EP1135966A2 - Dispositifs acoustiques - Google Patents

Dispositifs acoustiques

Info

Publication number
EP1135966A2
EP1135966A2 EP99958342A EP99958342A EP1135966A2 EP 1135966 A2 EP1135966 A2 EP 1135966A2 EP 99958342 A EP99958342 A EP 99958342A EP 99958342 A EP99958342 A EP 99958342A EP 1135966 A2 EP1135966 A2 EP 1135966A2
Authority
EP
European Patent Office
Prior art keywords
exciter
panel
exciters
frequency
loudspeaker according
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.)
Withdrawn
Application number
EP99958342A
Other languages
German (de)
English (en)
Inventor
Graham Bank
Mark Starnes
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
NVF Tech Ltd
Original Assignee
New Transducers Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by New Transducers Ltd filed Critical New Transducers Ltd
Publication of EP1135966A2 publication Critical patent/EP1135966A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R7/00—Diaphragms for electromechanical transducers; Cones
    • H04R7/02—Diaphragms for electromechanical transducers; Cones characterised by the construction
    • H04R7/04—Plane diaphragms
    • H04R7/045—Plane diaphragms using the distributed mode principle, i.e. whereby the acoustic radiation is emanated from uniformly distributed free bending wave vibration induced in a stiff panel and not from pistonic motion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/227—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only  using transducers reproducing the same frequency band
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/26—Spatial arrangements of separate transducers responsive to two or more frequency ranges
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers
    • H04R3/12—Circuits for transducers for distributing signals to two or more loudspeakers
    • H04R3/14—Cross-over networks
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS
    • H04R9/00—Transducers of moving-coil, moving-strip, or moving-wire type
    • H04R9/06—Loudspeakers
    • H04R9/066—Loudspeakers using the principle of inertia

