Reed that drops by over 12 cents under pressure!

[Nigel Champion]

I have one reed in a 1972 Crabb 48-key EC that drops by 12 cents under pressure.  It is one of largest/lowest reeds.

 

I've wracked my brains for a possible cause.  Any advice would be appreciated.

Nigel

[Matthew Heumann]

I found when restoring my baritone that the largest deepest notes were the most sensitive to incorrect profiling. If arched too much or too little or if the end is too curved, the damn things really go off. It took me quite a while to get each one just right. the other likely cause could be uneven snugness in the reed slot. I'm sure a few of our expert makers could also come up with some good solutions.

[d.elliott]

Usually this is a weak reed, either from over filling ,or cracking before tuning. The lower notes on English systems can be a bit of a compromise, If the reed is shorter (small scale)  the lower pitch being achieved as result of weighting to reed tip or filing the belly of the reed too thin. This over filling can be the result of re-work if the reed was made too sharp. Initially try swapping the reeds push to pull. if the fault moves with the reed, then a reed replacement  may be required. if the fault stays with the position then you are probably looking at valve, or chamber issues. You don't say which reed note, or if the recalcitrant reed is on bellows push or pull.

 

The other issue is as Matthew says on of profile.  If the fault moves with the reed, check the reed profile, it might be wanting to stall at over pressure and you may need to increase the reed tip gap.

[Chris Ghent]

If it returns to the original pitch after dropping 12 cents it is too thin in the belly. If it stays down it is cracked.   

[4to5to6]

On 8/18/2025 at 3:35 AM, d.elliott said:

The other issue is as Matthew says on of profile.  If the fault moves with the reed, check the reed profile, it might be wanting to stall at over pressure and you may need to increase the reed tip gap.

I would be interested in learning more about how the reed tip gap affects choking / stalling of the reed.