Reed Starts Fine, Then Goes Sharpas Bellows Close

[aldee]

THE REED IS O.K. FOR SHORT NOTES BUT WILL SHARPEN AT THE END OF A SUSTAINED NOTE.

 

I'VE TRIED CLEANING THE EDGES AND UNDERSIDE OF THE REED AS IN DAVE ELLIOT'S MANUAL

 

TO NO AVAIL.

 

THANKS IN ADVANCE FOR ANY SUGGESTIONS.

Edited September 8, 2006 by aldee

[Greg Jowaisas]

How are the valves? Check both valves for clearance (possible impingement on side of chamber) and closure.

 

Best of luck.

 

Greg

[Theo]

Is it only when the bellows are nearly closed that the notes sharpen? If so there could be some part of the nearest bellows fold that has come adrift and is able to touch the reed when the bellows are almost closed.

[Dana Johnson]

Is this a new problem, or just something you've noticed using the note for more things than you used to do. and also sharpen by how much?

Different things can affect reeds, and mid and low range reeds often behave differently than high range reeds. Mid and low reeds are often affected by not being cenetered in their slots. If a reed is off center, it will tend to blow flat very easily. The more off it is, the more pronounced until it actually starts to hit the side of the reed window. Then the opposite happens. Also, if a reed is clearing the window in the shoe, but swings far enough to hit the port wall in the reed pan, that can raise the pitch at higher volumes.

 

What you are experiencing though sounds like something I've seen many times as the reed experiences a difference in it's cavity surroundings. With the bellows oepned a bit, the reed has a certain relationship to the way the air behaves in that system. Essentially, the reed notices the junction between the very confined space of the reed window and port, and a comaparatively infinite space in the open bellows ( thousands of times the volume.) when the bellows is nearly closed, the reed starts to notice the bellows space more and interact with it more. the reed actually finds less air resistance as the cavities come closer to acoustic matching and now communicating instead of reflecting the pressure waves. The reduced air resistance leads to an increase in reed velocity and pitch.

 

Reeds are difficult to tune accurately for all conditions. Some reeds are stiffer and more independent of these processes, and some are very affected by them. Usually when you tune a reed, you tune for the mid range of playing volume, and it will be a little off one way or the other outside that playing range. The same goes for bellows extension. If a reed is tuned in a condition similar to a very open bellows, it will tend to sharpen with a closed bellows. A good reed will do this only by a few cents, but noticeably. If tuned with surroundings that feel like a closed bellows, it will play flat when the bellows is opened. You try to find some medium that leaves the reed lattitude on either side. Unless you have a condition like was mentioned in an earlier post where the bellows folds actually touch the reed, (this is a fairly abrupt phenomenon and not so common ). I think it is more likely that you are just dealing with the nature of the beast. If it is this sort of thing, you just need to look at it as part of the concertina sound and be glad you aren't playing Uilleann Pipes!

 

Check to see if other reeds have similar issues. Reeds that lie near the edge of the reed pan paralell to the folds are more prone to reed impingment on the bellows. Reeds who's tips are toward the center of the reed pan are not. Check to see whether the reed tends to be sharper at light playing pressures than at mid range pressures even with the bellows open.

[d.elliott]

I would suspect that a bellows fold is touching a reed, there are straightforward solutions, but usually more than one reed is affected

 

D

[d.elliott]

I would suspect that a bellows fold is touching a reed, there are straightforward solutions, but usually more than one reed is affected

 

D