waves becomes shorter. When the wavelength is equal to or less than the dimension of the radiation surface, the radiation phase of the speaker system exhibits obvious directivity, that is, the radiation sound pressure at different angles varies at the same distance. The larger the size and the higher the frequency, the stronger its directivity. Conversely, the smaller the size and the lower the frequency, the wider its directivity. Therefore, the directivity of the speaker system is related to two factors: frequency and the dimension of the radiation surface.

The audio frequency audible for human ears is between 20Hz and 20kHz. For low frequency signals, if more than one woofer units are used to playback the same signals, the coherence may be significant. With woofers have wide directivity in low frequency range, there may be only one woofer set to achieve constant sound field.

In contrast, high frequency signals may suffer from unsmooth frequency response curves, such as irregular changes or discontinuities in the curves, outside of the axial direction of the speaker due to the short wavelength. The higher the signal frequency input to the speaker, the stronger the directionality. In one or more embodiments of the inventive subject matter, as to such unsmooth off-axis frequency response curves in high frequencies, the tweeter unit of the speaker apparatus can be designed to compensate for the attenuation in off-axis directions of the sound field by digital signal processing and/or acoustic processing, to achieve a uniform and consistent sound field in all radiation directions of the speaker apparatus.

FIG. 1 illustrates an exemplary flowchart 100 of the method for reproducing a constant sound field (CSF) according to one or more embodiments of the present inventive subject matter. As shown in FIG. 1, the method starts from step S110. At S110, a speaker apparatus may be arranged with a woofer unit for playback of low-frequency audio and a tweeter unit for playback of high-frequency audio of a stereo input. In one or more embodiments of the inventive subject matter, the woofer unit may be arranged with a woofer, for example, facing towards the front of the speaker apparatus, while the tweeter unit may be designed to reproduce a Hi-Fi sound field with uniform and constant frequency responses in all directions.

Unlike mono speakers or stereo speakers, the tweeter unit in one or more embodiments of the present inventive subject matter may be designed as a tweeter combination structure with several tweeters to support several channels. In an example, the tweeter unit may be implemented by multiple horns facing in different directions within a 180-degree radiation range in front of the speaker apparatus, and each horn may correspond to one channel of the tweeter combination structure. Thereby, the off-axis arranged horns may be expected to compensate for frequency response attenuations in the off-axis directions of the sound field. The off-axis arranged horns may expand the sweet spot. Accordingly, at least three channels are required for the tweeter combination structure. In principle, a larger sweet spot can be obtained by increasing the number of channels. One or more embodiments of the present inventive subject matter will be explained with the example of the 3-horn array tweeter combination structure.

FIG. 2A illustrates a front view 200 of the speaker apparatus 210 for reproducing a constant sound field according to one or more embodiments of the present inventive subject matter. The speaker apparatus includes a woofer 220 located below and set towards the axial direction to reproduce low-frequency audio, and a tweeter unit located above and including three tweeters 230, 240, 250 facing in different off-axis directions to reproduce high-frequency audio.

As shown in FIG. 2A, in the example, the three tweeters 230, 240, 250 are arranged in parallel. A center tweeter 240 may be arranged on axis and oriented towards the axial direction, a left arranged tweeter 230 may be oriented towards the left off-axis direction, and a right arranged tweeter 250 may be oriented towards the right off axis direction. The center tweeter 240 may be considered as the tweeter facing to the 0-degree direction of the sound field, wherein an original sweet spot is located. The left and right tweeters 230, 250 are arranged towards the left and right at a certain angle apart from the axially oriented center tweeter 240. It may be expected that the frequency response in the left off-axis directions can be compensated by the left tweeter 230 facing to the left, while the frequency response in the right off axis directions can be compensated by the right tweeter 240 facing to the right. Thereby, the speaker apparatus 210 with the tweeter combination structure composed of these three tweeters 230, 240, 250, as well as the one woofer 220, can significantly expand the sweet spot and achieve a complete constant sound field.

FIG. 2B illustrates the top view 200’ of the speaker apparatus 210 of FIG. 2A for reproducing a constant sound field according to one or more embodiments of the present inventive subject matter. In a way of example, the left and the right tweeters 230’, 250’ are arranged towards the left and right each at an angle of 60 degrees apart from the axially oriented center tweeter 240’ . It may be expected that the sweet spot may be expanded to 120 degrees in the sound field.

