Building an Erhu — The Chinese Two-String Bowed Fiddle

The erhu has just two strings, a bow that lives trapped between them, and a little skin-covered drum for a body. It has no fingerboard, so you press the strings in mid-air and slide to every note between.

Cut a short, thick length of bamboo about 13 cm long, open at both ends. This little hollow tube is the sound-body of the erhu.

Soak a piece of rawhide, stretch it drum-tight over one end of the tube, glue and lash it down, and let it dry hard. This membrane is what makes the erhu loud, like a banjo head.

Push a long dowel neck down through the body near the skin end, so it stands up tall and straight from the drum.

Bore two holes near the top of the neck and fit a friction tuning peg into each, one above the other.

Run two strings from the base of the body up to the two pegs, close together and parallel — the erhu's whole set of strings.

Carve a tiny wooden bridge and stand it on the middle of the skin, under the strings, so the strings press down onto the membrane.

Tune the inner string to a low note and the outer string a fifth higher, like D and A. Twist the pegs to reach the two notes.

Tie a flat hank of horsehair between the two ends of a springy stick to make a bow, tight enough to twang.

Slide the bow hair BETWEEN the two strings. On an erhu the bow lives there permanently and cannot be taken out — that is why it plays only its own two strings.

Rub hard pine rosin along the bow hair so it grips the strings. Without rosin the hair is too slippery to set a string singing.

Draw the bow steadily across a string. Press the hair toward the inner or the outer string to choose which one sounds.

With no fingerboard, press a string in open air and slide your finger up or down the neck to glide smoothly between notes — the erhu's crying, singing voice.

The erhu makes sound the way every bowed instrument does: by stick-slip friction. The rosined hair grabs the string and drags it sideways until the string's tension tears it free; the string snaps back, is caught again, and the cycle repeats hundreds of times a second. This catch-and-release, called Helmholtz motion, keeps the string vibrating steadily for as long as you bow — which is why a bowed note can sing on and on while a plucked one quickly dies. Unlike a lyre or a guitar, the erhu's soundbox is a little DRUM: the strings press through the bridge onto a stretched skin, and that membrane radiates the sound into the air, exactly as a banjo head does, giving the erhu its bright, nasal, almost human voice. And it has no fingerboard — you stop the strings by pressing them in open air — so there are no fixed frets and you can slide through every pitch, which is why the erhu can weep and sing like a person. It grew from the bowed huqin fiddles of the Tang and Song dynasties more than a thousand years ago, and its two strings are tuned a fifth apart. Its cousins are the whole huqin family and, far to the west, every member of the violin family — all of them stick-slip machines singing through a resonating body.