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Chapter 5. DeskBeam Bass: > The DeskBeam in Principle - Pg. 149

MAKE: PROJECTS Eccentric Cubicle Figure 05.05: Dirt cheap and really freakin' loud. The dollar-store window alarm is virtually indistinguishable from similar items sold in $15.99 packs of four by A Major Name In Home Security. Figure 05.06: Batteries, buzzers, magnetic vane switches... It's a technological bargain bonanza! That's the part we're interested in. Put a cable and plug on a piezo element and you have a very sensitive, reasonably flat response contact mic. The pickup assembly is designed to be a standalone unit. Changing the location of the pickup points on the instrument can radically alter the timbre, with the added bonus of being able to use it as a stereo contact mic on just about anything that double-faced tape will stick to. So we need some piezo elements. They've been the com- ponents responsible for the piercingly loud alarm tone in clock radios since the late 70s, and there's even been a particular school of thought that vintage piezos are highly desirable for use as contact mics, due to their larger scale and heavier coat- ing of piezo crystals delivering a stronger signal. Personally, I'm ambivalent about that concept. Modestly driven contemporary piezos deliver in excess of 1,000 mA, which is a manly enough signal to drive any amplification system. We could do a thrift-shop safari in search of a matching pair of 30-year-old Citizen brand clock radios, but a much easier solution to sourcing piezos calls for you to head to a dollar store and grab two window alarms. [Figure 05.05] Pick up a 1 / 8 " miniplug stereo cable, while you're at it. Length is up to you, but you need at least one male end on it. If I find out you actually purchased a naked piezo element from an electronics supplier, I will seek you out and punch you in the brain. Cheap-ass alarms, like the one shown, use the same piezo elements as buzzers to generate their 90 dB of intrusion inhibiting might. [Figure 05.06] Besides the piezo element, each alarm unit includes a sep- arate stick-on magnet, three perfectly good AG-13 batteries, a weensy SPST slide switch, a magnetic vane switch, and a PCB sparsely populated with mystery capacitors and transis- tors. [Figure 05.07] All this in a stylish white plastic case, with informative packaging, indicating its effectiveness at warding off both Andy Capp and ham-smuggling bellhops. It's a pretty good deal for a buck, innit? Remove the piezo elements from the case with care. The crystals crack easily, and the disk they're layered on is shim- metal thin at best. Successfully wielding your trusty hobby knife on the glue line around the rim of the buzzer will reward you with an unbent, unscarred element. You'll need two. While the soldering iron is heating, snip off one end of the cable you bought, so that you have a length of 3 conductor wire terminating in a male 1 / 8 " TRS plug. 10 Strip about three 10 TRS = Tip-Ring-Sleeve. The name refers to the three different contacts on the plug. 138