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#16
02-08-2020, 08:17 PM
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#17
02-08-2020, 09:24 PM
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Or....
I still haven't done your experiment, but...
It is easy to hear the difference in my guitars when I raise the body in the air so the back is not touching me much or at all. In the air, Way louder and rings way longer. It is a great way to end a song, and tends to have showmanship as well. Another very interesting and informative thread! Thanks Tim Hope things settle down and we get to see more of your work! Have FUN Paul
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3 John Kinnaird SS 12c CUSTOMS: Big Maple/Cedar Dread Jumbo Spanish Cedar/WRC Jumbo OLD Brazilian RW/WRC R.T 2 12c sinker RW/Claro 96 422ce bought new! 96 LKSM 12 552ce 12x12 J. Stepick Bari Weissy WRC/Walnut More
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#18
02-09-2020, 10:18 AM
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Fred
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#19
02-10-2020, 07:02 AM
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Thank you for taking my challenge and trying the experiment. If are willing to try it again, try Fred's advice and put a towel under it. Or better yet, remove your guitar from its case and lay it flat on your bed with the guitar's back laying flat against your bedding and repeat the experiment. Quote:
Quote:
I hope others will take our challenge and try the experiment found on page one of this thread. We will talk more about it soon, I promise. I'm running short on time, sorry but I've got to get busy and make some sawdust...
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#20
02-10-2020, 09:02 AM
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This will be a fun thread to follow. I love experiments and I'll try the one you suggest on a couple of my guitars when I get home tonight. Congrats, Tim, on getting back to one of your R & D projects. And, that old church re-model sounds like an interesting project as well.
Best, Jayne
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#21
02-10-2020, 05:46 PM
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Will do, but I’m away for a month!
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#22
02-10-2020, 09:21 PM
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Hey Tim, I found a pic of the guitar we built using Blackheart Sassafras. It looks somewhat like yours, but yours has more of the figuring. Here 'tis:
IMG_3333.jpg
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#23
02-12-2020, 06:31 AM
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I hope you found time to try our experiment. If so, what did you learn? Quote:
Yes that's the one that I remember you building and maybe even exhibiting it at one of the last Healdsburg festivals??? Regardless, it was a beaut!
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#24
02-12-2020, 10:07 AM
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I tried this today with my Wilborn Lion (00 size) model, and I could hear a clear difference in the resonance when the guitar was in the case vs held at an angle. It's Koa back and sides with a redwood top. I have noticed when I'm playing that the guitar has more resonance and sustain when I hold it away from my body a bit.
Thanks for the thread, Tim! Looks like another gorgeous guitar in the works here! beth
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#26
02-13-2020, 08:29 AM
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Now to expound on Beth's answer, the reason that one should hear more volume, sustain and resonance is that you are hearing the top coupling with the back, which we call an "active back". As the top is set into motion, from the strings vibration, the top then moves the air within the body chamber and then that air (spring) begins to set the back in motion, which BTW is 180* out of phase with the top's movement. Now both top and back are vibrating so you should hear that the energy response is noticeably amplified. Although the back's contribution and output is largely dependent on the Q of the back and the way it is voiced. If the back has a high Q (low damping quality) then it is likely not to absorb much energy from the top but rather reflect more of it, much in the same way as a trampoline works. If the back has a low Q (high damping quality) then it is more likely to absorb vibration from the top and stifle the sustain and add to a faster decay of the note(s). If the player holds the back against their body then the back is turned into a "passive reflector" and will not vibrate in the same way that an "active back" would or could. In this playing position the player and audience are mostly hearing the top alone with very little influence and contribution from the back. A more simpler way of looking at this is to imaging throwing a tennis ball against damp ground with 6" tall grass (low Q and high damping, passive reflector) and measure how high the tennis ball bounced. Which would probably not be very high. Now take the same tennis ball and throw it against a trampoline (high Q low damping, active back) and as you might imagine the ball would bounce a LOT higher, right? You threw the tennis ball with the same force (string energy) but the tennis ball bounced a lot higher because the trampoline "actively" took that energy and bounced it back instead of absorbing it. This is what you will hear if you took the time to perform my experiment. When you tapped on the bridge, with your finger, while the guitar was in its case or laying flat on the bedding you hear mostly the top because the back was damped and wasn't as free to vibrate or bounce that energy back. When you lifted the neck, that allowed the the back to freely vibrate and couple with the top which then you heard the top and the back actively working together. The guitar is an extremely complex machine and my over simplified explanation are only scratching the surface of the actual science of what is really going on. Sorry for the long winded rambling. Now I need to head to the shop and make some sawdust. Quote:
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#27
02-13-2020, 09:29 AM
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Hi Tim,
I have yet to do the experiment but I imagine that I would experience something similar to what Beth reported. You stated that: "The guitar is an extremely complex machine and my over simplified explanation are only scratching the surface of the actual science of what is really going on." Maybe this is obvious but just so I am not over simplifying can you tell me if the same principle that you are referring is the same reason that some mandolin players use tone guards? Or since the guitar is a bigger chamber is there something else at play? Thanks in advance for you taking the time to reply in between sawdust activity.  Best, Jayne
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#28
02-14-2020, 06:45 AM
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Laminated Back
Hi Tim et all.