In such sound field, it is also necessary to consider the directivity of the tweeters arranged in the off-axis directions, and the interference caused by the sound wave propagation and coherence therebetween. The coherence between the tweeters has further become an issue to be addressed.

On the other hand, the woofer usually has a wide directivity in low frequency range. Due to such inconspicuous directivity features of the woofer, the speaker apparatus equipped with only one woofer may achieve a good low-frequency response in the sound field. Those skilled in the art may understand that low frequency audio can be filtered out by using a low pass filter and then be fed to the one woofer for playback.

When a stereo input including left and right channel inputs, L_in, R_in, has been input to the speaker apparatus, the low-frequency audio below a crossover point can be filtered and fed to the woofer. The crossover point for distinguishing the audio between the woofer and the tweeter unit may be set as a first crossover point f_c1. As an example, the first crossover point is set at 2kHz. Using the low-pass filter set of the first crossover point to filter and output the low-frequency audio, the channel output with the low-frequency audio to be fed to the woofer can be simply described as an audio chain, which describes all the processing from the channel input to output, as by filtering the left and right channel inputs L_in, R_in, through a low-pass filter and down-mixing into one channel output to the woofer. Namely, the audio chain for the woofer can be expressed as:
LPF₁ (L_in+R_in) (1)

Where, L_in represents the left channel input and R_in, represents the right channel input; LPF₁ is a low-pass filter of the first crossover point f_c1. Therefore, the left and right channel inputs L_in, R_in, are filtered and output through a low-pass filter LPF₁, and the filtered left and right channel inputs below the first crossover point are mixed, LPF₁ (L_in+R_in) , and fed to the woofer for playback, at S120 of FIG. 1.

In an instance, the first crossover point f_c1 is set at 2kHz. The filtered audio signals below 2kHz are to be fed to the woofer. Due to the fact that the woofer audio does not require the processing with the CSF algorithm in one or more embodiments of the present inventive subject matter, this part is not illustrated in following FIG. 3 which is the focus of the CSF algorithm for processing the high-frequency audio above the first crossover point to be fed to the tweeter unit for playback.

FIG. 3 shows a block diagram 300 with audio chains using the CSF algorithm to achieve a constant sound field reproduction through DSP and acoustic processing, in accordance with the one or more embodiments of the inventive subject matter. A dual-channel stereo may be input into the speaker apparatus, which includes a left channel input 310, L_in, and a right channel input 312, R_in. The left and right channel inputs 310, 312 firstly enter the pre-equalizer 320 to be separated into various frequencies. The pre-equalizer 320 comprises filters that, for example, may filter out high-frequency audio to be fed to the tweeter unit.

In contrast to the low-pass filter which filters out the low-frequency audio for the woofer, a high-pass filter, HPF₁, set to the first crossover point may filter and output the high-frequency audio. The filtered high-frequency audio shall be processed by using the CSF algorithm as channel outputs for the tweeter combination structure, and then fed to each of the tweeters in the tweeter unit for playback, accordingly. For the directional characteristics and interference effects of the high-frequency signal to be fed to the tweeters, the method provided in the present inventive subject matter may be applied to this part of the audio processing for tweeters.

Back to FIG. 2B, as the center tweeter 240’ is oriented axially at 0 degree of the sound field where the sweet spot of the sound field is located. It is possible for the center tweeter 240’ to directly playback a center channel output down-mixed from the left and right channel inputs, L_in+R_in. Therefore, referring to FIG. 3, the center channel output 362 to be fed to the center tweeter may be described as an audio chain as by high-pass filtering the left channel input 310, L_in, the right channel input 312, R_in, and the down-mixed 352 the filtered left and right channel inputs L_in+R_in into one center channel output 362 for the center tweeter. Namely, the audio chain for the center channel output 362 can be expressed as:
HPF₁ (L_in+R_in) (2)

Where, L_in represents left channel input, and R_in represents right channel input; HPF₁ is a high pass filter set of the first crossover point f_c1, which is at 2kHz, in the example.

