A flat topped tenor with a floating bridge

greenscoe

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On 19th May I asked why we all build ukes with the strings tied to the bridge.

https://forum.ukuleleunderground.co...we-tie-the-strings-to-the-bridge-on-a-ukulele

After this forum discussion, I set about to build a flat top tenor with a floating bridge to satisfy my curiosity. Regular readers of this forum will know that I have previously used a cheap Ammoon tenor kit from Ebay to test a soundboard. The laminate top is removed and replaced with the test top.

So once more that’s what I have done, again using Engelmann spruce.

Since the soundboard takes only vertical loading from the strings at the bridge and no string pull forces, the bracing needs only to consider this.

If the soundboard were round and wood had equal strength in all directions, then thinking of a loudspeaker, I would have simply added a circular patch under the bridge. But wood is strong along the grain and weak across the grain, so the soundboard needs additional strength across the grain.

An obvious bracing scheme would therefore use 1 or 2 ladder braces with or without a bridge patch. The location, dimensions and orientation (parallel or skewed) would need to be determined by experiment.

My thoughts however were to use 1 ladder brace under the bridge and a patch either side of this. These patches taper from 2mm to almost zero at their edges, giving more support across the grain than along the grain and most support closest to the bridge. The soundboard is 2mm thick.

The strings are attached to a maple ‘bracket’ on the butt of the box in mandolin fashion. I tried a short bridge (60mm) but think the instrument sounds and feels better with a longer (110mm) bridge which spreads the downward force over a larger area (the notched saddle is a scrap of acacia). There is no noticeable soundboard depression.

I don’t have a particularly good musical ear so characterising the sound is always difficult. Its loud with a percussive quality, it sounds like a spruce topped instrument with that quick and clear response. It has lots of sustain, bass is good, maybe treble is a little weak. I prefer it as a strumming instrument rather than a picking instrument. I am not disappointed with it but its not as warm or rich sounding as my best tenor to date. It's not so different from my other Engelmann instruments and it raises the question of how it could be improved given it's my first stab at a floating bridge instrument.

I am a hobby builder. As always, I post this to encourage others to have a go at your own ideas. I have tried to outline my thought processes, but of course I may be heading in the wrong direction-so follow at your own risk!

If you have made a floating bridge instrument, I for one would be interested in seeing how it was braced and your impressions of the way it sounds.

flt1.jpgflt2.jpgflt3.jpgflt4.jpgflt5.jpg

If you are interested in this thread, there's a follow on thread on a tenor with a floating bridge:

https://forum.ukuleleunderground.co...oating-bridge-tenor-with-segmented-soundboard
 
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What a great post! Meticulously done and researched. I only wish we could hear the instrument in an A - B comparison with a standard reference ukulele...

A couple of thoughts after looking at the pictures:

- The bridge patch looks rather large. Is this necessary to distribute the downward forces?

- The saddle appears to be made of wood. Why not a bone saddle?

- The bridge itself appears to be quite narrow. Why not a wider bridge to distribute the downward forces and the energy from the strings?

Anyway very well done.
 
Here is a Maccaferri style ukulele I built a few years ago. It has ladder bracing and a crease in the top, as in some Maccaferri instruments. I am not thrilled by how it sounds, as both my arch top and flat top instruments sound considerably better, so I have not pursued the project any further

https://photos.app.goo.gl/7jnaaJPivghnryRx9

Brad
 
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- The bridge patch looks rather large. Is this necessary to distribute the downward forces?

- The saddle appears to be made of wood. Why not a bone saddle?

- The bridge itself appears to be quite narrow. Why not a wider bridge to distribute the downward forces and the energy from the strings?

/QUOTE]

The 2 patches do seem quite large. It was difficult to guestimate their size, but they are thinned removing almost half their weight.

I have several tenors with an ebony nut and saddle. I dont think using wood affects volume and I suspect it results in a mellower tone.

