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Flattop bridges VS Archtop Bridges
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=41507		 Page 1 of 1
Author:  herry tze [ Fri Sep 27, 2013 11:31 am ]
Post subject:  Flattop bridges VS Archtop Bridges
Hi, I need your opinion for this result. beehive

I'm building 3/4 Acoustic Martin style5 for OLF 2013 New Builder Challenge and I have idea to change the Flattop bridge with the Archtop bridge model, what do you think of that? And I have problem with: flattop bridge with saddle is about 14mm tall and the archtop bridge with saddle is about 25mm. Do I need to shorten it and how? idunno. Modified for Back is arch with FlatTop that's why I inspired for archtop bridge.
Thank you all OLF'ers
Author:  herry tze [ Fri Sep 27, 2013 11:37 am ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
this picture downloaded from Stewmac but I will use later from my own build. archtop bridge with tailpiece
Author:  cphanna [ Fri Sep 27, 2013 12:16 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
Hi, Herry,
If I understand your concept correctly, I think the results would be difficult to predict. Archtop bridges drive arched tops in a different way than pinned bridges drive flat tops. Archtop bridges usually have a considerable string break angle over the saddle, and this is achieved with the combination of the top arch, plus a neck-to-body angle that is greater than the usual flat top neck angle. This break angle provides a lot of down-force and transfer of energy to the top. If you build a flat top that is fairly conventional in all other respects, and if you use an archtop style bridge and tail piece, you would have less string break and less down force. I think your guitar would be much more quiet, with less volume, power, projection, and so on. It would probably have less sustain and subtlety of tone, as well. However, I have seen a number of flat top guitars built with floating bridges and tail pieces, and the field is always open for experimentation. If you plan ahead for a possible change (install a bridge plate under the top, etc.) I believe you could try your floating bridge idea with no harm to the instrument. If you don't like the results, you could then install a traditional, pinned and glued bridge.

I am sure some other members have experimented with this concept, and will chime in to help you.

Patrick
Author:  herry tze [ Fri Sep 27, 2013 12:29 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
Yes Patrick I have installed a bridge plate under the top too. As you said I'll try my floating bridge before, but I still need suggestion about the height of that floating bridge, maybe without adjust the neck angle. Or I must adjust the neck angle if I use this floating bridge?
herry
Author:  Rodger Knox [ Fri Sep 27, 2013 12:35 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
It's possible, but if you decide to go with the archtop bridge, you will need to make some significant changes to you plans, most critically the neck angle.
With enough neck angle to make the archtop bridge work, you'll also need a wedge under the fingerboard over the top.
The bracing could also be changed to better suit the difference in the way the top is loaded.
Author:  the Padma [ Fri Sep 27, 2013 12:45 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
neck angle.
brace for downward pressure.
Author:  DennisK [ Fri Sep 27, 2013 1:03 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
I'd stick with a regular flat top bridge.

However, there is a third option, which is to use an archtop style bridge, with low break angle over the bridge, but sharp break angle within the bridge, that cancels out its twisting force one way or another. Unfortunately the design is patented over here, but I don't think that applies to East Java beehive

Here's where I originally learned about it: http://www.luthiersforum.com/forum/viewtopic.php?p=407422#p407422

So you cut slots in the saddle, that bend the string sideways to create a break angle, but the high and low strings are bent opposite directions so they cancel out eachother's torque. You actually don't need any vertical break angle at all, although a little bit (like using a 14mm tall bridge to keep the neck angle easy) might not be a bad thing.

If you do that style, you'll be in highly experimental territory, since very few builders have tried it before. You'll probably want to carve your braces down to almost nothing, and use solid wood linings instead of kerfed, to stiffen up the rim.
Author:  Alan Carruth [ Fri Sep 27, 2013 1:44 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
In his book on archtop guitar construction, Benedetto shows a six degree break angle over the bridge, much less than many flt top makers would consider 'barely adequate'. For the record, if my experimental results are any good, six degrees is enough, but you'd probably like more. Anyway, I've never seen an archtop with as much break and many flat tops have; on the order of 30 degrees or so. Archtops use a low break angle precisely to limit the downward static force on the top. Aside from collapsing the top (which happens) too much break angle kills the sound on an archtop.

Since an archtop guitar has a vaulted top that can withstand a more down pressure inherently than a flat top can, and some archtops collapse anyway, it should be pretty obvious that using a tailpieceand a tall bridge on a flat top is asking for trouble. You can, of course, use something other than break angle to stop the strings at the bridge: slots angled to the side is one solution.

