A Slapaphone makes sound when a paddle slaps the open end of a tube and sets the air inside ringing. The length of that air column decides the note. There is no skin, string, or bar. The air itself is the instrument.
If you are new to it, start with what a Slapaphone is.
Sound generation
- The paddle lands flat on the open top of a tube and seals it for an instant.
- That squeezes the air inside, like a short, sharp push.
- The air column bounces back and vibrates at its natural pitch.
- The paddle lifts off and the note leaves through the open end. The whole thing lasts a fraction of a second.
Why each tube plays a different note
Each Slapaphone tube is open at the top and closed at the bottom. A tube like that rings at a pitch set by the length of its air column: the frequency is roughly the speed of sound divided by four times the length. Halve the length and the note jumps up an octave.
| Note | Frequency | Approximate air column |
|---|---|---|
| F3 | 175 Hz | 49 cm |
| F4 | 349 Hz | 25 cm |
| F5 | 698 Hz | 12 cm |
| F6 | 1,397 Hz | 6 cm |
These lengths are a simple estimate. A real tube needs to be slightly shorter, because the vibrating air reaches a little beyond the open end.
Tuning with movable stoppers
On a Slapaphone built by Jeff Fahringer the tubes can all look the same length from outside. Inside each one is a stopper set at a different depth, and that stopper is the real bottom of the air column. Sliding it up or down changes the length and so fine-tunes the note.
Playing techniques
- Cover the whole opening. A paddle that lands half on the rim leaks air and gives a weak note.
- Let the paddle bounce. A quick strike and release gives the clearest tone.
- Use bare hands for a softer attack.
- Strike harder for volume, not pitch. The note stays the same however hard you hit.
Amplification
A Slapaphone is an acoustic instrument and is loud enough for a small room. On stage it is usually miked from above, with the microphones aimed at the tube openings where the sound comes out.
FAQs
What musical instrument makes a bong sound?
Tubes slapped on the open end, such as the Slapaphone and home-built PVC pipe instruments, give exactly that round “bong”.
How do pipes make music?
By trapping a column of air. Set that air vibrating, by blowing across it or slapping the end, and it rings at a pitch that depends on its length.
How much does a Slapaphone cost?
Used ones have been listed from about $70 to $1,000. See Slapaphone prices and where to buy one.
