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Thread: Mandolin size

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    I've been coming to this site for about a year, reading and learning from all the posts. First let me say I'm blown away by how much knowledge is concentrated here.. WOW..!
    I'm new to the Mandolin, only been playing for about 9 months, but addicted. I've contacted a builder and will be starting the project in about 4 months. Here's my question. Can the depth of the Mandolin be increased in size, in other words can the sides be made an 1/8 of an inch wider. The reason I'm asking is because I read so much about the bark and woody tone of the Gibson's. I'm wondering if this size change will increase the volume...?? I've been playing guitar most of my life but the Mandolin has sparked a new passion, one that was really needed..!! Thanks..!!!

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    Mike Parks woodwizard's Avatar
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    Gibson's are not really that wide. I'm not sure wider will help you that much.
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    Yank,
    Welcome to the Café and thanks for posting your question. This thread was covering your very question. An intersting 2 page read, a bit hot from time to time... but intersting.

    Jamie
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    coprolite mandroid's Avatar
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    that one change, in isolation, won't make it louder, if it's not going to be so, without that change in that particular dimension.

    A trifle more space in side , so 'Volume', as a measure of cubic space
    inches (fractions)
    or equivalent in, say, Milliliters, [or acre feet]

    would be applicable as it does separate the back from the front by that amount.

    Others want to offer the different rim widths on various mandolins they have handled.?
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    I may be old but I'm ugly billhay4's Avatar
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    Yank,
    There is no standard for a mandolin's size. They have been made in a lot of different sizes and shapes.
    The volume of a particular instrument is determined partly by the inside volume of the instrument, partly by the size and shape of the soundholes, partly by the wood the top is made of, partly by the arching of the top, etc.
    As you can see, there are so many factors that come into play here, you can't rely on changing one alone to produce a specific effect.
    If you want a loud instrument, convey this to a luthier and let him or her figure it out with the particular design, wood, etc. you want.
    Bill
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    Yank-

    Just a small suggestion- if you are as new to the mandolin as you say, it might be a nice idea to save your custom built mando for a year or two down the road. That way, your playing will have matured along with your tastes in mandolins. Play a bunch of instruments, get an idea what you like, and then have it built. That takes a little time and experience.

    The one thing I've learned for sure from following the forums (and classifieds) on MandolinCafe is that tastes *do* change, sometimes very quickly .

    After some time has gone by, you'll be able to answer that question about body depth, along with many others, through the persective of your own preferences and experience.


    Rick

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    I own four mandolins, two are Gibson made and they are both the same depth, one custom made and it is thinner in depth and a Ratliff which is deeper than the others..They all sound different so like Rick, said play a bunch of instruments and find out what sound you like and hopefully a luthier will be able to duplicate the sound you like...By the way, welcome aboard and good luck in finding what you want and like...Willie

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    In my own experience (albeit considerably more limited that that of many of the contributors to this board), the loudness (to avoid confusion, I will reserve the use of the term volume for its spatial sense) of a mandolin is not directly related to its body depth, rim width or body volume. As Bill Hay says, those are only few of a multitude of parameters which affect the loudness - and variation in loudness is only one of many effects on the sound that occur with variation in body size and shape.

    What I have noticed, however, is that variation body depth has a particular effect on the tone. An important factor in the tone of a mandolin is the way the sound is reflected within the body and out of the soundhole. The greater the distance between the back and the soundboard, the longer the delay between plucking the string and the reflected sound emerging from the soundhole. This reflected sound may not be the only sound you hear - vibrations are also transferred directly to the outside air from the soundboard and even from the string itself - but it is a large part of it. So the effect of a deeper body is similar, if on a more subtle scale, to the effect of snapping your fingers in a cathedral. Personally, I have come to prefer shallower-bodied instruments as, to my ear, a deeper body tends tp blur the attack, or 'punch'. But that is an effect that may appeal to some people.

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    Whistler, the modes of motion of the air in the body cavity are 3-D analogs of standing wave motion. If you consider a standing wave in a string, it is a single pulse that is 'reflected', but within a few cycles, the standing wave behavior is established. In mandolins, guitars, etc., air molecules are not literally reflected off the back plate and out through the soundhole. The air inside the cavity acts as a vibrating 3-D spring, in turn setting the mass of air in the immediate region of the soundhole vibrating. The time delay of which you speak is negligible. The dimensions of the soundhole and body cavity are parameters which affect the frequencies of the air resonances; the sound radiation comes from traveling wave propagation outside the body cavity which is initiated from the vibration of the mass of air in the immediate region of the soundhole. I don't doubt that you are hearing what you say, but your description of its' physical origin is incorrect.

    http://www.Cohenmando.com

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    Like I said in my first post... The knowledge on this site is mind-boggling. After reading some of these replies, I feel that I have stumbled upon a factor of hand made mandolin building that cannot, and never will be defined as an exact science. There are too many factors that are playing in the arena. Such as, volume, parameters and mass just to name a few. Then you have mass characteristics, such as type of wood, density of the wood, grain etc. not to mention the builder’s touch. Did I mention barometric pressure..? Then throw in the "Player", how he/she affects the strings, light touch, heavy touch, attitude etc. In other words no two mandolins will ever sounds the same; they may be close in frequency, but truly never the same...! Thanks you so much for the great responses... That's why I love this page and the Mandolin...!
    What an Art form….!!!!

