Thursday, April 3, 2008

seeking damping materials better than felt

On Wed, Apr 2, 2008 at 10:41 PM, Catherine Britell wrote on Cyberpluckers:

I may have missed it but I don't think anybody mentioned the effect of action on felt wear. I know that with my first autoharp, an OS Centurion, I was wearing out felts every 6 months or so, and then learned from George Orthey about bringing down the action and replacing the springs with lighter ones. That lengthened the life of the felts of that 'harp by 5-6 fold. And of course, the felts on the custom 'harps last even longer...I think because they're not having so much pressure put on them.


We can chase all sorts of factors, but the subject of new damping material for chord bars is suggesting that there is something awful about needing to replace a felt. Felt works very well, so it is a quest for greater durability, less maintenance. Changing felt is part of being a player on a "high maintenance" instrument. One may not need to do a full refurbishing, hiring someone to do that much, but does need to be able to keep playing when something goes wrong. Keep the supplies available and just do silicone, no synthetic rubber, no extra hard felt...change your felts, possibly one at a time.

It would be rare, I think, for all the felts to need replacement at once, unless they were never right or good quality. Then other than upgrading quality of material, one shouldn't think of it as this big project to replace them all. It was mentioned already about paying attention to those most often used chord bars.

When a string sounds buzzy or dead, CHANGE IT. Again, part of that is already owning the strings so it can be done on impulse, one string, one felt at a time, no big project planning effort, or waiting for an order...10 minutes instead of 5 hours.

Other factors

I think it is a good idea to avoid changing the heavy plain wires as long as possible. They will sound good indefinitely. They arch over any bridge for quite a long time, eventually settling more flat. New, larger diameter strings, (say #15-20 or lower, .028-.024 dia.) strings sit higher and will quickly ruin a set of felts, especially when the strings eventually settle away from the felt grooves to a lower position, and damping deteriorates.

I know about the trick of bending the string to remove the arch, but that can result in the string sitting too low, again a felt damping problem as a result. I don't bend strings until they are done stretching and the ball knot is firmly drawn down, able to hold tuning. Then the bend isn't going to move and create a different effect later. I am very careful with it, because if bent too far, realistically the string must be replaced.

Part 2

I am not getting how a lower, softer action lengthens the life of felts. It seems like saying that if one maintained better tuning, their felts would last longer, logically somehow disjointed. I suppose it can teach one that there is no need to be as aggressive in pressing a chord bar button, mashing the felt in the process. That is psychological more than mechanical, I think, part of a grander dynamic including the player.

Longer action could mean that one builds a certain momentum before slamming into the strings, inertia becoming a factor. I just think that is all too much to attribute to 1/16" of action (bar travel) at best. It's enough to say that close action improves the timing between the left and right hand, and that light springs simply make a nicer player experience and cause less wear on counter padding affected by spring tension preload, springs taller and stiffer than they need to be. If stiffer is bad, then less stiff must be good, except past the point where friction in the bar system is no longer overcome and the bars don't work as intended. I have actually encountered a bar or two where things didn't work quite right until I inserted a stiffer or taller spring. There then is a point that is "too light", or alternate springs simply become another adjustment option. Bars that work perfectly due to precision would be more expensive or would provide enough tolerance in spacing to ensure running freely, possibly taking away significant picking area after multiplying allowances by the number of bars.

So you have mentioned felts, strings, and springs in a few statements, possibly prompting quite a lot of discussion to sort it out.

Finally, harking back to Todd's OP information about new damping material, I would be delighted to see a better item, but we have been through this years ago about Sorbathane in various forms, Mark's mouse pad for one, being inferior to dense felt in ability to damp vibrations. It is practical, maybe, but not better or as good...same story as using silicone...not a panacea.

It isn't felt in general. It is dense and then fairly hard felt. Too soft and the felt requires too much maintenance. Too hard and the felt becomes a sound conductor, counterproductive. That is aside from hard felt being unable to conform to an uneven string bed. We should also consider that very hard felt is used for piano and cimbalom hammers. One could actually sound both a chord and the strings to be damped by quickly pressing and releasing a chord bar. Any string unintentionally struck, par for playing the autoharp, could also produce noticable sound, spoiling the chord.

I believe effective density is part of the problem with synthetic padding. Once it compresses to a certain density, it becomes a conductor. Some parallels can be drawn with deeply grooved felt, the felt likely packed quite densely at the bottom of the groove. Pressing harder on a bar isn't necessarily helpful. There is a point of diminishing returns, all mitigated by regularly changing to new felt, that is well adjusted by shimming or plumping techniques. The string surface is simply not flat and becomes the source of a number of problems.

Some of these lessons were learned with lockbars, using various materials and having locking mechanisms that created various amounts of damping pressure. Felt is not favored because it compresses and conducts a thumping sound from a damped string. Sorbathane pads (mouse pad et al.), the more forgiving, are covered with a layer of sheet felt to improve damping. Adjustment is very critical so the sorbathane doesn't become too compressed (dense). I like to use felt on lockbars but only because I do it and can stand the pain of getting it adjusted. I wouldn't offer it to someone else without discussion of caveats and options. Actually, I have not found a better alternative to George Orthey's idea of using Dr. Scholl's Molefoam over spacer layers made of Scotch Mounting Tape. Truly, when it comes to lockbars, damping is really put to the test. That is where the science of damping mostly originates, where small differences are measurable and significant.

To me, the ideal damping material would about 3/32" of semi-hard felt firmly bonded to a layer of spongy material just soft enough to respond to typical chord bar pressure, thin enough to be laterally stable. The ultimate test, smallest application is a 1/4" square. So that would be a special size of familiar chord bar felt fused to something like common mousepad. I have used exactly that in a few cases but it was tedious to make and I haven't yet achieved a good bond between the layers. Glue soaking into felt can harden and ruin the desired result, so no solution will be easy to find, any old glue will do.

Boyd Jackson, as a chemist interested in the subject, could make a real contribution by giving his material an F1 felt face and mastering how to bond the two materials firmly together to the point where very small pieces don't come apart after some torture in use.

Lastly, there is always a problem getting nice cuts on spongy material. I would be happy to see someone provide such material already cut into strips of common sizes. I can get pretty good cuts but I have special tools and had to learn some technique. It shouldn't be that hard to do well.

Bob Lewis

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