Patent ID: 9527439
Filing Date: 2016-12-27
CPC Classification: B06B,B60Q,G08B,G08G,G10K

Claim Text:
1. A multi-frequency alarm to generate a narrow band noise warning of a presence of a vehicle, comprising: noise signal circuitry generating a pseudorandom bit stream at an output bit rate and bit length to produce a noise signal that exhibits a multi-frequency spectrum; an active low-pass filter receiving the noise signal and producing a narrow band noise signal, the active low-pass filter configured to establish for the narrow band noise signal spectral characteristics exhibiting, at about 4 kHz, a high-frequency noise signal magnitude roll-off that attenuates frequencies greater than 4 kHz; an audio amplifier producing an amplified narrow band noise signal corresponding to the narrow band noise signal; and an audio speaker responsive to the amplified narrow band noise signal and configured to emit narrow band noise sound derived from the narrow band noise signal.