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noisy back rail cloth

  • 1.  noisy back rail cloth

    Registered Piano Technician
    Posted 01-21-2021 22:19
    Greetings all,
    Usually I ask questions about things that bother me but not the customers. Not this one.

    The piano is a Kawai grand KG-3D from the 1980s, and the customer was obsessing about noise which didn't seem that unusual to me for a piano of this age. I isolated the noise to the keys hitting the back rail felt--no jacks making noise, nothing else I could find, no clicks or anything else. Just the return thump. Same sound in non-damper areas.

    The ideal thing is to replace it, but I'm just wondering if there are any other solutions that will avoid a regulation job. Has anyone, for example, tried needling the felt? Using VS Profelt? I don't know whether the felt is totally glued down on this piano.

    thanks!

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    Scott Cole, RPT
    rvpianotuner.com
    Talent, OR
    (541-601-9033
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  • 2.  RE: noisy back rail cloth

    Registered Piano Technician
    Posted 01-21-2021 23:02
    As you suggested, one factor is whether or not the felt is glued all the way, or just at the front edge. If it is glued all the way, you might be able to cut the glue bond, but then you'd have hard glue in the felt, so you probably wouldn't get noise reduction that way. 

    The quietest design is two or three layers of felt and cloth, glued only along one edge. That's what some of the high end German manufacturers do. You might be able to devise a sandwich that duplicates the existing thickness, so you wouldn't end up with a regulation disaster. Alternately, you could also duplicate the existing cloth's thickness (just replace with one thickness), but Glue the replacement only along the front edge. Jurgen at Pianoforte Supply has 5, 6, 7, and 8 mm thicknesses, one of which should be very close.

    I doubt needling or Profelt would help. I haven't tried it on back rail cloths, but I have tried on key end felts to reduce the impact feel, and couldn't tell the difference. Similar lack of results on wipp cushions and the like - lots of work, minimal permanent improvement. To experiment with little time investment (besides R & R the action), you could steam the cloth with a travel iron, then follow with a heat gun to dry.

    It is possible some of the noise comes from the knuckles and perhaps wipp cushions. There is some bounce that occurs, so often return thunk comes from a few contributing factors at once. 
    Regards,
    Fred Sturm
    University of New Mexico






  • 3.  RE: noisy back rail cloth

    Member
    Posted 01-23-2021 10:12
    I am not sure if this piano has any metal rails in it but metal rails have a tendency to amplify sounds/noises. I would go with replacing the backrail felt and getting all of the old glue and felt off. New felt should only be glues on one edge not smeared all over. You may have to touch up the regulation because of the height changes the new felt introduces so it is important to match the thickness to the old. Jurgen is probably the best source. needling/fabric softener/vs is likely to give only temporary results. many times noise is the sum of the parts so you should look at other things as Fred points out- hard knuckles, whipp cushion felt and even the drop screw leather. all of the felt pads on the whippen as well as the jack adjustment felt.

    although i have not tried it it could help to put some rubber grommets in several open areas of the metal and maybe the wooden rails. this is what appliance makers have been doing on dishwashers and one of the reasons they run quiet. i have a bosch dishwasher that barely makes noise and replaced a brand that sounded like a cement truck

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    James Kelly
    Owner- Fur Elise Piano Service
    Pawleys Island SC
    843-325-4357
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  • 4.  RE: noisy back rail cloth

    Registered Piano Technician
    Posted 01-23-2021 13:31

    I like what Fred wrote – good points, all.

     

    I like to really isolate where the noisiest points are with action return noise.

    • Lift up the hammer, lift up the wippen with one hand, then tap the key down at the back to really tell how noisy the back rail cloth is. 
    • Next hold down the key at the back and drop the wippen on the capstan – it can be surprising!
    • Then keep holding the key down with the wippen sitting on the capstan, and drop the hammer shank down a few times to check knuckle noise.
    • Also, check how loose the key balance holes are.  Pick up the key fronts and drop them.  This can be a big source of action noise also!  If you remove the keys and wet size the balance holes (just with boiling water is fine, I don't like to harden the wood with glue unless they are really loose or overly soft feeling). After they're dry, re-fit them on the pins and keep them slightly snug. A little Teflon of some kind on the key pin helps this – they should slide back down to rest but not drop freely to rest.  This can help repetition sometimes, also, by reducing key bounce.

     

    Knuckles can be made quieter by needling through the core felt side to side right at the flattest point.

    Wippen heel cloth can be made very quiet by flipping the stack over and putting a few drops of warm 50% alcohol/water in the capstan dimple. 

     

    One thing I disagree with is regarding metal rails making more noise – in Kawai actions the spruce keyframe is a big part of the action noise being radiated into the air, not the action rails.  If you try tapping or thumping on action rails in various pianos, I find that the wood rails make just as much noise as metal ones - often more!  The Kawai rail is especially rigid and non-vibrating (look closely at how it is made), even when old like this – thumping on them transmits noise to the keyframe, but doesn't make any noise within the rail that I can tell.

     

    Finally, room acoustics REALLY contributes to how much action noise one hears.  A piano with the tail in the corner of the room especially, and a live environment with wood floors etc., will really boost the amount of action noise heard.  I have had some people just move the piano out of a corner and fixed the complaint that way.

     

    Good luck with it!

     

    Don Mannino

    Sent from Mail for Windows 10