Wide soundstage sound reproduction equipment

Abstract

Wide soundstage sound reproduction equipment The sound reproduction equipment (10) comprises: - an input (14) for a stereophonic signal; - a speaker (20) with: - a central loudspeaker (28); and - two side loudspeakers (24, 26) oriented to diffuse in opposite directions and each along a direction defining an angle between 25° and 155° with respect to the main direction of the central loudspeaker (28); and - a processing unit (30, 50) is suitable for sending: - to the central loudspeaker (28), an excitation signal (Sc) whose major component is a central signal (C) formed of the information common to the right (R) and left (L) channels; and – to the right (24) and left (26) loudspeakers, a signal whose major component is the uncorrelated right and left excitation signals (R', L') equal to the difference between the right (R) and left (L) channels and the center signal (C). Figure for the abbreviation: 1

Description

Title of the invention: Sound reproduction equipment with an expanded soundstage

[0001] The present invention relates to a sound reproduction device of the type comprising:

[0002] - an input for a stereophonic signal with a right channel and a left channel;

[0003] - an enclosure with:

[0004] - at least one central loudspeaker diffusing in a main direction; and

[0005] - at least two side speakers oriented to diffuse sound in opposite directions and each following a direction defining an angle between 25° and 155° with respect to the main direction; and

[0006] - an information processing unit for combining right and left signals left and control each speaker with a respective speaker excitation signal.

[0007] Audio content is generally recorded with two sound channels, one right commonly designated by R and the other left commonly designated by L. These two signals allow stereo sound to be reproduced from two speakers.

[0008] In order to benefit from the qualities of this format, the listener must have two speakers and place them in the same way as is done in a recording studio when creating the content.

[0009] Current practice favors listening to music from a single speaker, which is generally "mono". The right and left channels are combined by summing or by a specific algorithm into a single signal called "mono".

[0010] "Stereo" speakers intended for individual use are designed to reproduce stereo sound from two speakers, or groups of speakers, arranged in the same cavity of a speaker. They therefore cannot be correctly positioned relative to each other.

[0011] These enclosures have the following disadvantages:

[0012] - poor accuracy of the correlated content between the right and left signals due to acoustic interference (comb filter) generated by the reproduction of the same content by the two speakers or groups of speakers;

[0013] - a very limited stereo soundstage width effect in the case where the loudspeakers or Speaker groups reproducing the right and left channels are close together and angled towards the listener; and

[0014] - a loss of extreme high frequencies in the case where the loudspeakers or groups of loudspeakers speakers reproducing the right and left channels are not oriented towards the listener.

[0015] A solution was proposed by Reid Woodbury in 1989 in the magazine "Builder" of 1 / 89 on page 10.

[0016] From the stereo channels, it creates by matrixing three speaker signals, a first signal C for a central speaker formed from the sum C = L + R of the left channel L and right channel R; and two side speaker signals SL and SR for two speakers oriented in opposite directions along the same axis perpendicular to that of the central speaker, namely a left speaker signal SL = L - R formed from the left channel reduced from the right channel and a right speaker signal SR = R -L formed from the right channel reduced from the left channel.

[0017] This solution has significant drawbacks and is practically not used, due to interference between channels and poor localization of sources for the listener.

[0018] The invention aims to provide sound reproduction equipment that, using speakers arranged in the same enclosure and a stereophonic input signal, produces a wide soundstage for the user, with high precision in localizing sound sources and a frequency response free from interference.

[0019] To this end, the invention relates to a sound reproduction device of the aforementioned type, characterized in that the processing unit is adapted to address:

[0020] - to the center speaker or each center speaker, an excitation signal whose component majority is a central signal formed from information common to the right and left channels;

[0021] - to the right speaker, a signal whose major component is the signal uncorrelated right excitation equal to the difference between the right channel and the central signal; and

[0022] - to the left speaker, a signal whose majority component is a signal uncorrelated left excitation equal to the difference between the left channel and the central signal.

