Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Effect of pressure bar on string vibrations and tone?

I had been wondering about the effects of the "non-speaking lengths" on tone before I revived the D7 note mentioned in a recent thread about a possibly faulty hammer.

If running the plastic tip of a biro up the speaking length to the v-bar could affect the tone, what about the string on the other side of the v-bar? Would tweaking the strings at the pressure bar have an effect?

Well, you guessed it, it did. There was more of a singing quality and the sustain was longer, more pronounced. Just to make sure it was not just a figment of my imagination, I repeated the test on the other 58 notes along the pressure bar - by gently moving the strings above the bar sideways. The bells in "Oranges and Lemons", the nursery rhyme on London churches, bloomed and rang out.

Del has said (post #909400, 10/25/05 12:42 PM) that effective termination in vertical pianos depends on the pressure bar as well as the v-bar. Based on what Giordano and Korty wrote about their experiments on string and bridge movements, I guess the longitudinal vibrations in the string were being damped in some way, diminishing the power of the higher partials and overtones.

What should I do now? The piano is 86 years old and, maybe, the strings behind the pressure bar had never been disturbed before. The bar has a half moon profile and the curved surface feels slightly rough.

Should I release the pressure and clean up the bar, spray it with a cleaner or lubricant (which ones?), or leave well alone and carry on tweaking as necessary?

Continue to "pitch woo" with this piano. You will feel your love returned to you.

That is what I really think is going on. I do the same thing with some of my possessions.

Although it is possible to flex the strings on a solidly tuned piano and not disturb your recent tuning, to move them around under the pressure bar will at least disturb unisons somewhat. It is difficult to ascertain what is causing what when so much changes. A slight change in the unison will create the appearance of more sustain and not necessarily address the main cause.

I would be inclined to leave cleaning abd dressing the upper termination points until restringing time. You can be certain that removing the pressure bar will totally destroy the tuning, pitch and stability, even if you manage to put it back at the same tensions, extra work is to be expected at the next tuning.

Unless it is actually buzzing or your tuner reports poor tuning qualities (I have never come across an Ibach where this is a problem) there is nothing to be gained from removing the pressure bar. Seating both sides of all the termination points before tuning will accomplish the same effect.

Maximum transference of power comes from adjusting the resistance (flexibility) of the hammer to the resistance (flexibility) of the string(s). Somebody please correct me if this is off base but it's the way I find helpful to look at it. this balance of resistance is very important for adjusting sustain qualities and, unless the string is physically impeded by excessive dust and debris in the bridge notch or something similar, the hammer and action are the adjustable factors. Usually a single long needle parallel to the moulding will be enough if the hammer shape and everything else is good.

For sure, Jeff, but don't let The Bells of St Clement's and my piano mislead you. The main point of the OP is the effect the non-speaking length between the tuning pin and the v-bar can have on string vibrations and tone, as implied in the title.

Thank you, rxd, for your advice. I imagine everyone will agree with you about leaving the pressure bar well alone.

Seating the strings at both sides of the pressure bar before tuning makes absolute sense but I have not seen anyone say that before, other than BDB who mentioned taking off some tension to loosen any rust and even out tension when tuning.

There is no doubt that this procedure produced a really significant change in the Schiedmayer. I am sure a before and after frequency power spectrum analysis would prove the point.

The interesting to me question is why this can happen, though I think you cover that, rxd, by the string being "physically impeded". In this case, presumably, that means the string cannot move easily at the pressure bar in response to vibrations. As I mentioned in the OP I guess the power in the longitudinal vibrations dissipates at the bar.

In consequence, if Giordano and Korty are correct in what they wrote in 1996, and if I understand it correctly, the upper partials will suffer. Their measurements showed, as may be well known, that the power of these partials in the transverse waves of the string is much less, by several orders of magnitude, than that in the soundboard and the sound. In fact they say the piano string itself sounds like a guitar string.

They also suggest that the power in the longitudinal wave creates the equivalent of transverse vibration at the bridge due to small bulges and depressions in the surface of the string created by the movement of the longitudinal wave.

So I guess that anything that interferes with the the movement and reflections of the longitudinal wave between the tuning pin and hitch pin, other than the bridge itself, will affect its power and therefore the tone. Sometimes critically perhaps.

My tuppence worth.

You are talking about the "speaking" of the "non-speaking length" (ahem...)

Maybe you could have someone ELSE randomly dampen and undampen these non-speaking lengths, without you knowing which ones, and then YOU play the notes and see if you can tell the difference.


I just looked up the synopsis of the paper you are referring to:

"Motion of a piano string: Longitudinal vibrations and the role of the bridge

N. Giordano and A. J. Korty Department of Physics

Using strain gauges as a tool, new results have been obtained for the amplitude of the vibrations of the bridge and soundboard of a piano. These results should prove valuable for the construction of theoretical models of the role of the soundboard in sound production. In addition, they indicate that longitudinal string vibrations, i.e., the stretching and compressing of the string, make a very important contribution to the initial sound signal. The amplitude of this longitudinal motion is a nonlinear function of the transverse vibration amplitude. The mechanism by which the longitudinal vibrations couple to the bridge motion has also been considered. © 1996 Acoustical Society of America."


