Abstract: 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.

Abstract: 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.

Abstract: An audible alert device determines the effect of environmental factors upon the output sound pressure level of a transducer and establishes drive signal parameters adapted to the current operating environment. The drive signal parameters are based upon supply voltage, ambient temperature and/or resonant frequency. The drive signal is optionally a pulse width modulated signal for which the drive signal parameters represent the frequency and duty-cycle of the drive signal pulses. The audible alert device generates the drive signal using the drive signal parameters and delivers it to the transducer thereby controlling the output sound pressure level.

Abstract: A multi-tone vehicle motion alarm is provided as an augmentation of a single-tone alarm by imbedding in the alarm sound a plurality band-limited single-tone acoustic signals of different frequencies that are emitted in pulsed synchronism so that the warning signal is emitted in a form that allows directionality of the source to be determined by those around the alarmed equipment. This functional extension preserves many of the familiar aspects of existing alarms. Further, limiting the frequency band of the alarm reduces useless noise in the worksite. The preferred embodiment emits a pulsating tone alarm consisting of two discrete and identifiable monotones. The alarm is an extension of widely recognized pulsating reverse warning sounds. Additional tones may be employed to aid in the speed with which the sound source can be located with human hearing.