 RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Acoustically Isolate Your Window Air Conditioner
Posted: 29 Apr 2009 10:58 AM |
I’ve always compared my house to a tent with siding. New construction may keep the rain off your head, but it leaves a lot to be desired when compared to the stability and solidness of a solid stone or brick home.
So, I guess I wasn’t too surprised when I installed my new Sears Kenmore 75051 air conditioner into my bedroom window, only to find that the wall above and below the unit was acting as a reverberating echo chamber, especially with the low frequencies of the A/C’s compressor. Bummer!
I pulled out my trusty Radio Shack Sound Level Meter, and sure enough, the walls were vibrating well into the 80dB range, while the A/C was only at 78dB. This was measured at one foot from the unit and wall, with the compressor ON and the fan speed at high.
After reading some of the Internet solutions, like making sure the window glass was tight, and the unit was mounted correctly, I decided to try to acoustically isolate the A/C from the window frame.
I have storm windows installed, so I had needed to raise the air conditioner using a 2X4 support board. After removing the A/C, I covered the top of that board with unrolled foam pipe insulation (Home Depot). I power stapled the insulation to the board. Underneath the board, I positioned some hard rubber blocks (probably cut up mouse pads would also work). I also used foam strips to isolate the top window channel from the A/C.
Putting everything back together, and turning it on, the sound level was reduced to 72 dB at one foot from the unit, with “wall amplification” no longer present. The sound level at bedside was about 60 dB.
Still not a “Silent Night”, but certainly much better.
Ron K
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 17 May 2009 06:03 PM |
Oh Brother! What were they thinking?
Design Assumptions
1. Window air conditioners can be used in a bedroom.
2. People sleep in bedrooms.
3. People need quiet to sleep.
A constant sound of wind, the sound of rain or the ocean, can actually be soothing. The brain’s Reticular Activating System is very good at tuning out other sounds, such as a hum or white noise- and even snoring.
Reticular Activating System
But, the clunky sound of a compressor motor turning off and on all night can be very disturbing! Modern window units boast of high efficiency and energy saving features. Sadly, these “features” include turning the fan on and off, as well as the compressor, which make matters worse. It reminds me of the Government’s mandated requirement to make a 1-gallon toilet. The Industry complied, but the result was a toilet you had to flush five times to clear.
Now, as a Technologist, I’m all for lots of “Bells and Whistles”- literally. But, a beeper connected to a front panel control should only be implemented when pushing a particular button results in no other demonstrative control indication. In other words, if you push the FAN button, you not only hear the fan motor change speed, but there is also a lighted display indicating the speed change. An audible “BEEP” is not necessary. And when this beep sounds while the user is pushing buttons in the middle of the night, it is downright annoying and can wake up you partner! Internet responses to this problem suggest putting tape over the beeper, or ripping the !@#$%** thing out.
Of course, there is another design consideration, which the manufacturer must consider.
1. Make the unit cheap.
Selling the A/C for $100 means that it probably costs around $20 to $30 to produce. How good can it be?
Attention: Would the person who took my twenty-year-old air conditioner from the trash, please return it to me. :-)
Ron K
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bitbyter
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| Joined: 24 May 2003 |
| Total Posts: 266 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 22 May 2009 10:41 AM |
Hmmmm.
I have on thermostatic control for our house air conditioner and if I set it to 70 it keeps the whole house at 70 (more or less) except the room with the computer. You'd hardly know that room was air conditioned when the hardware is fired up. Ergo, there is a window unit in that room as well as the house system. This works reasonably well.
When we got the house system, because a family member was otherwise confined to a bedroom during pollen season, I saved the three window units. I gave one away to a family member. I put the second in the room with the computer gear.
On your advice, I will continue to hoard the remaining unit.
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 15 Jun 2009 07:47 PM |
The saga continues…
To say the least, the thought of having to remove the Kenmore from the window (again), packing it up, and “schlepping” it back to Sears did not sound very appealing. Yet, three weeks of interrupted sleep provided lots of time to think about the prospect. My “return-the-unit” timeframe was running out. So that’s what I finally did.
“The Blue Team” at Sears needed some convincing that the unit was defective, or else there would be a 15% restocking fee. I assured them that it certainly “sounded” defective to me!
I decided to try a Frigidaire FAX050S7A from Lowes. This base model has no frills, bells, or whistles. It has a mechanical thermostatic control. From what I could see at the store, it looked like it was well made, or at least better than some other similarly, low cost units.
I doubled the amount of insulation around the frame, and installed the A/C. It sounded somewhat quieter than the Kenmore, but still suffered from a great deal of vibration, especially with the compressor pumping away.
