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

55 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!

    • It sounds like you may need to contact a local HVAC person to check it out. Sorry, we are not an A/C repair company and can not help with this situation. Best of luck to you.

  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

    • If you could send me the dimensions along with a few digital images of the office area with the echo/reverb problem, I would be happy to start that discussion with you. We have quite a few choices for different acoustical panels to help with issues like that and each has its own respective advantages and disadvantages, as well as costs and aesthetics.

      The noisy A/C unit is a different game all together. Digital pictures also help with that, and if you could send me a bit of information about the nature of the problem and details about the situation, that will also help.

      Thanks,
      Ted

  4. Hi Ted, I hope that you’re doing fine. About 3 months ago you advised me on how to reduce vibration and noise from a noisy AC unit located on the roof next to my bedroom. You suggested to me that I should instal 4 Housed Spring Isolators in order to reduce vibrations from the compressor in the AC unit. I told the property owner about the vibration and noise in which impedes my ability to sleep, and a month later the owner installed 4 Housed Spring Isolators under the AC unit and in addition he added a sound plate under the compressor as well, and amazingly the noise from the compressor was reduced by about 60% , and this happened all because of your advise and I thank you for that.
    One more difficulty remains to be resolved and that’s the noise from the Initial Start of the compressor, another words every Initial Start of the compressor has a loud thumping noise and the AC mechanic doesn’t know how to fix this. Ted, do you have any suggestion of how to reduce the noise generated from the Initial Start of the compressor ? Does Thermostat has any bearing or effect on the Initial Start of the compressor?
    I thank you in advance for your suggestion.
    Sincerely yours,
    Roobik Gorjian

    • GREAT to hear that the spring isolators helped to reduce the noise. And, thanks for taking the time to let me know that it helped in your situation!

      Do you know if the start up noise is an airborne sound coming through the structure, or an initial vibration? Could you send me a few photos of the situation? That might help me make recommendations.

      Thanks,
      Ted

      • Hi Ted, and thank you for responding to me so quickly. You asked me whether the start up noise ” is an airborne sound coming through the structure, or an initial vibration is an airborne sound coming through the structure, or an initial vibration?”.
        The start up noise is an airborne sound ( like a loud click ) coming through the structure into my bedroom and this happens when the thermostat turns on the compressor. The AC unit belongs to my neighbor below me and it’s on the roof over my bedroom.
        Ted, I’m not allowed to go to the roof to take pictures of the AC, but the contractor showed me the installed Spring Isolators, as you recommended those a few months ago.
        I hope that I’ve given you enough information about the start up noise.
        Thank you,
        Roobik

        • If it’s an airborne sound, you might benefit from putting something like an acoustical Quilted Curtain between the compressor and the wall.

          If you can space the panel off the wall by a little bit (even an inch is fine) that is ideal.

          The product is an exterior-rated barrier that will block noise as well as absorb the sound that hits it. They are custom-made to size and UV-stable components are used. Kind of like a backstop for a baseball field, the size of the blanket depends on the size of the compressor and the distance between the compressor and the wall.

          Let me know if you have any questions. I would need some idea of the dimensions that you need to put a quote together for you.

          Thanks,
          Ted

  5. Thank you Ted for the information on Sound Blankets. If the property owner decided to go ahead with this I’ll let you know.
    Thanks again,
    Roobik

  6. Hi! the basic drawing is just what I had in mind for my neighbors ‘noise maker”. she said it would be okay, then changed her mind. “everyone” keeps telling her it will block the air flow and raise her electric bill. my front porch is unusable. it’s very close and runs all the time. any ideas? thank you carol

    • I would have her talk with an HVAC contractor or the manufacturer. People put fences and enclosures around the condensers all the time. As long as this is done properly, which I discuss in the blog article, the machine will be just fine. You will need to get an enclosure with a noise barrier around the thing to use your porch.

      Thanks,
      Ted

  7. Ted,
    We have two outside units which are elevated about 2 feet off the ground on a wooden platform. (flood area) The noise from the units is very annoying and i was looking to build a soundproof enclosure. I like your picture in the blog; is that PVC piping you are using in order to make the enclosure removable? Since you suggest a panel ‘double the height of the unit’, i would guess that if my units are 2 ft tall, i would need panels of at least 6 feet from ground to top…correct?

    Thanks for your help,
    Debbie

    • The white lines in the picture above are just me digitally modifying a photograph to show the idea I was talking about. As long as the PVC pipe is thick enough, there is no reason why it wouldn’t make a good frame for an enclosure. The curtains that we sell are UV-stable so you would not necessarily need to remove them, but that is up to you.

      Yes, your high assumption was correct. If the noise source is 4′ in the air, I would suggest a minimum wall height of 6′ off of the ground. The idea here is similar to a baseball backstop. The higher the fence, the more foul balls (or noise) it will stop.

      Thanks,
      Ted

  8. Ted,
    One more comment…..I just went to the website to check out the pricing for the acoustic panels and it appears they are only sold by the box. Is that correct?

    Thanks,
    Debbie

    • The Sound Silencer panels are sold online in full box quantities, but I would be happy to type up a quote for as many or as few panels as you would like. I would also be happy to put together a quote for the quilted blanket, which would likely offer you more performance than the Sound Silencer panels.

      Thanks,
      Ted

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