It is expected that the left and right tweeters oriented towards off-axis directions may compensate for the attenuation of the frequency response beyond the original sweet spot, while further addressing the sound field halo caused by the acoustic coherence therebetween. In the subject matter of the present inventive subject matter, for a radiation range of the speaker apparatus, adding appropriate inverted right and left channel inputs to each audio chain of the left and right channels, respectively, may enable the channel outputs to cancel out with each other.

As to the left channel output, while feeding the left channel input, L_in, an inverted right channel input, invert (R_in) , may be appropriately down-mixed therein, for cancelling the sound from the right channel by utilizing the coherence between different channels.

In contrast to the left channel, as to the right channel output, while feeding the right channel input, R_in, an inverted left channel input, invert (L_in) , may be appropriately down-mixed therein, for cancelling the sound from the left channel.

Due to the stronger directivity of the tweeter unit at the higher frequencies, the channel processing may also be performed by depending on the frequencies. In one or more embodiments of the present inventive subject matter, the whole high-frequency audio, above the first crossover point, will undergo the DSP processing to achieve the reproduction of a constant sound field. Furthermore, for the higher frequencies, acoustic processing may be combined into the design of the tweeter unit to enable the frequency responds curve of the reproduced constant sound field to be more uniformed. Therefore, a second crossover point can be set thereat in the left and right DSP module 330, 332. The directivity of high-frequency audio for the tweeter unit can be solved though the DSP, and acoustic processing shall be additionally adopted for the high-frequency audio above the second crossover point, to enhance the uniformity of high-frequency directivity. In other words, the high-frequency audio between the first crossover point and the second crossover point may be processed thought DSP; and the high-frequency audio above the second crossover point will be processed by the DSP combining acoustic processing, with reference to S130 of FIG. 1.

The inverted right channel input to be down-mixed into the left and right channel may be adjusted by applying with gains and/or delays in the left and right DSP module 330, 332. The gains and delays can be applied based on a uniformity of the left and right channel frequency response and the balance of sound pressure level, to achieve a constant sound field. The gains and delays can be applied according to the frequencies. For example, a first set of gain G₁ and delay D₁ may be applied in the range from the first crossover point f_c1 to a second crossover point f_c2, while a second set of gain G₂ and delayD₂ may be applied above the second crossover point f_c2.

In this way, for the right channel 360, the appropriate inverted left channel input 340 is processed in the left DSP module 330 and then output therefrom. The DSP processing in the left DSP module 330 shall be as:
LPF₂ [D₁ (invert (L_in) *G₁) ] , for f_c1<f< f_c2 (3) and
HPF₂[D₂ (invert (L_in) *G₂) ] , for f ≥ f_c2 (4)

and then the appropriate inverted left channel input 340 is to be down-mixed 350 into the right channel input 312. Therefore, the audio chain of the right channel 360 to the right tweeter can be described by down-mixing 350 the right channel input with the appropriate inverted left channel input 340 applying with different gains G₁, G₂ and delays D₁, D₂ corresponding to various frequencies, i.e., the audio chain for the right channel output 360 can be expressed as:
HPF₁ {LPF₂ [D₁ (invert (L_in) *G₁) +R_in] +HPF₂ [D₂ (invert (L_in) *G₂) +R_in] } (5)

Where, L_in represents left channel input and R_in represents right channel input; invert(L_in) represents the phase-inverted left channel input; HPF₁ is a high pass filter set of the first crossover point f_c1; LPF₂ is a low-pass filter set of the second crossover point f_c2; HPF₂ is a high pass filter set of the second crossover point f_c2; D₁ and G₁ represent the delay and gain applied between the first and the second crossover point, f_c1<f< f_c2, respectively; and D₂ and G₂ represent the delay and gain applied above the second crossover point, f ≥f_c2, respectively.

