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Very rapid double-double strike after a hard keystroke

  • 1.  Very rapid double-double strike after a hard keystroke

    Member
    Posted 08-11-2022 17:12

    Hi again,

    Same piano (with tubby bass strings) in previous post. Three adjacent notes have developed a very rapid and audible double-strike when played hard, ac#5, D5 and D#5. The best description of it is that it sound like slapback echo (which it of course not). What is the likeliest cause? 

    Thanks.  



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    Benjamin Lian
    88Keys Pte. Ltd.
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  • 2.  RE: Very rapid double-double strike after a hard keystroke

    Registered Piano Technician
    Posted 08-11-2022 17:58
    Is the hammer blow distance set up properly? As felt components compress (especially the wippen cushion and balance rail punching) the key height decreases & there's insufficient travel of the action parts to achieve letoff and after touch. Try raising the capstan for these notes. They may start behaving. Then explain to the customer that piano actions need regulation, even soon after purchase.

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    Patrick Draine RPT
    Billerica MA
    (978) 663-9690
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    Original Message


  • 3.  RE: Very rapid double-double strike after a hard keystroke

    Registered Piano Technician
    Posted 08-12-2022 07:08

    Have you checked for shallow key-dip? Back check problems like too close or not catching well?

     

    Just my thinking.

     

    Paul




    Original Message


  • 4.  RE: Very rapid double-double strike after a hard keystroke

    Member
    Posted 08-12-2022 07:53
    I will check once I figure out how to get at the action. The fall-board left hinge has a small flathead Philips retaining screw that has its drive stripped by another piano tech. 🤦‍♂️

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    Benjamin Lian
    88Keys Pte. Ltd.
    Singapore
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    Original Message


  • 5.  RE: Very rapid double-double strike after a hard keystroke

    Posted 08-12-2022 08:52
    I had a fallboard hinge screw that was stripped once. Try needle-nose vice grips first. I eventually had to I use micro easy-outs (not in a power drill! Do this by hand) and these wearable magnifiers were extremely helpful: https://www.amazon.com/gp/product/B01H8808H6/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1  I also put tape around the screw to protect the fallboard in case my tool slipped. Work slowly and carefully.

    Regarding double striking, as mentioned check after-touch. If there isn't enough this will prevent the hammer from moving away when key is depressed.

    If after-touch OK, note let-off. Is it sufficient? If it is, repetition spring may be too strong. Try setting repetition spring to just barely lifting hammer in the hammer-in-check test. If let-off is OK and spring OK, drop could be set lower; see if that works. If it does, rather than leave drop by itself low, I like to lower let-off to get to the point where there's simultaneous escapement (so raise drop back up tiny bit and lower let-off.)

    In any case if after-touch is good and spring is OK you'll be able to fix the problem by setting let-off/drop slightly lower. Test using a variety of blows, very soft to hard.

    Work on one key first and figure out what's happening.

    You could also try adjusting the gravitational acceler ... never mind.


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    Don Dalton
    Chester VT
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    Original Message


  • 6.  RE: Very rapid double-double strike after a hard keystroke

    Posted 08-12-2022 10:03

    If none of the regulation, drop, letoff, blow distance, and so on work, try repinning the hammer flange so it has more friction. And be sure to set up the back check geometry and hammer friction so that the hammer is properly caught, and then can rise when the key is slightly released. If the hammer flange doesn't have enough friction and the back check geometry isn't good, the hammer can bounce off the back check, and double strike.




    Original Message


  • 7.  RE: Very rapid double-double strike after a hard keystroke

    Member
    Posted 08-12-2022 10:23
    Thanks to all. Would it be possible to narrow down the likely causes if I said that the double strike is really fast. Sounds like a double tone. 

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    Benjamin Lian
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    Original Message


  • 8.  RE: Very rapid double-double strike after a hard keystroke

    Posted 08-12-2022 10:51

    Benjamin, a really quick double strike would suggest that the friction in the hammer flange is far too low, so the hammer is really flyaway -- and that the springs are set too strong.

    But also see if the hammers can get into check. Fiddle with the spring tension and the flange friction and the back check geometry until they do.




    Original Message


  • 9.  RE: Very rapid double-double strike after a hard keystroke

    Member
    Posted 08-12-2022 11:13
    Thanks Susan!

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    Benjamin Lian
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    Original Message


  • 10.  RE: Very rapid double-double strike after a hard keystroke

    Posted 08-12-2022 11:33

    Let me know how it turns out!




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  • 11.  RE: Very rapid double-double strike after a hard keystroke

    Posted 08-12-2022 12:45
    Sometimes if a hammer isn't checking simply roughing up the tail of the hammer-- lightly-- with rough sandpaper does the trick.

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    Don Dalton
    Chester VT
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    Original Message


  • 12.  RE: Very rapid double-double strike after a hard keystroke

    Registered Piano Technician
    Posted 08-12-2022 14:04
    Foreign object like a pen cap may  cause this.
    Original Message


  • 13.  RE: Very rapid double-double strike after a hard keystroke

    Registered Piano Technician
    Posted 08-13-2022 15:14

    Hi, Benjamin

    You've had some good suggestions here, but so far no one has mentioned the jack position. 


    The back of the jack should be in line with the back of the wooden knuckle core. IF it's too far back, then it will not clear the knuckle enough at the end of key stroke causing the knuckle to rebound on it rather than going into check. Check the key dip once the jack position is correct.

    if the jack position and key dip are correct, blow distance is correct, and let off and drop is correct, and aftertouch is good,  then check the repetition spring strength after measuring friction in the hammer flange. You may also need to check the tail arc as well as back check - to be sure the back check is not too far forward and having the hammer tail just bounce off or out, as well as the back check angle.

    BTW, I think that I saw that you're in Singapore, so it may be a wise move to check for high friction overall.


    Chuck 

    Chuck Cook



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    [Chuck] [Cook] [RPT]
    [Cook's Piano Service
    [Griffin] [GA]
    [770-229-4298]
    [800-390-4298]
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    Original Message


  • 14.  RE: Very rapid double-double strike after a hard keystroke

    Member
    Posted 08-13-2022 16:14
    Hi Chuck,

    Thank you for this, because knuckle rebounding on jack fits the symptom best. The sound from the second bounce is very faint. I will update my findings here once I'm able to remove the Philips screw with the stripped head. 

    The client is a piano teacher, so the root cause is more likely to be the action going out of regulation due to heavy use. One other clue that points in this direction is a couple of bobbling hammers in the bass. Friction due to Singapore's climate is not high on my list - the pianos that manufacturers send here generally fare well in our coastal tropical climate with minimum fuss.




    Original Message