You need to measure the width of the front cabinet of your speaker, along with the length of each side. You do not need to measure the length or width of the back of the cabinet. Just write down all the measurements and add the lengths of the sides you recorded.
Now you can cut a piece of black vinyl. The piece should be as wide as the width you measured and as long as the sum of the lengths you recorded. Set it aside.
You can now measure the length and the width of the back side of the speaker and cut another vinyl piece accordingly.
Cover the front side of the speaker with newspaper and use tape to put it in place. You can now spray a strong adhesive on both sides and the top of the cabinet.
Take the long piece of vinyl and apply it on the lower side of the right side and start running it upwards. Take it to the top part of the cabinet, followed by sticking it to the left side, working it downwards. In order to wrap the vinyl under the speaker cabinet, you can flip it over and expose the bottom area. Spray the adhesive and press the remaining vinyl against it. Make sure you do not leave any bubbles in the vinyl when applying.
Flip it back and spray the adhesive at the back of the cabinet and paste the other piece of rectangular vinyl against this panel.
If you find any wrinkles in the vinyl, remove them as much as you can. Allow the glue to dry up overnight, before you touch your speaker. Remove the newspaper which you applied at the front panel of your speaker. Repeat the process for every speaker you have.