Similarly, for the left channel 364, the appropriate inverted right channel input 342 is processed in the right DSP module 332 and then output therefrom, which shall be as:
LPF₂ [D₁ (invert (R_in) *G₁) ] , for f_c1<f< f_c2 (6)
HPF₂ [D₂ (invert (R_in) *G₂) ] , for f ≥ f_c2 (7)

and then the appropriate inverted right channel input 342 is to be down-mixed 354 into the left channel input 310. Therefore, the audio chain of the left channel 364 to the left tweeter can be described by down-mixing 354 the left channel input 310 with the appropriate inverted right channel input 342 applying with different gains G₁, G₂ and delays D₁, D₂ corresponding to various frequencies, i.e., the audio chain for the left channel output 364 can be expressed as:
HPF₁ {LPF₂ [D₁ (invert (R_in) *G₁) +L_in] +HPF₂ [D₂ (invert (R_in) *G₂) +L_in] } (8)

Where, L_in represents left channel input and R_in represents right channel input; invert (R_in) represents the phase-inverted right channel input; HPF₁ is a high pass filter set of the first crossover point f_c1; LPF₂ is a low-pass filter set of the second crossover point f_c2; HPF₂ is a high pass filter set of the second crossover point f_c2; D₁ and G₁ represent the delay and gain applied between the first and the second crossover point, f_c1<f< f_c2 , respectively; and D₂ and G₂ represent the delay and gain applied above the second crossover point, f ≥f_c2, respectively.

In the right channel, the appropriate inverted left channel input 340, D₁ (invert (L_in) *G₁) for f_c1<f< f_c2 , and D₂ (invert (L_in) *G₂) for f≥ f_c2, both have the coherence with the left channel input L_in from the left channel, and the coherent cancellation may occur therebetween. In contrast, in the left channel, the appropriate inverted right channel input 342, D₁ (invert (R_in) *G₁) for f_c1<f< f_c2 , and D₂ (invert (R_in) *G₂) for f≥ f_c2 , both have the coherence with the right channel input R_in from the right channel, and the coherent cancellation may occur therebetween. Accordingly, the sound between the left and right channel outputs may be cancelled out with each other.

After processing the right, center and the left channel 360, 362, 364, through the post- equalizer module 370, the processed high-frequency audio of the three channel outputs may be fed to the right, center and left tweeters 250, 240, 230 of FIG. 2A in the tweeter unit, where acoustic speaker design may be performed in acoustic processing module 380, and then to be converted into sound 390 for playback, accordingly. This step is described in S140 of FIG. 1.

Since a horn may have different coherence characteristic below and above one specific frequency, 7kHz in the example. As the frequency increases, the directivity narrows and the coherence weakens, the CSF algorithm requirements may be satisfied near 7kHz. In one or more embodiments of the present inventive subject matter, the second frequency point f_c2 thus may be at 7kHz. There may be strong coherence between horns below 7kHz. Above 7kHz, the coherence may be not as strong, instead with the stronger directivities.

In the process of controlling the frequency response effect of the sound field in this segmented frequency, the delays, D₁, D₂ set in the audio chain, as well as the gains, G₁, G₂, can be adjusted according to the reproduced frequency response curve and tuning of the sound field, so that the entire sound field has high fidelity and uniform frequency response effect. In an example, the delay gain setting can be D₁=0ms, G₁, =0dB, D₂=1ms, G₂=-6dB. In an example of a sound field, the gain and delay in the left and right audio chains can be the same or different.

In the example, the tweeter combination structure of the tweeter unit is designed as a horn array including three horns to adapt to the audio chains. Horn is a typical electro-acoustic device with the main frequency of 2kHz to 20kHz, with the segmented frequency at the second crossover point of 7kHz. Above 7kHz, the coherence of the reproduced sound field may be not as strong, instead with the stronger directivities. It may be desirable to introduce the Acoustic Processing to compensate for such sharp directivities in high-frequency areas above the second crossover point.

In one or more embodiments of the present inventive subject matter, the tweeter combination structure of the tweeter unit may be processed in the acoustic processing module 380, for example, by changing the dimensions and/or angular arrangements of the horn array, such as shown in FIG. 2B, where the left and right horns each may be arranged at an angle of 60 degrees from the center horn, thereby expanding the sweet spot of the reproduced sound field to 120 degrees. In other instances, more than three horns may be used, and be arranged in other orientations. More horns and channel outputs may achieve a larger sweet spot, in practically.

Additional or alternatively, a horn typically includes a compression driver for emitting sound plus a horn throat, and a horn opening. For example, regarding to the acoustic processing, the shapes of the combined horns can be designed. For example, the use of catenary, hyperbolic, exponential horns, etc. may be given priority. In other way, when the structural limit is relatively large, other curves being as smooth as possible can be used to define the horn, and try to ensure a smooth transition from throat to mouth of the horn.