The actual difference in the way the strings drive the bridge on archtop and flat top guitars is really pretty small. If you think about a string vibrating 'vertically' with respect to the plane of the top, there are two main signal forces it can put on the top of the bridge. One is a 'vertical' force, caused by the up and down motion of the string, and the consequent vertical angle it makes as compared with it's normal axis. It's usually called the 'transverse' force. This pushes the top like a loudspeaker cone, and works the same way on arch top and flat top guitars.

The other main driving signal is caused by the fact that the string tension rises when it's displaced from a straight line. Since this happens twice per cycle as the string vibrates, this force, which I call the 'tension' signal, tugs the top of the bridge toward the nut at twice the frequency of the 'transverse' signal. This is the force that is not in play in driving an archtop, since the tension is taken up by the tailpiece.

In general, if you compare the 'transverse' and 'tension' signals:
1) the transverse signal averages about seven times as strong,
2) the transverse signal is driving the top in 'loudspeaker' fashion, with the whole lower bout (at least) tending to go in the same direction at any given time. This is much more effective at moving air than the rocking motion of the tension change signal, since the 'up' ad 'down' areas in front of and behind the bridge tend to cancel out,
3) tops are made to resist rocking of the bridge, since this is the static force that kills tops by 'bellying'.

I've done a few tests that involve driving the strings in different ways that result in primarily 'vertical' and 'horizontal' motion of the string with respect to the top. Vertical motion will drive the top effectively via the 'transverse' string force, and also with the 'tension' signal. Horizontal driving only drives the top with the 'tension' signal. Vertical driving tends to result in a lot more sound than horizontal: in my tests around 20 dB more, or about 100 times as much power.

In other experiments, I've found that increasing the 'tension' signal power in driving the top (by raising the string height off the top) did not noticably increase the output of a guitar, but did result in a change in timbre that people could pick uot reliably in recordings.

The weight of evidence I have, then, says that, while archtops are driven a little bit differently than flat tops, that's not the main reason they sound so much different. At any rate, if bridge rocking via the tension signal was the main driver on flat tops, and archtops worked primarily by the transverse signal, then archtops should sound an octave lower than flat tops with the same strings. Do they?
Author:  cphanna [ Fri Sep 27, 2013 6:35 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
Hey, Herry,
When I responded previously, I was writing from instinct. I was pretty sure someone like Alan Carruth would chime in with better knowledge and I am glad he did. Listen to his advice, and ask him more questions if you are unclear. He has tested out many theories and methods, and has a lot of experience--much more than I do. I am sure he will give good advice based on his own research.

Patrick
Author:  herry tze [ Sun Sep 29, 2013 9:16 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
thank's alot for my senior's, many new things that have not occurred by me.

this picture I've done for my 1st electric guitar (I like to learn the standards of ancient or plan, but I also really liked and wanted to try new things).
I throw on the saddle bottom because I see too high, whether as said by dennisK like that I can do.
This is the easiest way for me than the neck angle :lol:
Author:  philosofriend [ Tue Oct 01, 2013 11:55 am ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
Regarding Alan's excellent reasoning and final question: Archtops do not sound an octave lower, but I wonder if others would agree that they never have as much of the clear bright jangly top end that many flattops have when the strings are brand new. Perhaps that aspect of the sound is influenced by the tension signal.
Perhaps I have not played enough archtops and others can correct me. I had a (spruce topped) Gibson Johnny Smith, but I haven't played a pre-electric style archtop voiced for its acoustic tone. I have read that when pickups became normal that the bracing became more substantial.
Author:  Alan Carruth [ Tue Oct 01, 2013 2:08 pm ]
Post subject:  Re: Flattop bridges VS Archtop Bridges
Arch tops have, well, arched tops. The vaulting that helps them resist the down force of the bridge also stiffens the top up a lot, particularly in the lower resonant modes where the whole top has to bend. Also, arch tops tops are almost always thicker than flat top tops, which also makes them harder to move, particularly at higher frequencies. The other major difference is that they usually have F-holes, which make the 'main air' pitch much higher, and also 'hear' different internal resonances. It's likely that some of the difference in the characteristic timbre is due to the loss of the 'tension' signal, and the 'longitudinal' signal that goes along with it (which I've been avoiding in this thread), but there are plenty of other differences that seem to account for most of the change IMO. It's possible to make an archtop guitar that will function acceptably as a Classical guitar, which is about as far from the usual sound as you can get. What's interesting in the ones I've made is that there's something 'lute like' in the timbre; they do really well with the 'early' repertoire. Go figure.
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