Good explanation of the voicing process. But when an accordion gets tuned the tuner (repairer) should make sure that tuning and voicing are always combined. An important part of the tuning process is checking whether L, M and H reeds start simultaneously at low volume, as much as possible. I especially check playing the LH register which shown voicing issues on many accordions.
Paul, I want to ask you - on the highest tones of my bassoon switch all the reeds start sounding with the same amount of pressure, but two of them sound quieter and the last one, the A sounds louder. So, is there a possibility that, although a correct voicing is done, there still is some difference in volume and is just some inexplicable reed thing? ?
Accordions are mysterious... but... the voicing is something to be checked visually. It is not very critical regarding how easily the reeds start to sound, but it is more critical for the volume they produce. But then there are also material differences between reeds, and there is the effect of the resonance chamber (inside the reed block) that can amplify one frequency more than another... It is often impossible to make all the reeds sound the same (except for their frequency). If reed block construction were approached in a more scientific way... things might improve.
A loose and perhaps warped reed block is indeed a possible cause of weak sound, and also causes problems with the tuning of the reeds. One way to tell is to place a reed block on a glass pane to check whether the bottom is perfectly flat. Another thing to do is to put the block in the accordion without fastening at the "high" end and check whether it has any wiggle room in any direction (rotation, sideways motion). If it does then it needs "spacers" to block it in place. A spacer on top of the foot where the block is held in place (never on the bottom of course) may help prevent "roll" and a spacer at the far end of the block helps to prevent any longitudinal motion. Checking whether reed blocks are firmly in place is the first thing to do before starting work on valves, voicing and tuning. Sometimes a reed block is warped such that it does not sit firmly on the soundboard somewhere in the middle. You notice that because notes in the middle (typically around 1/3 from the lowest notes) will go up under pressure when you pull but not or less so when you push... Some accordions actually come with a clamp that adds pressure to the center of the reed block, just to ensure there is no leak there caused by warping. There is almost no end to what can be wrong in an accordion... and I'm sure you have seen all possible ways by now!
