Long scale octave mandola bracing

[Philip Pittman]

I'm about to build a long scale octave mandola (some would call it a mandocello) and would welcome some input on bracing. At this point I should say that I've only ever built one instrument - a guitar from a kit by LMI. I plan to build a teardrop shape, 20 inch body, joined at 12th fret,24.9 inch scale, tuned GDAE. Strings will be .014 - .052 which gives around 24% more tension than a "standard" mandola, for which I have a ladder bracing pattern, consisting of three transverse braces and one diagonal (treble) brace and so one idea is to increase the brace cross section by this percentage.
My concern is that with such a large body and extra string tension there may be insufficient strength in the bracing.
I'm choosing ladder rather than X bracing as I want to retain the characteristic sound of the mandolin family.
Is this bracing sufficient ?
Should I add an extra transverse brace ?
Should I add longitudinal bracing ?
Should I go to an H or A pattern ?
Any help most gratefully received.

[sunburst]

A couple of things:
-I think of anything 25" or less as a rather short scale for a mandocello, and with the fairly light string set you are using the tension on the instrument will not be unusually high (The tension can be calculated).
- I don't think you mentioned whether this is to be a flat top or a carved arched top. That would make a considerable difference in how I would decide to brace the top.

[Philip Pittman]

A couple of things:
-I think of anything 25" or less as a rather short scale for a mandocello, and with the fairly light string set you are using the tension on the instrument will not be unusually high (The tension can be calculated).
- I don't think you mentioned whether this is to be a flat top or a carved arched top. That would make a considerable difference in how I would decide to brace the top.

John, this will be a flat top (with a 12ft radius). Strictly speaking this is a long scale mandola and has lighter strings than a true mandocello. My reference point for the string tension and bracing is a mandola design not a mandocello, hence my concern.

[Graham McDonald]

What the OP is describing would be more usually called an octave mandolin or even an Irish bouzouki at that standard guitar scale length, rather than a mandocello. I am puzzled by what I would see as very heavy stringing. The top string is tuned to E, which is the same as a guitar top string and you want to use two .014" strings. That is putting a lot of string tension on the instrument and I would worry that the soundboard bracing would have to be so heavy to hold the instrument stable that it might not make much sound. I would also suggest that ladder bracing is necessarily needed for a mandolin family sound.

Cheers

[Philip Pittman]

What the OP is describing would be more usually called an octave mandolin or even an Irish bouzouki at that standard guitar scale length, rather than a mandocello. I am puzzled by what I would see as very heavy stringing. The top string is tuned to E, which is the same as a guitar top string and you want to use two .014" strings. That is putting a lot of string tension on the instrument and I would worry that the soundboard bracing would have to be so heavy to hold the instrument stable that it might not make much sound. I would also suggest that ladder bracing is necessarily needed for a mandolin family sound.

Cheers

Thanks for your comment. The string tension works out at 224 lbs, compared to for example 160 - 180 for a 6 string guitar, 181 for a more conventional octave mandola and 250 for a 12 string guitar.
Visit http://www.oddyluthiers.co.uk/mandocello.htm for a look at the instrument I'm trying to copy.

[sunburst]

I'm in the camp who feels that bracing pattern is far less important than plate stiffness vs weight. In other words, I don't think the positioning of the braces matters as much as having braces that are appropriately placed and sufficiently stiff to perform their structural job while not being so stiff as to unduly raising the frequency of plate modes. In light of that, I would X-brace it, though I realize that ladder bracing would be much more in keeping with traditions when it comes to instruments shaped similarly to that.

[Philip Pittman]

I'm in the camp who feels that bracing pattern is far less important than plate stiffness vs weight. In other words, I don't think the positioning of the braces matters as much as having braces that are appropriately placed and sufficiently stiff to perform their structural job while not being so stiff as to unduly raising the frequency of plate modes. In light of that, I would X-brace it, though I realize that ladder bracing would be much more in keeping with traditions when it comes to instruments shaped similarly to that.

Thanks John, I'm certainly coming round to that point of view, especially given my relative inexperience. It would be a safer option to go with X-bracing as their is a wealth of information available as to how to do it with the larger body size. For me, keeping with tradition is less important than producing an instrument that is structurally and sonically sound first time around !
Unless anyone comes up with an equally safe option with alternative bracing, I think I'll go with your suggestion.

[Graham McDonald]

I am still puzzled as to why you would want that much string tension on an instrument of that string length. I would also note that the information out there on X bracing is mostly concerned with fixed bridge guitar bracing, not a mildly-domed-over-bracing soundboard with a floating bridge and tailpiece. It is an entirely different set of forces and stresses and there has been little written or published on that. It might be worthwhile getting in touch with the Oddy folks and see what they think about bracing and string tension.

And that should have been" ladder bracing is NOT necessarily needed for a mandolin family sound"

Good luck

[Philip Pittman]

Graham,
Many thanks for your input - much appreciated. My string tension is calculated based on the same string gauges and scale length as the Oddy instrument but I've been unable to get further information from them. I could go to slightly lighter strings and reduce the tension to, say, 205 lbs by going to .013 - .049 strings and then I'm only about 13% more tension than a shorter scale mandola, but I'm still worried that I may need increased structural bracing for the larger body. What do you think about adding some longitudinal bracing, either H or A shape and perhaps eliminate one of the transverse braces ?

