research | acoustics.02

Soundproofing is done to either block noise from entering a room or to block noise from leaving a room. Soundproofing works by using materials that either reduce sound or absorb sound. While sound usually cannot be blocked one-hundred percent, a substantial noise reduction is possible.

A thick wall or other material is used to reduce sound. Permanent walls, temporary walls, foam, room dividers and curtains are among the materials that are used to reduce sound. Soundproofing materials for reducing sound are often made out of wood and fiberglass, but there are many other materials that can be used as well. Forming an air tight barrier around the walls or curtains increases sound reduction by preventing noise from getting through the air holes. A common saying is, If water can fit through the area, so can sound. Now you cannot make a room totally air tight or you would not be able to get enough oxygen, but you can limit air spaces to minimize noise. Another noise reduction method that is commonly used is to build two walls or two doors with an airspace in between. The two doors or walls provide extra material to block sound. The air space in the middle creates a sort of bubble that helps to block sound.
Absorbing Sound
A problem with reducing sound with thick walls or doors is that the sound can bounce off the walls or doors and create an undesirable echo effect in the room.This issue is dealt with by using materials that will absorb the sound. Dense foam is a popular material used for sound absorption. Foam and other soft materials absorb sound because the sound travels into the soft surface and gets reduced as a result. Foam and other soft materials can be placed inside a wall or attached to the outside of a wall.

Sound can enter though doors, windows, thin walls, the floor or even the roof. When soundproofing a room, it is important to evaluate the room to see which areas need to be soundproofed. Stand in the room, listen and walk around to try to follow where noise is getting in or out.

Every time sound waves change substrates, they loose energy. The ideal way to set up the acoustical tiles will be in concentric layers so as to force the sound to travel through tile, air, tile, air, tile, air, ect. in as many layers as possible. Also, to consider the primary frequency of your’ motor is most likely 60Hz (the carrier wave of standar AC current). The wavelenth for this frequency is approximately 19 feet, so you want your’ layers of tile to be around 5 feet thick (1/4 wavelenth) in order to effectively dampen 60Hz. A thinner stack of tile/air will definetly dampen higher frequencies, but may not do much for the rumble.
After writing this, I realize that it may be easier/cheaper to simply replace the blower but if you try the tiles, I’d be interested to know just how much quieter this makes your’ blower. In theory, you should loose about 20dB which is the equivalent of 1/100th the acoustical energy


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