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Thread: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mandolin

  1. #1

    Default Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mandolin

    Sorry, no pics, I'm in a digital equipment crisis right now.

    Materials and Dimensions of fix:

    Quartersawn western red cedar 2cm thick, quartersawn mahogany (African?) 2 cm thick

    13cm long, 1cm wide, arch in middle 5cm long and 40mm tall, compensated bridge.

    So I changed the strings on a Hora 23" flat top OM from extra lights to J80's, and I noticed the banjo bridge it came with started to dimple down.

    I made another 10cm bridge with wider feet, but the same problem.

    I decided on a Bigfoot bridge, knowing that having wider, longer feet would negatively impact the sound but needing to preclude further caving.

    I tried all solid mahogany, it worked, but sounded poorly. I hollowed it out to reduce mass but it still sounded bad.

    Knowing that less mass is more sound, I then took three pieces of western red cedar, a very light and rigid wood, from a guitar top and glued them together, noticed that if I had the grain running parallel to the top it didn't bend at all, as opposed to grain at right angle to top, and then laid up a thin piece of mahogany on top. I know this is not protocol, the grain and all, but I needed strength.

    Shaped it so that the bridge was compensated, which cured the unsightly problem of having to cock the bridge on the top and, voila. 10-15% loss of volume, tone remains, and now my bouzouki won't implode. There is some very minor dimpling now, distributed over a much larger area. A fair tradeoff and a very enjoyable day.

    Hopefully this is the cure, will update if my OM explodes overnight.

  2. #2
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    Default Re: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mando

    Remember when you first posted about this instrument, and you noted that there was no arch to the top? And I said my big concern would be eventual top collapse? Well, I hate saying "I told you so", but....

    These things are what they are. I know you said you were impressed with the build quality but they can't be offered at that price point without cutting some corners. Proof of that is the factory ultra light strings,which they appear to use for good reason.

    You can't add arch to the top after the fact. This is a basic design flaw. As I see it if you want to bother your only solution would be to remove the back and beef up the bracing somehow, with extra reinforcement where the bridge feet rest. This would stiffen the top and it may lose some tone but al least it wouldn't self destruct. You could compensate for the loss of tone somewhat by making a properly designed one piece bridge from hard maple. The banjo bridge was a poor substitute to start with. Your premise that "less mass is more sound" is somewhat flawed in my opinion. Most mandolin family instruments use ebony or rosewood, and violins use hard maple. I think your mahogany and cedar experimental bridges will not work. There have been some great threads recently on bridge design. These should point you in the right direction. But nothing will work right until the top is reinforced.
    Don

    2016 Weber Custom Bitterroot F
    2011 Weber Bitterroot A
    1974 Martin Style A
    Fender Octave Mandolin c.2004-2008

  3. #3

    Default Re: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mando

    Quote Originally Posted by multidon View Post
    Remember when you first posted about this instrument, and you noted that there was no arch to the top? And I said my big concern would be eventual top collapse? Well, I hate saying "I told you so", but....

    You can't add arch to the top after the fact....

    Your premise that "less mass is more sound" is somewhat flawed in my opinion. Most mandolin family instruments use ebony or rosewood, and violins use hard maple. I think your mahogany and cedar experimental bridges will not work....
    1. You hate saying. Top didn't collapse, that's been prevented by Bigfoot. This fix is posted to address a common problem throughout the stringed instrument world.

    2. I can and I have. I've installed profiled shims on the braces. Even replaced braces, all in situ. Just like mandos, violins and guitars, no problemo. I take the back off. In fact, I've successfully rebuilt the tops to several mandos using this method. I don't bill myself, so it's within my limited budget, and it keeps me busy in my premature retirement.

    3. The experiment is a success, I had to go through a couple of tries to make it work. The OM didn't explode last night, top is stable.

    Less mass is more sound, more mass absorbs sound. More mass is okay for high tone, but mid and low tones are killed by mass. This isn't an opinion. It's why bridges aren't carved from stone, it would simply kill the mids and lows, although the highs would shine. It's why braces are scalloped. It's why tops are thin instead of a thick block of wood. It's common practice to hollow out floating bridges to address this issue, my gypsy jazz and big box jazz guitar bridges are so altered. So I came up with an idea that might even improve a mandolin/bouzouki's response if someone chooses to implement it. I'm planning on trying a cedar bridge on my mandolin for a comparison vs. the rosewood bridge. Just for fun. Also a three ply, cedar/mahogany/cedar, right angle to the top. I've found, on banjo bridges for instance, that even replacing the string-slot ply on top of the maple bridge with different grades of hardwood significantly changes the sound of the individual string. Hornwood for unwound, African Blackwood for wound really works for me. Hornwood brighter highs, Blackwood warmer mids.

    The issue of a bigger foot is exactly the same as installing another brace on top instead of inside, and a lower mass bridge/brace makes sense. We don't use hardwoods for braces due to the mass issue, they would simply kill the sound, we usually use spruce, a low-mass very strong wood.

