How to Quiet Noisy A/C Compressor

Please keep in mind this is my quick Photoshop sketch simply to illustrate the theory explained below.

As the weather heats up, and summer gets into full swing, we are getting more and more calls as well as E-mails about air conditioning compressors bothering home owners as well as neighbors. The problem can be fixed fairly easily and inexpensively, but either way, it needs to be done correctly. In some cases, doing ALL of the things that I will discuss below are not possible, so you have to do the best you can with the limitations of your situation. If you have questions, please feel free to contact me  to discuss the particulars of your problem. Often times digital pictures of your area are a great help.

Here in the Midwest, air conditioning units are installed outside on ground level, somewhere near the house – and most often, on the side of a house that is near a neighbor. When the air conditioning turns on, the compressor outside comes alive, which generates a fair amount of mechanical noise. Whether the exterior of the house has siding, concrete, wood, or stucco, the sound tends to bounce off the house and usually heads directly toward neighboring windows.

To fix this problem, you are going to need to build an “enclosure” around the unit. This will require a bit of construction on your part, and there are a few things to consider – acoustical performance, not inhibiting the operation of your system and aesthetics.

The first thing to consider is the location of the walls of your enclosure – which is the most critical aspect of approaching this situation. Now, I’m not an HVAC Contractor, so please forgive me if I am not exactly correct here… The purpose of the compressor outside of your house is to cool and compress the Freon in the AC lines. This is why the large volume of air coming out of the top of the unit is warm. If that airflow is inhibited, you can seriously damage your HVAC system. The compressor needs a certain distance around (and over) it to allow the system to operate correctly and for servicing the unit – so if you have any questions, please contact a local HVAC contractor for advice.

Let’s talk about the walls of your enclosure…

The first two things to think about – from an acoustical standpoint are that you need to eliminate the “line-of-sight” sound travel. No matter what kind of acoustically absorbent or “sound proof” product you line an enclosure with, if you can still SEE the unit, you have not chosen the most efficient approach. I understand that sometimes this is not possible, but I wanted to point out that it is definitely ideal. If you are considering building walls only (i.e. no roof) I would suggest a wall height that is double the height of the noise source. For instance, if your AC unit is two-feet tall, your wall height should be four-feet. If that is not possible, which often times it isn’t, the higher the better. If you need a shorter overall enclosure, I would suggest making an angled roof over at least part of the compressor. If you can imagine the top of a back-stop for a baseball field, that is the type of overhang I am talking about.

The acoustical treatment…

We have two different products that can be used outdoors to treat the inside of the enclosure – both of which need some kind of substrate to attach to. The most common lining for the air conditioning enclosure is the Sound Silencer acoustical panels. These panels come in a 1″ and 2″ thickness, and are sold in 2′ x 4′ panels. The 1″ thickness normally sells for about $5.50 per square foot, or $44.00 per panel, and the 2″ thickness sells for about $7.50 per square foot, or $60.00 per panel. They can be cut with a table saw or skill saw. Cutting the 2″ panel can get just a little tricky, so please call to discuss the installation details. This panel is going to need a sheet of plywood to attach to – and can attach with a construction grade adhesive (PSA-29) or simply with screws and washers. The 2″ Sound Silencer panel is rated with an STC of 13, and an NRC of .70.

There is one quality of the Sound Silencer acoustical panels that you need to consider when thinking about using this product. We have found recently that with prolonged ultra violate exposure; the polypropylene core of the panel starts to break down. This happened MUCH, MUCH faster with the white, so for exterior applications, ONLY use the charcoal color. The charcoal dye acts like window tint, protecting the polypropylene from the sun. If the area is shaded for most of the day, or if the panel has a roof, you will be fine with this product. It is going to be the most effective when backed with a solid board of plywood, rather than spanning gaps in a privacy-style fence.

Another, and more costly lining is our Exterior Grade Sound Blanket. This product is commonly used on chain-link or privacy style fences. This panel is constructed by quilting a nominally 1″ or 2″ thick layer of light density fiberglass to a 1/8″ thick, Gray, reinforced layer of mass loaded vinyl. We make these panels specifically to the sizes needed on a per-job basis. Our most common application for this product is around large air-handlers for commercial applications simply because these machines normally have chain-link fences around them. When we fabricate these panels, we will pound grommets through the top, middle and bottom of each, and line the vertical seams with an exterior grade Velcro to attach one panel to the one next to it. Because these panels are made on a per-job basis, I would rather provide a quote based on your measurements than on a ballpark price, but if you would like some idea, the cost usually falls in the $14.00 per square foot neighborhood.

The Exterior Grade Sound Blanket solution will out perform the Sound Silencer panels in most instances simply from an acoustical standpoint – but the applications are not normally an apples-to-apples comparison. The Quilted Curtain panels have an STC of 27 and an NRC (with the 2″ facing) of .85.

This entry was posted in Commercial, Exterior Noise Control, Industrial, Residential, Soundproofing by Ted W. Bookmark the permalink.
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About Ted W

My name is Ted Weidman. During my time at Acoustical Surfaces, Inc. I have helped countless people with all kinds of different noise problems. I have a background in education, which hopefully helps me explain noise, sound, and acoustics in a way that is easy to understand.

Please contact me with any questions you may have.

direct: 952.466.8225 | office: 800.527.6253 | fax: 952.448.2613

42 thoughts on “How to Quiet Noisy A/C Compressor

  1. Great article. Between that and your response to comments I am a believer :-). I have a compressor unit right outside my bedroom window, about a foot from the exterior wall. The fan noise as well as the noise that occurs when the unit kicks on or off is particularly loud even with my window closed. I am hesitant to build too much if a barrier between my window and the unit because I don’t want to kill my view. Any recommendations?

    • It’s always best to try to stop the sound as close to the source as possible, but in this case it would likely inhibit the view from your window. I’m a bit hesitant to try to make this recommendation because there is a decent chance that the sound is coming through the wall of the house as well, but you could potentially start with one of our Climate Seal acoustical window inserts.

      It’s very common that the weakest link in a wall is the windows and it’s usually a logical place to start with for acoustical treatments/improvements. But because most AC systems produce a relatively loud and quite low set of frequencies, it may or may not offer a substantial enough reduction for your situation. One cheap and easy “test” approach would be to cover the window with a piece of 5/8″ sheetrock and use a standard sticky-back weatherstripping to make the sheetrock air-tight to the window. Leave that in place for a day or two and if it gives you enough reduction, the Climate Seal will block a bit more and be perfectly see-through and easily removable.

      If you’d like a quote or need more information, please let me know. I would simply need your address, phone number, the measurements for the window, and a digital picture or two.

      Thanks,
      Ted

  2. Please answer asap anyone! The ac outside is silent, don’t know whether ac is broke? It feels like fan is only running! I can’t afford to have it fixed, please help!

  3. Hi Ted: I’d sure like to get advice and a quote on a couple of noise issues.

    First is our office- the reverb is awful! Bare tile floors and bare sheetrock (painted) with high ceilings. What would you need, a few photos?

    Also have a very noisy A/C unit. Looks like I found the right place!

    Michael Spencer

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