Bridge patch?

Hi everyone, just looked through the old posts but turned out to be a bit of a minefield.
So far, on my first and second builds, I've followed the Stewmac tenor template bracing patterns. The top has 3 fan braces with a bridge patch in between the 2 outer fan braces and the centre fan brace notched to accomodate the patch.
I've also seen pictures of other patterns where the bridge patch extends beyond the outer fan braces and is then rounded. In this case , all the fan braces are notched.
My question is: Is there any advantage in having this extended bridge plate? I'm also talking about hardwood tops like mahogany. Thanks Mike

Advantage....more room for a signature. Its up to the builder really. A longer bridge patch is more traditional for ukuleles because its more traditional with guitar makers.
People seem to like the sound of the Stewmac design so it must be OK as is.

Build one with a short patch and one with a long patch and send us a sound sample comparison.

I was thinking it might be a structural thing rather than tonal, such as a prevention for the splitting of the top around the edges of the bridge. I don't know, just a guess. I've noticed one or two of the top builders on here use the extended patch, so there must be something in it.

My thoughts: A longer bridge patch reinforces horizontally whereas the stress is longitudinal and this longer (wider) patch isn't going to do anything to prevent bellying which is the main problem. In my mind the bigger bridge patch footprint just makes the top thicker in that area which is not a good idea because it might deaden the top. I just borrowed (stole?) the SMD dimension and I think it is a good one. Works for me. However, this is an area where a person could tinker.

I am a hobby maker with about 25 instruments (guitars and ukes) made to date. Only 3 or 4 of them have a bridge patch: all of them have tied classical guitar style bridges. If I were to use a pinned bridge I would use a hardwood bridge patch to reinforce the soundboard.

We all know that wood is much stronger along the grain than across it. A soundboard therefore is orientated with the grain parallel to the strings (has anyone ever made an instrument with the grain running across the soundboard?). So a soundboard could be fairly thick and have no bracing below the lower soundhole transverse brace. But such a soundboard, if it were to cope with string tension, would be too thick and inflexible and not good for sound production.

Bracing is therefore about making a thin soundboard (good for sound production) strong enough to withstand string tension and if possible also enhance the acoustic response.

There are many on this forum more experienced and knowledgeable than me on past and present practice. Suffice it to say that many modern instruments have fan type bracing (try typing either "classical guitar (or ukulele) soundboard bracing" into Google and look at 'Images' to see the huge variety available).

The speed of sound across the grain is only 20 -30% of the speed along the grain. Any bracing such as a long bridge patch (with grain thats at right angles to the strings) therefore helps transmit vibration from the strings across the soundboard. It will also make the soundboard much stiffer and may require action elsewhere in the bracing system.

Tenor ukes most commonly employ 3 fans (with or without patch). The exact thickness of the soundboard and the dimensions/locations of the bracing/patch vary with each design.

In practice, makers settle on a specific set of bracing and use their experience to fine tune each soundboard. They carve away the braces and evaluate the modification by flexing and tapping the soundboard until it feels/sounds right. This is something that beginners aren't able to do.

Learning to make a great uke is therefore about starting off with a basic design and making small changes in order to learn how these influence the sound of the instrument. Variability in build practice and materials obviously muddies this. Altering the length (or thickness) of the bridge patch on your design is one such small step.

http://www.amjbot.org/content/93/10/1439.full

an instrument with the grain running across the soundboard

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I'm pretty sure harps are made with the grain running crosswise
Miguel

lauburu said:

I'm pretty sure harps are made with the grain running crosswise
Miguel

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I was thinking about guitars, ukes, mandolins, lutes etc. It's possible to make one with the grain at right angles to the strings and therefore have to use more bracing parallel with the strings. It seems like a bad idea (a very stiff soundboard) but I was musing that someone may have tried it and might like to tell us whether the instrument was a complete failure. I am always surprised that ladder bracing works on lutes, early guitars etc. My first instrument was a classical guitar with Torres type fan bracing and this has always seemed to be the obvious way to brace a soundboard.

Ladder bracing gives a different tone. I've tried two experimental guitars (Torres size) but ladder braced. I couldn't really get them to work the way I envisioned. It tends to affect the bass, not the treble. Unsurprisingly the bass doesn't sound too dissimilar to the smaller ladder braced guitars. There's a certain woodiness to the sound but not the deeper fuller bass you get with fan bracing. Of course there's nothing wrong with a woody sounding bass if that's what you like. So it's perfectly fine for lutes and small romantic guitars with their brighter tone, limited bass. Most people want and expect a totally different sound from a bigger guitar though.
Now ladder bracing on a Uke could make for a very interesting build. I don't see why it wouldn't work, given that bass is out of the equation.

Michael N. said:

Ladder bracing gives a different tone. I've tried two experimental guitars (Torres size) but ladder braced. I couldn't really get them to work the way I envisioned. It tends to affect the bass, not the treble. Unsurprisingly the bass doesn't sound too dissimilar to the smaller ladder braced guitars. There's a certain woodiness to the sound but not the deeper fuller bass you get with fan bracing. Of course there's nothing wrong with a woody sounding bass if that's what you like. So it's perfectly fine for lutes and small romantic guitars with their brighter tone, limited bass. Most people want and expect a totally different sound from a bigger guitar though.
Now ladder bracing on a Uke could make for a very interesting build. I don't see why it wouldn't work, given that bass is out of the equation.

