I have a nice Remo brand djembe with a synthetic material head. It had a sort of ringing noise that lingered after every strike, though; something that I didn't like. I wanted a deeper sort of more jungle drum voice to it. Both of those elements were fixed by resting layers of blue x-ray film material on the original drumhead. The more layers, the more deadening of the ring. The round layers, were first taped together and then joined by a silicone rubber flap to the outer ring of the drum, so that it could be used with either voice by raising or lowering the layers via the flexible bridge of silicone. I always seem to use the deeper sound, though, and eventually eliminated the silicone bridge, just taping the layers down to the head with electrical tape.
Accessory maraca sounds, and clacking noises were added to the outer rim of the drum head using silicone rubber. Silicone's springiness makes it great for holding film cans, and other things, that hold the maraca seeds. Some of the containers are allowed to move downward and strike the drum body, adding the clacking sound option for harder strikes.
This is a great way for a drummer to round out the percussion background, since you can make single sounds, or multiple sounds, just by striking one or more things at a time.
Hear how it sounds in the last step.
Step 1: Attaching the Add-ons
In that first ring around the drum head, I embedded some string, to keep the silicone ring from stretching and coming loose. After the ring had hardened up, I continued with the silicone, making bridges and attaching the sound makers to the bridges. The rubber bridges wobble nicely, so the shaking of the maracas goes on for a while after they are struck.
With practice, you can just extrude silicone and build up the bridges in the air. As an alternative, you can make them flat on a non-stick surface, such as polyethylene plastic (stretched trash bags work). Then, when dry, stick them to the ring with more silicone. You have to be creative as to how you hold parts in place until the silicone hardens up. I set the drum next to a table and rested things on the table while making the flexible connecting bridges.
One layer of x-ray film material on the drum head will kill some of the drum's ringing sound. Two layers kills it more, and so on. The number of layers allows for adjustment to personal taste. Mine has five layers. I eventually just taped the layers down on the head, which holds them more securely during playing than the rubber bridge did. The tape can be peeled up later to remove the layers of film.
Remember that, due to the weight of the units, the rubber bridges will bend downward some. If you want them to stick straight out, you have to aim them a little upward when you put them in place.