    4. I addressed the possibility of a caved top in original review. http://www.mandolincafe.com/forum/sh...ouzouki-Review

    If I didn't know what I'm doing, I wouldn't have been able to afford a profiled or carved top anyway, but retro-fitting a flat top to be profiled is no issue, for me at least.

    The reason this was posted was for those with bouzoukis, OM's, and mandos, as well as tail-piece guitars, etc with collapsing tops to have an alternative to otherwise trashing a decent instrument.

    Now, if you have a carved top OM you'd like to donate, I wouldn't turn it down.

  4. #4
    Registered User Jim Adwell's Avatar
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    Default Re: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mando

    As an experimenter myself, I approve of the OP's efforts, although I probably would have replaced the strings with another set of ultra-lights and avoided the whole issue of a collapsing top that way, or just built a new OM the way I wanted it to be (which coincidently I'm doing right now) and experimented with bridges on that, if I felt the need.

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    Default Re: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mando

    It seems, High Lonesome, that your solution satisfies you. Best of luck to you with your bouzouki.

    I note that in your original review you pronounced it "structurally sound". The evidence you present is to the contrary however. In your own words you say there is still some " very minor dimpling, spread over a much larger area". So an improvement but certainly not a cure. But many vintage instruments have minor dimpling or sinkage and as long as it's stabilized and not getting any worse you should be able to play it for some time.

    I am still a little puzzled by your viewpoints on bridges. I looked in vain for professional makers who install hollowed mahogany or western red cedar bridges and found none. Everyone seems to use ebony, rosewood, or maple, in that order of popularity. Still, bridge design is definitely an area of ongoing experimentation. Red Henry opines that Gibson started using ebony for bridges mostly because of how they look, not as the best choice for sound. Still, I would be very interested indeed if some if the professional builders who hang out here would chime in with their opinions on your solution. Maybe I just think about bridges all wrong and I need straightened out. I'm not a professional builder but I know some of the best builders in the world hang out here. And I'm sure they all have very strong opinions about bridges!
    Don

    2016 Weber Custom Bitterroot F
    2011 Weber Bitterroot A
    1974 Martin Style A
    Fender Octave Mandolin c.2004-2008

  6. #6

    Default Re: Bigfoot Cedar Bridge to Prevent Caving- Flat Top Octave Mando

    Quote Originally Posted by multidon View Post
    It seems, High Lonesome, that your solution satisfies you. Best of luck to you with your bouzouki.

    I note that in your original review you pronounced it "structurally sound". The evidence you present is to the contrary however. In your own words you say there is still some " very minor dimpling, spread over a much larger area". So an improvement but certainly not a cure. But many vintage instruments have minor dimpling or sinkage and as long as it's stabilized and not getting any worse you should be able to play it for some time.

    I am still a little puzzled by your viewpoints on bridges. I looked in vain for professional makers who install hollowed mahogany or western red cedar bridges and found none. Everyone seems to use ebony, rosewood, or maple, in that order of popularity. Still, bridge design is definitely an area of ongoing experimentation. Red Henry opines that Gibson started using ebony for bridges mostly because of how they look, not as the best choice for sound. Still, I would be very interested indeed if some if the professional builders who hang out here would chime in with their opinions on your solution. Maybe I just think about bridges all wrong and I need straightened out. I'm not a professional builder but I know some of the best builders in the world hang out here. And I'm sure they all have very strong opinions about bridges!
    Structurally sound with the original strings, I changed the strings from probably light to regular. I really like the sound of the heavier gauge. Would've reverted to lighter strings if this fix didn't work, but it did. Your picking, I'm grinning.

    I've been a luthier for 45 years, was a full time professional luthier for two and a half decades dealing mainly in restoration, am an instrument preservationist, have tricked out instruments my whole life,unfortunately broke my back just before taking line supervisor position with Gibson in Tennessee, have built instruments, and have sat down with engineers to consider sonic issues re: string instruments. Am I tooting my own horn? Yes, but it's a decent tune nonetheless.

    I'm not great on the physics end, but greater mass to reduce transmission of vibrations is why cast iron tables and parts, as opposed to aluminum or steel, are sought out for shop equipment. So much mass that no rattle or other vibration can occur, as can happen with lighter metals. It's why your car rattles, but the concrete road underneath it doesn't.

    Here's a great link on bridge transmission/reduction of vibrations through the bridge on violins:

    http://lyramusical.com/guide/2012/08...ge-for-violin/

    Here's one on hollowing out floating bridges on guitars:

    http://www.lehmannstrings.com/Articles/selmer.htm

    Stradivarius used to candle his top tables, he went for mass, not thickness alone. Later restorationists thought his production house made a mistake, and recut top tables to a uniform standard thickness, destroying some fine instruments.

    I love wood. Man has tried, and failed, to recreate this wonderful creation. It's been found that instruments do play in. Especially on spruce/cedar/pine tops, the vibrations break the resinous caps on the end of the cells, resulting in a longer cell with some resin coating the inside. Your instrument will actually become warmer and more responsive the more you play it.

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