Bellying of the sb and harp’s action

[Giorgi Rusnak]

I have a question which I would like to address to those few knowledgeable pedal harpmakers participating in this forum.

Pedal harps develop a significant amount of belly over time. Calculations tell that the approximate number is around 12-16 mm + the deflection of the harp’s neck. This significantly reduces the vibrating lenghts of the strings.

Probably one can’t overcome this by simply moving the bridge pin or changing the amount of grip.

So the soundboard deflection has to be taken into account when calculating the positions for action’s axilsfourchettes. But in what way exactly?

As the vibration length of a long string becomes 15-20 mm shorter, not only the distance from the bridge pin to the first fork changes, but the ratio between upper and lower forks placement changes too and this will certainly affect the intonation. How this should be properly compensated?

Thank you

[carl-swanson]

Giorgi- You’ve described the situation very well. I’m about to go to a concert so I don’t have time to write a response right now. I’ll try to put one up in the next day or so.

[Giorgi Rusnak]

Thank you, Carl. Would be really nice to have this clarified. I look forward for your reply.

[Giorgi Rusnak]

Another thing I’m puzzled with is the detuning factor from added tension on the bass wire strings.

When the string is gripped with forks, additional tension occures, as the length is shortened and the frequency slightly shifts too. On gutnylon strings this factor is insignificant and we don’t hear the difference in intonation.

On wire strings however the detuning would be noticeable. I believe that to compensate this bass forks are placed on some other distance than 118 allowing longer vibrating length? Is there any specific formula for this?

This should not be confound with the added pressure disks can excert on thin&short strings of 1st and 2d octaves.

[Giorgi Rusnak]

Carl,

Wurlitzer seemed to use a special metal anchoring of the strings:

http://www.wurlitzerharps.com/Wurlitzer1532patentb.html

Probably it was designed specifically for removing the bellying effect, as with such anchoring the tension was not applied directly to the soundboard. Looks simple and ingenious, but did it work and how did it affect the sound?

It is generally accepted that every good harp has to develop a belly, which contibutes to acoustics of the instrument. Might be this is another myth…

As an expert on Wurlitzer harps what can you say about this invention? Was it successful? I think no pedal harp nowadays has this anchoring system. Or perharps Swanson harps have it?

Thank you

[carl-swanson]

I’ve seen that patent application too, but I have never seen an instrument that had it. It may be that they tried it and found it had a detrimental effect of the sound. I’ve seen other ideas as well that basically reinforced the string bridge, sometimes with metal, sometimes with wood “wings.” They always seem to make the sound tubby and boomy. The Pleyel chromatic harp had major metal reinforcement on the underside of the soundboard, which was necessary because of the enormous tension from two sets of strings. It did a wonderful job of keeping the soundboard flat, but at an enormous cost to the sound. So there’s no simple answer. I always tell people interested in this that you have as a builder an imaginary set of scales in front of you. On one side is ‘sound.’ On the other is ‘structural stability.’ The more stable you make the instrument, the more sound you will loose. The better the sound you create, the less stable and long lasting you make the instrument The trick is to find the optimum balance.

[carl-swanson]

Giorgi- I’ll try to address your questions. It sounds like you are trying to design an action that will take into account the pulling up of the soundboard. GOOD LUCK!!!

Any action is designed for specific string lengths. When the board pulls up(and the neck pulls down!) those string lengths shorten and the action is then out of regulation. The natural and sharp positions will be too sharp. To correct this, the adjustable nut has to be moved down and/or the disc in natural or sharp position or both has to be changed to a smaller disc. But there is only so far that the adjustable nut can be moved down and changing to a smaller disc, particularly in sharp, only works in the upper registers of the instrument. So adjustment has it’s limits.

But there is something else that happens when the board pulls up. In addition to the string length getting shorter, the string position also moves to the left of center as it passes through the discs. When this misalignment becomes bad enough, the board has to be replaced even though it is not broken. This is simply the nature of the instrument.

The problem with virtually all harp actions is that the design was worked out on paper and did not account for the immediate shortening of the string length as the instrument is strung for the first time, caused by the slight pulling up of the board and the slight pulling down of the neck. The worst areas that are affected are the 3rd and 4th octaves, but particularly the third(the low swing of the neck). I copied a Wurlitzer concert grand action when I designed my action. I chose that action for many reasons too numerous to go into here. Suffice it to say that the Wurlitzer concert grand action was the best action every built, bar none. The one change I did make was to move the screw holes for the screws that hold the adjustable nuts in place. I moved them down closer to the discs. What I found was that on my new instruments, all I had to do was push the adjustable nuts up as far as they would go and the instrument was regulated.

If you are going to start from scratch and design a new action, I would use an existing instrument as a prototype. Analyze what works and what doesn’t on that instrument, carefully notate the changes you feel are needed, and then copy that action, using the changes you notated. Copy of course the string lengths on this prototype instrument as well.

