Use a large flat screwdriver and small hammer to pop the lens off the nearest plastic wall clock.
This part is called the "resonator". You can use a lot of different things for this part, such as a Styrofoam plate or bowl, or a plastic clam shell from the deli. In fact, to tell the truth, these lighter-weight objects will tend to sound better than a clock face. Listen to this goofy video to hear a variety of resonators in action. See the article "Essentials of Hula Mic Design" for more guidance and ideas.
You really don't want noisy things rolling around inside your microphone, so open up the hoop and dump out the ball bearings inside. Our hoop was held together with a couple of staples. They came out and went back in quite easily.
Your hula hoop may not be round. Look for two places where the diameter is about the same. Attach the four large binder clips to the hula hoop more or less at these points, as shown. Measure the distance between clips and adjust them until they are more or less equally spaced.
Attach the small clips evenly around the clock lens (or other resonator).
Hook a pair of bungee cords to each of the large binder clips. Now hook two cords to one small clip as shown; look at the picture. Repeat for the opposite small clip. Now repeat for the other two small clips. If you do not do it in this order, you may have trouble with the small clips popping off of the resonator.
If you buy ready-made mini bungee cords, look for 9" or 10" cords. You may need to play around with different resonators or different size binder clips until you find a combination that works well with the available bungees.
If you buy materials for making your own mini bungees: cut the cords about 12" long; tie a tight knot close to one end; tie a loose knot an inch or two from the other end. This will make it easy to adjust the length of the cords until you find the optimum length. Ours ended up 9-1/2" long tip-to-tip.
Stick the piezo sensor of your contact mic to the center of the resonator, on the convex side.
If you are experimenting with lots of resonators, use Poster Putty (Plasti Tac, Blue Tack, etc). If you are ready to mount the piezo permanently, use good carpet tape (double-stick tape). Press gently! Ceramic piezo sensors are delicate and can crack! On the other hand, the better your piezo is stuck to the resonator, the better it will sound, so be patient and gentle, and do a good job.
If you are using the Cortado Contact Mic Kit by Zeppelin Design Labs, build a basic contact mic following the Assembly Manual (free download), or buy a ready-to-use mic. Alternatively, you can try this project with any contact microphone or pickup you happen to have on hand, but beware: some of them may sound crummy. See our article "Essentials of Hula Mic Design" for guidance and details.
Mount the mic to a mic stand using an improvised bracket like we did; or use duct tape; or hang it from the ceiling with string; or have two lovely assistants hold it up for you. Strap the Cortado, or the cable from the piezo, to the hula hoop, so there is no stress on the piezo. We stuck the mic to the stand with Velcro.
The Cortado needs phantom power. You can run a mic cable to your recorder or mixing console and get the phantom power from there; or use an Espresso Portable Phantom Power Supply and a special adapter cable, and record straight into your smart phone; or, move a jumper inside the Espresso and run the signal from your Hula Mic straight into a guitar amp! Yow!
You can use other contact mics or pickups as well, most of which do not require phantom power -- but they may require a preamp or DI box. Consult with a music store or audio...Read more »