I was trying to keep down the weight of the soundboard and bridge to increase volume. I chose to beef up the soundboard a little with the patches but keep the bridge as light as possible. However I did move from a 60 to 110 mm long bridge to spread the load across the board. I am not sure what a wider bridge would achieve.

I should add that overall I don't think I am structurally so far away as the soundboard has not deformed under string load nor does it feel too tight when picking as does an overly braced soundboard on a fan braced instrument.
 
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Here is a Maccaferri style ukulele I built a few years ago. It has ladder bracing and a crease in the top, as in some Maccaferri instruments. I am not thrilled by how it sounds, as both my arch top and flat top instruments sound considerably better, so I have not pursued the project any further

https://photos.app.goo.gl/7jnaaJPivghnryRx9

Brad

Thanks for your response Brad. You dont say how many braces you used or where they were positioned. However since you say it didnt work out well I dont suppose it matters.

Before I joined the forum 6 years ago, I know you were involved in encouraging makers to try producing an archtop. When I made mine you were not active on the forum and my attempts at seeking advice were not successful. Initially I was happy with the way it sounded but over time I came to find it rather weak sounding. I suspect I left the soundboard too thick. I have subsequently tried to improve it by further thinning but its mostly now a rather attractive wall hanger. I did buy several sets of maple/spruce violin wood to pursue archtops but I have never felt the urge to try again. This flat top is far better sounding than my archtop!

https://forum.ukuleleunderground.com/showthread.php?103447-First-archtop-tenor-uke&highlight=archtop
 
I made a mahogany-topped parlour guitar with a floating bridge.

Parlour guitar front (small).jpg

The bracing was just two ladders across the lower bout, one angled. I didn't use a bridge patch, because the bridge is placed above the lower brace.

Top bracing (small).jpg

One important difference, which you can't see here, is that the braces are curved so that the top has a side-to-side arch, rising maybe 5mm after string tension. That let me brace lighter, and I also think it might improve the tone (but that's a guess!).

It sounds like a mahogany-topped guitar, but I think it emphasises the mid-frequencies more than all the others, perhaps more so than a conventional design mahogany parlour. It's very responsive indeed, so it needs care when playing not to sound "boomy", but it can be very loud and not boomy if you control it carefully.

I've made a few ukes along these lines, though not always angling the bracing, but I can't find pictures. They, too, emphasis the mid-range more than their conventionally-bridged cousins.
 
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One more thought - my tenor guitar which I made is floating bridge, and just uses a standard banjo bridge. Sounds very good, not at all banjo-like, though the top is yew which will change things.

This is so completely different from what you have that it might be worth a try. Whittling up a banjo bridge should be a very quick and simple job.
 
One more thought - my tenor guitar which I made is floating bridge, and just uses a standard banjo bridge. Sounds very good, not at all banjo-like, though the top is yew which will change things.

This is so completely different from what you have that it might be worth a try. Whittling up a banjo bridge should be a very quick and simple job.


Thanks for your 2 responses. Your ladder bracing is sort of what I would have expected since I have a couple of ladder braced parlour guitars not of my making and both with pinned bridges. I also realised that the top should be slightly curved and put a curve on my lower transverse brace and the brace under the bridge: they were glued in place in my domed go-bar deck. The dome was barely noticeable before the strings were added-the top is now flat and not sunken.

I took a banjo bridge off one of my banjo ukes and tried it on this instrument. It made the action a little higher but I dont think the sound was significantly different.

You mention your instrument being very responsive: I think that's probably what I mean when I say my instrument is loud and has a percussive quality.
 
Aloha Greenscoe, thanks much for the links you provided, now that I have a much better idea of your knowledge and experience, I have a much better chance at providing you with some useful information. I will start with your arch top and do some more on my Maccaferri later.