By chance, I picked up the foam top of the packing material, and placed it lightly on the front of the unit just to see how it muffled the sound. WOW! I had rediscovered the phonograph! Well, at least the old acoustic horn part. The foam acted as an acoustic amplifier, and I was better able to pinpoint from where on the chassis the vibrations were coming.
I decided to open the front of the air conditioner and do some “fiddling”. The front cover can be removed by pulling off the two control knobs, and removing the two screws located on each side of the cover near the bottom. It is also necessary to remove the strip of insulated tape on the bottom of the cover. The next step requires some pulling and twisting of the sides to release two plastic tabs on each side of the cover. These are located approximately 2-½ inches from the top and bottom of the front panel sides. It wasn’t too difficult to remove, as the new plastic is relatively flexible. What it will be like in a few years is another matter.
I discovered something very interesting inside. The housing, which separates the inside coil and fan from the outside of the unit was made of the same molded foam as the shipping container's packing material. How sad!
Anyway, I started adding strips of insulated tape around the edges of the front cover. I also did the same for the removable filter. Perhaps the most significant change was to add a supporting strip (made from an 8 inch piece of a yard stick and covered in white duct tape). This strip was placed behind the front grill and seemed to reduce vibrations.
All my modifications could be easily removed, in case I need some warranty work down the road.
Ron K
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 18 Jun 2009 02:31 PM |
There's an App for That!
I'm not kidding!
I knew my iPod Touch was a really neat gadget, but I never thought I'd be using it as a vibration monitor!
If you have a Touch or an iPhone, check out the Apps Store for "iSeismometer" (Free) or, if you need more intricate data analysis, try iSeismograph ($.99).
Unbelievable!
Ron K |
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 26 Jul 2009 06:21 PM |
Epilogue...
I was in Lowes, discussing replacement windows with the salesman. I happened to mention my window box A/C. He stated that as far as he knows, all the replacement window manufacturers have a clause in their warranty stating that installation of a window air conditioning unit will void their guarantee.
Just something to think about...
Ron K |
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 09 Apr 2010 02:45 PM |
Year Two!
It was time again to reinstall my A/C into the bedroom window (I remove it every fall).
Based on my previous year's work (see above) I knew what I had to do. I added some additional foam from thick discarded mouse pads at the bottom of the window frame, then used the covered 2 X 4 from last year. The big change this year was to add another strip of foam pipe insulation between the lower window sash and the top of the A/C unit, thereby acoustically isolating the sash and its glass from the A/C vibration. This seemed to help.
Still, there was lots of humming from the unit, especially with the compressor on. I decided to investigate further, and see how my trusty iPod Touch could help. Were there Apps to change the Touch into a digital acoustic test instrument? Certainly!
Last year I used a Radio Shack Sound Level Meter for measuring the air conditioner's noise. Once I constructed a microphone for the 2nd generation Touch Microphone I found there were several free sound level meters to choose from in the APPS Store. (Digital Sound Meter FREE, WideNoise). In addition, since I was also interested in the frequency content of the noise, I downloaded two free, real-time audio spectrum analyzer apps; ianalyzer Lite and RTA Lite. The experiment indicated that there was a spectral peak at 60Hz. I guess that shouldn't have been a surprise.
Now all I have to do is to construct an acceptable-looking acoustic band-stop Helmholtz resonator filter tuned to 60 Hz and place it in front of the A/C unit.  Ha! Ha!
Ron K
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bitbyter
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| Joined: 24 May 2003 |
| Total Posts: 266 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 10 Apr 2010 12:09 AM |
| http://en.wikibooks.org/wiki/Engineering_Acoustics/Filter_Design_and_Implementation |
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 10 Apr 2010 11:01 AM |
Good Reference! Thanks!
I'll be sure to use those equations in my new book, My Life Inside a Waveguide, or at my new website, Tune-a-Room.com :-)
Ron K |
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 03 May 2010 08:06 PM |
It's amazing how permeable 60Hz can be. Those waves seem to penetrate just about anything- thick foam, blankets, and lots of other materials I've tried.
I found a great resource with lots of good links at: Recording .org
Did you know a wall has a resonant frequency of 42 Hz? :-)
RonK
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bitbyter
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| Joined: 24 May 2003 |
| Total Posts: 266 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 20 May 2010 06:30 PM |
| http://www.northerntool.com/shop/tools/product_200259024_200259024 |
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RonK
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| Joined: 02 Jun 2003 |
| Total Posts: 715 |
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Re: Acoustically Isolate Your Window Air Conditioner
Posted: 20 May 2010 08:03 PM |
Thanks for the earplug suggestion. I DO use them. Unfortunately, they attenuate the high frequencies much better than the low (60Hz) frequencies.
My latest experiment is to remove the A/C's directional louvers. These cause lots of eddies and vortexes as the air passes through, which translate into noise.
Ron K |
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