Accordion · 6 min read

How an accordion actually works

Inside the box: free reeds riveted to plates, two per note, leather valves, a pallet board, reed blocks and register sliders. A plain mechanical explanation.

2026-05-04

The reed is the whole instrument

Everything an accordion does comes down to a strip of hardened steel about the size of a fingernail clipping, riveted at one end over a rectangular slot in an aluminium plate. Air pushed through the slot drags the free end of the tongue with it, the tongue springs back, and the cycle repeats a few hundred times a second. That is the note. The reed is called free because it swings through its slot rather than beating against a surface, which is the difference between an accordion and a clarinet or an oboe.

Pitch depends on the mass and stiffness of the tongue, not on the size of the instrument or the length of any air column. A low reed is long and often has a blob of solder near the tip to slow it down. A high reed is short and thin. This is why a small 48-bass student box and a concert instrument can produce the same written notes, and why tuning an accordion means filing metal off a reed rather than turning a peg.

Reeds are usually mounted in pairs on a plate, one facing out and one facing in, and the plates are fixed to wooden reed blocks with wax. Good instruments use hand-finished reeds of harder steel with tighter slot tolerances; cheap ones use machine-stamped reeds that need more air and respond slowly at soft dynamics. The difference is audible in the first ten seconds of playing.

Two reeds per note, one each way

A free reed only speaks when air moves through it in one direction. So every note on the treble side needs two reeds per rank: one that sounds when you compress the bellows, one that sounds when you draw them open. They sit back to back on the same plate, facing opposite ways.

That would waste air, because the idle reed is just an open hole. The fix is a valve, a strip of leather or plastic glued along one edge of the plate so it lies flat over the slot of the reed that is not speaking and lifts away from the one that is. These valves are the first thing to fail in a neglected instrument. Curled or stiff valves cause slow response, a breathy leak, and the peculiar sensation that an accordion is fighting you.

On a well-set-up instrument the two reeds for a note are tuned to the same pitch within a cent or two, so the push and the pull sound identical. On a diatonic button accordion they are deliberately tuned to different pitches, which is why those instruments play a different note in each direction. Piano accordions and chromatic button accordions are unisonoric: same button, same note, both ways.

The bellows does the work your breath would

The bellows is not a bag you squeeze to make noise. It is a pressure regulator, and it is the only part of the instrument that controls dynamics. Fingers control which notes sound; the left arm controls how loud, how sudden, how sustained, and how the note dies. A player who has good fingers and a dead bellows arm sounds mechanical, and no amount of practising the notes fixes it.

Because reed response is pressure-dependent, an accordion can crescendo on a held chord, which a piano cannot. It can also articulate with the bellows alone, sharp jabs of pressure against stationary fingers, which is the basis of bellows shake and of most of the rhythmic vocabulary in the contemporary repertoire. There is an air button near the left strap that opens a large valve so you can reset the bellows without sounding anything.

Bellows are made from folded card, cloth and leather with metal corner protectors, and they are airtight only if every gusset and corner is sound. A bellows that bleeds air makes the instrument feel heavy and imprecise long before you can hear an actual hiss.

Keys, pallets and reed blocks

Press a treble key and a lever lifts a pallet, a felt-and-leather pad, off a hole in the pallet board. Air can then travel from the bellows through that hole into a chamber in the reed block behind it, where the reeds for that note are waiting. Release the key, a spring pulls the pallet back down, and the note stops. The whole mechanism is levers, springs and felt, with no electronics anywhere unless someone has added a microphone system.

The left hand works on the same principle but the linkage is far more elaborate. One bass button has to open several pallets at once so that a chord sounds, and the rods that do this are packed into the bass machine, a dense cage of pivoting metal that is the single most intimidating thing to look at inside an accordion. It also explains why a 120-bass instrument weighs what it does.

Registers, cassotto and why one box sounds like six

Most accordions carry several reed ranks per note: a low one at sixteen-foot pitch, one or two at eight-foot, and a high one at four-foot. Register switches move sliders that cover or uncover the chambers for each rank, so you can combine them. That is where names like bassoon, clarinet, musette and master come from. Two eight-foot ranks tuned slightly apart produce the beating wobble of musette tuning, beloved in French and Italian playing and tolerated less well in Bach.

Better instruments add a cassotto, a resonance chamber built into the body so that one or two ranks speak sideways through a wooden tone chamber before reaching the grille. The result is rounder and darker, and it is the main reason a concert instrument does not sound like a very good student model. Accordions we sell and service at A&G Academy in Singapore get checked on exactly these points, because a leaking valve or a sticky slider will undo any amount of practice.

Frequently asked

Does an accordion have strings inside?

No. There are no strings anywhere in an accordion. The sound comes from free reeds, small steel tongues riveted over slots in metal plates, set vibrating by air from the bellows. People often assume strings because the left-hand side is loud and percussive, but that is reeds too, just more of them sounding at once.

Why does an accordion sound different when you push and pull?

On a piano accordion or chromatic button accordion it should not. Each note has separate reeds for each direction tuned to the same pitch. If push and pull sound different, a valve is curled or the tuning has drifted. Diatonic button accordions are the exception: those are built to give different notes each way.

What do the switches on an accordion actually do?

They slide covers over the reed chambers, switching whole ranks of reeds in and out. A switch does not change the notes, only which combination of low, middle and high reeds speaks. Selecting one middle rank gives a clean clarinet tone; adding a second slightly detuned rank gives the wavering musette sound.


Learning or buying in Singapore?

A&G Academy teaches accordion, bayan and double bass, and sells the instruments we teach on. Ask us anything — we'd rather talk you out of the wrong instrument than sell you one.

Ask on WhatsApp See instruments