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View Full Version : Question about soundboard on quirky cigar-box uke



dreamer9
09-04-2011, 07:48 PM
I'm no luthier. I'm just a guy who has some hand tools and enjoys a good design/build project now and then. Most recently my three year old got an aloha uke and I decided I wanted to make a cigar box style tenor uke to play around with him. I want to use mostly stuff out of my stock of wood in the garage, so my "cigar box" i'm making from quite sturdy black walnut, a fair bit thicker than cigar box material. I did order a redwood soundboard and some other essential parts, like corian nut/saddle and bracing set, patch set, fretwire.

As I said, I like to do some crazy design, but it's also true that I like good sound.

My question is, with an exceptionally strong/thick back and sides, can I put the bridge on the lowest side and set up a saddle like on a violin, with one supporting bar beneath the soundboard? I assume it would allow the soundboard to vibrate more and increase the sound output, but is the opposite true? Will that dampen the sound? I've seen this type of setup, but I don't know if it sounds okay.

Even beyond that, can I make a suspended bridge and saddle, or does the soundboard need the bridge and saddle touching it to transfer vibration? My assumption is that the soundboard would get all the vibration it needs, through the air, from suspended strings. I would assume in fact that the soundboard would get more energy from the strings without the interference of the bridge.

I'm curious about the possibilities of design and how they would affect the sound produced. Thanks for reading.

Sven
09-04-2011, 10:52 PM
... or does the soundboard need the bridge and saddle touching it to transfer vibration?
Yes.

My assumption is that the soundboard would get all the vibration it needs, through the air, from suspended strings. I would assume in fact that the soundboard would get more energy from the strings without the interference of the bridge.
No. (No!)

If you use a floating bridge and the strings attached to a tailpiece, try it with and without the supporting soundpost.

ProfChris
09-04-2011, 11:45 PM
A standard bridge makes the soundboard vibrate by rocking it back and forth.

A floating bridge (as on a violin, mandolin or banjo) pumps the soundboard up and down. On a banjo this is loud because the head is very thin. On a mandolin and violin the top is arched and carved (and the coundpost on a violin makes the back vibrate as well). On a flat wooden soundboard, this setup is generally quieter than a standard bridge.

If your back and sides are very heavy, then a soundpost would tend to stop the top vibrating, making the uke even quieter.

As a general rule, the more lightly built your uke (including back and sides) the louder it is.

So, unless you want a super-quiet uke, I'd thin down back and sides and use a standard bridge setup.

Liam Ryan
09-05-2011, 12:46 AM
I've got no idea what you're trying to do but why reinvent the wheel?

A nice thin, lightly braced top with a fixed bridge will make a great sounding uke.

ksquine
09-05-2011, 05:03 AM
I think you're mixing up terms here. By bridge, I think you mean tail piece....where the string ends are tied like on a mandolin?? We call the bridge the chunk of wood that sits on the top and the saddle is the narrow point where the strings land. A typical uke has a one piece bridge/tie block and a separate saddle on top of the bridge.
Yes you can do a floating bridge and tail piece like on a mandolin, violin or archtop guitar.
No, it won't make it louder. A typical uke bridge already has a steep break angle where the strings go down from the saddle to the tie-off point. Usually at least 30deg! It would be hard to get more than that with a tail piece set up....you would probably get less.
I don't think the break angle is important to volume anway, beyond some minimum angle.

dreamer9
09-05-2011, 07:05 AM
Thanks everyone, that satisifies a lot of my curiousity/questions.

ProfChris
09-05-2011, 07:54 AM
One further point for you to consider. Where you place the bridge (ie the part which transfers the string vibrations to the top) makes a huge difference to the quality and volume of the sound. If you place it near the edge of the top it does very little work. Placed in the middle of a wooden top it might do too much.

Most instruments with a wooden top place the bridge about 2/3 of the way between where the neck joins the body and the tail. This applies whether you use a fixed bridge, or a floating bridge + tailpiece.

Moving it too far from this position will probably give you a poorer sounding instrument.

So when designing you (1) decide your scale (in this case tenor, around 17 inches); (2) decide your body size, (3) decide where the bridge goes; and (4) working backwards from all that, work out how long the neck has to be and where it joins the body. Eg 17 inch scale, 12 inch body, bridge is 8 inches from where the neck joins the body, thus neck has to be 9 inches from body join to nut, plus however much you need for your peghead design.

dreamer9
09-06-2011, 02:08 PM
Thanks again ProfChris, I wouldn't have known that the placement on the top had all that much effect.