Definitions

  • This invention relates to acoustic devices including a panel -form member relying on bending wave action with a distribution of resonant modes of surface vibration for acoustic operation, and has arisen specifically in relation to panel -form loudspeakers.
  • panel-form loudspeakers are amenable to optimisation as to geometries and bending stiffnesses of the panels concerned, and as to locations of excitation exciters of and for those panels. Even as so optimised, circumstances can arise where, in operation, some frequencies are candidates for variation of their contributions, e.g. troublesome in some way such that reduction, even substantial suppression, of their contributions would be useful. Indeed, one particular example concerns coincidence frequencies that, at least in large panels, result in directional radiation at extreme angles to the panel surface and produce irregularities beyond dimensionally related smoothing effects inherently useful in smaller panels.
  • a bending wave loudspeaker comprising a panel capable of supporting bending waves; a first exciter mounted on the panel for exciting bending waves in the panels to produce an acoustic output, wherein the acoustic output response of the panel driven by said first exciter has an feature at a known frequency; and a second exciter mounted on the panel for exciting bending waves in the panel to produce an acoustic output, wherein the second exciter is arranged such that when the first and second exciters are commonly driven the feature is smoothed.
  • the second exciter may be arranged at a predetermined distance from the first exciter to smooth the feature.
  • the relative phase and gain of the first and second exciters may be controlled; the second exciter may have a filter, attenuator, delay, phase control, signal processing and/or a variable gain control in association with it. Since, in general, it is the relative amplitude and phase of the signals provided to the two exciters that matters, alternatively or additionally a filter, attenuator, delay, phase control, signal processing or variable gain control may be provided in association with the first exciter.
  • the second exciter may be connected in phase or in anti-phase with the first exciter. A combination of any or all these methods may be used.
  • the feature may be a peak, prominence or elevation in the acoustic output (sound pressure level) as a function of frequency for constant excitation voltage.
  • the loudspeaker according to the invention may accordingly have an improved frequency response in that the feature is smoothed.
  • the first and second exciters are preferably connected in phase between common terminals. This is readily done by connecting like exciters the same way round in a series or parallel arrangement; bending waves may then be emitted in phase. Of course, when the exciters are half a wavelength apart at a particular frequency the phase relation at that frequency will cause a desired degree of cancellation to give control and/or smoothing.
  • the first and second exciters would tend to produce destructive interference over a broad frequency range resulting in low output, especially at low frequencies.
  • the first and second exciters may be driven in phase to enhance the acoustic output. Only at the known frequency will the bending waves excited by the two exciters be in anti -phase and hence cancel. Accordingly, the loudspeaker according to the invention can have an improved response at the particular known frequency.
  • the panel may be anisotropic, and have different coincidence frequencies associated with first and second axes.
  • the second exciter may be spaced away from the first exciter along the first axis to smooth the coincidence frequency feature associated with the bending waves along the first axis, and a third exciter may be provided spaced away from the first exciter along the second axis at a distance substantially equal to one half the wave length of the bending waves at the coincidence frequency associated with the second axis.
  • a fourth exciter may be provided; the first, second, third and fourth exciters may define a rectangle on the surface of the panel . Further exciters may be added as required, for example to provide sufficient output power.
  • the exciters may be separate transducers; for example, each exciter may comprise a voice coil fixed to the panel and a magnet assembly arranged for motion relative to the voice coil.
  • the exciter may be inertial, i.e. the magnet assembly need not be fixed to a separate frame, but the force on the panel may react against the inertia of the magnet assembly. If the exciters are driven in phase, some of the parts may be common.
  • the first and second exciter may comprise a single transducer having a coil and a magnet assembly, the coil having a first region contacting the panel (the first exciter) and a second region contacting the panel (the second exciter) , the two positions being spaced apart by one half wavelength of the bending waves at the known frequency.
  • the second exciter may be located close to the first exciter and driven in anti-phase.
  • a bandpass filter may be used so that the second exciter is only driven in a predetermined frequency range around the known frequency.
  • a reduced number of exciters may be arranged to operate at high frequencies well above coincidence, for example in order to reduce interference effects at these frequencies. This may be done by arranging filters in association with the exciters already described so that only one of them operates at higher frequencies. Since this may upset the electrical and mechanical symmetry of the first, second, third etc. exciters, as an alternative one or more further, separate, higher frequency exciters may be provided. The provision of only a single higher frequency exciter may be advantageous to reduce acoustic interference effects at higher frequencies.
  • the low and high frequencies present in a drive signal may be separated by a cross-over circuit or circuits for feeding the higher frequency exciter with frequencies above the cutoff and the other exciters with frequencies below the cutoff.
  • the detailed design of cross -overs is well known in the loudspeaker art; the cross-over may be as sharp as required. The cross-over should not be confused with the bandpass filter mentioned earlier, although the circuitry for each may be combined if convenient.
  • a bending wave loudspeaker comprising a panel capable of supporting bending waves, first and second exciters mounted on the panel for exciting bending waves in the panel to produce an acoustic output, wherein the first and second exciters are spaced apart by a distance of one half wave length at a predetermined frequency, so that when the first and second exciters are commonly driven the acoustic output of the panel is affected at the predetermined frequency.
  • the first and second exciters may be connected in anti -phase to enhance the acoustic output at the predetermined frequency, or in phase to smooth or reduce the acoustic output at that frequency.
  • An enhanced response at a particular frequency is particularly useful for sirens and other acoustic warning devices, where it is only required to produce output at known frequencies.
  • the first and second exciters may be connected in phase. In this case, other features described above with reference to the first aspect of the invention may also be used, if convenient.
  • a method of suppressing an feature in a frequency response of a bending wave loudspeaker having a panel (11) capable of supporting bending waves, and a first exciter (13) mounted on the panel including determining a frequency at which the response of the first exciter on the panel has a feature, providing a second exciter (15) on the panel arranged such that when the first and second exciters (13,15) are commonly driven the feature is smoothed.
