Tone Testing — Pineapple Tenor Ukulele Class

Listening to the wood

Two rigs live here. The Chladni rig makes vibration visible — sand on a driven plate gathers into the patterns of standing waves. The tap-tone & deflection rig measures — how stiff a plate is under load, and what notes it rings at when tapped. Both are science experiments that build intuition, not plate-tuning targets: there are no published pass/fail numbers for tenor ukuleles, so we compare against the instructor's finished tenor instead.

Chladni rig

A signal generator makes the tone, a small power amplifier gives it muscle, and a puck transducer bolted to the plate shakes it. Sprinkle fine dry sand on the plate and sweep the frequency — the sand migrates to the nodal lines, drawing each mode shape.

Cables you need

Generator → amp: one shielded cable, BNC male at the generator end — BNC-to-RCA if the amp has an RCA input, BNC-to-3.5 mm if it has an AUX input.
Amp → puck: 16–18 AWG two-conductor speaker wire, amp OUT+ to puck (+), OUT− to puck (−).
Amp power: a regulated 8–25 V DC supply matching the barrel size and polarity printed on the unit.

Start settings Sine wave, 40 Hz, 0.5 Vpp, 0 V offset. CH1 on, CH2 off. Sweep 25–80 Hz slowly.

Power-up order Amp volume to zero → power the amp → enable CH1 → raise volume gently until the sand just moves.

Know the limit The puck's usable range is 20–80 Hz — low modes will show, higher ones may not. Never force it with more power.

Download the Chladni Rig Manual (PDF)

8 pages: full wiring, setup, operating procedure, protection limits, troubleshooting, and a one-page operator card for the bench.

Tap-tone & deflection rig

A simple bench rig that measures two things about every plate before it goes into a body:

Deflection: a 1 kg load on a 7-3/8 in support span, measuring how far the plate bends — a direct read on stiffness.
Tap tone: tap the plate and capture the ring with a phone microphone and a free spectrum-analyzer app — the peaks are the plate's resonances.

Students work in buddy pairs with assigned roles, and every measurement goes on the build specification sheet that follows each ukulele. There are no pass/fail targets — the instructor's own finished tenor provides the class reference values.

Test Rig Build Document Parts list, assembly, and both measurement methods — loaded deflection plus phone-mic tap tones.
Download PDF
Student Measurement Protocol Step-by-step buddy-pair procedure that maps every reading onto the build spec sheet.
Download PDF