Tostra

Converting a cello for a fifth string?

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Hi everybody
I've been playing around with luthiery for a couple of years. Nothing big, just restored a couple of violins, rehaired some bows, done some setups and is just about to be done with my very first instrument built from scratch. It's just an electric guitar, but it's a nice one and it's a start. 

Now here's the thing: I'm a cellist. I can play a lot of strings, but I want to have an instrument that I've worked on that I can play a little more seriously than violins and guitars, partly so I can see if the things I do actually feels right if you're a more experienced player. 
I found an old cello on ebay that, sadly, has been sanded down. Even though it's a shame, it's a great opportunity for me to sget into working on cellos, have an instrument to play that I've been working on and also carry out a dream I've had about getting a stained black cello, not just black paint or lacquer. All of that I can finally do without ruining a valuable instrument.
I don't expect much from it tonally, (it doesn't seem to me like it's overly well built) but of course I can hope.

That was a lot of background... My actual question is: Would it be possible to convert a normal cello into a five string one (I'm thinking low F rather than high E)? I realize it's a big and risky procedure, but I wanted to ask some more experienced builders what it would take. The idea came to me a couple of hours ago, so I haven't thought it all through yet, but here are my thoughts so far:

1 - Will the neck be able to take the pressure?
2 - Will I be able to make the fingerboard wide enough by just "fanning" it out a little from the neck rather than getting it square?
3 - I expect the tone of the cello to be changed, but would it necessarily be to the worse? I'm thinking that the bass bar is positioned for a four string bridge and would sound worse with a wider bridge? Now this is just pure guesswork, I haven't looked much into the construction's affect on tone even though I find it really interesting.
4 - If I plug the pegholes and drill new ones, would the pegbox then be strong enough to support an extra string?
5 - I'm used to four string cellos of course. I expect there to be a very different arch on the strings and a smaller spacing. How should I make that arch for best playability and does anybody know how big of a difference the spacing makes?

I hope somebody has the patience and experience to help me out here. Please tell me if I've forgotten something.

Have a great day :-)
Tobias

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1- Will the neck be able to take the pressure?

Yes,


2 - Will I be able to make the fingerboard wide enough by just "fanning" it out a little from the neck rather than getting it square?

I don't know what you meant here, but you may use the existing fb if it is wide enough, just make a new nut, or worse case, you need  a little wider fb.


3 - I expect the tone of the cello to be changed, but would it necessarily be to the worse? I'm thinking that the bass bar is positioned for a four string bridge and would sound worse with a wider bridge? Now this is just pure guesswork, I haven't looked much into the construction's affect on tone even though I find it really interesting.

Existing strings will sound more or less same, but low F will not sound good, very flubby bc of low tension, also what kind string are you going to use?


4 - If I plug the pegholes and drill new ones, would the pegbox then be strong enough to support an extra string?

Yes, but it would be crowded, so you will hit other peg when tuning.


5 - I'm used to four string cellos of course. I expect there to be a very different arch on the strings and a smaller spacing. How should I make that arch for best playability and does anybody know how big of a difference the spacing makes?

You can use same arch (curve), slightly smaller spacing, but not too small. You use same width bridge, no need for wider width, just make spacing  F to A wider about 55mm.

 

My main concern is the quality of the low F string, it will not sound as good as you imagine in your mind, because the string would be enormously thick and low tension. Cello is not made for optimum sound for C string let alone lower F.

My advice is to install  F, C, G, A on a regular cello for you to find out how it sounds, if it doesn't sound good, it won't sound good when you have 5 strings.

Koo Young Chung

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25 minutes ago, chungviolins said:

My main concern is the quality of the low F string, it will not sound as good as you imagine in your mind, because the string would be enormously thick and low tension. Cello is not made for optimum sound for C string let alone lower F.

My advice is to install  F, C, G, A on a regular cello for you to find out how it sounds, if it doesn't sound good, it won't sound good when you have 5 strings.

 

Yes, this. I can't imagine a low F would sound good (or at least acceptable) on a cello. It's the same reason I think 5 string violas sound better than 5 string violins. The body of a violin can't make a C string sound.

Try the suggested experiment before you get too involved.

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That's not a bad idea actually.But I haven't considered floppyness an issue. On guitars you use thicker/heavier strings to obtain a non-floppy, low tone, I was going to do the same on the cello: Find a gauge that would let me match the tension with the other strings, but get an F. 
But the thing about the cello not being good for producing such low notes... That might be a bigger issue, and that's why I asked if I had to modify the bass bar. 

When I say tone, I'm mostly worried about the top four strings. I don't need great resonnance and so on on the F, just a low sound that's fairly tight. It's mostly going to be there so I can use it occasionally or for effects. I wouldn't do it, however, if having an extra string had a negative effect on the other strings that I'm going to play more.

