AIR CONDITIONER SOUNDPROOFING
Things you need to know
There are several types of air conditioners, each presents different problems regarding quieting, but generally most have some things in common.
1) Older units are more noisy than newer units, mostly because they are near the end of their lives, while newer units are likely inherently quieter.
2) Compressors make more noise than fans and when near worn out can be very difficult to quiet down. Replacement is the only option.
3) Fan blades can make a lot of noise if coated with dirt through long use and can become imbalanced, causing bearings to go bad, adding to noise. Cleaning them can not only reduce sound, but add years to their lives.
4) Sometimes it’s cheaper to replace a whole unit (even if it’s not yours!) than it is to try to remodel against the noise.
These are difficult to quiet and many times it’s not the noise of the unit that’s the problem, it’s the noise that comes in when it’s OFF, because the air flows right through it from outside in and so does the sound of traffic, etc.
If you removed the front vent panel and filter, you can see outside! Therefore, sound has an unimpeded path into the room. Such a condition can be helped by a shield fitted to the outside of the unit, thereby making the airflow and the sound take a right angle path into the air intake of the aircon. Lining the shield with sound absorbing closed cell foam will really help reduce sound coming in. Your local sheet metal shop can make one for you if you give them the dimensions of the unit it to which it is to be fitted.
Pad mounted (Outside) Units:
These types move a lot of air and are usually pretty noisy, even when new. They tend to be large, because they cool (and sometimes heat) large areas. Because the sounds from them are loud and varied, (A combination of compressor and integral fan noise, as well as vibration), trying to soundproof them directly with material on them is usually fruitless and some sort of barrier/fence must be set up.
If it is a roof mounted assembly, make sure there are adequate vibration pads under it to help reduce vibration transmitted into the roof. A noise barrier made of MLV can help reduce noise created and going down through the roof. If mounted on a concrete pad there will not be this kind of problem.
Determine direction of the soundpath that is causing the problem and plan a fence barrier between it and the target of the sound. (A bedroom window, for instance). Build a fence (no gaps in the slats!), at least 8′ high and 6′ wide that goes all the way to the ground as close to the unit as practical and line it with sound absorbent closed cell foam. 1″ thick is a good choice. If the soundpath is angling upwards, add a overhang to your fence to help block the path. If there is more than one soundpath, a fence in the shape of a “V” or even 3 sided like a “U” may be necessary. In some cases a boxed in area may be needed, complete with a roof to contain the sound. Access doors and ventilation will have to be planned for this type of solution. Some hints on how to baffle a noise source is here.
Attic Fans and Air Conditioners:
Some times it’s necessary to “Hang” these units from vibration mounts rather than set them on pads to reduce vibration to an acceptable level. When belts are used to drive the fans, problems can arise due to wear and aging of the assemblies and bearing blocks. Units that are comparatively quiet can become very annoying over time as loose parts begin to sound off. Usually it’s necessary to add sound barrier and vibration absorbing mat around the installation to reduce sound transfer into the structure of the building. This is best done at initial installation rather than later when it will be much more difficult.
Ducts/ducting and air vents.
Ducting needs to be covered with closed cell sound absorbing foam (not open cell foam), for sound and thermal insulation. Metal ducting needs to be physically isolated from the fan shroud or aircon unit with a flexible coupling. Otherwise is will re-radiate sound vibration along it’s length. Fiberglass or flexible ducting usually won’t have this problem, but will lose thermally if not insulated.
Liquid soundproofing can be painted/sprayed on or in the metal ducting for even more sound vibration reduction.
Vents are a problem if the design causes an air noise. To see if this is a problem, temporarily remove one to see if the sound level drops appreciably.
Watch for vents to rooms that have a single common feed up through the wall- (or down through the floor to the ceiling below), if you can peer though the vent into the other side, it means sounds in one room will transfer to the other room.
If you are buying an AirCon, don’t just take the sound ratings the dealer may give for quietness- find out where the different brands/models are installed and go check them out- you will definitely be glad you did!