In different audio chains, different curves can be used to meet different sound field requirements. In this way, by multi-dimensionally arranging the horns designed for different frequencies, and through special processing near the throat, a constant frequency response effect can be achieved within the entire radiation range of the speaker device.

In one or more embodiment of the present inventive subject matter, additionally or alternatively, the tweeter unit processed in the acoustic processing module 380 may be configured by modified the transducer of the speaker. Other than the tweeters that can be typically an electro-acoustic device, full-range speakers may be adapted for the transducer design. The “full range” connotes the speaker that covers the entire auditory range of the human ears, and naturally carries directivity characteristics. The high-frequency directivity characteristics of a single full-range speaker can be equivalent to the tweeter with horn, enabling adapted to the multiple channel outputs in non-coherence of the high frequency range and overcoming the issues with sharp directivity in the high frequency range. So the two may be replaced with each other.

In one or more embodiment of the present inventive subject matter, additionally or alternatively, the tweeter unit processed in the acoustic processing module 380 may be further include waveguide design. Acoustic waveguide can be complex acoustic structural devices, which can be able to emit sound waves directionally and may play an important role in sound tuning. The design of waveguides may be very complicated. the usage of sound field simulation tools may be helped for designing the waveguide, thereby enhancing the uniformity of the sound field and facilitating to design a constant sound field speaker.

At last, at S150 of FIG. 1, the audio chains, such as the gains and the delays, may be adjusted, as well as the tweeter unit configuration, such as the shape and the number of horns therein, may be modified. Instead the transducer and/or the waveguide design may also be applied, to achieve a constant sound field.

FIG. 4 illustrates an exemplary energy distribution map 400 of the speaker apparatus for reproducing a constant sound field, optimized for interference by a three-horn combination structure in the high-frequency range, in accordance with the one or more embodiments of the inventive subject matter. The lighter grayscale in the energy distribution map, the higher energy distributed herein. It can be seen from FIG. 4 that, within the whole 180-degree radiation range in the figure the overall energy distribution is relatively uniform in the sound field reconstructed by the three horns 430, 440, 450 facing on axis at 0 degrees, left off axis at 60 degrees, and right off axis at 60 degrees, respectively.

FIG. 5A illustrates an exemplary directivity comparison diagram 500 for reproducing the frequency response of a sound field in speaker devices of different design tweeter combination structures, while FIG. 5B illustrates an exemplary directivity comparison diagram 500’ for reproducing the frequency response of a sound field in speaker devices of different design tweeter combination structures using the CSF algorithm, in accordance with the one or more embodiments of the inventive subject matter. In both FIGs. 5A and 5B, the dotted line represents the directivity line 510, 510’ formed by a mono speaker, and the curve depicted by the dashed line represents the directivity line 520, 520’ formed by stereo speaker (dual channel) . There is no CSF processing used in the implementations of mono speaker nor stereo speaker, and the shapes of either the dotted directivity lines 510 and 510’ for the mono speaker are the same, and the dashed directivity lines 520 and 520’ in these two figures are the same. The solid lines in FIG. s5A and 5B depict the acoustic performances of CSF feature speakers. In FIG. 5A, the CSF feature comes from the designed horn array. And in FIG. 5B shows the acoustic performance of the CSF featured system including the usage of the CSF algorithm. By comparing the solid lines in FIGs. 5A with 5B, it is obvious that the directivity line 530’ of the CSF featured system in FIG. 5B has achieved in a larger and wider area, and the energy distribution of acoustic radiation in all directions of the space can be distributed more evenly, than the directivity line 530 of the horn array designed with CSF features.

