Bench Degree·CYMATICSchapter

Before You Start

One page. The parts list for the whole volume is Appendix A, at the back of the book; Chapter 1 will tell you what it needs. This page is the part you should not find out later.

The hazard in this book is your hearing, and it gives no warning. A metal plate driven at its own pitch is an efficient loudspeaker, and the tones in this book sit where the ear is most sensitive. Put a sound level meter app on a phone at the bench, and wear ear plugs or muffs whenever it reads above 85 dBA. Every 3 dB above that halves the safe time: 100 dBA is safe for under 15 minutes a day. Hearing lost this way does not come back, and ringing in the ears afterwards means you have already gone too far.

Mains electricity stays inside a safety-listed power brick. Nothing on this bench runs above 24 V. The small amplifier boards used here drive both speaker wires, so never connect either one to ground, and turn the volume to zero before connecting anything.

Sand is mostly crystalline silica, and the danger is its dust. Use washed play or craft sand, never crush or grind it, never sieve it dry indoors, and clean up wet. Table salt has no such problem, which is one reason it comes first.

Fine powders go into the air, which is the point of Chapter 7. Use flour or cornstarch and keep the quantities small. Never use lycopodium powder, the classic laboratory choice: a cloud of it burns explosively.

Cut metal is sharp and vibrating metal bites. File every cut edge, lock-nut anything that vibrates, wear safety glasses, and keep fingers off the rim of a plate running at high volume.

Water and electronics share a bench in Chapter 8. The speaker sits below the dish, the amplifier stays well away from it, and nothing that carries mains comes near either.

Glass breaks. The wine glasses in this book are rung gently and never driven towards breaking; Chapter 9 explains why you should not try.

Ultrasound in Chapter 21 is silent and still loud. You cannot hear 40 kHz, so no meter app will warn you. Keep your head well away from the levitator, keep running times short, and keep children and pets out of the room.

Bench Degree

Get the degree without the diploma.

Learn the material, not how to pass the exam.