Unfortunately I ran into some health issues before you started building your instrument, so I wasn’t able to supply you with any details. Benedetto’s book is a great source for general information on arch top construction but is about steel string guitars. Here are some specific dimensions that I use on a tenor arch top ukulele.
Top thickness recurve area - 1.8mm
Top thickness center - 3.5mm
Back thickness 10% less than top
Rib depth 35mm
It looks to me from the picture of your instrument, the rib depth may be the problem. It looks to me like it may be in excess of 50mm, which means it is too far away from the top and is unable to support the top’s vibrations. You can measure to make sure, but if I am guessing correctly, I would consider popping the back off, reducing the rib depth to 35mm and putting the back on again.
Brad
 
I haven't built a floating bridge instrument. But thinking of similar instruments e.g. banjo I would think the aim is to get the rim/sides to be as stiff as possible to resist the pull of the strings from one end to the other. Then the top should be as thin as possible, relying on the rim/sides to take all the string tension. Otherwise I wouldn't expect there to be enough downward movement of the soundboard. Just my opinion.
 
I haven't built a floating bridge instrument. But thinking of similar instruments e.g. banjo I would think the aim is to get the rim/sides to be as stiff as possible to resist the pull of the strings from one end to the other. Then the top should be as thin as possible, relying on the rim/sides to take all the string tension. Otherwise I wouldn't expect there to be enough downward movement of the soundboard. Just my opinion.

Thanks for your response. I have made 2 banjo ukes and it is important that the rim is stiff for the reason you state especially if the instrument is open backed. For that reason banjo ukes often have a 'stick' running through the hoop. Some uke makers consider that thick sides and solid linings both contribute to keep the energy in the soundboard making for a better response. I often use laminated linings and sometimes side stiffeners.

When it comes to wooden soundboards on ukes of all sizes there is an optimal thickness, too thick and there is low volume, too thin and the instrument sounds more like a banjo than a uke. By this I mean it sounds tinny or trebly, has no sustain and may make popping sounds when some notes are played. This is not just my opinion/experience but one that is regularly stated on this forum.

I have 6 tenors with Engelmann spruce tops all initiall thinned to 1.8mm. On this floating bridge uke, I thinned to 2mm because I knew I would be using less bracing and didn't want the soundboard to dip under the bridge. This instrument is very loud and punchy.

So again, I thank you for you contribution. This is a discussion forum, so I encourage all to dip in, that's the way we all learn.
 
Aloha Greenscoe, thanks much for the links you provided, now that I have a much better idea of your knowledge and experience, I have a much better chance at providing you with some useful information. I will start with your arch top and do some more on my Maccaferri later.

Unfortunately I ran into some health issues before you started building your instrument, so I wasn’t able to supply you with any details. Benedetto’s book is a great source for general information on arch top construction but is about steel string guitars. Here are some specific dimensions that I use on a tenor arch top ukulele.
Top thickness recurve area - 1.8mm
Top thickness center - 3.5mm
Back thickness 10% less than top
Rib depth 35mm
It looks to me from the picture of your instrument, the rib depth may be the problem. It looks to me like it may be in excess of 50mm, which means it is too far away from the top and is unable to support the top’s vibrations. You can measure to make sure, but if I am guessing correctly, I would consider popping the back off, reducing the rib depth to 35mm and putting the back on again.
Brad

Thanks for that Brad. The sides are 45mm deep and I think all the other dimensions were roughly as you have stated. The soundboard was of lime not spruce so that may be a factor. I cant remember whether I used 2 or 3 braces on the top so it may be that it was over braced. I have moved on and dont intend further work on this one.

One day I'll wake up and decide its time to make another archtop. Its just unfortunate that with no examples of builds to see its hard to get a handle on how to get the best from an archtop and to rekindle my interest. I like to try alternate types of uke which normally take less time than a standard uke. The archtop took a lot more time than any other uke I've built.
 