[0023] Depending on the specific embodiment, the equipment comprises one or more of the following characteristics:

[0024] - the proportion of the majority component in the signal addressed to the loudspeaker is variable depending on the signal frequencies;

[0025] - for at least certain frequencies of the signal, the information processing unit is also suitable for addressing:

[0026] - to the or each central loudspeaker, a minority component formed from the signal The uncorrelated right excitation signal is equal to the difference between the right channel and the central signal, and a minor component is formed from the uncorrelated left excitation signal, equal to the difference between the left channel and the central signal.

[0027] - at the right speaker, a minor component formed from the excitation signal left uncorrelated equals the difference between the left channel and the center signal and a minority component formed from the central signal equal to the correlation of the right and left channels; and

[0028] - at the left speaker, a minor component formed from the excitation signal uncorrelated right equal to the difference between the right channel and the central signal and a minority component formed from the central signal equal to the correlation of the right and left channels;

[0029] - the angle is between 70° and 110°;

[0030] - the enclosure comprises two central loudspeakers diffusing in opposite directions following the main direction,

[0031] and the processing unit is suitable for sending to the two central loudspeakers the excitation signal whose major component is a central signal equal to the correlation of the right and left channels.

[0032] The invention will be better understood upon rereading the following description, given solely by way of example and made with reference to the drawings in which:

[0033] - [Fig. 1] Fig. 1 is a schematic view of a sound reproduction device according to the invention;

[0034] - [Fig.2] Fig.2 is a perspective view of a sound reproduction device according to the invention as seen from the side; and

[0035] - [Fig.3] [Fig.3] is a front view of the sound reproduction equipment of the [Fig.2],

[0036] The sound reproduction equipment 10 illustrated in [Fig.1] is adapted to be connected to a stereophonic signal source 12 through a right input 14 for a right channel marked R and a left input 16 for a left channel marked L.

[0037] The sound reproduction equipment includes a speaker 20 delimiting a box in which several speakers are arranged, fixed in position relative to each other.

[0038] The enclosure comprises two lateral loudspeakers, right 24 and left 26, arranged to emit in opposite directions. Their axes are, for example, coincident and thus define an angle of 180° between them.

[0039] More generally, the axes of the right and left speakers are angularly offset by an angle greater than or equal to fifty degrees.

[0040] The angle between two directions, axes or lines is defined as follows. The angle between two lines defining the diffusion angles of two loudspeakers is understood to be the angle between the direction vectors of these lines, whether or not these lines are sequential.

[0041] Thus, if and are direction vectors of two lines di and d2, then the angle between the two lines is given by 0 = cos 7 [dî* d21 ) where || • || denotes the norm and llRÎM ^11 | • | the absolute value.

[0042] Alternatively, speakers 24 and 26 are replaced by groups of right and left side speakers, each group being powered by the same speaker signal.

[0043] The enclosure further comprises a central loudspeaker 28 or a group of central loudspeakers 28 whose dispersion axis forms substantially equal angles with the dispersion axes of the side loudspeakers. Thus, the dispersion axis of the central loudspeaker is positioned substantially along the bisector of the angle formed by the dispersion axes of the side loudspeakers 24 and 26 when the dispersion axes are coplanar.

[0044] If the axes of the side speakers are coplanar and if the center speaker has an axis not included in the plane of the axes of the side speakers, the axis of the center speaker is such that its orthogonal projection onto the plane of the axes of the side speakers is substantially coincident with the bisector of the axes of the side speakers or reduced to a point. In the latter case, the axis of the center speaker is perpendicular to the plane of the axes of the two side speakers.

[0045] The diffusion directions of the side speakers 24, 26 each define with the diffusion direction of the center speaker or each center speaker 28 an angle between 25° and 155° and preferably between 70° and 110° and even more preferably close to 90°.

[0046] In the embodiment presented, the enclosure 20 comprises two coaxial central loudspeakers 28 arranged with their diffusion directions opposite.

[0047] As an alternative to the embodiment described opposite [Fig. 1], the sound reproduction equipment comprises more than two central loudspeakers 28 arranged in the same plane. The central loudspeakers are distributed angularly around an axis of the sound reproduction equipment, which advantageously coincides with one of the diffusion axes of the lateral loudspeakers or is angularly offset by an angle between 25° and 155° and advantageously between 70° and 110° and even more preferably close to 90°.