This seems to be talking about the "non-speaking" lengths at the other end.

How can anyone aurally tune or voice a piano if everything they hear is a figment of their imagination?

... and now a lady has just walked in out of the blue to give me a massage ... more later!

If a tree falls in the forest and there is no one around to hear it, does it make a noise? See, we cannot get away from perception. (I am fascinated by the discovery of "dark matter.")

Doing what I suggested would determine if this IS a figment of your imagination.

But as far as tuning, that is what checks are all about. You can have progressive 3rds and not have an equal temperament. But if you have progressive 3rds and 6ths then it surely is ET.

The "speaking" of the "speaking length", actually, in response to the question "Interesting that X should have an effect, seeing that X is not even part of the speaking length?".

For X read non-speaking length, tuning pin, pressure bar, hitch pin, or whatever.

The non-speaking lengths can certainly have an effect. One post I read said re-seating the string at the hitch pin brought a dead note back to life.


Yes, if damping were the issue, but the strings were re-seated at the pressure bar and took on a new lease of life. I hope the change is not reversible.

To illustrate the difference, let's bring back Jurgen's roomful of experts from the other thread for a before and after experiment. At the end, the presenter talks about bloom and sparkle and says he replaced the 80 year old strings. Ok we can hear that, the experts retort, but what about those unisons?

It would be interesting to know to what extent re-seating strings at the pressure bar is general practice. I can see it might usually be unnecessary.


Giordano and Korty measured the transverse and longitudinal vibrations at the bridge because they were interested in how energy was transferred to the soundboard. As we are talking about wave motion, it's reasonable to assume measurements of the vibrations at the other end of the string would have been equivalent.

This brings us to Del's comments about the termination points:

The duplex string segment sings anytime its natural fundamental vibrating mode ends up close to the fundamental, or some partial of that fundamental, and the string deflection angle is small enough to constitute an inefficient termination to the speaking length.

To repeat energy transfer across the string termination is a function of the shape of the termination point (i.e., usually the V-bar), the string deflection angle, and the length of the duplex string segment.

With one or two notable exceptions, upright pianos rarely, if ever, have string noise problems through the tenor and treble sections even though their string deflection angles across the V-bar are often quite low. And despite the fact that vertical piano V-bars are often very poorly shaped. The reason they do not is because there is a pressure bar very close to that V-bar. The duplex string segment between the V-bar and the pressure bar is very short. Hence the string termination is very efficient despite the shallow string deflection angles typically found here.

Del's first paragraph shows he is talking about the transverse vibrations everyone associates with piano strings. The Giordano and Korty paper and the synopsis emphasise the importance of the longitudinal vibrations which store much of the potential energy. As the angle at the v-bar is likely to be quite low, according to Del, the longitudinal wave will tend to carry on while the transverse waves are largely reflected.

I guess it is this energy that will be lost if, as rxd puts it, the string is physically impeded. This could happen if there is some crud at the pressure bar that interferes with the stretching and compression of the string. Remove that and the longitudinal wave will carry on to the tuning pin where it will be reflected back towards the bridge.

So thank you to Mark for raising the question even though one or two of the unisons are howling a bit in protest at the answer.

That's most of the change in my pocket for now.

Ian:

I have no idea where to even start in response. I don't think you are interested in following what I or anyone else is saying. You seem to have a "Damn the torpedoes full speed ahead!" attitude.

Ian, I hope I'm not being pedantic but your statement that seating the string at the hitchpin will bring a dead string back to life is a bit Lazarus for me the way I read it!! It will, however be enough to get that bit extra from a note if necessary.

Jeffs' comment about seating round the pressure bar I agree with. While it does have its effect on the sound, I rarely find it necessary. I am never fighting for extra sound with an upright in most upright type circumstances. I will say, however, that a good 10 second scrub round there with a fairly stiff brush will approximate the results that Ian got with a biro pen and padded screwdriver but without disturbing the tuning. I have a plastic brush that I found in the road one day when I was riding my bike about 10 yrs ago. One of the most useful tools I ever had.

Seating strings to the extent practiced in the past 30-40 years was almost unheard of in regular piano service. I thInk it was Yamaha that first recommended it as a regular part of maintenance.

Although I use seating and leveling when the sound of the note demands it, I must admit to benign neglect in this area. I prefer the warmth that develops in the sound when strings haven't been seated for a few years. I always seem to have more than enough quality well defined sound without it.

I haven't seen much crud around pressure bars lately but I have seen some In the past that were turning green and fuzzy.

I often service pianos that are regularly tuned by someone else so I have an arsenal of techniques that don't disturb the tuning.

rxd, no you're not being pedantic, I can't find the post about the dead note and the hitch pin again. I came across it by chance and made a mental note when looking at what Ed Foote and others had to say about tightening coils.

People have described Schiedmayer & Soehne tone as mellow and, sure enough, a recording showed it was lacking higher partials compared with other pianos from Germany and Stuttgart. These have now returned adding an extra dimensions to the tone. That's worth a tuning.

