Duo-Art Playing Too Loud
By Pete Knobloch
INTRODUCTION: My name is Pete Knobloch. I'm in Phoenix, Arizona, and have been working on various types of player pianos for about 6 years now.
After working on about 4 older uprights, which all required major stack work, I found a Duo-Art Grand and my interests then moved to reproducing pianos. I am currently running out of room with 3 grands and 4 uprights in the house.
PROBLEM: I am having problems with the volume on my 1926 Steinway Duo- Art grand playing too loud. This piano has been with me for about 4 years now. The pneumatics seemed to be okay when I first bought the piano, but they started to leak more as time went on. Some of the notes started to drop out after playing the piano for about 8 hours a week over a period of about 2 years. I compensated for this by increasing the zero adjustment on the expression box as time destroyed the old pneumatic cloth.
After putting up with this for about 4 years and getting enough experience working on other pianos, I removed the stack and installed a complete new set of pneumatics (which I built). The Zero-Adjust was regulated back to the proper setting using the Duo-Art Test Roll. The piano plays beautifully when playing very quiet passages but drives every one out of the house when playing loud.
Another secondary problem that popped up is that there is a point where the playing volume seems to increase exponentially. This happens somewhere above level 10 or 11 (#2 and #8 accordion pneumatics closed). I never noticed this problem until after fixing the stack problems. I measured the distance that the accordion pneumatics would move for all of the 15 volume settings and it moved the specified 1/16 of an inch. Note: I disabled the Crash value because all it did is aggravate the problem.
I have made 2 changes to fix the loud playing problem but I am still not satisfied:
1) I Reduced the pulley diameter on the motor from the original size of 1-5/8 inch to 1-3/8 inch. This was the smallest pulley that I could find. This reduced the speed of the pump which has reduced the maximum vacuum going to the stack. The piano volume was made significantly quieter with this one change. It was still playing too loud and the exponential loudness problem got more pronounced.
2) I reduced the distance that the accordion pneumatics would close. The larger #8 pneumatic was originally set to 0.5" so I readjusted it to 0.4" and changed the remaining 3 to be half the distance of the previous. This was done to both accordions (Theme and Accompaniment). Doing this change has brought the volume down to a level where it is okay with the top lid of the grand closed but I would rather play it with the lid open. The exponential loudness problem moved to where it is hardly noticeable for some unknown reason.
Something else that affects the vacuum level to the pump is the spill valve found on the expression box. As the expression level gets louder this value closes, giving more vacuum to the regulator to drive the stack. I would think that this exponential loudness problem was because of this spill value not operating properly but the piano doesn't change volume at all if I manually open and close the spill value with my hand while the piano is playing. The pump motor is only stressed. Because of my change described in section 2, this isn't a real problem any more unless I go back to standard accordion distances of 1/2, 1/4, 1/8, and 1/16 of an inch.
What should I do at this point to reduce the volume some more? Did Aeolian have another method of regulating the volume such as changing the spring weight (ft/lb)?
Should I continue reducing the total amount of travel of the accordion pneumatics even though the Reblitz book states it to be 1/2, 1/4, 1/8, and 1/16 of an inch? This is the easy way to solve the problem and it doesn't seem to have any other after affects.
I don't know when the expression box was rebuilt but I know that new cloth has been glued just under the wood inspection cover. It seems to be working very well with the exception of moving too much air when playing loud.
My next step would probably be to reduce the speed of the vacuum pump again by having the pulley turned on a lathe. The only problem with this is that I have seen other problems pop up if I try to do this manually by letting the belt slip on the motor pulley.
Does any one have any suggestions or comments about this problem?
Pete Knobloch
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