Classifications

• • 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
  • H04R3/04—Circuits for transducers for correcting frequency response

Definitions

• the present invention relates to the field of analog signal amplifiers, and in particular the field of audio amplifiers.
• the biasing point of the transistors or output electron tubes and the amplitude of the input signal are such that the entire signal is included in the portion between the cut-off zone and the saturation zone.
• the amplifier operates in the linear region of the transistor and the output signal is linearly proportional to the input signal. The point of rest is usually placed halfway between the cut-off and the saturation.
• Class A amplifiers exhibit low distortion and high fidelity, but the power consumption is high due to the need for a bias voltage even in the absence of a signal. Due to the existence of a significant quiescent current, the power of such amplifiers is generally limited, and the problems of heating and heat removal are important. They require because of the high consumption a powerful and bulky power supply.
• Class B amplifiers the positive and negative portions of the input signal are separately amplified. As a result, in the absence of a signal, the quiescent current is zero. The consumption of such amplifiers is therefore much lower than that of a class A amplifier, but the mode of operation of the transistors results in larger distortions than for a class A amplifier, especially for weak signals.
• class AB An alternative is class AB.
• the power stage is close to that of a class B amplifier, but a non-zero bias current is applied to reduce the distortion occurring for weak signals.
• the efficiency of such amplifiers is relatively low.
• Counter-feedback circuits can take many forms. There are global counter-reactions that act on all gain stages and "local" counter-reactions that occur at a single stage at a single gain stage. These counter-reactions can work on the current or the voltage of the signal.
• One of the aims of the present invention is to provide an improved amplifier having a low distortion rate with a class AB mounting, and taking into account possible defects in the output load, in particular the loudspeaker, and the listening environment.
• the prior art also knows velocity bridges or Voigt type speed bridges.
• This type of bridge of the prior art is shown in Figure 1, but has never been used in the design of amplified speakers.
• This type of speed bridge has the characteristic of transforming the speed of a membrane into an electrical voltage.
• One of the objects of the present invention is therefore to provide a particularly powerful amplified loudspeaker, the latter being made from an amplifier comprising a bridge type Voigt or specific speed bridge.
• the invention relates, in its most general sense, to an acoustic enclosure comprising at least one loudspeaker and associated with at least one class AB analog amplifier, said amplifier comprising a speed bridge circuit comprising means said negative feedback means comprising a voltage feedback and a current feedback, said current feedback consisting in part of said loudspeaker, the ratio of voltage feedback and the feedback current being predetermined, the enclosure further comprising a filter for linearizing the response of said enclosure at the output of said amplifier, as a function of said feedback ratio in voltage and current.
• the current feedback signal takes into account the motional impedance of said circuit output load.
• the ratio between the voltage feedback signal and the current feedback signal is between 0.4 and 0.5.
• FIG. 1 represents the class AB amplifier according to the invention comprising the Voigt type velocity bridge
• FIG. 2 represents an example of linearization filters of the frequency response of the enclosure according to the invention.
• the present invention comprises, in a first aspect, an analog amplifier of the Voigt type.
• an analog amplifier of the Voigt type In particular, the following notations are used in the figure:
• Rm and Rt constitute the voltage feedback; Rm mass side, Rt output side (S)
• Rv resistance connecting the common point of Rm and Rt to e-.
• Rc resistance connecting e- to the common point of Rsh and Zhp.
• A gain in open loop.
• G gain with feedback.
• Zhp is the impedance of the loudspeaker
• the velocity Vmb of the speaker diaphragm is proportional to the potential difference Ut-Uc, according to the relation:
• the present arrangement consists of taking the feedback signal by means of a voltage divider (Rv and Rc) connected to the points T (Ut) and C (Uc) brought back to the value ⁇ .
• the operation of the differential amplifier is such that
• the amplifier then operates as a voltage generator. ⁇ / Rm + Rt
• the amplifier operates as a voltage generator, according to Thévenin's model, with a very low internal resistance thanks to the feedback.
• the parameter ⁇ therefore defines the ratio between the voltage feedback and the current feedback.
• the internal resistance of the amplifier or the damping factor (Zhp / Zs) make it possible to correct the overvoltage factor Qt of the loudspeaker and loudspeaker.
• a decrease in Qt is therefore caused by a decrease in Zs, which amounts to decreasing Rb, or by increasing the damping factor.
• an increase in the overvoltage factor Qt is caused for an increase in Zs or a decrease in the damping factor.
• This adaptation is achieved by filtering at the output of the amplifier to linearize the frequency response of the enclosure by compensating for variations in the motional impedance.
• the emotional impedance reflects the variations of the environment of the speaker.
• the speaker is developed in an ideal listening environment.
• FIG. 2 Illustrated in FIG. 2, use is made, for example, of an acute / medium filter as defined in FIG. 2B, and a serious filter as defined in FIG. 2A.
• the acute filter illustrated in FIG. 2B comprises a capacitor 6 of 3.3 ⁇ F in series, a self 8 of 0.33 mH at ground, a capacitor 7 of 4.7 ⁇ F in series, a self-reactor 9 of 0.33 mH to ground, and a resistance of 5.6 Ohms in series.
• the severe filter illustrated in FIG. 2A preferably comprises a 1 mH inductor 1 in series, a series plug consisting of a resistor 2 of 8.2 Ohms, a self-reactor 3 of 2.2 mH and a capacitor 4. of 10 ⁇ F.
• the voltage bridge with double voltage and current feedback according to the invention can be used in an amplified enclosure.
• a splitter filter is used to orient the high frequencies upwards. speaker and bass frequencies to the bass speaker.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Amplifiers (AREA)
• Circuit For Audible Band Transducer (AREA)

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Publications (1)

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• 2005
  • 2005-04-05 FR FR0503358A patent/FR2884077B1/fr not_active Expired - Fee Related
• 2006
  • 2006-04-05 EP EP06743637A patent/EP1878302A2/de not_active Withdrawn
  • 2006-04-05 WO PCT/FR2006/000752 patent/WO2006106231A2/fr not_active Ceased

Non-Patent Citations (1)

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