NOISE REDUCTION DEVICE

Abstract

A noise reduction device includes a main tube having a first pass-through area where a fluid enters the main tube, and a side-branch connected to the main tube. The main tube includes a narrowed section having a second pass-through area that is at least 25% (preferably, at least 50%, and more preferably, at least 60%) smaller than the first pass-through area, and the side-branch is connected to the narrowed section of the main tube. Where the side-branch is connected to the main tube, the side-branch is preferably sealed-off by a cover that is acoustically transparent, which may be impermeable for the fluid. Such a noise reduction device is advantageously used in a fluid displacing appliance (e.g. a vacuum cleaner), including a motor for displacing the fluid (e.g. gas or liquid).

Claims

1. A noise reduction device, comprising: a main tube having a first pass-through area where a fluid enters the main tube; and a side-branch connected to the main tube, wherein the main tube comprises a narrowed section having a second pass-through area that is at least 25% smaller than the first pass-through area, the side-branch being connected to the narrowed section of the main tube.

2. The noise reduction device as claimed in claim 1, wherein the second pass-through area is at least 50% smaller than the first pass-through area.

3. The noise reduction device as claimed in claim 2, wherein the second pass-through area is at least 60% smaller than the first pass-through area.

4. The noise reduction device as claimed in claim 1, wherein the side-branch is connected to the main tube, the side-branch is sealed-off by a cover that is acoustically transparent.

5. The noise reduction device as claimed in claim 4, wherein the cover is impermeable for the fluid.

6. A fluid displacing appliance, comprising: a motor for displacing a fluid, and a noise reduction device comprising: a main tube having a first pass-through area where a fluid enters the main tube; and a side-branch connected to the main tube, wherein the main tube comprises a narrowed section having a second pass-through area that is at least 25% smaller than the first pass-through area, the side-branch being connected to the narrowed section of the main tube.

7. The fluid displacing appliance as claimed in claim 6, wherein the side-branch is connected to the narrowed section perpendicularly.

8. The fluid displacing appliance as claimed in claim 6, wherein the side-branch is connected to the main tube, the side-branch is sealed-off by a cover that is acoustically transparent.

9. The fluid displacing appliance as claimed in claim 8, wherein a thickness of the cover is in an order of magnitude of 0.01 mm.

10. The fluid displacing appliance as claimed in claim 8, wherein the cover is impermeable for the fluid.

11. The fluid displacing appliance as claimed in claim 6, wherein the second pass-through area is at least 50% smaller than the first pass-through area.

12. The fluid displacing appliance as claimed in claim 6, wherein the second pass-through area is at least 60% smaller than the first pass-through area.

13. The fluid displacing appliance as claimed in claim 6, wherein the fluid displacing appliance is a vacuum cleaner.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 shows a cross-section of a main tube of an embodiment of a noise reduction device in accordance with the present invention;

[0013] FIG. 2 shows several side-branches connected to a narrowed section of the main tube of FIG. 1;

[0014] FIG. 3 illustrates a connection of a side-branch to a main tube of a preferred embodiment of a noise reduction device in accordance with the present invention;

[0015] FIG. 4 illustrates how a single quarter wave tube can reduce noise by 10 dB over a certain bandwidth; and

[0016] FIG. 5 illustrates how 8 single quarter wave tubes can reduce noise by 10 dB over a certain bandwidth.

DESCRIPTION OF EMBODIMENTS

[0017] FIG. 1 shows a cross-section of a main tube MT of an embodiment of a noise reduction device in accordance with the present invention. A flow direction F of a fluid (liquid, gas) is indicated by an arrow. At an entrance E of the main tube MT, a pass-through area A1 is indicated. The main tube MT has a narrowed section NS, which has a pass-through area A2<A1.

[0018] FIG. 2 shows several side-branches SB connected to the narrowed section NS of the main tube MT of FIG. 1. The side-branches SB have mutually different lengths so as to be tuned to mutually different frequencies of the noise to be reduced. The side-branches SB may be perpendicular to the narrowed section, or at a different angle. The various side-branches SB do not need to have identical widths. The main tube and the various side-branches do not need to have round pass-through areas, so that e.g. a square or oval shape is possible, and they may be curved rather than straight. In this way, it is possible to “hide” the noise reduction device within limited available space imposed by the design of the appliance in which the noise reduction device is to be applied.

[0019] FIG. 3 illustrates a connection of a side-branch SB to the narrowed section NS of the main tube MT of a preferred embodiment of a noise reduction device in accordance with the present invention. A membrane structure M covers the entire opening of the side branch SB. Doing so results in 2 advantages: the fluid flow through the main tube MT is not disturbed by turbulences caused by the presence of the side-branches SB, and the side-branches SB do not collect any dirt that may be present in the fluid, thereby losing their effectiveness as regards noise cancellation. It is advantageous to keep the impedance of the membrane M as low as possible to reach maximum noise cancellation properties. To that end, the membrane M should be thin, having a thickness that is preferably below 0.1 mm, and preferably in the order of magnitude of 0.01 mm, such as provided by plastic used for plastic food bags. A mesh having small holes (e.g. 0.3 mm) appeared to do well as regards not diminishing noise reduction too much, but less well as regards mitigating turbulences in the main tube. This aspect of the invention could also be used in a noise reduction device in which the at least one side-branch is connected to a main tube that is not narrowed.

[0020] FIG. 4 illustrates that a single quarter wave tube tuned to a frequency of about 1100 Hz can reduce noise by 10 dB over a bandwidth of almost 300 Hz (so from about 950 Hz to about 1250 Hz). The horizontal axis shows the frequency in Hz, while the vertical axis shows the noise reduction in dB. FIG. 5 illustrates that 8 single quarter wave tubes tuned to mutually different noise reduction frequencies can together reduce noise by 10 dB over a bandwidth of about 900 Hz (from about 250 Hz to about 1150 Hz). For this purpose, the side-branches SB may have a smaller cross-section area than the pass-through area A2 of the narrowed section NS of the main tube MT. While not shown in FIGS. 4 and 5, the quarter wave tubes also result in noise reduction at odd multiples of the noise reduction frequencies to which they are tuned.

[0021] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. For example, instead of side-branches that are adjacent to one another, side-branches may be nested, i.e. concentric. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. Measures recited in mutually different dependent claims may advantageously be used in combination.