The Bach 6C: Trumpet's Most Overlooked Mouthpiece Size

Walk into any trumpet section and you will find 3Cs, 5Cs, and 7Cs everywhere. You will almost never find a 2C, 4C, 6C, or 8C. Bach's "even" sizes are the least-discussed models in the whole catalogue — not because they are worse, but because almost nobody tries them. The 6C is the best case for why that is a mistake.

Why the Even Sizes Are Rare

Bach's trumpet mouthpiece numbering runs from wide rim diameters at low numbers (1, 1½) down to narrow rims at high numbers (10, 12, 14), with cup depth marked by a letter suffix — A is the deepest cup Bach makes, getting progressively shallower toward F. Most players are introduced to the line through a school-issued 7C or a step up to a 5C or 3C — the three sizes that ended up, by historical accident as much as design, dominating shelf stock at every music store. The 6C sits between two of the most popular sizes in the world and gets skipped by players who never had a reason to try it.

Where It Sits

Here is the detail most players never check: the 6C and 7C share the exact same 16.20mm rim diameter. The 5C is only 0.05mm larger at 16.25mm. In raw geometry, the 6C is not really a midpoint between two different sizes — it is closer to a rarely-stocked twin of the 7C. What separates the C-cup models in this range is not diameter but rim contour and bite, which Bach's numbering does not directly encode. Players moving from a 5C to a 6C commonly describe the sound as cleaning up — less spread, more focus — for what is, on paper, an almost imperceptible geometry change. That is the actual case for trying one: it is one of the lowest-risk experiments in the entire Bach catalogue, precisely because it is not a big jump from what you already play.

The Chet Baker Connection

The 6C's best-known association comes from Chet Baker. Following the 1966 assault that badly damaged his mouth and teeth, Baker had to rebuild his embouchure essentially from nothing — and multiple equipment retrospectives and player accounts place him on a 6C-sized mouthpiece as he did it, valuing the range and control it let him retain over the fuller sound of a larger piece. It is a useful data point, not a prescription: Baker was rebuilding a damaged embouchure under specific physical constraints, not choosing a 6C from a position of unlimited options. But it illustrates exactly what the size is for — control and range retention over maximum tonal breadth.

Who Should Try One

If you play a 5C and want to check whether a marginally tighter rim cleans up the tone without changing anything else about your setup, or you play a 7C and are curious whether the 6C's slightly different bite feels better for long sets, this is one of the lowest-stakes tests available — you are not gambling on a real size change, just a rim contour comparison at essentially the same diameter. It is not a lead-trumpet piece and it is not a deep, dark solo piece; it is a clean, orchestral-leaning middle ground.