FIG. s 6A and 6B illustrate exemplary comparison diagrams 600, 600’ of the normalized audio frequency responses at various angles and directions in the sound field reproduced by the mono speaker and the CSF feature speaker, respectively, including the comparison data of the CSF speaker to the similar dimension of the mono speaker, in accordance with the one or more embodiments of the inventive subject matter. In the diagram 600 of FIG. 6A, solid line 610 depicts the frequency response curve of the sound field reproduced by a mono speaker in the 0- degree axial direction, dashed line 620 depicts the frequency response curve of the sound field reproduced by the mono speaker in the 30 degree off axis direction, and dotted lines 630 depicts the frequency response curve of the sound field reproduced by the mono speaker in the 60 degree off axis direction. In contrast, In the diagram 600’ of FIG. 6B, solid line 640 depicts the frequency response curve of the sound field reproduced by a CSF feature speaker in the 0-degree axial direction, dashed line 650 depicts the frequency response curve of the sound field reproduced by the CSF feature speaker in the 30 degree off axis direction, and dotted lines 660 depict the frequency response curve of the sound field reproduced by the CSF feature speaker in the 60 degree off axis direction, respectively. By comparing the frequency response curves 610, 620, 630 of the mono speaker in FIG. 6A to those frequency response curves 640, 650, 660 of the CSF feature speaker in FIG. 6B, it can be seen that the frequency response curves in the 0 degree direction of the sound field axis are both flat for the CSF feature speaker and mono speaker as normalization. However, for other off axis directions, the frequency response curves 650, 660 of the CSF feature speaker are relatively flatter in shape, and its frequency response curves in all directions are much closer to achieve constant, than those 620, 630 of the mono speaker. Accordingly, frequency responses of the CSF feature speaker in all directions both on axis and off axis may be more consistent and more constant than those of the mono speaker.

In summary, the tweeter combination structure with horns can be adjusted according to speaker configuration. It is preferable to uniformize the speaker directivity depending on the performance of transducer and CSF design target.

A speaker apparatus with a CSF featured tweeter unit has been provided in one or more embodiments of the present inventive subject matter. In one instance, the tweeter unit can be a designable tweeter combination structure equipped with a horn array, including horns oriented in different directions in space to obtain a reproducible sound field with constant frequency responses within the entire radiation range of the speaker apparatus. Additional or alternative designs for the tweeter unit, such as in designing transducers and waveguides of the speaker may also achieve the similar acoustic effects.

In summary, the present inventive subject matter provides a method for designing a constant sound field speaker, which utilizes a CSF algorithm to process audio chains fed to the tweeter unit. The CSF feature speaker apparatus can be applied with multi-channel configuration with more than or equal to 3 channels, and either 1-way, 2-ways, 3-ways or more ways speaker configurations, wherein the horns adopted in the tweeter unit can be adjusted according to speaker configuration, which can be optional depending on the performance of the transducer and the CSF design target.

Based on the method provided in the present inventive subject matter, a constant sound filed can be achieved by using digital signal processing and acoustic processing. The advantages of the method may include that all details in stereo music can be maintained; enlarged sweet spots in the entire sound field may be achieved; and the correct sound stage in sweet spot range may be delivered.

Any combination of one or more computer-readable media may be used to perform the method provided in one and more embodiments of the present inventive subject matter. The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. The 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. More specific examples (non-exhaustive list) of the computer-readable storage medium may include, for example: an electrical connection with one or more wires, portable computer floppy disks, hard disks, random access memory (RAM) , read-read-only memory (ROM) , erasable programmable read only memory (EPROM or flash memory) , optical fibers, portable compact disc read only memory (CD-ROM) , optical storage devices, magnetic storage devices, or any suitable combinations of the foregoing. In the context of the disclosure, the computer-readable storage medium may be any tangible medium that can include or store a program for use by or in connection with an instruction execution system, apparatus, or device.

As used in the disclosure, an element or step listed in the singular form and preceded by the word "one/a" should be understood as not excluding a plurality of said elements or steps, unless such exception is specifically stated. Furthermore, references to "embodiments" or "examples" of the disclosure are not intended to be construed as exclusive, also including the existence of other embodiments of the recited features. The terms "first" , "second" , "third" , etc. are used only for identification and are not intended to emphasize a numerical requirement or positioning order of their objects.

References in the present inventive subject matter to the method for reproducing a constant sound field include the following content:

Item 1: In one or more embodiments, the present inventive subject matter provides a method for reproducing a constant sound field, comprising steps of:

reproducing, via a woofer, low-frequency audio below a first crossover point from a left channel input and a right channel input; and

reproducing, via a tweeter unit, high-frequency audio above the first crossover point with constant frequency responses in all direction;

wherein the tweeter unit may be configured to reproduce a constant sound field using a constant sound field algorithm with digital signal processing (DSP) in a frequency range above the first crossover point and below a second crossover point as well as with acoustic processing combined with the DSP in the frequency range above the second crossover point.

