4 Bridge System Madness.

[dan in va]

+1 to Skunkwood's comment. David Grisman's F5 had the bridge base bobbed back in the mid 1970's, and later he went back to the original long style....i wonder why. There have been numerous testimonies of tops sinking under 2 footed bases and not affecting the middle section, and full contact bridge bases solved the issue.

Good on y'all if it works. However, the old style long base seems to reach the tone bars and distribute the force over more of the top -- a full contact bridge even more. So for a short bridge to work on traditionally designed tops, will something need to be changed to make the shorties work long term?

[David Houchens]

IIRC, John Hamletts Tail pieces were near in-line with a standard bridge spacing.

[Pete Jenner]

I certainly don't mean to sound argumentative -- and I mean to encourage your experiment! -- but I believe that you are wrong about the spreader-with-feet not acting as a secondary bridge.

The tension in the strings causes them to bear down on the main bridge (usually through the saddle, or in your case, through 4 separate saddles), and after the strings are sent into vibration by the energy introduced by the pick, some of that vibration, and energy, is transmitted through the bridge and down into the top. But not all of it. Quite a bit of the remaining vibrational energy travels rearward, beyond the bridge saddle, and towards the tailpiece. In fact, that is the reason that many mandolinists use rubber grommet dampers, Weber "wood nymphs", or bits of felt or leather to dampen these vibrations, which can cause parasitic, unwanted sounds. And this same vibrational energy is also what causes loose tailpiece covers to rattle! So, it is a significant amount of energy. In your current setup, you are coupling the vibrational energy of the strings behind the bridge to the mandolin top through the feet of the string spreader. It will definitely act as a secondary bridge. Whether it turns out to be a small or a large perturbation, over-and-above the primary bridge, remains to be determined, but an effect is to be expected. Also, by bearing down, the two feet of the spreader will tend to produce a NODE line (a line of zero vibrational amplitude) in the complex modes of vibration of the top, thereby suppressing any of the (many) vibrational modes that happen to have high amplitude under the location of the spreader feet. (This is equally true of the regular mandolin bridge, which is one of the reasons why Lloyd Loar moved the F5 bridge more towards the center of the top, by lengthening the portion of the neck before it reached the body to 15 frets, compared to the earlier, shorter-neck F4). That will also change the sound, for sure.

Anyway, theory only tells us so much. You have to do the experiments! But, I hope you agree, these need to be "cleanly designed" to test what you think you really want to test -- and not something else. If you want to test the effect of 4 separate bridge saddles instead of just 1 common saddle, you ought not (1) mass-load and dampen the strings behind the bridge position with a spreader, and (2) have that spreader transmit vibrations to the top. It's still an interesting sonic experiment as you have it, of course, but I would not know how to interpret the results. Any change in sound or timbre could be due to the separate saddles, but it could equally well be be caused by the spreader. Or both! You will be left with a mystery. You want to design your experiment to change as few things at a time as possible.

Yes I do agree the spreader is not a great idea but will have to remain until I have an alternative. I don't think it will establish nodes or node lines any more than a planted piny or resting arm would. The downwards pressure on the blocks from the strings at that point is only sufficient to immobilise the spreader and that is one of the thicker parts of the top. But it is all speculation on my part and the goal remains to replace the spreader with a better solution.

[Pete Jenner]

IIRC, John Hamletts Tail pieces were near in-line with a standard bridge spacing.

Maybe he'll be willing to sell me one if that's the case.

[Pete Jenner]

"Kevlar body armour donned and securely fastened, I sit prepared for the ridicule, derision and ignominy that will doubtless ensue from this thread....."

Quite possibly the most insightful thing ever stated here!!!!

Peter, good on ya' for the creativity and curiosity and even bolder for wilingness to stand naked and post it around here; keep it up! As for the crusty crusty whole lotta nuthin' nay sayers....a simple two word phrase comes to mind.....

j.
www.condino.com

Thanks James.

[Pete Jenner]

OK Peter, you have strung this rascal up, what does your ear tell you? First impression?

Initial impression is that it doesn't sound too different from the standard 2 footed bridge but I'll start taking some measurements this afternoon or tonight.

[Pete Jenner]

Just a as a general note on this exercise, it is not designed to take over from or make the standard bridge designs redundant.
I'm just trying to shed a bit more light on bridges and explore possibilities. If it turns out this system has a place in the world of mandolin bridges, that's great. If not, that's fine too.

One thing I have discovered is that the thumb wheels on the D and A strings are nearly impossible to access. Eventually they will be will replaced by hex nuts like the ones used in Marty Jacobson's bridges.

[Pete Jenner]

+1 to Skunkwood's comment. David Grisman's F5 had the bridge base bobbed back in the mid 1970's, and later he went back to the original long style....i wonder why. There have been numerous testimonies of tops sinking under 2 footed bases and not affecting the middle section, and full contact bridge bases solved the issue.