[0048] The sound reproduction equipment includes a conditioner 30 consisting of an information processing unit designed to perform the processing described below.

[0049] The conditioner includes an extraction stage 36 suitable for producing, from the right R and left L channels received from inputs 14 and 16, a central channel C formed from the information common to the right R and left L channels.

[0050] The extraction stage 36 is suitable for ensuring a correlation function. Alternatively, the stage 36 implements a calculation algorithm for the center channel C in the frequency domain as described in the article Frequency-Domain Two-to Three-Channel Upmix for Center Channel Derivation and Speech Enhancement, Earl Vickers1, STMicroelectronics, Santa Clara, CA 95054, earl.vickers@st.com.

[0051] The conditioner 30 further comprises two subtractors 44, 46, connected respectively to input 14 to receive the right channel R and to input 16 for the left channel L. On their other inputs, the subtractors 44, 46 receive the same center channel C, so that each subtractor 44, 46 respectively provides the difference between the right channel R and the left channel L and the center channel C. At the output of these subtractors, two uncorrelated right and left channels are obtained, denoted R' = R - C and L' = L - C.

[0052] These conditioned signals are received at the input of a distributor 50 adapted to also receive distribution coefficients stored in a distribution module 52 connected to the distributor 50. The distributor 50 is formed by the same information processing unit as the conditioner 30.

[0053] The distributor 50 has three inputs for the conditioned channels, namely the uncorrelated right channel R' and left channel L', the central channel C.

[0054] The splitter has three outputs for excitation signals of the three loudspeakers and in particular right excitation signals SR- and left excitation signals SL- for the right and left loudspeakers 24 and 26 respectively, a front center excitation signal noted Sc for the center loudspeakers 28.

[0055] The sound reproduction equipment finally includes three amplifiers 54, 56, 58 for the SR-, SL- and Sc speaker signals.

[0056] The outputs of amplifiers 54 and 56 are connected to the side speakers or speaker groups 24 and 26 while the output of amplifier 58 is connected to the center speaker or speaker group 28.

[0057] The distributor 50 is suitable for defining each of the excitation signals as a linear combination of the conditioned channels R', L' and C. The linear application giving the excitation signals of the loudspeakers as a function of the conditioned channels is defined by a matrix Ma or Mb whose coefficients are stored in the distribution module 52.

[0058] Two matrices Ma and Mb are stored.

[0059] Matrix Ma is used for combining conditioned channels for frequencies below a reference frequency fref, while matrix Mb is implemented for signals with frequencies above this reference frequency. fref. The reference frequency frefest is between 100 Hz and 1000 Hz and preferably approximately equal to 500 Hz.

[0060] The matrices Ma and Mb are expressed below.

[0061] For Ma: ' 11 le lr ' lL'\ / SM cl cc cr C = Sc <rl rc rrl xR1! ! Sr1^

[0062] For Mb: (100| IL'X 0 10 c = Sc ho 1 / XR'I ^Sru

[0063] Thus, these matrices are such that for frequencies above fref, the excitation signals SL', Sc, SR' are each equal to the channels L', C and R' respectively by application of the matrix Mb.

[0064] For frequencies below fref, the excitation signals are defined by application of the matrix Ma which ensures that each excitation signal is formed mainly from the corresponding channel and secondarily from the other two channels.

[0065] Thus, the right excitation signal SR', respectively left SL', is formed predominantly of the right uncorrelated channel R' = R - C to which is added a minority component of the left uncorrelated channel L' = L - C and a minority component of the central channel C, respectively of the left uncorrelated channel L' = L - C to which is added a minority component of the right uncorrelated channel R' = R - C and a minority component of the central channel C.

[0066] For the purposes of the application, a major component in a signal is understood to be a component representing more than 50% of the signal and a minor component is understood to be a component representing less than 50% of the signal.

[0067] Thus, the coefficients of the matrix Ma are such that 11 > 21c, 11 > 21r, rr > 2rl and rr > 2rc.