  • the second exciter may be provided on the panel at one half of the wavelength of bending waves in the panel at the known frequency.
  • the step of determining the frequency may determine the coincidence frequency associated with a predetermined direction.
  • a panel -form loudspeaker relying on bending wave action with beneficial distribution of resonant modes of vibration has control of at least one frequency in accordance with spacing between at least two exciter means as associated with the panel concerned.
  • Direction of said spacing is also significant.
  • bending waves in a particular direction of spacing between two exciter means are affected at a frequency corresponding to said spacing.
  • Two such frequencies can be suitably affected by different spacings in the same direction, typically to each side of exciter means at an optimised location, or in different directions for frequencies as associated with such different directions.
  • said spacing will be in a corresponding said direction, i.e. parallel with one of length or width sides or axes. Indeed, it is practical to deal with a least one each of frequencies related to length and width of such rectangular loudspeaker panel, whether by additional exciter means respectively spaced relative to optimised location for one exciter means or each relative to a different optimised location for exciter means .
  • optimised locations are used for exciter means
  • optimised exciter locations also having association with said one direction and spacing; further association with additional exciter means at different directions and spacings from the same optimised location of further additional exciter means at spacings meaningful to purposes hereof .
  • Embodiments of this invention affording reduction up to suppression on a selective frequency basis are seen as having particularly useful application to achieving improved acoustic performance relative to the above- mentioned particular problems concerning coincidence frequencies, as will be specifically described and illustrated.
  • Embodiments of this invention affording reinforcement on a selective frequency basis are seen as having particularly useful application where such as a warning siren is required and/or greater loudness or override for messages etc (then feasibly with operation relative to a selected frequency band) .
  • signal components to be affected have directivity in output from loudspeaker panels, embodiments of this invention can be deployed in connection with desired directivity effects, including reducing or emphasising same.
  • Implementations of this invention at least for selective frequency reduction/suppression and involving spaced exciters operating in phase are seen as having some degree of equivalence to larger area excitation, thus possible use of effectively or actually larger area exciter means, then with compensation for inevitable frequency band effects available by way of smaller area exciter means at other locations along with any appropriate pass filtering.
  • Figure 1 is an schematic view of a loudspeaker according to the invention
  • Figure 2 is a plan view of a first embodiment of the invention
  • Figure 3 is a side view of the first embodiment
  • Figure 4 is a graph of acoustic power output at 80° to the perpendicular axis towards the horizontal, using two exciters spaced apart in the horizontal direction, and for comparison using a single exciter
  • Figure 5 is a graph of acoustic power output at 80° to the perpendicular axis towards the vertical axis, using exciters spaced apart in the vertical direction, and for comparison using exciters not so spaced;
  • Figure 6 shows a crossover arrangement of the first embodiment
  • Figure 7 shows an alternative crossover arrangement
  • Figure 8 shows a second embodiment having nine exciters ;
  • Figure 9 shows the crossover arrangement in the second embodiment
  • Figure 10 shows the electrical impedance of the second embodiment ;
  • Figure 11 shows simulated panel displacement for a one-dimensional sample using two exciters;
  • Figure 12 shows simulated panel displacement for the sample of Figure 11 driven with only one exciter
  • Figure 13 shows the on-axis pressure response of the arrangement of Figure 11;
  • Figure 14 shows the sound pressure as a function of angle at 541.7 Hz
  • Figure 15 shows the sound pressure as a function of angle at 2039 Hz
  • Figure 16 shows the sound pressure as a function of angle at 4515 Hz
  • Figure 19 shows a side view of the loudspeaker shown in Figure 18;
  • Figure 20 shows measured results for the panel of Figures 18 and 19 driving one exciter
  • Figure 21 shows measured results for the panel of Figure 18 and 19 driving two exciters.
  • Figure 22 illustrates a further arrangement.
  • v(f, ⁇ , ⁇ ) is the wave velocity, dependant on f
  • FIG. 1 shows a schematic diagram of a loudspeaker according to the invention.
  • a panel 11 has first 13 and second 15 exciters mounted on its surface. Measurements are taken by moving a microphone 17 around a horizontal path 19 to measure the acoustic power response as a function of angle from the centre line 21 perpendicular to the panel .
  • the first exciter 13 is arranged at an optimum exciter location for coupling to resonant bending waves in the panel, as taught in other patents and applications in the name New Exciters limited, such as WO97/09842.
  • the second exciter is spaced away from the first with the aim that the response at extreme angles and associated with coincidence frequencies is smoother.
  • FIG. 2 and 3 shows a specific embodiment of the idea.
  • a rectangular anisotropic panel 11 measuring 1450mm by 1100mm has a 10mm thick core 25 and 0.106mm thick skins 27 made of epoxy loaded with carbon fibres. The skins are attached to the core with 90gsm (grams per square metre) epoxy film 29 loaded on a cotton carrier. Mountings 23 are provided, to support the panel in use.
  • the panel had a bending stiffness B of 184Nm along the first, long axis 35, 71Nm along the second short axis 37, and an areal mass density of 1.92kg/m 2 .
  • the coincidence frequency is the frequency at which the wavespeed in the panel matches that in free air, taken to be 344m/s. Using the above parameters and equation 1 the coincidence frequency associated with waves in the x direction can be calculated to be at 1924Hz. One half wavelength at this frequency is 89.583mm, so the second exciter 15 was mounted at 90mm from the first 13 along the long axis.
  • the two exciters 13,15 only corrects the feature with regard to beaming in the horizontal plane (the x-axis 35) . Beaming can however also occur in the y-axis 37. Since the panel is anisotropic, the coincidence frequency and wavelength of waves along the y-axis is different. The half-wavelength separation at coincidence is calculated in the same way as above to be 54mm. Accordingly, third and fourth exciters 17,19 are provided spaced 54mm from the first and second exciters 13,15 along the y axis. The four exciters form a rectangle. The reason for the use of the rectangle is that it preserves physical symmetry. This in turn makes the mechanical impedance of the exciters substantially equal and so makes the group easier to drive.
  • the loudspeaker according to the invention provides improved response, even on axis, in these realistic conditions.
  • a higher frequency exciter 21 is provided (Figure 2) to operate at high frequencies only.