The effects were quite consistent from note to note across the 59 keys. I am not a great believer in boasting about special ailments, or having any at all, but there it is.

I wish I too had picked up a stray brush marked "For cleaning pianos". Whether it would have done the trick I shall never know.

Jeff

Yes, damn the torpedoes; they all going off in the wrong direction, wasting a lot of energy. Treading on a landmine in a post is worse. Point taken.

I happened to see you chopped down a tree at the weekend. Did it make a satisfying noise?

Speaking of perception, the Christmas lectures for kids at the Royal Institution in London and on the BBC this year were about the workings of the brain. The presenter focused the audience's attention by asking them to count how many times some jugglers tossed Indian clubs at each other. No one noticed the gorilla walk across the back of the stage.

When it comes to pianos, one can take this perceptions and preconceptions thing a bit far. Jurgen had a good story about auto-suggestion, but rxd's party piece about fixing the weakest note scarcely comes into that category. I was reminded of it the other day and spot on the screw was not quite tight.

All this is a roundabout way of saying I thought you had jumped on that bandwagon with your proposal of having someone dampen some notes and see if I can tell the difference. There really is no need. Reshaping heads, tightening loose plate bolts, and increasing the blow distance had each had an immediately noticeable effect on the sound. The pressure bar effect was right up there with them.

Did you mean dark matter as an allusion to longitudinal waves in strings? There are some parallels; you can't see them but it seems they need to be there for a piano to sound like a piano. By the way, how do you dampen them?

PS Lisa, who interrupted my notorious post, is no figment of anyone's imagination.

Ian:

Just because you are convinced of something, does not mean the rest of us should believe it too, or believe it for the same reason. That is why I suggested the blind damping test: to provide more convincing info for all of us.

But I was just now thinking about what you actually did. You moved the strings sideways on the v-bar and pressure bar. There are times I have done the same thing. Usually it is to get the strings to work better with a damper, but it will also change the tone because of where on the hammer the strings strike! It is much like using the una corda pedal to use a softer part of the hammer to change the tone, or even addidng some shims to the una corda stop to soften the tone of the entire piano in an emergency.

What you are experiencing may have nothing at all to do with longitudinal waves. We did get diverted with the feather treatment when what was actually done physically moved the strings.

Oh, and there were many satisfying sounds involved with the raccoons.

Jeff:

Yes, quite right, but does not mean you should disbelieve it either. I'd agree it's generally a good idea to add an "or something else" to any list of possible explanations.

To recap and clarify, I did two separate things for different reasons. The first to restore sound to D7 which was "dead", a light touch to start with and moving the strings at the v-bar to make sure (D7 only). Days later, the second was triggered by Del's post about the pressure bar being an essential part of the termination in vertical pianos, and associating that with the question about coils and the non-speaking length affecting tone.

To start with I just wanted to see whether re-seating D7 at the pressure bar would make any difference. Rather to my surprise it did, D7 sustain compared to C7, E7 and the sharps. For all the other notes I flexed the strings only on the non-speaking side above the pressure bar, as little as possible to have an effect, as assessed by comparing each note with its tweaked and untweaked neighbours.

I can't see how I can do a blind damping test now. Instead I'll record some notes over the weekend and see how the before and after frequency spectra compare.

Ian:

Maybe I am misunderstanding what you think is going on.

Is this what you think: that the non-speaking portions above the v-bar are affecting the tone? If so a blind test, by randomly damping and undampening a non-speaking length, can still be done.

Jeff

Good point.

I think a change in the nature of the contact between the strings and the pressure bar has affected the tone.

I do not think the portions of the string between the v-bar and the pressure bar and between the pressure bar and the coil have any discernible effect. My attempts to dampen them have made no difference.

Well I just did a test on a single F2 string on a spinet with Pianalyser. For the first stike I had the weave removed between the tuning pin and the v bar. The second strike, I completely dampened off that portion between the 2 with a rubber mute and my finger pressed against it. You can see from the two readings, nothing unusual happens. No partials removed or lessened, or changes in amplitude. The backstring going down to the hitch pin may be a whole different story but those short lengths of string running from the v bar or the pressure bar to the tuning pin do nothing with the tone other than maybe play with ones mind, if they are inclined to presume something is happening.

First strike with no dampening or cloth weave...


Second strike with string dampened....

Thank you, Emmery, for taking the time and trouble to do the experiment. The result was, I imagine, no surprise to you. One of those devices would have saved me some time! Had to make recordings instead, then used Sonic Visualiser to compare them with those I made last May after I had reshaped the hammers.

Jeff, here are the results for one note. Nothing to do with the hammers or the strings changed until a week ago when I flexed the strings above the pressure bar.

E4 Before


E4 After

Note: the noise below the fundamental, on the left side of the spectrum chart, may be from the fan in my laptop.

The $64 question is what might account for the increased power of partials 6 to 10 and the higher frequencies evident in the lower screen showing the analysis of today's recording?

Knocking crud away from the termination point?