Good on y'all if it works. However, the old style long base seems to reach the tone bars and distribute the force over more of the top -- a full contact bridge even more. So for a short bridge to work on traditionally designed tops, will something need to be changed to make the shorties work long term?

The 'Heretic' is X braced with the X crossing not far in front of the bridge position.

[Marty Jacobson]

You would lose the normal rocking motion that a traditional bridge applies to the top plate. BTW, bridges don't transmit vibrations to the top. The bridge acts as a lever, more of a mechanical force, not like electricity.

Why do you think that? Just curious.

[dan in va]

Pete, the X braced top seems like a good idea with your bridge idea. It wouldn't be hard to add a little brace under the bridge if any sagging started. Thanks for the update, and i hope you'll revisit the thread over time.

[Bertram Henze]

The good thing I see there is decoupling of transversal guidance from vertical and longitudinal adjustment, like in a nut/zero fret combination.
I am not sure about the decoupling of courses from each other, though: what happens to overtone injection? Does the high D (A strings 5th fret) still make the open G strings ring along as strong as it used to? The camps are divided in how that would be a good or a bad thing, but I for once would miss the richness in overtones.
Also, I am not sure about busting common myths - for each myth busted there will be two new ones created. But that's a welcome enhancement in oncoming Cafe discussions on the "Jenner 4 cylinder engine"

[Pete Jenner]

I think you may have a point about the de-coupling adversely affecting overtones Bertram. I put the original bridge back on with the string spreader in place and there was a very noticeable improvement in the sound.

So... I've come up with a way to couple the posts below the thumb wheels and still allow them to be adjusted forwards and backwards. This will probably take me all night so bear with me.

[Michael Lewis]

Pete, I think your idea can benefit from side to side stability. If you elongate the feet for each bridge to give that stability the feet will have to run past each other. If you angle them slightly they will form a continuous contact base of bypassing pieces. Diamond shaped feet would form a single "foot" of four pieces. Imagine smooth straight edges along the base front and back, with diagonal lines showing the edges of the individual feet. I don't have a thousand words.

Also, you state the separate pieces together weigh less than the original style bridge. I think you may get better sound with a bit more weight, but experimenting will show you what works best. It may well prove that different weights work best for different strings (frequencies).

Though this design will be a bit more fiddly and have more pieces than the standard design it may well be a superior concept.

[Pete Jenner]

Thanks Michael. It's very useful to get all this input from great builders.

[Bertram Henze]

Don't forget to make recordings of all possible configurations. Don't rely just on memory. I guess we all are looking forward to a big acoustic bridge concept tasting showdown in the end.

[Pete Jenner]

I spent hours trying to get Audacity working with my hardware today and gave up in frustration.

...then I remembered the mic has an off switch. ...stupid bloody off switch ....should be illegal.

[Bertram Henze]

...then I remembered the mic has an off switch.

Being freaked out with the overlooked obvious is a sure symptom of mental overload and insomnia. Rest is brain's best friend.

[Pete Jenner]

So now that I have audacity working, should I plot the spectra on a logarithmic scale or linear?
Should I save a text version of the spectrum data or take a screenshot of the graph?

[Bertram Henze]

So now that I have audacity working, should I plot the spectra on a logarithmic scale or linear?
Should I save a text version of the spectrum data or take a screenshot of the graph?

- logarithmic is better
- screenshot is more colorful

But we like to hear it, too!

[Pete Jenner]

I was thinking of just playing single notes on open and fretted strings or should I play some tunes as well? Tunes won't sound great because I only have one E string at the moment - no spares until Monday.

[Bertram Henze]

Single notes are ok (how about one scale over 2 octaves from G to g') and most reproducible, but the courses should be complete. No need to hurry. I'd expect this to be more of a longterm project, no?

[Pete Jenner]

Absolutely. It may go for months ...or years.

[Michael Bridges]

Take your time, Pete! I get this mental picture of yo starting to look like Doc Brown , running around your shop. "To sleep, perchance to dream"

[Pete Jenner]

Take your time, Pete! I get this mental picture of yo starting to look like Doc Brown , running around your shop. "To sleep, perchance to dream"

I've got no idea what you're talking about Mike but If my calculations are correct, when this baby hits 88 miles per hour... you're gonna see some serious sh*t.

[fscotte]

but I for once would miss the richness in overtones.

In the piano world, it's called sympathetic resonance, and adds a great deal to the acoustic piano sound. Thus the reason why so many digital pianos sounds like, er digital. They try to emulate the resonance, but it's not real. I think if an instrument is in tune, those resonances is what adds to the complexity of the sound.