Erhu construction

[ychent]

This thread is just some of my questions and thoughts that expands upon the "building an erhu" thread. Please shine in and share your knowledge!

I've always wondered what are the specs that goes into erhu constructions? I've read a couple of books on violin acoustics, and it's mighty impressive how everything on violin construction is precise down to the level of art: the type/age/dryness of the wood, the thickness of the bridge, the curvature of the bass bar, the tension on the sound post, angle of the neck, the type of glue and varnish used on the wood, the curvature and thickness of the face boards, the size and position of the sound holes.... it's a beautiful blend of art and science.

It would be TERRIFIC if someone can shed some light on the construction of erhu. More than just the specs, I would love to learn how does each part influence the timbre and quality of the sound? How does any specific processing technique influence the sound? How does the shape and thickness of the resonator body influence the sound? Does the type of resonator decor over the sound hole influence the timbre? What is an ideal erhu?

Also, are there new research being done that aims to revolutionalize erhu? There are some innovative technologies and research in the acoustics of violin; Texas A&M professor Nagyarvy is able to deteremine the chemical treatment used in the famous stradivari violins, and by using the same process as well as spectra analysis, he is able to produce violin that rivals the strads (see www.nagyvaryviolins.com/ and agnews.tamu.edu/dailynews/stories/BICH/Sep2203a.htm). Is there similar research being conducted for erhu?

[ychent]

It seems that no one is very interested in this topic. That's kinda sad. Anyhow; I came upon an article that discusses the physics of erhu acoutistics by Erika Rose McLaughlin, presented in Whitman Undergraduate Conference, spring 2000, as I was digging through the threads. If I may summarize his findings (http://triangular.stormloader.com/erhu.html):

1. The first part of the article is a detail description of the physical dimension of erhu.

2. the initial energy source in the erhu's sound production comes from the bow setting the string into motion through a process based on friction. The rosin causes friction between the bow and the string, which allows the bow to pull the string aside with its motion. When the string has been pulled aside far enough to build up potential energy outweighing the force of the bow, the string releases from the friction grip of the bow and moves in the opposite direction. This creates the oscillation that produces the note.

3. contrary to popular belief, horse hair does not have barbs that catch the string during bowing. The friction is generated solely by rosin.

4. The energy is transferred efficiently from the string to the resonating parts through the bridge because the angle of the bowing produces string oscillation in nearly perpendicular plane to the python skin. Violin, on the other hand, has its strings oscillate in nearly parallel plane to the bridge, making the transfer much more complicated to describe.

5. The bridge is a simple wedge-shaped wood that keeps in contact with the python. A hole drilled parallel to the strings causes the vibrations of each string to be transferred more directly down to the skin reduce additional sympathetic vibrations to travel across the bridge from string to string.

6. The use of strings quianjing is the cause behind uneven notes between up-stroke and down-stroke on inner string when tuned to D because the string quianjin allows the inner string to slip back and forth, therefore changing its length and tension. This property is eliminated if a fixed wooden nut is used instead of quianjin, producing more even pitch that sounds closer to viola than normal erhu.

7. The nasal quality of erhu timbre is the result of high numbers of harmonics, most prevalent in the 2nd and 3rd harmonics, but it can be up to 16th. The lack of finger board also leads to the unstable oscillation that contributes to the erhu timbre.

[calden]

ychent:

Thanks for all the great research!

It's not that no one else is interested - it's just that we're more interested in lots of other things, and need to prioritize. I have a friend who is an extremely well regarded luthier. All the top strings artists in our city go to him for purchases and tweaking their violins, violas, cellos, and basses. He can't play at all, except to draw a bow or pluck a note to find the sound he's going for. I know other people who are master musicians and don't care if their bridge is maple, mahogany, or mahjong, or don't care if the sound goes up around the C scroll before it goes out the F hole or not.

So I hope that a lack of resounding interested isn't read as NO interest. It's great that you're taking the initiative to dig this up. I'm always up for reading about it! In fact, I'm moderately interested in possibly building an erhu and maybe tweaking the design a bit. I've thought about a very light and thin piece of wood, fortified with carbon fiber and resin, to replace the skin head. One could do a lot with controlling the tone by having a head that is manipulatible.

Carlos

[maaltan]

thin piece of wood... it might work. but carbon fiber laminate of some sort would be probably be enough. Depending on the epoxies used and weave pattern of the fiber, carbon fiber can be made as flexible or rigid as you want. in fact, if you contacted a carbon laminate shop with some solid specifications, they could probably manufacture a very functional and reproducible erhu head.

In fact, i just got through watching a special on the history channel (odd subject for "history"but anyway) these people were making 100% carbon fiber bodied western stringed instruments. The only thing that wasn't carbon fiber was the bridge and strings. the bow body was even carbon fiber. They had violins to double-base cellos. They claim 3x the volume and clarity of wooden counterpart. they did not review that in the show. Apparently the violins rival stratavarius.

I am not 100% these are the people on the show but the instruments look the same.

www.luisandclark.com/violin.php

[calden]

Wow. Can a carbon-fiber erhu be in our futures? No worries about humidity at all - in fact you could do street busking in the rain, water dripping from your bow tip (made of carbon fiber and synthetic horsehair, of course.)

I know that a lot of experiments have been done with guitars - Rainsong guitars have been fooling around with it for years: www.rainsong.com/

I've also seen luthiers use Nomex, a honeycombed shaped composite material, to reinforce extremely thin guitar tops (the thinness makes them very responsive to vibrations, thus very clear and loud.):

www.holtierluthier.com/models.htm

That's kind of what I was thinking of with the erhu top. Maybe just thin Nomex with a very thin sheet of responsive wood, like cedar. If it were just carbon fiber it might be too stiff. To replicate the snake skin's flexibility you'd have to find something that is not stiff.

I've often thought of using Fibreskyn. It's a mylar-based drumhead material used mostly for ethnic instruments - African drums, banjo heads, etc., where one wants a textured head material that replicates the inconsistent thicknesses of a goat skin, ibex skin, calf skin, etc. Here's some examples from Amazon:

www.amazon.com/exec/obidos/search-handle-url/index=mi-index&field-keywords=fiberskyn&results-process=default&dispatch=search&platform=gurupa/ref=pd_sl_aw_tops-1_mi-index_25772828_2&results-process=default

If you were really into making something for erhu, you could take a prime chunk of snakeskin and make a mold, then form a fibreksyn head from that, incorporating the little raised scale patterns, as well as the proper thickness. Whatever function those shapes play in producing the sound would be part of the synthetic head.

Carlos