Fig. 1 A contact mike like these takes ten minutes to make and costs less than $5 in parts.
Hybrid kits that mix acoustic and electronic percussion are a great way to extend your sound palette. If you have an electronic drum module in your system that has an unused trigger input, why not put it to work with something you can assemble yourself? A piezo-based drum trigger is easy to build, and it can be attached to any acoustic drum in your kit. Although there are a number of off-the-shelf triggers on the market, it’s a lot cheaper to build your own. And you might have the parts already in your possession.
If triggering isn’t your bag, no problem: This piezo pickup project provides a cheap and easy way to amplify sounds that would normally go unheard, while allowing you to process subtle harmonics that are below the threshold of audibility. Ever wonder what a Slinky really sounds like? Care to send your cymbals or some scrap metal through a stomp box? The DIY contact mike lets you do both, and a whole lot more.
Fig. 2 Piezo discs come in a variety of sizes, typically 0.12"–2.5" in diameter.
A piezo is essentially a thin metal disc with a hard, ceramic material in the center. As a high-impedance, passive transducer, it converts mechanical energy to electrical energy. The name piezo has its roots in the Greek word for press or squeeze, which provides a clue as to how the disc works: Crystals and certain ceramic materials generate an electrical signal when stress is applied.
Once the piezo is hooked up, it is referred to as a “contact mike” because it needs to touch the object we want to amplify: Place an amplified piezo against a surface and you will hear vibrations that are typically inaudible. A contact mike doesn’t pick up sound from the air like a dynamic or condenser mike, so it can be used at higher volume levels.
Well-made piezoelectric transducers can be very sensitive, making them perfect for amplifying acoustic string instruments such as guitars and banjos. The only downside is that the piezo’s frequency response is weighted toward the midrange, and they can sound tinny depending on what you use as an amplifier. Nonetheless, for the purposes of a cheap drum trigger, they’re just right.