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Old 29th January 2012, 03:46 AM   #1
spazz is offline spazz  United States
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Default Ideas needed - silencing air vent

Hi all-

I have spent too much time trying to find a way to silence an air vent on a very loud, but otherwise very good, air purifier. From 5 ft away, I am getting 65 dB using an android device/app (in a hallway with hard wood floors).

Although some noise is coming off the motor and the intake filter, it is not nearly as bad as the noise coming off the exhaust vent at the top. That would be the thin circular slit at the top of the unit.

The noise profile has a substantial high/mid frequency component, and sounds a lot like white noise.

Initially I was hopeful that dispensing with the top cover of the unit (the panel with the handle bar and the switch and LEDs) would solve the problem, mainly by getting rid of the vent it self. Unfortunately the bottom/internal surface of that panel is an integral component of the fan assembly, where the special geometry of that surface somehow stabilizes the rotating blower fan (although there is no contact at all).

The two general directions I see for this are 1) to place a series sound foam panels on top, parallel to the air flow, in a kind of concentric circle shape, with one circle inside the vent perimeter and one outside or 2) placing the entire unit in a larger cylindrical or box-like structure that would have a lower chamber for the intake and an upper chamber with an exhaust muffler.

Your help is greatly appreciated!




Click the image to open in full size.

Last edited by spazz; 29th January 2012 at 03:53 AM. Reason: attaching img
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Old 29th January 2012, 03:57 AM   #2
scott17 is offline scott17  United States
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I wish I had an answer for this one, but it appears as though we have been transported into another entirely different realm with regards to DIYAudio.
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Old 30th January 2012, 05:39 PM   #3
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Well quieting air vents in dedicated listening and home theater rooms is always a problem so it's not that far of topic.
In fan design efficiency and silence are at the opposite ends of the scale. The slower the air flow the better. Big ports are better than small ports. Try some fiberglass baffles.
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Old 30th January 2012, 05:56 PM   #4
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Quote:
Originally Posted by spazz View Post
Hi all-

I have spent too much time trying to find a way to silence an air vent on a very loud, but otherwise very good, air purifier. From 5 ft away, I am getting 65 dB using an android device/app (in a hallway with hard wood floors).

Although some noise is coming off the motor and the intake filter, it is not nearly as bad as the noise coming off the exhaust vent at the top. That would be the thin circular slit at the top of the unit.

The noise profile has a substantial high/mid frequency component, and sounds a lot like white noise.

Initially I was hopeful that dispensing with the top cover of the unit (the panel with the handle bar and the switch and LEDs) would solve the problem, mainly by getting rid of the vent it self. Unfortunately the bottom/internal surface of that panel is an integral component of the fan assembly, where the special geometry of that surface somehow stabilizes the rotating blower fan (although there is no contact at all).

The two general directions I see for this are 1) to place a series sound foam panels on top, parallel to the air flow, in a kind of concentric circle shape, with one circle inside the vent perimeter and one outside or 2) placing the entire unit in a larger cylindrical or box-like structure that would have a lower chamber for the intake and an upper chamber with an exhaust muffler.

Your help is greatly appreciated!




Click the image to open in full size.
There is no simple solution to this one. Best way is to put it in another room or hallway outside yours and let diffusion (of the bad and good air) do it's trick.

If you put it inside any type of box, cylinder, or special container mentioned, you start to defeat the defeat the efficiency by restricting the airflow either by exhaust or intake. If the air doesn't move that quickly away from it (use of mufflers) you'll end up re-cleaning the clean air that is exhausting out of it since it can't get it away far enough.

Reminds me when my mother used to cook. Think of a smoke filled oven from a too well done roast in a small kitchen with those slat type of doors and a swinging door and a really poorly designed "exhaust" fan going full tilt. Close the lightweight swinging door and the slat folding door and voila, your noise is cut down significantly, especially all the higher end and mids fan whine. Couldn't smell the smoke either, the door was just restrictive enough. Open the door and you get the smoke.
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Old 2nd February 2012, 03:41 AM   #5
Wizard of Kelts
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I don't have any experience with type of thing, but this is what I would try.

I assume this thing is at least a couple of feet high and a few feet away from your normal sitting position.

I assume the vent you are talking about is the one the arrow is pointing to.
Attached Images
File Type: jpg Honeywell purifier.jpg (54.9 KB, 22 views)
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Old 2nd February 2012, 04:06 AM   #6
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What I would do is make a cylinder of open-cell foam, perhaps 12 or 18 inches wide and perhaps a half inch thick or so, with the stretchable bottom fitting around the top 2 inches of the purifier and the remaining 10 or 16 inches extending up. The top would be open to the air.

I don't believe this sock will cut down the air circulation much-the exhaust still has a huge amount of space in which to escape. But what the cylinder will do, whether made of open-cell foam or some other sound absorbent material-is absorb the mid and high frequency sound coming directly at your ears from the machine. You would only get the reflected sound off the ceiling and walls, which is likely to have to travel a good deal longer to reach your ears and will therefore be reduced in spl. You can also put sound absorbent material on the nearest walls to cut the sound down further.

As to open-cell foam, while I have not obtained any, I see that it is available in various widths from McMaster-Carr . Measure the circumference of your purifier, get a piece of open-cell foam that length or longer in a 12 inch or 18 inch width, then glue the two ends together to make the cylinder.

Like I said, I haven't tried it but that is what I would try if I had the problem.

Good luck, and sorry for the amateurish drawing.
Attached Images
File Type: jpg Honeywell purifier with sock.jpg (27.6 KB, 20 views)
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Last edited by kelticwizard; 2nd February 2012 at 04:14 AM.
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