[Graham McDonald]

Phillip, I still can't follow your reasoning for wanting more tension than a short scale mandola. Guitars and many of the octave mandola/bouzoukis around work just find at the common guitar tension of 170-180 lbs. Top bracing will depend on several factors, including string tension, bridge height and the break angle of the strings over the bridge. On a flat-top (albeit with curved braces) with a floating bridge and tailpiece, there is a lot of compressional force trying to collapse the body lengthwise with the common problems of distortion around the soundhole as the neck pulls up and the dome of the soundboard sinking under the bridge/ Longitudinal braces may well help, but it is a larger body than I have every tried using them on. Perhaps contact Steve Knightley who seems to be an enthusiastic endorser of Oddy instrument and ask him.

Cheers

[Philip Pittman]

Graham, my only reasoning is that I like the look and sound of the Oddy instrument and would like to try and copy it as closely as possible. That said, many thanks once again for your comments. I've calculated that I can get the tension below 180 lbs with .012 - .047 strings, still maintaining the 24.9 scale, so maybe that's what I should do. Also I've found a comment from you in a Jan 25, 2010 post concerning an OM with longer than normal body. You suggest using longitudinal braces from the tail block to presumably some point past the soundhole and a transverse brace just in front of the bridge. Also there is a brace between the soundhole and neck.
Maybe this is the answer to my dilemma !

[Tavy]

As Graham, I think your original string gauges are way over the top: not only will you have to build the body like a tank, but you would struggle to make a neck strong enough to withstand the tension (and remember there's rather less wood in an OM neck than a guitar). Oh and you would never be able to press the strings down! Something like 12-42 would be the normal gauges for an OM of that length, 12-47 might be OK, but watch the neck if you up the bass side too much.

[Philip Pittman]

OK, so maybe my most recent post above is the way to go.
Any further comments please ?

[Bernie Daniel]

OK, so maybe my most recent post above is the way to go.
Any further comments please ?

Ok, I'll make a comment. You seem to be building an octave mandolin on a mandocello scale? In fact your first post kind of indicated that is your target. But I don't understand the reason for doing this.

You can get the octave mandolin sound using the conventional octave mandolin scale length of 21 - 22 inches.

Buy going with a longer scale I believe one very undesirable thing that you are accomplishing is making an octave mandolin that is as hard to play as mandocello?

Compared to a mandolin or mandola both the octave mandolin and the mandocello are much more demanding on the hands much bigger stretches. In fact I think the stretches are difficult even compared to a guitar?

Thus a mandocello is much more difficult to play then an octave mandolin?

So back to my original question what do you believe you are gaining with the longer scale length and the octave range?

[Graham McDonald]

Bernie, there is a whole musical sub-culture based around guitar scale octave mandolin, aka the Irish bouzouki. More in Britain and Ireland than the US perhaps, but just about every band in the world who plays 'Celtic' music has one.

There is nothing odd about wanting to build one, though Philip's model is more based on a German mandocello from the 50s or 60s.

Cheers

[Bernie Daniel]

Bernie, there is a whole musical sub-culture based around guitar scale octave mandolin, aka the Irish bouzouki. More in Britain and Ireland than the US perhaps, but just about every band in the world who plays 'Celtic' music has one.

There is nothing odd about wanting to build one, though Philip's model is more based on a German mandocello from the 50s or 60s.

Cheers

True. I'm familiar with bouzoukis and long neck tenor banjos too. I actually don't see bouzoukis as much in Celtic bands around here there but they are seen for sure. I just don't see the advantage of a long scale octave mandolin? Why have the frets any farther apart than you need them to be? The bouzouki string sets are light gauge 0.011" to 0.040" -- essentially long mandolin strings? My octave mandolin strings (21" scale) are a little heavier: 0.012" to 0.046" But you can make chord formations on an octave that you can't on a mandocello? That to me is significant because the bouzouki is typically a chordal or counterpoint instrument in TIM not a driving the melody? I have made a couple of "citterns" or 10 course mandocellos and there of course is the same issue the octave mandolin tone range on a mandocello or guitar scale. The videos are great though.

[Graham McDonald]

I see/hear a tonal advantage. The lighter a string gauge is for a particular pitch the more harmonics there are in the sound of each note, an extra harmonic richness I prefer over the 'thuddier' sound of the short OM scale. I have never thought of playing a bouzouki as I would an octave mandolin. They are much more about drone strings and implied chords and fragments of the melody and when played well can certainly drive the melody.

Cheers

[Bernie Daniel]

I see/hear a tonal advantage. The lighter a string gauge is for a particular pitch the more harmonics there are in the sound of each note, an extra harmonic richness I prefer over the 'thuddier' sound of the short OM scale. I have never thought of playing a bouzouki as I would an octave mandolin. They are much more about drone strings and implied chords and fragments of the melody and when played well can certainly drive the melody.

Cheers

Kind of like how the longer scale (25.5") sets the tone of a Martin guitar apart from a Gibson (24.75") scale I guess. I have a Gibson Advanced Jumbo with the 25.5" scale and it sounds very much like a D-28.