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Greenscoe,

I really enjoy reading posts on unconventional builds.
From the respondents' ideas and comments, and your wondering of how to move forward, some ideas you could consider. Most have already been touched on:

Eliminating the bridge patch, as there are no rotational forces.
Placing a slimmed down single ladder brace directly under the floating bridge.
Increasing the upward curve in the ladder brace … (you mentioned that it pretty well straightened out).
Reducing the top thickness slightly.
Reducing the mass of the bridge.
Anchoring the strings a little lower, at the top/butt plane (even if slightly) to increase the string break angle. A degree or two of neck set would raise the bridge height a bit to accommodate this as well. A small difference here should have significant influence on the string down force presented to the soundboard.

OR, perhaps, none of the above :)
 
bazuku:

It's always good to know that there are forum members who are interested in alternative builds.

I make ukes purely as a hobby: I have a house full of instruments which I play rather badly. My interest is therefore in making something different, not one more of something I already have.

As for your list, I have no problem with compiling such a list, it's all about which factor(s) to select. I'm often inclined not to choose proven methods just to see where the alternative takes me.

However I'm always interested to see and hear what others are doing and what they find to be successful
 
Thanks for your response. I have made 2 banjo ukes and it is important that the rim is stiff for the reason you state especially if the instrument is open backed. For that reason banjo ukes often have a 'stick' running through the hoop. Some uke makers consider that thick sides and solid linings both contribute to keep the energy in the soundboard making for a better response. I often use laminated linings and sometimes side stiffeners.

When it comes to wooden soundboards on ukes of all sizes there is an optimal thickness, too thick and there is low volume, too thin and the instrument sounds more like a banjo than a uke. By this I mean it sounds tinny or trebly, has no sustain and may make popping sounds when some notes are played. This is not just my opinion/experience but one that is regularly stated on this forum.

I have 6 tenors with Engelmann spruce tops all initiall thinned to 1.8mm. On this floating bridge uke, I thinned to 2mm because I knew I would be using less bracing and didn't want the soundboard to dip under the bridge. This instrument is very loud and punchy.

So again, I thank you for you contribution. This is a discussion forum, so I encourage all to dip in, that's the way we all learn.

Very happy to contribute.

But I think you have missed the point. You described the uke as lacking treble, yet have noted that banjos sound trebly due to their thin tops. So there is probably a trade-off on this design. Go thin and sounds trebly (like a banjo). Go a bit thicker and it lacks treble. That is presumably a consequence of less upwards or twisting force on the bridge.

There may not be a way of getting both to be as you want them with this design. Others I'm sure may disagree.

I've restored a few bowl-back mandolins with very similar floating bridges. Very thin tops, less than 2mm. And much more tension through the strings.
 
I'm often inclined not to choose proven methods just to see where the alternative takes me.
Your attitude is commendable and deserves support.
I have spent an inordinate amount of time, not trying to reinvent the wheel, but trying to modify it too often.
However, after many more failures than successes, there came a stage in life when time became more precious, so I decided to defer to the long-established status quo of building.
I learned to appreciate that generations of sharper minds than mine had laid down lifetimes of hard-fought ground work that I was not using to advantage.
This led to a complete reversal of thinking and I started building traditional, rustic style instruments, where deviation from the mean was regarded as frivolous at best, or blasphemous at worst.
This style of building has the added bonus of not requiring the kind of sophisticated skill set displayed to perfection by the elite of our fellow forum members.
I do not mean to discourage or trivialise experimentation, as there can be no progress without it, but from experience, I feel that time is short, rabbit holes can be deep, and it is sometimes easier to just skirt around them.
Regardless, I really admire your enthusiasm in your search for answers.
 
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Thanks for the posting Greenscoe.
I have been working on an experimental tenor project and am nearing the end with making the nut and bridge/saddle. My top is spruce and has a 25’ radius and is about 2.3 mm thick in the middle tapering at the edges to about 1.8 and is skin braced only in the center at about 1.2 mm. After seeing your success with this type of set up, I plan to do something similar. Still trying figure it all out. IÂ’ll post results when finished.
 
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