The F Attachment

What the thumb trigger really does to the slide: every position measured in centimetres, side by side, and when to use it.

the short answer

Pressing the trigger makes the whole horn 33.5% longer — a perfect fourth lower — so every slide position moves 33.5% further out. Only six fit on the slide.

Top row: the seven ordinary B♭ positions. Bottom row, in green: the trigger positions T1–T7, measured with the same formula, and (small numbers) where each one lands in B♭ positions. T7 — low B — would need 75.7 cm of slide, past the end.

try it: one slide, two horns

thumb trigger down · slide at 0.0 cm — where B♭ position 1.0 would be

Slide 0.0 cm out from closed — 1st position (1.00 in B♭ positions).

the notes this slide spot gives you

the exact comparison

Slot	B♭ side: slide out	B♭ side notes (h2 · h3 · h4)	Trigger: slide out	Lines up with	Trigger notes (h2 · h3 · h4)
1	0.0 cm	B♭ · F · B♭	0.0 cm	1.0 — 1st position	T1: F · C · F
2	8.1 cm	A · E · A	10.9 cm	2.3 — between 2nd and 3rd	T2: E · B · E
3	16.8 cm	A♭ · E♭ · A♭	22.4 cm	3.6 — between 3rd and 4th	T3: E♭ · B♭ · E♭
4	25.9 cm	G · D · G	34.6 cm	4.9 — a short 5th	T4: D · A · D
5	35.6 cm	G♭ · D♭ · G♭	47.5 cm	6.2 — a long 6th	T5: D♭ · A♭ · D♭
6	45.9 cm	F · C · F	61.2 cm	7.4 — past 7th — the very end of the slide	T6: C · G · C
7	56.7 cm	E · B · E	75.7 cm	8.6 — off the end of the slide	T7: B · G♭ · B

Measured for an effective B♭ air column of 2.74 m. Real horns differ by a centimetre or so — every slide is tuned by ear — but the pattern is fixed by physics: the trigger gaps are always 1.335 times the B♭ gaps.

same note, with and without the trigger

C
Without: 6 (45.9 cm)
With trigger: T1 (0.0 cm · 1st position)
saves 45.9 cm of reach
B
Without: 7 (56.7 cm)
With trigger: T2 (10.9 cm · between 2nd and 3rd)
saves 45.9 cm of reach
F
Without: 6 (45.9 cm)
With trigger: T1 (0.0 cm · 1st position)
saves 45.9 cm of reach
E
Without: 7 (56.7 cm)
With trigger: T2 (10.9 cm · between 2nd and 3rd)
saves 45.9 cm of reach
E♭
Without: not on a straight tenor
With trigger: T3 (22.4 cm · between 3rd and 4th)
D
Without: not on a straight tenor
With trigger: T4 (34.6 cm · a short 5th)
D♭
Without: not on a straight tenor
With trigger: T5 (47.5 cm · a long 6th)
C
Without: not on a straight tenor
With trigger: T6 (61.2 cm · past 7th — the very end of the slide)
B
Without: not on a straight tenor
With trigger: off the end of the slide

when players use the trigger

C (h3) in T1 instead of 6th — the classic. Same slide as 1st, so B♭–C–B♭ needs no slide move at all.
B♮ (h3) in T2 instead of 7th — T2 is a long 2nd (10.9 cm), not a 7th (56.7 cm).
Low F and E (h2) in T1 and T2 instead of 6th and 7th, for anything quick down there.
The missing low notes E♭, D, D♭ and C below the staff exist only on the trigger: T3, T4, T5, T6.
F (h4) in T1 — an alternate to 1st position when you are already on the trigger (C–F becomes a lip slur).
Positions are wider — reach T3 at about a short 4th, T4 at a short 5th, T5 at a long 6th. Don’t place them where the B♭ numbers are.

the catches

Low B is missing. T7 would be 75.7 cm out; a tenor slide ends near 64 cm. Pull the F tuning slide to E to get it, then re-learn the trigger positions.
T6 (low C) sits a little past 7th — the very end of the slide. Get there early.
Tune the F side too. Play C in 6th, then C in T1, and move the F tuning slide until they match.
The extra tubing resists a little more. Keep the air moving through trigger notes so they don’t go stuffy.
A glissando can’t cross from one side to the other — the trigger is a switch, not a slide.

why the trigger positions are further apart — the maths

1 · A fourth lower

B♭ down to F is five semitones. Pitch falls by 2^1/12 per semitone, so the tube must grow by 2^5/12 = 1.3348 — almost exactly 4 ÷ 3 = 1.3333. The rotor switches in 0.92 m of extra tubing.

2 · Same semitone, longer tube

One semitone lower always means the whole tube × 1.0595. A longer tube needs a longer piece added: on the F side every gap is 1.335 × the B♭ gap. 1st→2nd: 8.1 cm vs 10.9 cm.

3 · Six fit, seven don’t

B♭ 7th is 56.7 cm out. × 1.335 = 75.7 cm for T7. The slide runs out near 64 cm, so T6 (61.2 cm) is the last trigger position that exists.