Sound travels from the device that emits it to your ear on waves. These waves will bounce off of the walls or objects that are not designed absorb them. In building a soundproof box, you want to create a box where the sound will travel and gradually be absorbed until it lessens. Soundproof boxes can be any size as long as they are large enough to contain the item.
Locate or build a box that is 18 to 25 cm (7 to 10 inches) larger on all sides than the item you will be placing inside. The intensity of the sound, measured in decibels, is also a factor in the size and the amount of soundproofing material you will need to use. Factors to consider in determining the size of the box include how much space you have to work with, and having a box that will be large enough to allow you to install additional sound absorbing baffles if need be.
Glue the soundproofing material to the inside of the box you are using. You can use a variety of options, including egg cartons, pieces of rug, fibreglass cloth or you can even buy soundproofing mats that can be cut to the size and shape you need.
Cut cardboard into squares that are half as tall as the interior of your box. Apply your soundproofing material to both sides of these squares and install the squares at 90 degree angles to the walls inside your box. These squares are called "baffles." Installing them inside your sound proof box provides more surface area for the sound to be absorbed by.
Install the item you need to soundproof into the box. Close the box, turn on the item and see if your soundproof box is effective. Even the best soundproof box may not dampen all of the sound. In these situations you may need to reconsider the location of the object, or use a different dampening material inside the box.
Compare the prices of different soundproofing material. Old or extra carpeting will work, as will egg cartons, polystyrene foam and fibreglass cloth. There is specific soundproofing material that can be purchased at music instrument or home improvement retailers.