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 expanded sound stage

[0001] The present invention relates to sound reproduction equipment, 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 loudspeakers oriented to diffuse in opposite directions and each following a direction defining an angle between 25° and 155° relative to the main direction; and

[0006] - an information processing unit for combining the 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 make it possible to reproduce stereo sound 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 the recording studio when creating the content.

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

[0010] "Stereo" speakers intended for use alone are designed to reproduce stereo sound from two loudspeakers, or a group of loudspeakers, positioned in the same cavity of an enclosure. They cannot therefore be correctly positioned relative to each other.

[0011] These speakers 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 stage width effect in the case where the speakers or groups of loudspeakers reproducing the right and left channels are close together and oriented towards the listener; and

[0014] - a loss of extreme treble 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 "Bulder" of 1 / 89 on page 10.

[0016] From the stereo channels, it creates by matrixing three loudspeaker signals, a first signal C for a central loudspeaker formed from the sum C = L + R of the left L and right R channels; and two lateral loudspeaker signals SL and SR for two loudspeakers oriented in opposite directions along the same axis perpendicular to that of the central loudspeaker, namely a left loudspeaker signal SL = L - R formed from the reduced left channel of the right channel and a right loudspeaker signal SR = R - L formed from the reduced right channel of 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 aim of the invention is to propose sound reproduction equipment which, from loudspeakers arranged in the same enclosure and a stereophonic input signal, makes it possible to produce, for the user, a wide sound scene, with significant precision in the location of sound sources and a frequency response free from interference.

[0019] To this end, the invention relates to sound reproduction equipment of the aforementioned type, characterized in that the processing unit is capable of addressing:

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

[0021] - to the right speaker, a signal whose majority component is the signal decorrelated right excitation equal to the difference of the right channel and the central signal; and

[0022] - to the left loudspeaker, a signal whose majority component is a signal decorrelated left excitation equal to the difference of the left channel and the central signal.

[0023] Depending on the particular embodiments, 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 decorrelated right excitation signal equal to the difference of the right channel and the central signal and a minority component formed by the decorrelated left excitation signal equal to the difference of the left channel and the central signal

[0027] - at the right loudspeaker, a minority component formed from the excitation signal left decorrelated equal to the difference of the left channel and the central 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 minority component formed from the excitation signal decorrelated right equal to the difference of 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 has two central loudspeakers diffusing in opposite directions following the main direction,

[0031] and the processing unit is capable of addressing to the two central loudspeakers the excitation signal whose majority 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 description which follows, given solely by way of example and with reference to the drawings in which:

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

[0034] - [Fig.2] [Fig.2] is a perspective view of sound reproduction equipment according to the invention 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.l] is adapted to be connected to a source 12 of stereophonic signals through a right input 14 for a right channel denoted R and a left input 16 for a left channel denoted L.

[0037] The sound reproduction equipment comprises an enclosure 20 delimiting a box in which several loudspeakers are arranged immobilized in position relative to each other.

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

[0039] More generally, the axes of the right and left loudspeakers 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 mean 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' / Î^T- ) where |j • || denotes the norm and | • | the absolute value.

[0042] Alternatively, the loudspeakers 24 and 26 are replaced by groups of right and left side loudspeakers each by group, each group being supplied by the same loudspeaker signal.

[0043] The enclosure further comprises a central loudspeaker 28 or a group of central loudspeakers 28 whose diffusion axis delimits with the diffusion axes of the lateral loudspeakers substantially equal angles. Thus, the diffusion axis of the central loudspeaker is arranged substantially along the bisector of the angle delimited by the diffusion axes of the lateral loudspeakers 24 and 26 when the diffusion axes are coplanar.

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

[0045] The diffusion directions of the side loudspeakers 24, 26 each define with the diffusion direction of the or each central loudspeaker 28 an angle of 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 central coaxial loudspeakers 28 arranged with their diffusion directions opposite.

[0047] As a variant of the embodiment described with reference to [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 is advantageously coincident with one of the diffusion axes of the lateral loudspeakers or is angularly offset by an angle of between 25° and 155° and advantageously between 70° and 110° and even more preferably close to 90°.

[0048] The sound reproduction equipment comprises a conditioner 30 formed from an information processing unit capable of ensuring the processing described below.

