[Antonio Freixas]

I think the why its desirable is that without the bladder, the big bass reeds have trouble reliably sounding – if I open the valve THEN blow, its difficult to get the reed to sound with good attack. If I pressurize the chest THEN open the valve, the reed sounds reliably.

Very useful, thanks!

– a charged bladder is necessary for reliable sounding because of initial puff volume

I think air chambers that are either rigid or incorporate a bladder would be equally capable of providing an initial “puff” of high pressure. From my analysis, I suspect the bladder just maintains the higher pressure longer.

A reed’s first swing is small and it builds up with time. The more massive bass reeds may just need a bit more time to get going. The pressure in a rigid case may drop too quickly once the exhaust is opened for them to get going.

In case it’s not clear: I’m agreeing with you, but trying to be a bit more precise about the “puff”.

– a discharged bladder will stop reliable sounding because it lowers the speed of pressure rise

I think you are saying that your test could also be interpreted to imply this, but I’m not sure what “this” is.

If you are saying that when the bladder is discharged you can’t get notes to sound, your test already shows this.

If you are saying something about what happens when a bladder discharges while blowing, I would say that I suspect the bladder never fully discharges while blowing. I believe the only way for it to fully discharge is to hold a key pressed without blowing or take your mouth off the mouthpiece for a while. If you leave it discharged before pressing the next key, we’re back to the first statement.

So I’d say the bladder is there to get the notes going, period.

Could you test this? Sort of. You have to blow hard enough to expand the bladder to its maximum. At this point, the bladder acts just like a rigid air chamber both in volume and pressure. You would want to hold a single note open while you do this. This would make the statement “bass melodicas don’t work well without bladders” false except when you are starting to sound a reed.

The real test would require replacing the bladder with a rigid air chamber and seeing if you could maintain a note once you got it going (even if it was hard to get it going). This would be a difficult test. 🙂

You could also check to see what the bladder does while playing. Just remove the cover and watch the bladder as you play. On my M37C, the bladder never fully deflates as long as I’m blowing. In fact, if I blow harder, it inflates more.

Have you tried a vibrato?