Item 2. The method of item 1, wherein the tweeter unit can be configured as a tweeter combination structure comprising at least three tweeters, wherein high-frequency audio fed as at least three audio chains up-mixed from the left channel input and the right channel input into the at least three tweeters, correspondingly.

Item 3. The method of item 1 or 2, wherein the at least three audio chains comprise at least one left audio chain and at least one right audio chain, and wherein the DSP comprises down-mixing the left channel input and the inverted right channel input into at least one left audio chain, and down-mixing the right channel input and the inverted left channel input into the at least one right audio chain.

Item 4. The method of any of items 1-3, wherein the at least three audio chains comprise a center audio chain which is down mixed by the left channel input and the right channel input.

Item 5. The method of any of items 1-4, wherein the first crossover point is set to be the crossover point between the woofer and the tweeter unit, and wherein the second crossover point is set to be the segmented frequency of the tweeter unit.

Item 6. The method of any of items 1-5, wherein the at least three audio chains each may be applied for delays and/or gains, and the delays and/or the gains may be set with different values above and below the second crossover point in each of the at least three audio chains.

Item 7. The method of any of items 1-6, wherein the tweeter unit may be implemented by a horn array.

Item 8. The method of any of items 1-7, wherein the tweeter unit can be configured by arranging number, orientations and shapes of horns in the horn array.

Item 9. The method of any of items 1-8, wherein the tweeter unit may be configured by arranging a full-range speaker, into which the at least three audio chains are fed, respectively, for reproducing the constant sound field.

Item 10. The method of any of items 1-9, wherein the speaker apparatus comprises a waveguide, and the tweeter unit may be designed using sound field simulation tools to design the waveguide, to reproduce the constant sound field.

Item 11: In one or more embodiments, the present inventive subject matter further provides a speaker apparatus for reproducing a constant sound field, comprising:

a woofer configured to reproduce low-frequency audio below a first crossover point from a left channel input and a right channel input; and

a tweeter unit configured to reproduce high-frequency audio with constant frequency responses in all direction;

Item 12. The speaker apparatus of item 11, wherein the tweeter unit further comprises a tweeter combination structure comprising at least three tweeters, wherein high-frequency audio is fed as at least three audio chains up-mixed from the left channel input and the right channel input into the at least three tweeters, correspondingly.

Item 13. The speaker apparatus of item 11 or 12, wherein the at least three audio chains comprise at least one left audio chain and at least one right audio chain, and wherein the DSP comprises down-mixing the left channel input and an inverted right channel input into at least one left audio chain, and down-mixing the right channel input and an inverted left channel input into the at least one right audio chain.

Item 14. The speaker apparatus of any of items 11-13, wherein the at least three audio chains comprise a center audio chain which is down mixed by the left channel input and the right channel input.

Item 15. The speaker apparatus of any of items 11-14, wherein the first crossover point is set to be a crossover point between the woofer and the tweeter unit, and wherein the second crossover point is set to be a segmented frequency of the tweeter unit.

Item 16. The speaker apparatus of any of items 11-15, wherein the at least three audio chains each may be applied for delays and/or gains, and the delays and/or the gains may be set with different values above and below the second crossover point in each of the at least three audio chains.

Item 17. The speaker apparatus of any of items 11-16, wherein the tweeter unit may be implemented by a horn array.

Item 18. The speaker apparatus of any of items 11-17, wherein the tweeter unit can be configured by arranging number, orientations and shapes of horns in the horn array.

Item 19. The speaker apparatus of any of items 11-18, wherein the tweeter unit may be configured by arranging a full-range speaker, into which the at least three audio chains are fed, respectively, for reproducing the constant sound field.

Item 20. The speaker apparatus of any of items 11-19, wherein the speaker apparatus comprises a waveguide, and the tweeter unit may be designed using sound field simulation tools to design the waveguide, to reproduce the constant sound field.