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    Dave - Thanks for setting me straight. It is not unknown for me to expound authoritatively on subjects I don't know much about.

    Quote Originally Posted by
    The time delay of which you speak is negligible.
    Yes, now you mention it, if sound takes about a millisecond to travel a foot, then 3/4" isn't going to make much of a difference. It is entirely possible that what I think I hear is partly a result of my ill-formed understanding of acoustics. But I have to say that your post above doesn't come much closer to explaining things - it's all a bit technical for a mandolin player. I just pick 'em up and play them - and build a few.



    Quote Originally Posted by
    The dimensions of the soundhole and body cavity are parameters which affect the frequencies of the air resonances;
    That much is clear. But given a constant body volume and soundhole size, what are the specific effects of varying the soundboard area and body depth (i.e. large soundboard area - shallow body v. small soundboard area - deep body)? I don't expect a simple answer, but I would like to have a better understanding. I've
    already spread too much misinformation.

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    For a comprehensive introduction aimed at (nontechnical) luthiers, try

    "An Introduction to Guitar Acoustics", by Thomas D. Rossing, in "The Big Red Book of American Lutherie, Volume Two, pp 124-134, available from the GAL,

    and
    "Sound Radiation from Guitars", Rossing, Ibid, pp 144-152.

    For mandolin specifics, you need the Cohen & Rossing papers, referenced on the "Acoustics" page of my website,

    http://www.Cohenmando.com

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    I agree that you should develop your chops, play a variety of mandolins and then decide what you want. So much depends on music style, personal preference as to F or A style. Be patient.

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    I may be old but I'm ugly billhay4's Avatar
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    Dave,
    I'd like to ask a question, a real question not a prelude to a quibble with something you said.
    If the air inside a mandolin "acts as a vibrating 3-D spring, in turn setting the mass of air in the immediate region of the soundhole vibrating", why isn't the vibration of the outside air more generalized? In other words, as I understand your post, the outside air is vibrated mainly in the vicinity of the soundhole. What is the mechanism for this? Is it the fact that there is air to air contact there? or some other mechanism I don't know about?
    Appreciate your continued efforts to educate us.
    Bill
    IM(NS)HO

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    I've got a question: How about the distance between your ear and the sound hole, do air vibrations stay concentrated or do they radiate outward and diminish...?
    Now I'm getting silly...Sorry...!!

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    First, I don't know what you mean by "why isn't the vibration of the outside air more generalized?" Aside from that, your current question is more fundamental. That's gratifying to a crabby old academic, but also time consuming for me to answer. Fortunately, some simplistic answers have already been committed to print in a largely non-mathematical form for luthiers. Look at the following references:

    (1) "Basics of Air resonances", W.D. Allen, in "The Big Red Book of American Lutherie, Volume One", pp 8-12. Originally published in American Lutherie #1, 1985.

    (2) "Tuning Air Resonances", W.D. Allen, in "The Big Red Book of American Lutherie, Volume Two", pp 6-11. Originally published in American Lutherie #13, 1988.

    While Allen's descriptions were somewhat simplistic, they were nevertheless very helpful for luthiers. Some interesting new work has been done since the time of Allen's articles, though.

    The molecules in the cavity of an instrument are moving in random directions, crashing into the walls of the cavity and into each other. Think Molecular Kinetic Theory ("MKT") from freshman chemistry. The pressure in the cavity is not directional; it is uniform (i.e., the same) in all directions. In other words, the pressure everywhere in the cavity is approx. 1 atmosphere. When the plates move away from each other in the bellows motion (i.e., the (0,0) mode), there is a pressure decrease in the immediate vicinity of the inner plate surface, which cause a slight tendency for molecules to move as a group toward the plate. When the plates are moving toward each other, there is a slight pressure increase in the immediate vicinity of the inner plate surfaces, and the molecules have a slight tendency to move away from the plates. The alternating pressure changes result in a motion like an alternating expansion and contraction of a balloon shaped like the interior of the cavity, and that is the Helmholtz or first air resonance motion. Since the air has mass and some "springiness", and since sound propagates at a different velocity in the air than it does in solids, the (1st) air resonance occurs at its own frequency. In the vicinity if the soundhole(s), the pressure differences from the group motions of the molecules cause pressure differences in the soundhole air mass, so it is set in motion, in turn setting air outside the cavity in motion, which is how the low frequency sound radiates.

    At much higher frequencies, when the velocity of the plate surface becomes equal to or greater than the velocity of sound in air (ca 800 Hz?), most of the sound is radiated from air motion outside of the plates. The plate motions create pressure differences outside the plates which result in group motions of the outside air. Those group motions are propagated spatially in the usual way (see, e.g., Allen's articles).