[0068] Similarly, the central excitation signal Sc is formed mainly from the central channel C to which is added a minor component from the left uncorrelated channel L' = L - C and a minor component from the right uncorrelated channel R' = R - C.

[0069] Thus, the coefficients of the matrix Ma are such that cc > 2cl and cc > 2cr.

[0070] It is understood that the diffusion of a central loudspeaker signal formed by the Correlation of the right and left channels or more generally of the information common to the right R and left L channels and the lateral diffusion of the right and left channels diminished by the signal containing the information common to the right R and left L channels makes it possible to avoid interference and this makes it possible to increase the width of the scene perceived by the listener.

[0071] According to an embodiment illustrated in Figures 2 and 3, the sound reproduction equipment 200 comprises a speaker, generally cylindrical in shape with a horizontal axis. The cylinder has a flat section 202 forming a base that allows it to be positioned stably with its horizontal axis.

[0072] On the end lateral faces, the enclosure includes two passive radiators 204.

[0073] On its side wall, the enclosure has two side speakers 224, 226 arranged in the same transverse plane of the cylinder passing through the axis of the cylinder and a central speaker 228 placed in a median position.

[0074] The plane containing the axes of the two lateral loudspeakers are angularly offset by 72° around the axis of the cylinder with respect to the diffusion direction of the central loudspeaker 228 as illustrated in [Fig.2].

[0075] The two side speakers have diffusion directions angularly offset by 52° as illustrated in [Fig.3]

[0076] Under these conditions, the diffusion directions of the two side speakers 224, 226 are angularly offset from the diffusion direction of the center speaker 228 by 73.9°.

Claims

Demands

1. Sound reproduction equipment (10) comprising: - an input (14, 16) for a stereophonic signal with a right channel (R) and a left channel (L); - a speaker (20; 200) with: - at least one center loudspeaker (28; 228) diffusing in a main direction; and - at least two side loudspeakers (24, 26; 224, 226) oriented to diffuse each in a direction defining an angle between 25° and 155° with respect to the main direction; and - an information processing unit (30, 50) for combining the right (R) and left (L) signals and controlling each loudspeaker with a respective loudspeaker excitation signal (SR -, Sc, sL o, characterized in that the processing unit (30, 50) is suitable for addressing: - to the center loudspeaker(s) (28; 228), an excitation signal (Sc) whose major component is a center signal (C) formed from the information common to the right (R) and left (L) channels;- to the right speaker (24; 224), a signal whose majority component is the uncorrelated right excitation signal (R') equal to the difference between the right channel (R) and the center signal (C); and - to the left speaker (26; 226), a signal whose majority component is an uncorrelated left excitation signal (L') equal to the difference between the left channel (L) and the center signal (C).

2. Equipment according to claim 1, characterized in that the proportion of the majority component in the signal addressed to the loudspeaker is variable depending on the frequencies of the signal.

3. Equipment according to claim 1 or 2, characterized in that for at least certain frequencies of the signal, the information processing unit is capable of further addressing: - to the center speaker or each center speaker (28; 228), a minority component formed of the uncorrelated right excitation signal (R') equal to the difference of the right channel (R) and the center signal (C) and a minority component formed of the uncorrelated left excitation signal (L') equal to the difference of the left channel (L) and the center signal (C); - at the right speaker (24; 224), a minority component formed from the uncorrelated left excitation signal (L') equal to the difference of the left channel (L) and the center signal (C) and a minority component formed from the center signal (C) equal to the correlation of the right (R) and left (L) channels; and - at the left speaker (26; 226), a minority component formed from the uncorrelated right excitation signal (R') equal to the difference of the right channel (R) and the center signal (C) and a minority component formed from the center signal (C), formed from the information common to the right (R) and left (L) channels.

4. Equipment (10) according to any one of the preceding claims, characterized in that the angle is between 70° and 110°.

5. Equipment (10) according to any one of the preceding claims, characterized in that the enclosure comprises two central loudspeakers (28; 228) diffusing in opposite directions along the main direction, and in that the processing unit (30, 50) is suitable for addressing to the two central loudspeakers (28; 228), the excitation signal (Sc) the majority component of which is a central signal (C), formed of information common to the right (R) and left (L) channels.

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