  • the lower and mid- frequencies, including coincidence, are produced by the first through fourth exciters 13,15,17,19. This frequency range division can reduce undesirable high frequency interference effects caused by multiple driving exciters.
  • the exciters are preferably driven by a cross-over circuit 20 as shown in Fig. 6.
  • the first through fourth exciters are connected between shared common terminals, namely a drive input point 22, and ground 24.
  • the terminals may be connected to a signal source such as an amplifier.
  • the higher frequency exciter 21 is connected in parallel to an inductor L3 and both are connected in series with a capacitor C3 ; this may be driven from the common terminals or from separate terminals.
  • the first through fourth exciters 13,15,17,19 are commonly driven, divided into two parallel pairs in series.
  • This exciter array is connected in series with an inductor L2 , resistor Rl and capacitor C2 in parallel, which provide a weak filter for providing additional control of the frequency response.
  • this weak filter is connected in turn to the input 22 through an inductor LI and to ground 24 through a capacitor Cl, to provide low-pass action.
  • Figure 8 shows a variation of the above embodiment having further exciters.
  • the first through the fourth exciters are as in the previous embodiment.
  • fifth 41 and sixth 43 exciters are provided at good locations for coupling to resonant bending waves in the panel.
  • Seventh 45 and eighth 47 exciters are associated with the fifth and sixth exciters respectively, spaced apart from them along the horizontal axis 35. This is because irregularities due to directionality in the horizontal plane is of much greater significance to listeners than vertical irregularities, and such irregularities can be corrected by horizontal spacing.
  • a ninth exciter 49 is also located spaced away from the fifth exciter in the opposite direction to the seventh exciter at a different spacing along the first axis.
  • the crossover system associated with the full nine- exciter system is shown in Fig. 9. Its calculated or simulated electrical impedance is shown in Figure 10.
  • the resistance drops to a minimum of 8 ohms at between about 12KHz and 500Hz; this is particularly friendly to input signal amplifiers and will readily afford scope for connecting other systems in parallel with the loudspeaker panel 30, if and as desired, and reduces chances of amplifier overload.
  • the cross-over provision actually allows only the fifth exciter 41 to be active for high frequency acoustic output radiation, and is an effective extension of other improvements to high frequency response.
  • the full nine-exciter system of Figure 3 has a beneficially optimising effect as to angularity in acoustic output behaviour and extension of low frequency operation.
  • Measured echoic response is shown graphically in Figure 8 on an on-axis basis together with an extreme 80-degree angle basis.
  • Multiple exciters as used herein offer greater control over directivity, and increase maximum SPL levels and bandwidth. This control is achieved by effectively disabling or causing destructive superposition in relation to selected bending waves in a panel, the frequency region affected being controlled by specific locations of the exciters in the area of the panel, and readily including whatever coincidence frequency or frequencies apply with achieved removal of about lOdB SPL maximum otherwise occurring at extreme angles to the panel surface.
  • Typical loudspeakers of the large size indicated in Figures 1 and 2 often serve as centre channel loudspeakers, perhaps also viewing screens for so-called home-movie or multi -media installations.
  • a four-exciter configuration can be used with all exciters operating on a full-range basis in a series- parallel combination, say to yield a 6 ohm load to a signal supply amplifier.
  • input signal frequencies above the region for cancellation of the effects related to coincidence frequencies could be radiated from the exciters 13 and 15 by connecting a high pass filter across the other exciters, see Figure 7 and capacitor 39. This can produce a higher frequency lift (if required or desired and variable by way of a suitable resistor in series with the capacitor 39) and reduce interference effects at high frequencies that may be audible to a listener walking round the panel .
  • the phases of currents flowing in each of the exciters should change as little as possible, and any necessary compensation should be applied, e.g. a 6 ⁇ F capacitor will result in a 12 -degree current phase shift at 2KHz and that can be equated to a separation spacing reduction of 3mm, which can be compensated by a like increase in the separation spacing between the exciter pairs 13,15 and 17,19 in Figure 2 or 8.
  • Using a series resistor with the capacitor 55 can reduce the compensating change of separation.
  • Figure 11 shows a calculation of panel displacement using two spaced exciters at 71, 73
  • Figure 12 shows as a comparison panel displacement using only one exciter at 71.
  • Both Figures relate to calculations using energy supplied by the exciters at the coincidence frequency.
  • Both these figures are simplified in that the panel is modelled in one length dimension and one perpendicular dimension. Accordingly, some of the complexity of real two-dimensional panels bending to cause displacement in the third dimension is lost. Nevertheless, the results show the large panel displacement at coincidence seen in Fig.12 using only one exciter being substantially cancelled in the arrangement of Fig.11 with two exciters. In the acoustic domain this effect results in a reduction in the sound pressure level at extreme angles to the panel surface at the coincidence frequency. That is because the large panel displacement couples to air to produce sound at extreme angles, and this coincidence effect (often known as beaming) is reduced.
  • FIG. 17 shows the result, again with one and two exciters.
  • the peak at coincidence (around 2000 Hz) is significantly larger with one exciter than with two.
  • the test sample is shown in Figures 18 and 19 and is made of 3.5 mm thick aluminium honeycomb 51 with carbon fibre skins 53 and a vinyl cover 55 stuck to the front face with 50gsm thermoplastic scrim.
  • the panel is a rectangular panel measuring 220mm along the short axis 57 by 440mm along the long axis 59.
  • First and second exciters 61,63 are mounted on the panel; they are each 25mm exciters with a reduced mass ring coupling them to the panel.
  • the first exciter 61 is located at 94mm along the short axis and 195mm along the long axis measured from the nearest corner; the second exciter 63 is mounted 43mm from the first exciter at an angle of 22.5° towards the nearest corner from the direction of the first long axis.
  • Figure 20 shows the acoustic power measurements with this panel driven with the first exciter 61 and Figure 21 shows the results driving both exciters 61, 63. It should be noted that in both of these Figures the data below 200 Hz should be ignored as it is not accurately captured by the measurement equipment. From a comparison of these graphs it can be seen that the peak at the coincidence frequency
  • this panel is sufficiently small in the direction along the short axis (220mm) that coincidence beaming in the direction of this axis is not a significant problem. Accordingly, good results can be obtained using only two exciters.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Multimedia (AREA)
  • Diaphragms For Electromechanical Transducers (AREA)
  • Piezo-Electric Transducers For Audible Bands (AREA)
  • Transducers For Ultrasonic Waves (AREA)
  • Audible-Bandwidth Dynamoelectric Transducers Other Than Pickups (AREA)
  • Circuit For Audible Band Transducer (AREA)