Look carefully at how each chain of the action works and how much rotation you get from each disc. There are some actions, by famous makers no less, where certain discs have almost no rotation at all, making them very difficult to adjust. Make careful notes on the rotation as well so that when you take the action apart you can look at the action arm for that disc and make changes that will give you more rotation. Choose the action carefully that you want to use as a prototype. I strongly recommend you use a Wurlitzer action.

[Giorgi Rusnak]

Hi Carl,

Thank you for such detailed response. I’m pretty sure this thread will be beneficial to many, not just me.

Yes, I’m designing a new action. It will have a different mechanical concept (how many times have you heard this?:)). Less movable parts and in traction only. So I’m using an existing instrument only to have an approximate idea on the diameter of the disks for each string, the amount of rotation, size and placement of adjustable nuts, etc.

Certainly I would like to take into account the pulling up of the sb already when designing the action on paper (in CAD actually).

From what you wrote, it looks like the best way to deal with it, is to place the adjustable nuts in such a way, that once the vib. lengths have shortened you can restore the original length by moving the nut up, until you compensate the bellying. Rather than to move it down and change to a smaller disk. Is this the idea?

If indeed on well built harps the amount of belly is around 15mm max – it is definitely possible to do and way easier.

[Giorgi Rusnak]

Yes, I found an older thread on harpcolumn about the same.

http://www.harpcolumn.com/forum/message-view?message_id=1629438

The discussion ended with the point that it will drastically impact the sound, so not a good idea at all.

Anyone experimented with horizontal wood bracing?

[carl-swanson]

-From what you wrote, it looks like the best way to deal with it, is to place the adjustable nuts in such a way, that once the vib. lengths have shortened you can restore the original length by moving the nut up, until you compensate the bellying. Rather than to move it down and change to a smaller disk.-

You’ve got it exactly backwards. If the string lengths are shorter due to the soundboard pulling up and/or the neck warping down, then to compensate(and correct the regulation) you have to move the adjustable nuts down, not up. This is because, with shorter string lengths, the distance between the adjustable nut and the natural disc, and between the natural disc and the sharp disc, are now too great and have to be reduced. So in a perfect world, on a brand new instrument, the adjustable nut positions are as high as you can get them, because as the instrument ages, the only direction they are going to go is down.

I would also want to have as large a disc as possible in sharp position, particularly in the 3rd octave, again, because as the instrument ages, you are going to have to change to a smaller disc size to bring the sharp position down. I’m talking ONLY about double prong discs here, not single prong. For single prong discs, you want the smallest disc you can get away with in sharp position, because as the instrument ages, you will have to correct sharp by replacing the disc with a larger sharping disc.

[Saul Davis Zlatkovski]

It would seem to me that the answer to movement of the harp’s component parts is to make all the external parts of the action ADJUSTABLE. Put multiple holes in the discs for the pins? Allow for different-sized discs. Make the adjustables truly adjustable, including the stationery nuts. Etcetera. Jim Buxton told me that the pedal springs could be at the top of the pedals instead of the bottom.

Why does the string need to be pinched? Could not a “thumb” push out against the string, and its pad could be moved up or down as needed? The newer levers do something like that.

Could not a thin metal strip run underside the center strip to reinforce it without impacting the sound? Titanium or aluminum or something?

[Giorgi Rusnak]

Carl,

You wrote:

>>>But there is something else that happens when the board >>>pulls up. …the string position also moves to the left of >>>center as it passes through the discs. When this >>>misalignment becomes bad enough, the board has to be >>>replaced even though it is not broken.

Looks like Camac has resolved this to certain extent by using an improved stationery nut. Like the one described here:

http://www.freepatentsonline.com/4696217.pdf

I believe Camac uses similar system on 23 of the strings, not just for those nuts in the bass range.

Camac also claims to have designed individual disks for nearly each string for improved intonation… No simple way to overcome all the bottlenecks of harp’s action:).

Thank you for all the suggestions – very helpful, I incorporated most of them into my design. The action is finished. Now follows the most difficult part – building the actual instrument.

[Saul Davis Zlatkovski]

Bellying is desirable, as it results in a more fulsome tone, the problem is to limit its extent, and to keep the action completely adjustable enough to account for changes in angle and position.

[sherry-lenox]

I cannot figure out the configuration of the tailpiece from the drawings duplicated here, but would a Wurlitzer harp that is in original condition be likely to have this?

If I look down through the back of my harp, I see a piece with a shape somewhat like one of the shapes in the picture, and it looks as if it is under the pedal extensions.

My sound board is very thin with very slight bellying.

[HBrock25]

Hello,

Congratulations for the forum and respects to the great professionals. An honor Mr. Swanson.

Let me please a humble contribution, and certainly will be invented, but I have done very well.

Thank you very much

https://dl.dropbox.com/u/98721591/adjustable-disk-pedal-harp.jpg

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