Understanding Acoustics

[Biagio]

We have been having a long and sometimes intense discussion on a different thread so I thought I would start a new one rather than go way off topic there.

If anyone wants to understand the fundamental aspects of acoustics here is one excellent presentation from The Great Courses company:

“How Music and Mathematics Relate”

Don’t panic. The presenter does an excellent job of going through everything step by step and the course is not expensive. He is a violinist but the concepts are entirely applicable to any instrument.

Full disclosure: I have no relationship with this company.

Cheerio,
Biagio

[wil-weten]

Great idea to start this thread, Biagio.
In another thread I just read charles-nix message “I wonder if one can “voice” a soundboard after the harp is built to alter its resonance?”

I am not a builder, nor do I have solid knowledge of building. The only thing I have heard, is that when playing a certain string generates a wolf tone, builders may add some extra some material in the sound box to mute the unwanted effect. To find out the best place, they may experiment first with some easily removable material. They don’t experiment ‘in the blind’, but I don’t know how they make an educated guess about the probable place to add some extra weight.

As to the actual question, if at all possible, I guess one would have to remove the soundboard first and perhaps one may thin it in some places in order to get more resonance in part of the harp, and put it back on, but this would be rather time consuming and so rather pricey.

[Biagio]

Wil,

Yeah, once it is glued on the SB would be messy to remove to say the least. High end makers may use different techniques to tune the board prior to putting it on but the general approach is known as the Chladni effect. The idea behind that is that the board will resonate in different nodes; one way of applying the test would be to scatter glitter over the board and tap it to see the pattern that creates. They would then tune the board by hand planing it.

The same could be done with more modern tools and instruments. I think Professor Kung mentions that in his lecture series.

Someone on the Harpmakers forum discussed the removable weight approach you mention – I think they used sticky putty – and that is also how amplifier pickups would ideally be placed. Tacye might remember who it was discussing that on the Harpmakers forum and know more about it – after all she is a physicist.

I can’t speak for others but personally I’ve never gone to that extent, not considering myself to be a “high end builder” LOL. Since I did not have a drying booth back then I was content with aircraft grade laminate. Or if I wanted to use solid wood, I bought a ready-made board from some one who did (grin).

Diverging a little….we know that Dusty uses mahogany for the first 3 1/2 octaves and spruce for the lower ones, due to their experience with mahogany on hammer dulcimers. I’ve often wondered whether they ever considered alder (which is plentiful here) and keep meaning to ask.

Biagio

• This reply was modified 5 years, 5 months ago by Biagio.

[Biagio]

Yeah, that would be messy to say the least. High end builders tune the board beforehand using the Chladni effect. The idea there is that a board will resonate in different nodes when tapped and those can be seen using glitter or more sophisticated measurements.

I think that Professor Kung addresses Chladni in one of his lectures.

Biagio

[wil-weten]

Thanks for mentioning the Chladni effect, Biagio.
I just found a great article explaining it:
Controlling the motion of multiple objects on a Chladni plate.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5023966/

Fortunately, it gives a very easily understandable introduction to it in the abstract, before it becomes too technical for me in the part in which the results are discussed. In the article a great many sources for further reading are mentioned.

[Biagio]

Good article Wil. If you are inclined to delve deeper the ISFHC archivist – Musicmakers – has a CD available: “The Science of Harp Making.” Some of those articles get pretty dense reading (a couple discuss the Chladni effect in detail), others are accessible and quite interesting, even on occasion amusing. Mark Bolles’ article “The Great Wire Harp Wars” is hysterical.

[Tacye]

I don’t remember the discussion about putty, but someone (I think Howard Bryan) pointed out that a single string with odd resonance can sometimes be cured by using a heavy washer to add mass between the string rib and knot. It is a usefully removable thing to try.

[wil-weten]

Tacye, it was in the German harpforum where a (now retired) professional harpbuilder ‘Bernard’advised ‘Knetgummi’ (later on had all his messages deleted but from the reactions on his messages, lot can be reconstructed 🙂 Another German harpbuilder and harp repairer also uses putty rubber.

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