US 4,396,799 AGranted

Combination of a loudspeaking telephone set and a hand set for soft speaking

AssigneeU.S. Philips Corporation

InventorsKlaas R. Franzen, Gijsbert W. Versteeg, Cornelis M. A. Theunisse

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Abstract

Loudspeaking telephone set having a hand set connected thereto for soft speaking. When the hand set is placed on the telephone set, the microphone and the loudspeaker being in the switched-on condition, there is a risk that oscillations or singing will occur due to acoustic feedback. In order to avoid this risk, the hand set is provided with an ultrasonic transmitting device and the telephone set is provided with an ultrasonic receiving device 13. The receiving device comprises means to determine the propagation time of the ultrasonic signals and means for affecting the gain of the loudspeaking channel of the telephone set in dependence on the propagation time.

Claims6

Dependent claims

A combination of a loudspeaking telephone set and a handset having a microphone and a receiver connected thereto, the loudspeaking telephone set including a loudspeaking channel and a loudspeaker connected thereto,

said combination telephone set further comprising an ultrasonic transmitting device for transmitting ultrasonic pulses in free space, an ultrasonic receiving device for receiving ultrasonic pulses from free space, said ultrasonic transmitting device comprising an ultrasonic transducer and said ultrasonic receiving device comprising an ultrasonic transducer, one of said transducers being incorporated in the handset and the other transducer in the loudspeaking telephone set, means in said receiving device for determining the propagation time of the ultrasonic pulses between said handset and said loudspeaking telephone set, and means for controlling the gain of the loudspeaking channel based upon said propagation time.

Dependencies are inferred from the claim text.