[0049] The conditioner comprises an extraction stage 36 capable of producing, from the right R and left L channels received from the 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 capable of providing a correlation function. Alternatively, the stage 36 implements an algorithm for calculating the central 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 Vickers1,1 STMi- croelectronics, Santa Clara, CA 95054, earl.vickers@st.com.

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

[0052] These conditioned signals are received at the input of a distributor 50 capable of further receiving 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 right R' and left L' decorrelated channels, the central channel C.

[0054] The distributor has three outputs for excitation signals from the three loudspeakers and in particular right SR- and left SL' excitation signals for the right and left loudspeakers 24 and 26 respectively, a front central excitation signal denoted Sc for the central loudspeakers 28.

[0055] The sound reproduction equipment finally comprises three amplifiers 54, 56, 58 for the loudspeaker signals Sr-, SL' and Sc.

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

[0057] The distributor 50 is capable of 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] The matrix Ma is used for the combination of the conditioned channels for the frequencies lower than a reference frequency fref while the matrix Mb is implemented by the signals of frequencies higher than this reference frequency fref. The reference frequency frefest comprised between 100 Hz and 1000 Hz and preferably substantially equal to 500 Hz.

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

[0061] For Ma: / / / le Ir \ [L'\ cl cc cr C = Sc \ ri rc rr / \R'l \SrJ

[0062] ForMb: / 10(v ISL,\ 0 1 0 C = sc 10 0 1 / \R'! \sj

[0063] Thus, these matrices are such that for frequencies higher than 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 lower than fref, the excitation signals are defined by applying the matrix Ma which ensures that each excitation signal is formed mainly from the corresponding channel and in a minority from the other two channels.

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

[0066] For the purposes of the application, the term majority component in a signal means a component representing more than 50% of the signal and the term minority component means 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 minority component of the left decorrelated channel L' = L - C and a minority component of the right decorrelated 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 horn relationship 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 reduced 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 an enclosure of a generally cylindrical shape with a horizontal axis. The cylinder has a flat 202 forming a foot allowing it to be stationed in a stable position with its horizontal axis.

[0072] On the end side faces, the enclosure comprises two passive radiators 204.

[0073] On its side wall, the enclosure comprises two lateral loudspeakers 224, 226 arranged in the same transverse plane of the cylinder passing through the axis of the cylinder and a center speaker 228 placed in the middle position.

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

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

[0076] Under these conditions, the diffusion directions of the two lateral loudspeakers 224, 226 are angularly offset relative to the diffusion direction of the central loudspeaker 228 by 73.9°.

Claims

Claims

1. Sound reproduction equipment (10) comprising: - an input (14, 16) for a stereophonic signal with a right channel (R) and a left channel (L); - an enclosure (20; 200) with: - at least one central loudspeaker (28; 228) diffusing in a main direction; and - at least two lateral loudspeakers (24, 26; 224, 226) oriented to diffuse in opposite directions and each in a direction defining an angle of between 25° and 155° relative 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 (Sæ, Sc, SL), characterized in that the processing unit (30, 50) is capable of addressing: - the or each central loudspeaker (28;228), an excitation signal (Sc) whose majority component is a central signal (C) formed from information common to the right (R) and left (L) channels; - to the right loudspeaker (24; 224), a signal whose majority component is the decorrelated right excitation signal (R') equal to the difference of the right channel (R) and the central signal (C); and - to the left loudspeaker (26; 226), a signal whose majority component is a decorrelated left excitation signal (L') equal to the difference of the left channel (L) and the central 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 or each central loudspeaker (28; 228), a minority component formed from the decorrelated right excitation signal (R') equal to the difference of the right channel (R) and the central signal (C) and a minority component formed from the decorrelated left excitation signal (L') equal to the difference of the left channel (L) and the central signal (C); - to the right loudspeaker (24; 224), a minority component formed from the decorrelated left excitation signal (L') equal to the difference of the channel left (L) and the central signal (C) and a minority component formed from the central signal (C) equal to the correlation of the right (R) and left (L) channels; and - at the left loudspeaker (26; 226), a minority component formed from the decorrelated right excitation signal (R') equal to the difference of the right channel (R) and the central signal (C) and a minority component formed from the central signal (C) equal to the correlation of 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 capable of addressing to the two central loudspeakers (28; 228), the excitation signal (Sc) whose majority component is a central signal (C) equal to the correlation of the right (R) and left (L) channels.

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