    Yank, if a silly question is offered, it would be silly to attempt to answer it.

    http://www.Cohenmando.com

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    Yank,
    Sound moves through air like ripples through water. They diminish with distance depending upon a variety of factors. It's easier to hear a concert closer to the player rather than farther away, right... See this website for details I have long forgotten.

    Jamie
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  18. #18

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    Since I have tried many body depths in my instruments, I'll offer something to this for what it is worth.
    Given plates which are worked equally in two otherwise identical, thinner and thicker bodied instruments, a deeper bodied mandolin simply has more overtones (identifiable character). Just as trebles are reflected out from the surface of the plates, so also are they reflected into the cavity where they interact with current bass notes and sympathetically inspire new ones. From close on, the player can hear this "complexed" timbre very well. The audience seems to hear it less.
    The timbre of the bass, though, is directly (as opposed to, but also as well as, indirectly) affected by body depth. With more air to push, I have found deeper bodied instruments have a more complex bass (so "bass too", or really: everything). Something I like very much. If taken too far though, or if the plates are not made a bit thicker and stiffer to compensate (for the extra work) the plates cannot push the air inside adequately, the bass becomes muddy, the trebles thin and lifeless.
    In either case, it only changes timbre, not volume, until you make the cavity too small and then the bass just sounds thin.
    Volume, for the most part and in normal cases, I find, comes entirely from how one works, thins, arches, and graduates.
    To get a dry tone, I'd recommend a thin, standard body. Obviously, that's what most folks are doing with f-holers.

    In closing: my knowledge of these things is strictly colloquial, and sometimes very hard to put into words. I done did me best though.. to convey how I see it.

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    Dave C. - I was taught in my acoustics lectures (which formed part of a Musical Instrument Technology' course) that the parameters that determine the Helmoltz frequency are: cavity volume, neck width (i.e. soundhole area) and neck length (i.e. plate thickness at the soundhole). It could be that I didn't listen properly (not unlikely) or I was taught a somewhat idealised version of the theory. But, all other parameters being equal, would it be correct to say that a given cavity size will result in the same Helmholtz frequency, regardless of whether that cavity size is arrived at by means of a deep body and small soundboard or a shallow body and large soundboard? Or is this not the case?

    W.D. Allen's 'simplistic' descriptions sound like they could be the thing for me. I've got a pair of ears, but not much between them.

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    I may be old but I'm ugly billhay4's Avatar
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    Thanks, Dave,
    What I meant is why is the vibration concentrated around the soundholes and not generalized over the body of the instrument?
    I think I understand your explanation and appreciate the effort.
    Bill
    IM(NS)HO

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    For the "classic" Helmholtz resonator, that is correct. There is also a formula for a "neckless" Helmholtz resonator. See Fletcher & Rossing, "The Physics of Musical Instruments, 2nd Ed., p. 14. There is quite a variety of Helmholtz resonators. Fletcher & Rossing deal with a few of them, including stringed instrument bodies, which are essentially neckless Helmholtz resonators.

    What I was trying to get at above, without going into any "math" (to which a lot of people are averse), is that the most basic aspects of a cavity or Helmholtz resonance are that the air in the cavity volume acts as a spring, and the mass of the air in the neck, or soundhole area, acts as a piston whose resonant frequency is determined by its mass and the stiffness of the spring. That isn't exactly what BillHay asked, so I got diverted. If I answered every question in totality, I would be writing for days, which is obviously not practical for me.

    It's true that the Helmholtz resonance frequency of a deep-bodied instrument with small plate area could be the same as that of a shallow-bodied instrument with large plate area. One factor necessary for good low-frequency and midrange response, though, is that the first air resonance frequency needs to be close enough to the lowest plate mode frequency that the plate and air modes interact (i.e., "couple") strongly. A deep box with small plates would have trouble with that, since the lowest plate modes would tend to be high. Conversely, it is possible to make a box with too large plate area and too shallow depth. In that case, the plate mode frequencies could be too low to interact strongly with the Helmholtz resonance, and once again, the interraction or coupling would be weak.

    Further complications are that an ideal Helmholtz resonator has rigid walls, and the excitation of the air resonance comes from outside. In a stringed instrument, the walls of the cavity are vibrating and providing the excitation for the cavity resonance. The plates and the air mass interract ("couple") and exchange energy. That energy exchange perturbs both the plate motions and the air motions, causing both to occur at different frequencies than they would in the absence of each other.

    All of this stuff is in Fletcher & Rossing, and much of it is in Rossing's "The Science of Sound", a book written for a nonmajors course (or as physicists sometimes say, a "physics for poets" course).

    http://www.Cohenmando.com

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    That makes things a lot clearer. Thanks very much, Dave, for taking the time to explain.

    I hope my questions (and your answers to them) are useful to Yank as well - I didn't mean to hijack his thread.

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