By "fanning" I meant have the sides of the fingerboard go outwards in an angle instead of going straight up. Does it make any sence or should I draw it?

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I got it, you want to make the fb wider, that means you may not have a smooth transition from neck though, or you have to make neck crosssection more pointy to make a smooth transition to the slightly wider fb.

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I've been looking for F strings, but the best thing I can find is thicker C strings. Maybe I can have one made, but I'm starting to back off a little bit, actually. I really want to have the extra string to play with, but I really don't want to get worse access or tone on the other strings... I'll have to decide on that, but has anyone tried a five string? Maybe they could describe the differences..?

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1 hour ago, Tostra said:

I've been looking for F strings, but the best thing I can find is thicker C strings. Maybe I can have one made, but I'm starting to back off a little bit, actually. I really want to have the extra string to play with, but I really don't want to get worse access or tone on the other strings... I'll have to decide on that, but has anyone tried a five string? Maybe they could describe the differences..?

Have you considered using a bass string? 

Perhaps even a flatwound electric bass string could work. 

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5 hours ago, Tostra said:

I actually just talked with my dad about that exact thing :-)
The ball ends though, aren't they too big?

The ball ends shouldn't be an issue even if so. 

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So finding strings won't be an issue, that's great :-)
If the fingerboard and everything cn actually be somewhat unmodified, I think I'm going to first finish it as a four string cello and see how it'll sound if I string it up with a low F. If it's great sounding in generak, I might just leave it as is instead of modifyind it further. If it sounds amazing with an F string I'll have it strung DGCF and then probably add an A at some point. 

The reason why I'm going to do it in steps like that is that it doesn't seem to me like the fingerboard needs a different curvature, so I could just make the fifth peg hole and a new nut, bridge and tailpiece later. Better safe than sorry, I don't like trying things out when I have no Idea what to expect. I think I might want to try it though, it sounds like it's definitely possible :-)

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6 hours ago, Tostra said:

>>

 I don't like trying things out when I have no Idea what to expect.

>

Gee, I'm the opposite.  I love surprises.  

It's great when you try something and it works as expected.  But if it doesn't give the expected results that's good too because it means you were going in the wrong direction but you still learned something important. 

A real bummer is when you think you are  changing something important and nothing changes--that seems like a real waste of time but at least it shows that particular something was not important which is also important to know and  you can go on to exploring other changes.

A bad case is when you don't want to make any changes at all and you control everything as carefully as possible to avoid surprises and the outcome is still different from what was expected.  This means you are not controlling something that is important which is also important to know.

Maybe its best to just make instruments and not give a sh--about what happens or why.

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Haha, I agree on that. What I meant was: I want it to be an at least decent cello in the end, and even though I believe it'll sound fine with an F, I want to try it before I make an extra peg hole.

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Here is what I do. I learned this from a guy in SLC who converted basses to 5 string. 

Find a wide blank. Since the cellist does not wrap their thumb around the bass side of the board/neck, then you can leave the board overhanging the bass side. This one is simply softened, I have scalloped the overhang from the bottom to make it look nicer. I guess that you could also flare out the treble side in order to get more width. The one pictures is 33.7 at the nut.IMG_1853.thumb.JPG.9b90506cdae4d40aab9cf0b311e23a29.JPGIMG_1854.thumb.JPG.eb53966ae2580ceabb26b8adde53e297.JPGIMG_1855.thumb.JPG.b6dc311c8bd8c383a7a9010db8258ec3.JPG

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Oh, interesting... The fretboard is 33,7 cm at the nut? What did you do with the bridge? Is it wider than usual?

And how did you make room for an extra peg?

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Bush the holes and use 3/4 sized pegs. There is usually a bit of room to carve the pegbox a little longer at the top. The strings at the bridge are spaced at a normal(for me) 16.5 mm apart. The outside strings are very close to the edges of the bridge, but if you look around you will find that some bridges are a little wider than others.

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Not sure what you mean, can you take a photo of the pegbox?
Do you redrill all the peg holes for 3/4 size pegs or is it just the fifth one that you add further up where there is some room and then leave the existing ones as is?

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Okay, so you plugged all the holes and redrilled them for 3/4 pegs? Did you carve out the top of the peg box to get more room? 

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I just measured my regular cello. It's 31,8mm at the nut and that's what I'm used to. I think I can give it one mill on each side by making the pointy profile, and then I would have the  same width as yours, but centered. That's probably what I'll do if the neck on the other cello is as wide as mine. 

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10 hours ago, Tostra said:

Okay, so you plugged all the holes and redrilled them for 3/4 pegs? Did you carve out the top of the peg box to get more room? 

yes

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