Which design is best? Do you have a DIY question? Philippe Decuyper, a.k.a. PFozz on the edrumforfree forum, solves readers’ problems in each edition of digitalDrummer. Whether repairing existing equipment or building your own, Philippe will find the answers. Just email your questions to editor@digitaldrummermag.com. This month, there are two winners – Murray Jackson from Calgary in Canada and Mark Hetherington from Melbourne, Australia – both of whom asked about the benefits and disadvantages of the various drum trigger assemblies.
IN MY FIRST column, I identified the piezo transducer as a good candidate to build a pad. But, as our questions suggest, there are a number of ways of mounting the piezo in a drum pad. All have their pros and cons. The “crossbar” is the most common in the DIY community. It works well with modern modules and it is compatible with positional sensing. Positional sensing? A bit of theory...
A piezo transducer (which acts as a microphone) produces a waveform that is interpreted by your module. Using a crossbar-type trigger with a mesh head, the produced frequencies vary depending on distance between the impact point and the physical link that connects the piezo to the head. To understand how this works, think back to throwing a pebble into a pond in your youth. This action produces a wave. If you use a small stone, the wave will be of low amplitude, while a large piece of concrete produces a wave of high amplitude. This phenomenon applied to a pad illustrates velocity.
As an unlucky fish, you would feel the frequencies issued by our stones. When a stone hits just above the fish, it receives much more “bass”. The frequency corresponds to the distance between waves and mostly how thick these are.
If you think of a piezo under a mesh head as a fish in a pond, the piezo will receive more low frequencies (long waves) if a strike occurs next to it. Therefore, positioning the piezo in the middle of the head allows the module to sense a centred strike. If digitalDRUMMER, JULY 2010
you are very curious, you can try to plug a mesh head trigger into your sound card and start to analyse frequencies. In practice...
While the velocity is computed by a module whatever the type of pad, positional sensing can only work with a piezo mounted on the centre of a crossbar-type trigger or a basket-type assembly.
A number of DIYers use reflection plates instead of baskets or crossbars because they are easy to use, and produce good triggering results – both as single-zone and dual-zone triggers.
A “reflection plate“ is a sort of extension of the piezo brass part. With this design, velocity detection will be more or less uniform on the whole surface of a pad, and produced frequencies will be more or less the same whatever the position of impact. Positional sensing is therefore impossible. Similarly, a noncentred piezo will usually avoid “hot spot” issues, but it will not allow positional sensing.
Even using a crossbar with a centre-mounted piezo, positional sensing may not work very well. Bear in mind that manufacturers like Roland design algorithms of their modules especially for their pads. So, should we avoid reflection plates? Not at all. A reflection plate has its advantages. As mentioned previously, velocity response is often more uniform. Such a trigger is also often more sensitive and will work well with older modules that require more gain from pads. You can use real acoustic heads with such triggers and you can build flat pads. It’s also a very good option for a kick trigger.
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