CS231682B1 - Connexion for automatic evaluating of resonant frequency of loudspeaker - Google Patents

Abstract

The wiring is designed for automatic speaker resonance frequency evaluation. When connecting the speaker, j amplifier system - speaker oscillates at a resonant frequency that can be expired delays necessary for steady state oscillation meter frequency. Loop the speaker after disconnecting the speaker positive feedbacks open and system returns to the idle state.

Description

The subject of the invention is a circuit for automatic evaluation of the resonant frequency of the speakers.

The measuring method used so far, prescribed according to ČSN 36 8262 / consisting in finding the maximum impedance of the loudspeaker by manual tuning of the generator, is not suitable for band production due to its slowness. More preferably, the method is to provide a positive feedback loop in which the loudspeaker determines the frequency at which the entire system oscillates. The disadvantage is that when the loudspeaker is disconnected, oscillations of undefined amplitude and frequency arise, which is not a malfunction during manual operation of the device, but causes difficulties in automatic evaluation.

The above drawbacks are overcome by the circuitry of the present invention, which is that the feedback resistor is not permanently connected to the amplifier input, but is connected through the relay contacts only when the loudspeaker is connected to the appropriate terminals. Connecting the loudspeaker closes the auxiliary AC circuit, the relay closes and its contact connects the feedback resistance to the amplifier input, so that the whole system oscillates at the resonant frequency of the loudspeaker. When the speaker is disconnected, the relay opens, disconnects the feedback resistor from the amplifier input, and the entire system returns to the idle state. Relay switching is therefore fully automatic, so you only need to connect it to the device to measure and evaluate the resonant frequency of the speaker.

The attached drawing shows the wiring for the automatic resonant frequency evaluation of the loudspeaker. The feedback resistance θρθ ^{2 of} the amplifier output 9 is connected to one terminal

231 882 speaker 1 and at changeover contact 4 relay 14 *

An AC voltage source 8 is connected to the break contact of relay 14 via a resistor 2. The switch contact 6 of relay 14 is connected to the input of relay 9 and simultaneously to the signal input 17 of the frequency evaluation circuits 18 and to the input of the delay circuit 15. connected to the control input 16 of the frequency evaluation circuit 18. A second loudspeaker terminal 1 is connected to a resistor 10, to which the AC amplifier 11 is connected in parallel. This is followed by a transducer 12 and a DC amplifier 13 for switching the relay 14.

The connection according to the invention works in such a way that, after the loudspeaker is connected. to the terminals 2 and 19, an auxiliary circuit powered by an AC power source 8 is closed via the limiting resistor 2 ® of the relay contact 14 and the contact 5, thereby producing a small AC voltage of the order of millivolts at the resistor 10. After amplification by AC amplifier 11, rectification by rectifier 12 and further amplification by DC amplifier 13, this voltage causes the relay 14 to close. whose contacts and 6 close the positive feedback loop. The correct choice of the time constant behind the rectifier is important here. After switching on, relay 14 must be held in this state for a time sufficient to oscillate the loudspeaker 1 - amplifier 9, which is approximately 0.3 sec. Once the oscillation occurs, further holding of the relay 14 is no longer triggered by the auxiliary voltage but by the oscillations of the system until the loudspeaker 1 is disconnected. The reléεχββ relay returns to the idle position when the feedback loop is disconnected, so the entire system is again in the idle state. This is important because it allows the derivation of control signals for the circuit 18 from the fact that, at the input of the amplifier 2 ^e fo Oh no AC. As soon as this voltage exceeds a certain adjustable limit, which occurs almost immediately after the loudspeaker 1 is connected to terminals 2 and 19, a delay circuit 15 consisting of a Schmitt flip-flop and a monostable flip-flop is actuated and over time. sufficient to stabilize the oscillations of the loudspeaker 1, the evaluation circuit 18 is actuated. In order to re-evaluate the resonant frequency, it is then necessary to disconnect and reconnect the loudspeaker, which is in accordance with the measurement requirements of the belt production.

The circuit according to the invention is particularly suitable for use in the field of electroacoustics.

Claims (1)

OBJECT OF THE CLIMBING 231 682 Circuit for automatic evaluation of speaker resonance frequency, characterized in that the feedback resistor (3) is connected from the amplifier output (9) to terminal (2) for connection of one speaker output (1) and simultaneously to changeover contact (4) of relay (14) ) to which an AC voltage source (8) is connected via contact (5) and resistor (7), while relay contact (6) (6) is connected to the amplifier input (9) and simultaneously to the signal input (17) of the circuits to evaluate the frequency (18) and to the input of the delay circuit (15), the output of which is connected to the control input (16) of the frequency evaluation circuit (18), and to the terminal (19) a resistor (10) is connected to which in parallel the AC amplifier (11), the rectifier (12) and the DC amplifier (13) are connected in series for switching the relay (14).