Claims

A method for reproducing a constant sound field, comprising steps of:

reproducing, via a woofer, low-frequency audio below a first crossover point from a left channel input and a right channel input; and

reproducing, via a tweeter unit, high-frequency audio above the first crossover point with constant frequency responses in all direction;

wherein the tweeter unit may be configured to reproduce a constant sound field using a constant sound field algorithm with digital signal processing (DSP) in a frequency range above the first crossover point and below a second crossover point as well as with acoustic processing combined with the DSP in the frequency range above the second crossover point.
The method of claim 1, wherein the tweeter unit can be configured as a tweeter combination structure comprising at least three tweeters, wherein high-frequency audio fed as at least three audio chains up-mixed from the left channel input and the right channel input into the at least three tweeters, correspondingly.
The method of claim 2, wherein the at least three audio chains comprise at least one left audio chain and at least one right audio chain, and wherein the DSP comprises down-mixing the left channel input and the inverted right channel input into at least one left audio chain, and down-mixing the right channel input and the inverted left channel input into the at least one right audio chain.
The method of claim 2, wherein the at least three audio chains comprise a center audio chain which is down mixed by the left channel input and the right channel input.
The method of claim 1, wherein the first crossover point is set to be the crossover point between the woofer and the tweeter unit, and wherein the second crossover point is set to be the segmented frequency of the tweeter unit.
The method of any of claims 1-5, wherein the at least three audio chains each may be applied for delays and/or gains, and the delays and/or the gains may be set with different values above and below the second crossover point in each of the at least three audio chains.
The method of claim 2, wherein the tweeter unit may be implemented by a horn array.
The method of claim 7, wherein the tweeter unit can be configured by arranging number, orientations and shapes of horns in the horn array.
The method of claim 1, wherein the tweeter unit may be configured by arranging a full-range speaker, into which the at least three audio chains are fed, respectively, for reproducing the constant sound field.
The method of claim 1, wherein the speaker apparatus comprises a waveguide, and the tweeter unit may be designed using sound field simulation tools to design the waveguide, to reproduce the constant sound field.
A speaker apparatus for reproducing a constant sound field, comprising:

a woofer configured to reproduce low-frequency audio below a first crossover point from a left channel input and a right channel input; and

a tweeter unit configured to reproduce high-frequency audio with constant frequency responses in all direction;

wherein the tweeter unit may be configured to reproduce a constant sound field using a constant sound field algorithm with digital signal processing (DSP) in a frequency range above the first crossover point and below a second crossover point as well as with acoustic processing combined with the DSP in the frequency range above the second crossover point.
The speaker apparatus of claim 11, wherein the tweeter unit further comprises a tweeter combination structure comprising at least three tweeters, wherein high-frequency audio is fed as at least three audio chains up-mixed from the left channel input and the right channel input into the at least three tweeters, correspondingly.
The speaker apparatus of claim 12, wherein the at least three audio chains comprise at least one left audio chain and at least one right audio chain, and wherein the DSP comprises down-mixing the left channel input and an inverted right channel input into at least one left audio chain, and down-mixing the right channel input and an inverted left channel input into the at least one right audio chain.
The speaker apparatus of claim 12, wherein the at least three audio chains comprise a center audio chain which is down mixed by the left channel input and the right channel input.
The speaker apparatus of claim 11, wherein the first crossover point is set to be a crossover point between the woofer and the tweeter unit, and wherein the second crossover point is set to be a segmented frequency of the tweeter unit.
The speaker apparatus of claim 11-15, wherein the at least three audio chains each may be applied for delays and/or gains, and the delays and/or the gains may be set with different values above and below the second crossover point in each of the at least three audio chains.
The speaker apparatus of claim 12, wherein the tweeter unit may be implemented by a horn array.
The speaker apparatus of claim 17, wherein the tweeter unit can be configured by arranging number, orientations and shapes of horns in the horn array.
The speaker apparatus of claim 11, wherein the tweeter unit may be configured by arranging a full-range speaker, into which the at least three audio chains are fed, respectively, for reproducing the constant sound field.
The speaker apparatus of claim 11, wherein the speaker apparatus comprises a waveguide, and the tweeter unit may be designed using sound field simulation tools to design the waveguide, to reproduce the constant sound field.