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M75 "Thumping"

rfrench5 24 January 2014

Greetings,

I'm back at my lovely M75. So I have been noticing there is a pronounced 'thumping' on all of the black keys from middle Bb to the end of the instrument range. When I say 'thumping' when I hit any of those black keys, whether the dampening bar is pressed on or off, there is a annoying thump - along with the bar note.

This thumping only seems to affect the black keys from middle Bb upwards. None of the white keys seems to be affected.

Things I have tried to resolve the thumping:
1. Completely remove and take apart the instrument (twice) and put it all back together again.
2. Tighten the black key cords. The cords are in very new condition having been replaced back in September 2013.
3. Check all of the frame pieces to ensure they are fitted correctly.
4. Check all of the posts and rubbers on each of the posts.
5. Also put a little bit of sprayed silicon (on a piece of cloth if needed) on the metal pieces which are in close contact or touching, such as the frame pieces and even the pedal nuts and bolts.
6. I closely examined where the the thumping noise seems to be coming from. It does not seem to be coming from the spring mechanism. It seems to be coming on the frame pieces itself, and again only on the black keys from middle Bb upwards. I compared the bouncing on the bar when it's hit (either dampened or not) with a white key, and it seems comparable.
7. Review and tried all of the things identified in the Maintenance section of this forum (I think Marie-Noelle posted a message about the posting.)

Things I have not done or tried yet:
1. Replace the entire dampening bar with the VanderPlas silicon dampening pad

Is there any other things I can try or to look at, such as pads on the black keys frame pieces which are in contact with the large side pieces? This has got me a little stumped as to what's causing the thumping.

Thanks in advance,
Roger

Comments

tpvibes Fri, 01/24/2014 - 13:49

Is the thumping low frequency or high?

Do you hear the thump with the damper released (pedal down)?

Does it change depending on where you strike the bar (edge, middle)?

Are the bars bumping the rail below or the blades in the resonators?

Tom P.

rfrench5 Fri, 01/24/2014 - 14:53

It happens when:

1. Pedal up or down. Doesn't matter. Frequency is a thump, low I guess. A thump is a thump.
2. Bar is striked on edge or middle
3. Bars are not bumping on the blades of the flutter inside of the resonators

Vince H Fri, 01/24/2014 - 16:07

It helps to have a helper when you are looking for the cause of noise. When you strike the bar, a lot of force travels through the bar, to the bar supports, the damper pad/damper bar (If you are not depressing it), and to the edge of the frame and down to the floor.

There could be a loose junction at any point--where the cross-bar/lyre post intersects the sides of the frame is one likely culprit; even though the pedal is down, that junction gets loose. Wheel inserts at the base of the legs is another. Try putting some shock absorbing substance under all four wheels--does that get rid of the thump? It could even be the location of the vibe--maybe you moved to a hollow floor space. You just have to check everything and eliminate causes one at a time. The good thing is you'll be tightening fixtures as you go. The bad thing is it takes a lot of time.

At any rate--you need to work one variable at a time.

rfrench5 Wed, 01/29/2014 - 19:33

Thanks Vince and other for the suggestions and ideas. You get to really really know your instrument if you can carefully take it apart and understand where everything fits in into the function of sound creation of the instrument. I'm sure most of everyone realizes this already.

So I did all of those things suggested by Vince and others, and then it really wasn't to any avail. But one other comment got me thinking, and that was to unattach the springs. I tried that on the black keys and because the chords were not tense, vibration and energy (sound) could not be transmitted 'as efficiently' as if it were tightened, which makes sense. Any of the unwanted, non-bar sound created by striking the bar gets transmitted back to the frame, and other hard components, in part by the cord it self. If the cord is loosened, then it can't transmit the unwanted vibrations (sound).

I then loosened up the cords a small reasonable amount, put the springs back into place. Thus the pair of chords on both the white and black keys was loosened a small amount, and this seemed to greatly diminish the "thumping" on the black keys which I was hearing in the 3rd octave.

The next thing is to replace the felt dampening bar with one from Vanderplas. I hope it will really deduce the weird little buzzing and other unwanted sound behaviours.

Thanks,
Roger

IndianaGlen Tue, 02/04/2014 - 10:59

Could it be the rubber spacers between the bars on the black keys? Perhaps they are old, hard/dry and are bouncing. You may be able to take some tape or fit some rubber bands around them to see if that quiets things down. If they are dry, it's easy to replace them.

-IG

IndianaGlen Sat, 01/25/2014 - 18:00

-- If the thumping is happening with the damper on or off, I don't see how replacing the damper felt would make it go away.

-- Pull out the resonators and put the bars back on and see if the thumping goes away.

--Usually those sounds are worse with softer mallets, get the thumpeist mallets and it may help isolate the noise.

-- Get helper to hit the bar over and over and try pushing on each rail on each end, lift up each corner from the bottom of the vibe by about 1/2" push the center support bar back and forth, push on the pins that lock the bar in place. Remove the white bars and see if it goes away, Try loosening the cord by unhooking the springs.

-- Push down on the resonators (if they are back in).

-- If it's an older m-75 my guess is one of the rails is moving a little sideways and snapping back.

I hope this helps.

BarryK Sat, 01/25/2014 - 21:28

I have noise from my resonator rack when I hit the accidentals. The force goes from the bars to the posts, to the frame, to the resonator hangers, which vibrates the rack of resonators. I hear a click (not a thump).

Your post inspired me to fix mine. What I did was stuffed some rolled up fabric (e.g., socks) between the frame and the resonators so that the resonators are tight against the resonator hangers.

Good luck finding your thump.

Barry

Randy_Sutin Mon, 01/27/2014 - 20:45

I have no idea if any of these will help.. worth trying, though.

- one thin layer of moleskin between bottom of ends of rails and nearby frame parts. This may affect dampening, but if it cures the thump, the rest can be dealt with.

- take off the damper bar, wrap the ends of the damper bars with a couple layers of teflon tape to tighten up the hinge and remount it.

- make sure the mounting screws on the motor and controller are tight.

Best of luck.

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