speech problem on slider chest

[EdStauff]

On a mechanical action chest (tracker/slider), what could cause faulty speech on the release of a key?

When I release a key in the upper register, the sound doesn't cut off cleanly, but dies with a whimper or a wheeze, as if the palette wasn't closing fast enough. The "wheeze" only lasts around 1/5 of a second, but is very noticeable on the higher pitched ranks, and is especially ugly on the Trumpet when played solo. The problem is always there; it's not intermittent. It only happens (or is only noticeable) in the higher notes, starting around 15 notes above middle C.

This is an 8-stop manual chest (not a pedal chest) in good condition, vintage 1989. It has no doubling or borrowing, but does have one double-draw. I've had the bung off and examined the palettes, but I couldn't see anything obviously wrong.

Anybody have any ideas as to the cause (or, more importantly, a fix)?

Thanks,

-- Ed

[Larason2]

There are a couple of possibilities. A wheeze happens when there is wind being forced through a very narrow passage. It happens on the close of the pipe, which is when the interior pressure suddenly spikes up, so the leak is pushing out. More wind consumptive pipes produce a louder wheeze.

Working from the pipe down, it could be a problem with the pipe or the pallet valve, but I think this is unlikely since it applies to so many notes at the same time. It could be a problem with the release valve on the wind chest or bellows. It could also be a crack or leak anywhere in the wind system. What you would need to do is have someone inside the pipe chest when a pipe is being closed, and then locate the wheeze based on where it sounds like it is coming from. Sealing the leak or adjusting the valve would be something a pipe organ builder would need to do though, I would say. If it's a crack/leak, you may be able to temporize measures with a bit of hot glue until they get there, however.

[myorgan]

An unprofessional question I have is, Could it be lack of pressure causing the pallet not to close? I would think the power of the wind would need to be high enough to close the pallet. Where it appears to be "very noticeable on the higher pitched ranks," it appears to apply to one end of the compass rather than the entire stop.

Have there been any recent changes in the winding system that you know of? Also, to help diagnose, try it with full organ and again with only one stop to see if the issue changes in that scenario. Could someone have wanted a doorstop and took a weight or two off the reservoir?

Michael

[Larason2]

You're right it's possible, but usually if the wind chest pressure is too low, it will cause the pipes to sound flat. Usually the internal wind pressure pushes the pallets closed, so I guess it could be possible. I think it's more likely a crack somewhere though!

[edkennedy]

I'm going to suggest a different reason. An 8 rank chest is quite deep, meaning the channels for each note are long, and hold a fair amount of pressurized air. An 8' Flute stop, which uses a lot of air volume will almost instantly exhaust the pressurized air in the channel after the pallet is closed. A reed stop, which uses less air volume, may sound for a short while after the pallet closes using the pressurized air remaining in the long channel. If I am right, if you draw both the flute and trumpet stops, the trumpet will now stop instantly when the key is released.