Debris blower with sound attenuation resonator
A blower apparatus includes a fan and motor generating an airflow from an inlet end to an outlet end of the debris blower. The airflow defines an airflow axis and a cross-sectional plane normal to the airflow axis. An enclosure provides an airflow path towards the outlet end. A resonant chamber is proximate an airflow entrance end of the enclosure. The resonant chamber has first and second sections encompassing corresponding first and second volumes of different sizes. The different sizes are selected to form an acoustic resonator. The acoustic resonator attenuates noise from the blower over a selected attenuation frequency range.
1 . A debris blower, comprising:
an axially-arranged fan and motor together configured to generate an airflow from an inlet end to an outlet end of the debris blower, the airflow defining an airflow axis and a cross-sectional plane normal to the airflow axis;
a motor enclosure configured to both secure the motor to a housing of the debris blower and provide an airflow path around the motor; and
a resonant chamber proximate an airflow entrance end of the motor enclosure, the resonant chamber partially surrounding the motor enclosure, wherein the resonant chamber comprises first and second sections encompassing corresponding first and second volumes of different sizes, the different sizes selected to form an acoustic resonator configured to attenuate noise generated by the debris blower.
2 . The debris blower of claim 1 , further comprising:
an inlet grate proximate the airflow entrance end; and
a wall member that protrudes from the inlet grate towards the fan and motor, the wall member separating the first and second sections.
3 . The debris blower of claim 2 , wherein the wall member comprises a semicircular shape.
4 . The debris blower of claim 2 , wherein the wall member comprises major surfaces that are aligned with an airflow direction in the resonant chamber.
5 . The debris blower of claim 1 , wherein the airflow entrance end of the motor enclosure protrudes into the resonant chamber to define the first volume.
6 . The debris blower of claim 1 , further comprising a blower inlet section having a first end coupled to the second section of the resonant chamber, the resonant chamber having a larger cross-sectional area projected on the cross-sectional plane than that of the blower inlet section at the first end.
7 . The debris blower of claim 6 , wherein the blower inlet section comprises a second acoustic resonator with an open end facing an inlet duct of the resonant chamber.
8 . The debris blower of claim 1 , wherein the motor enclosure protrudes into the resonant chamber such that the first volume surrounds part of the motor enclosure and the second volume abuts the airflow entrance end of the motor enclosure, wherein the first volume comprises a circular annulus, and wherein the second volume comprises a cylinder.
9 . The debris blower of claim 8 , wherein the resonant chamber further comprises a third section located at an airflow inlet end of the resonant chamber opposed to the motor enclosure, the third section encompassing a circular annular volume.
10 . The debris blower of claim 1 , wherein the first and second volumes are centered relative to each other.
11 . The debris blower of claim 1 , further comprising a sound dampening foam applied to an inner surface of at least one of the inlet end, the outlet end, and the resonant chamber.
12 . The debris blower of claim 1 , wherein the acoustic resonator attenuates noise above 1 kHz.
13 . The debris blower of claim 1 , wherein the acoustic resonator attenuates fan tip noise of the blower.
14 . The debris blower of claim 1 , wherein the acoustic resonator comprises a quarter-wave generator or a Helmholz resonator.
15 . The debris blower of claim 1 , wherein the motor comprises an electric motor.
16 . The debris blower of claim 1 , wherein the acoustic resonator is located between the fan and an operator of the debris blower, the acoustic resonator attenuating noise from the blower transmitted to the operator.
17 . A method, comprising:
forcing air from an inlet end to an outlet end of a debris blower via an axially-arranged fan and motor; and
attenuating noise generated by the debris blower via an acoustic resonator that at least partially encloses an airflow entrance end of a motor enclosure, the motor enclosure securing the motor to a housing of the debris blower, the acoustic resonator partially surrounding the motor enclosure, and the acoustic resonator comprising first and second sections encompassing corresponding first and second volumes of different sizes selected to form the acoustic resonator.
18 . The method of claim 17 , further comprising attenuating the noise via a second acoustic resonator with an open end facing an inlet duct of the acoustic resonator.
19 . The method of claim 17 , further comprising attenuating the noise via a third section located at an airflow inlet end of the acoustic resonator opposed to the motor enclosure, the third section encompassing an annular volume.
20 . The method of claim 17 , further comprising attenuating the noise via a wall member that protrudes from an inlet grate towards the fan and motor, the wall member separating the first and second sections.