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Thread: Tone bars on the back?

  1. #26
    Mandolin & Mandola maker
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    Default Re: Tone bars on the back?

    The only reason why I braced the back was to stiffen it so as to raise the modal frequencies to something I knew from past experience would give the good tone I wanted. All back bracing does is to stiffen the back, and you would only do that to a back that was not stiff enough. The reason for the good tone is because the modal frequencies have been raised in a back that was a bit too floppy for the top. I could have achieved that by using a stiffer piece of wood for the back, but that is not always desirable or possible. It certainly works, some of my best sounding mandolins have a braced back, but just gluing a brace on a back and expecting it to improve the tone has a fairly low probability of success.
    Peter Coombe - mandolins, mandolas and guitars
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  2. #27
    Registered User Richard Sanabia's Avatar
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    Smile Re: Tone bars on the back?

    I enjoy these great posts. I thank all who jump in with their research, viewpoints, and experience. Without thinking about the effect of bracing or tone bars on the back, I put a "X" brace on the back of a "falling apart" Stella that I put back together, in order to strengthen the thin, (did lots of sanding to clean it up), repaired back. The result was a mandolin that is louder, clearer, and has better sustain, and a "chirpy" bell-like tone, and is noticeably sweeter than my Kentucky oval hole, which is very nice also. I was VERY pleased with the result. I really like Stella mandolins.
    Richard in Tennessee

  3. #28
    Registered User Yonkle's Avatar
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    Default Re: Tone bars on the back?

    I was going to reply, but decided this question is totally.......... well they say there is no such thing as a stupid question, but on the other hand...... ?? !!
    Shalom,Yonkle (JD)

  4. #29

    Default Re: Tone bars on the back?

    Looks at "Yonkle's " comment

    Interesting , so YOU HAVE tried this and can enlighten us to your expertise , or is it that you just decide without testing what is or isnt stupid because you are head and shoulders beyond the rest of us in ability ?

    In my "limited" experience , i have found several things that worked that I had doubts about.

    However it is sooooooooo nice to know that we have men of your calibre who can stear us laymen away from doing somthing "out of the accepted norm"

    I will sleep better now

  5. #30
    Registered User fscotte's Avatar
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    Default Re: Tone bars on the back?

    I think I know why folks don't place braces on the back of a mando, too hard to shave em after assembly. The braces on the top are shaved down before assembly. But many folks adjust the back plate after assembly by sanding and scraping to tune the overall sound. Sanding down a brace in the back is tough.

    Well, I've been doing tonebars on the back for a few mandos now. Usually just a transverse brace in the upper bout. And I have a sanding tool to tackle the brace through the f-holes.

    If light and stiff is what we want, maybe one transverse brace can replace oodles of mass in the back plate upper bout, the thick part that leads up to the neck, ala Loar grads. I highly recommend some builders try it. One brace replaces lots of mass.

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  7. #31
    Registered User fscotte's Avatar
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    Default Re: Tone bars on the back?

    I'm really surprised this hasn't been investigated further. I've scoured the internet and MandoCafe archives and found little interest, but those who did back bracing, which are far and few, had great results.

    So am I on my own here? I'm kinda looking for a counter argument to stop me. What am I missing?

    Are we really wanting light and stiff for the back? If you can take a back plate from 150 grams to 120 grams with a brace.. Why aren't there more folks doing this? Tradition? Looks?
    Last edited by fscotte; Mar-22-2017 at 9:49am.

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  9. #32
    Registered User Steve Sorensen's Avatar
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    Default Re: Tone bars on the back?

    Now, many years after posing this question, I have come to think of the back as the "woofer" speaker component of the sound system -- that is, like bigger speaker components, the primary function is to pump air. As with these components, that means you are building for a mass in the center which is able to move with the sound energy because it is surrounded by a flexible perimeter.

    To this same end, "thinner across the board" is not necessarily better. The mass in the center of the back takes energy to move and delivers that energy more effectively with the longer wavelength bass generation from the top. Backs which are thin all the way across, even if very thin at the edges, I believe can do more harm than good to the balance of response in the instrument.

    While this is an over-simplification, the concept helps one consider how one might change mass, stiffness, or flexibility to areas of the back.

    To this same point, if a mandolin has a correctly graduated back to be actively responsive to the top, one can see why the freeing cage of a Tonegard makes such a difference in power and balance.

    Steve
    Steve Sorensen
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  11. #33
    Registered User Drew Egerton's Avatar
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    Default Re: Tone bars on the back?

    Steve,

    Just build them all to sound like Danny's VX. That thing was amazing, especially for being brand new!
    Drew
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  13. #34
    Registered User fscotte's Avatar
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    Default Re: Tone bars on the back?

    Quote Originally Posted by StevenS View Post
    Now, many years after posing this question, I have come to think of the back as the "woofer" speaker component of the sound system -- that is, like bigger speaker components, the primary function is to pump air. As with these components, that means you are building for a mass in the center which is able to move with the sound energy because it is surrounded by a flexible perimeter.

    To this same end, "thinner across the board" is not necessarily better. The mass in the center of the back takes energy to move and delivers that energy more effectively with the longer wavelength bass generation from the top. Backs which are thin all the way across, even if very thin at the edges, I believe can do more harm than good to the balance of response in the instrument.

    While this is an over-simplification, the concept helps one consider how one might change mass, stiffness, or flexibility to areas of the back.

    To this same point, if a mandolin has a correctly graduated back to be actively responsive to the top, one can see why the freeing cage of a Tonegard makes such a difference in power and balance.

    Steve
    Yet many Loars are heavy at the upper bout spine, and quite thin in the center of the back. That spine is in an area where there is little movement in terms of flexibility. I know some builders are carving thin all the way around and leaving the center heavier, like you suggested above.

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  15. #35
    Registered User fscotte's Avatar
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    Default Re: Tone bars on the back?

    Not saying you cannot have mass in the center to "pump" like a woofer. A brace simply keeps the "stiffness to mass" ratio higher - I think this is something we all strive for in plates. You could have as much mass in the center with a brace, while keeping the stiffness/mass ratio higher, than without a brace.

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  17. #36
    Registered User fscotte's Avatar
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    Default Re: Tone bars on the back?

    A little more to chew on.

    Doing some more real world comparisons, using deflection testing in combination with tap tuning (attached to rim). Plates that are equal in deflection and tap note, one with brace, one without, yields a savings of 20+ percent in weight. At least for my A-style plates. My plates are generally between 130 - 170 grams, depending upon the wood. That's 30+- grams lighter when a brace is glued directly down the centerline.

    I see no reason not to use a brace. If higher stiffness to mass ratio is what you're trying to achieve.

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  19. #37

    Default Re: Tone bars on the back?

    Quote Originally Posted by MikeEdgerton View Post
    Well this message posted by Rick Turner pretty much sums it up for me, I'll change my view to his view of the bars being 50/50 (structual/tone) unless somebody else can direct me to the post that I can't seem to find. I also ran into this tragic/humorous post from James Condino.
    Mike, My research suggests that the tone bars in the top served both to provide support for the pressure points under the bridge, as well as shape the resonant frequency of the top. So your comment on 50-50 is quite reasonable.

    David

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