Abstract

L'invention concerne un procédé permettant de réduire les phénomènes intervenant à des fréquences particulières comme les coïncidences. Un panneau (11) comprend des excitateurs (13, 15), disposés pour réduire le phénomène, qui peuvent être attaqués en phase mais qui sont espacés d'une distance sensiblement égale à la moitié de la longueur d'onde des ondes de flexion dans le panneau à la fréquence particulière considérée.
EP99958342A 1998-11-30 1999-11-29 Dispositifs acoustiques Withdrawn EP1135966A2 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB9826164.7A GB9826164D0 (en) 1998-11-30 1998-11-30 Acoustic devices
GB9826164 1998-11-30
PCT/GB1999/003956 WO2000033612A2 (fr) 1998-11-30 1999-11-29 Dispositifs acoustiques

Publications (1)

Publication Number Publication Date
EP1135966A2 true EP1135966A2 (fr) 2001-09-26

Family

ID=10843276

Family Applications (1)

Application Number Title Priority Date Filing Date
EP99958342A Withdrawn EP1135966A2 (fr) 1998-11-30 1999-11-29 Dispositifs acoustiques

Country Status (8)

Country Link
EP (1) EP1135966A2 (fr)
JP (1) JP2002532038A (fr)
CN (1) CN1328762A (fr)
AU (1) AU1571800A (fr)
BR (1) BR9916144A (fr)
GB (1) GB9826164D0 (fr)
TW (1) TW469746B (fr)
WO (1) WO2000033612A2 (fr)

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BR9916144A (pt) 2001-11-06
AU1571800A (en) 2000-06-19
WO2000033612A2 (fr) 2000-06-08
TW469746B (en) 2001-12-21
GB9826164D0 (en) 1999-01-20
CN1328762A (zh) 2001-12-26
WO2000033612A3 (fr) 2000-08-17
JP2002532038A (ja) 2002-09-24

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