MULTI-FREQUENCY ALARM FOR EMITTING NARROW BAND NOISE

摘要

A multi-frequency alarm (10) generates a narrow band noise (MFA-87, -97, 102, -107) warning of a presence of a vehicle. The alarm includes noise signal circuitry (30) generating a pseudorandom bit stream to produce a noise signal that exhibits a multi-frequency spectrum; an active low-pass filter (40) 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 a high-frequency noise signal magnitude roll-off that attenuates frequencies greater than 4 kHz; an audio amplifier (50) producing an amplified narrow band noise signal; and an audio speaker (60) responsive to the amplified narrow band noise signal and configured to emit narrow band noise sound derived from the narrow band noise signal.

主权项

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.