Device for Electronically Generating the Radiation Effects Produced by a Rotary Loudspeaker

The invention relates to a device for electronically generating the radiation effects produced by a rotary loudspeaker with the aid of a radiator, to which the audio signal is applied both directly and via a delay means with a variable delay which is controlled by a sub-audio frequency generator.

Such a device is known from German Offenlegungsschrift No. 22 61 405. However, this device merely enables the frequency modulation produced by a rotary loudspeaker to be simulated, but the associated amplitude modulation, which is necessarily in synchronism therewith and which is particularly distinct at a rotation frequency of approximately 0.7 Hz for the "chorus" or cathedral effect, is completely absent.

It is an object of the invention to introduce the amplitude modulation into the radiated signal with minimal cost.

According to the invention this is achieved in that two controllable amplifiers are provided, to which the delayed and the undelayed signal are jointly applied, the control input of the one amplifier being connected directly and the control input of the second amplifier via an inverter stage to the output of the subaudio-frequency generator, and the outputs of the two controllable amplifiers each being connected to a loudspeaker or to a loudspeaker combination.

In a further embodiment of a device in accordance with the invention a low-pass filter is included between the subaudio frequency generator and the control inputs of the controllable amplifiers.

Thus, it is achieved that the amplitude modulation at higher modulation frequencies (tremolo) is not as distinct as in the case of the chorus effect.

The invention will now be described in more detail with reference to the drawing.

The audio signal source LF is connected to the inputs 1 of the controllable amplifiers V.sub.1 and V.sub.2 and to the input 1 of a delay means DL with a variable delay time. The output 0 of said delay means DL is also connected to the inputs 1 of the controllable amplifiers V.sub.1 and V.sub.2.

A subaudio-frequency generator G is connected to the control input C of the delay means DL and via the low-pass filter, which in the present instance consists of a resistor R and a capacitor C, to the control input of the controllable amplifier V.sub.1 and via an inverter stage I, which in the present example takes the form of a 180.degree. phase shifter, to the control input 1 of the controllable amplifier V.sub.2. The outputs of the controllable amplifiers V.sub.1 and V.sub.2 are each connected to a sound radiator, which in the present example consists of one loudspeaker L.sub.1 and L.sub.2 respectively.

The operation is as follows:

Via the controllable amplifiers V.sub.1 and V.sub.2 the signals from the audio signal source LF are applied directly to the loudspeakers L.sub.1 and L.sub.2 respectively, and to the delay means DL. The audio signal arrives at the output 0 after a certain delay and thus also at the inputs 1 of the controllable amplifiers V.sub.1 and V.sub.2. The delay time is sinusoidally varied by the preferably sinusoidal voltage of the subaudio-frequency generator G, so that the audio signal at the output 0 of the delay means DL is sinusoidally modulated in frequency. In synchronism with this frequency modulation the signal is amplitude modulated in phase opposition in the controllable amplifiers V.sub.1 and V.sub.2, so that at the output of the amplifiers V.sub.1 and V.sub.2 an amplitude-modulated undelayed signal and a synchronous frequency and amplitude modulated delayed signal are obtained, and radiated as a sound signal by the loudspeakers L.sub.1 and L.sub.2.

When the cross-over point of the low-pass filter RC is selected at approximately 1 Hz, the maximum amplitude modulation and change of the apparent location of the sound source are obtained with a modulation frequency of 0.7 Hz, resulting in a very pleasant chorus effect. At the normal tremolo frequency of 6 to 7 Hz the amplitude modulation is less distinct, which in the present example is obtained by means of the low-pass filter.