Alan:
There is a "maple bridge page" which could give you some ideas. The website might have been "Red Henry". He had a lot of stuff on banjo, mandolin and mando cello bridges. It might give you a starting point for your design.
good luck
Bob
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| Author: | alan stassforth [ Fri Mar 16, 2012 8:39 pm ] |
| Post subject: | Non "fixed" bridge questions. |
I was thinking about doing a non fixed bridge with a tailpiece on the lap steel in my avatar, which is on the back burner, and no where near finished. The bridge would be like an archtop jazz box, with a simple tailpiece mounted on the tail, where the end wedge is. I layed it out on paper, and with a bridge height of 11/16", I get a 7 degree string angle. Is that enough? Also, any info on bridge weight, length, width, and height would help. What do these dimensions do to tone and output volume? It's an experimental guitar, so.... Thanks. |
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| Author: | Jeff Highland [ Sat Mar 17, 2012 3:56 am ] |
| Post subject: | Re: Non "fixed" bridge questions. |
The break angle is probably adequate, but IMHO using a tailpiece/floating bridge on an instrument which has not been designed and braced for it is a bad idea. The resultant downwards pressure will probably cause the top to sink. The load on the tailblock from the tailpiece can also deform the top. |
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| Author: | gozierdt [ Sat Mar 17, 2012 6:04 pm ] |
| Post subject: | Re: Non "fixed" bridge questions. |
I agree with Jeff. I did what you are suggesting on a Martin O-size replica I made because I wanted a travel guitar with easy on/off bolt-from-the-top neck & detachable strings. I used standard X-bracing. The guitar plays and sounds great, but the top sunk right after I finished it. It's been stable for about 4 years since, but I'm planning on doing another one with modified bracing to better support the top. |
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| Author: | alan stassforth [ Sat Mar 17, 2012 6:52 pm ] |
| Post subject: | Re: Non "fixed" bridge questions. |
Yeah.I started thinking about it more after Jeffs reply. Thanks Jeff! I didn't tuck the x ends into the linings, which I should do if I go with this idear. Gonna think about it more though, because I built a squarenck with a tailpiece and a glued bridge, and it sounds pretty darn good. Loud beast! Lots of treble too! Might be because of the radical arc to the top and back. I've tried putting very heavy strings on this, (.070" on the 6th) and it held up. So nobody has experimented with bridge weight, size etc. on trebs and bass tones? |
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| Author: | Alan Carruth [ Sun Mar 18, 2012 1:15 pm ] |
| Post subject: | Re: Non "fixed" bridge questions. |
I'd call seven degrees of break angle barely adequate. Iirc, Benedetto shows a six degree break in his archtop book. I used a break pretty close to 5-6 degrees in my most recent string height and break angle experiments, and saw some evidence that suggests it might not be enough. OTOH, from what I've seen, too much downbearing can kill the sound too, so you want to keep it to a minimum. I think of the function of the bridge as telling the string how long it is, so that it will know what note to make. It does this by having a fairly large impedance mismatch with the string, so that most of the energy is reflected back into the string and only a little leaks into the guitar to produce tone. The heavier and stiffer the bridge-top system is at the end of the string the greater the mismatch: you have less trouble with 'wolf' tones, and less sound too. The trick is that 'impedance' has to be defined with respect to frequency: it's the ratio of force over velocity at a given frequency. Basically, the impedance of the top-bridge system will be lowest at resonant pitches of the top, and highest in between those pitches. Adding either mass or stiffness will tend to raise the impedance, but mass has more effect on high frequencies, and stiffness on lows. So, making the bridge heavier, without adding stiffness, will tend to kill sound a bit, and will cost more in high frequency response than low frequencies. The guitar will probably seem 'bassier', since that's the way the response has been shifted, and you may not notice a small drop off in output. Adding stiffness without adding mass has the opposite effect: the balance is shifted toward the highs, with more of the loss of output in the bass end. Since all the usual variables come into play here; the mass of the top and bridge, the stiffness of them, what strings you use, the relative humidity, phase of the moon, whether you get this nailed during the current conjunction of Venus and Jupiter, the stock market, and the wholesale price of chocolate in Cote D'Ivoire, it's a little hard to make exact recommendations.... I'd try a stiff, light bridge, and add mass with poster adhesive to find out how heavy to go. |
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| Author: | alan stassforth [ Sun Mar 18, 2012 2:30 pm ] |
| Post subject: | Re: Non "fixed" bridge questions. |
Thanks for the input. Alan, that makes sense to me. One reason I'd like a non fixed bridge is I could experiment easily by simply removing, shaving, listening. I don't really know how to design like an engineer, I just put stuff together, and hold my breath when I string it up. That guitar has a 15/16" saddle height, 5 degree break angle, and is braced strangely. It needs more angle, as some strings get some extraneous noise, which doesn't matter too much because the bar adds lots of ext. noise. |
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| Author: | unkabob [ Sun Mar 18, 2012 8:31 pm ] |
| Post subject: | Re: Non "fixed" bridge questions. |
Alan: There is a "maple bridge page" which could give you some ideas. The website might have been "Red Henry". He had a lot of stuff on banjo, mandolin and mando cello bridges. It might give you a starting point for your design. good luck Bob
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