With laminating the back, do you think it's better to laminate in form to the back radius then add back braces or laminate flat then let the braces do their work per normal? Peter
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#29
02-14-2020, 07:30 AM
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I'll be the first to admit that I know VERY little about mandolins. I did look up the tone guard and here is what I found: What's a Tone-Gard™ For? The Tone-Gard™ is designed to isolate the back of a mandolin (or any similar instrument) from the player's body, producing more volume and enhancing the tone. You can test the concept right now without a Gard. Play your instrument normally, while facing a wall about a foot or two away, allowing the sound to bounce back directly so you can hear how your instrument projects. After you are used to the sound, hold the mandolin by the neck so that the back of the instrument is a couple of inches away from your body. Now try playing some chop chords. Go back and forth, against and away from your body, and you will notice a difference. You will hear a difference just hitting one chop and letting it ring while holding against you, then away. (If you don't hear the difference, it's time to visit an audiologist — no kidding.) Seems their approach and results mirror what I have described previously above. Thanks for sharing that information Jayne. Quote:
First of all, welcome to the forum. IMO I do think it would be better to laminate in a form. The laminated joint places the glue in shear, as are individual braces, but since there is more gluing surface in a lamination of the entire back plate(s), it would make more sense to lay it up in a form instead of having smaller braces, which have far less gluing surface area to maintain the arch of the back. Most of us have seen back brace glue joints pop loose but I've never seen a laminated back separate unless it was subjected to extreme moisture conditions. Now if we are factoring in tone, then a laminated back would almost always lose over a solid and conventionally braced back. A laminated back would usually have higher damping characteristics but can be effective passive reflectors like some of the older Guild guitars were. Thanks for posing a great question and spurring some interesting thought and dialog.
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#30
02-14-2020, 09:47 AM
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Hi, Tim,
I’m glad to see you “back!” Sorry, Dad joke. I couldn’t wait until June. Seriously, though. Laurence Juber (former guitarist in Paul McCartney's post-Beatle band "Wings" and fingerstyle guitar player who has covered many Beatles tunes) has reported that he purposely plays with the guitar away from his body and angled slightly down to reduce the damping effect you are referring to. Though I will never be a luthier like you (there's too much other stuff I need to do) I can attest that people write off the effect of how various parts of a guitar vibrates. I was there with you as you "read the tea leaves" on how the upper bout of the soundboard is not as "inert" as many are lead to believe. I'll go one further to attest that even the neck vibrates. When I made the necks for my two builds I would find that even holding them during the fitting phase to the "box" would muffle its voice somewhat. I think that's why people are confused why they hear weird overtones up by the headstock. Usually that means that loose metal components in either the truss rod fitting or the tuning machines are vibrating. From a player's perspective I think that's why I like open strings better. Tuning the strings to open G is especially hypnotic because the lack of any obstruction just seems to make the guitar sing "ohmmmmm!"
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(2006) Larrivee OM-03R, (2009) Martin D-16GT, (1998) Fender Am Std Ash Stratocaster, (2013) McKnight McUke, (1989) Kramer Striker ST600, a couple of DIY builds (2013, 2023) Last edited by Neil K Walk; 02-16-2020 at 10:08 AM.
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