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I've always been intrigued by ladder bracing. So simple. So primative. So intuitive. So I did some research on the question on the interwebwaves and the funny thing is, almost without exception the results were positive. Now there is always bias towards the positive when a person invests a lot of time and effort in a build so one has to temper rave reviews and cast the jaundiced eye. I also did a lot of research on Kashi bracing. Here I found reviews mixed and tending towards the negative. There are Kashi supporters who can be rather passionate about the pluses of the system, but they tend to be in the minority of luthiers who tried it. Is it possible that all the newer systems like fan bracing or X-bracing are just overly fussy innovations that are actually inferior to good old ladder bracing? I'm not convinced of that, but it is possible I suppose.

Yes but if you look at when ladder bracing was in it's prime you will find that the guitars of the period were small. People who seek out ladder braced guitars are interested in that type of sound. If you gave it to a player who only used a large Torres fan braced instrument they would likely think it was poor, unresponsive, funny sounding. I'm certainly not decrying ladder bracing, I make them myself. In fact the guitar that I play is a small romantic ladder braced instrument. I use it primarily for playing Bach because that particular guitar and it's bracing seems perfectly suited for that music - clarity of sound, not muddy and the bass to treble response is much better balanced ie. the bass is not overpowering. I also play a bit of Brazilian Baden Powell type stuff. It's not very suited to that style of music, I have to turn to a much bigger fan braced guitar for that.
But in terms of a Uke (completely different instrument of course) then ladder bracing will work. Baroque guitars tend to be ladder braced and they have a very limited bass output, in fact some say that they haven't got any. It's tonality is much closer to a uke than a modern guitar, which is why I think it will work for ukes. Just keep the bar/bracing in keeping with the size of the instrument. The common ladder brace is just one diagonal bar ahead of the bridge. Some were not diagonal but simply glued as per harmonic bars. Often the latter romantic guitars made around 1850 had two bars, the diagonal bar ahead of the bridge and a scalloped bar just behind the bridge. That scalloped bar looked a little like a modern sculpture. You can see it on one of the experimental guitars that I built:



Here's the other experimental guitar, clearly shows the positioning of these bars. I don't think I scalloped the bar behind the bridge on this particular version.

Michael, its good to see these photos and hear of your experience with different types of bracing.

The original posting was about the length of the bridge patch. My response was to try to explain that the patch is simply part of the whole soundboard bracing system which attempts to cope with the perhaps conflicting requirements of structural integrity and acoustics. I made the point that any bracing across the soundboard would facilitate better vibration transfer across the soundboard (but affect its flexibility).

In a recent post, ( http://forum.ukuleleunderground.com/showthread.php?123165-Tap-tone/page2 ), printer 2 provided some images of the various modes of vibration of the top. Each bracing system will determine the relative importance of each mode and hence colour the overall tonal response of the instrument.

Now that I've thought about it, it seems to me that a ladder bracing system would not favour monople or dipole modes, and a lighter and more flexible fan system would do so. This would explain the fact that a ladder system shows less bass response: the clarity of sound is perhaps explained by the rapid transmission of sound both along and across the soundboard facilitated by this bracing system.

I have done bridge patches too. In fact there was a real fashion for them 20 or 30 years ago. Of course they are often put in directly beneath the bridge, which itself acts like a very substantial brace. I can't say whether a bridge patch is a good or a bad thing. I don't think they are necessary in order to make a fine or great sounding instrument, I've heard too many great sounding instruments that don't have a bridge patch, so I guess it comes down to personal choice and whether you can make either system work. Actually most systems do work, it's just a matter of whether they satisfy your expectations of what is a good or a bad sound. You aren't going to please everyone, there's just too many people who have different ideas of what sounds good.
Back to ladder bracing and it's limited bass extension. I don't wish to exaggerate, it's a little less than the fan braced instruments that I've built. That doesn't make it bad, it just means that most players might dislike it because they will be expecting something that they are more accustomed to i.e. a slightly fuller bass. These can be very small differences though. Given that ukes don't do bass (not in the real sense) there is scope for ladder bracing. It almost certainly has been done before on ukes, perhaps many times. There are just too many people making instruments that it certainly has been done. It's obviously not common but that may be due to many uke makers copying what happens in the guitar world. Ladder bracing represents a very, very tiny minority of guitars. The uke isn't a guitar though, so it would be silly to rule it out. If I find the time I'll make a ladder braced uke, even if it's just a quick experimental knocked up model.

Michael N. said:

I'll make a ladder braced uke, even if it's just a quick experimental knocked up model.

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Excellent idea! That way I don't have to do it...

"If I find the time I'll make a ladder braced uke, even if it's just a quick experimental knocked up model."

1,000 hero points if you follow through on this!

I want to go the other way. Got this idea in mind that users speaker driver principles for maximum volume and lots of low end. The only bracing in the lower bout would be curved and well away from the sides (keyhole shaped). The top would taper out towards the sides, ending up <1/2 the usual top thickness. Oh, and for relevance to the thread, it'd have a bridge patch, but only a narrow one.

I think the only way to get maximum volume is to produce a very thin responsive soundboard and keep as much energy in that soundboard as is possible. I think that is the principle behind the Smallman concept. The back/sides are thick/heavy, designed so that they don't sink energy away from the soundboard. Nylon or gut strings don't have the tension of steel, therefore limited in energy. You have to try and maximise what you have, make it very efficient.
Of course that may come at a price and usually it results in a certain tonality, some like it whilst others think it the work of the devil.

Makes sense. The thoughts behind the tapered/sculpted soundboard are about increasing air movement due to the thin edges (think the flexible strip around the outer diameter of a speaker cone) while maintaining a mass in the center behind the bridge (the magnetic driver in the speaker). I imagine there's a trade-off there between response (lighter) and sustain (heavier)?

And yeah, I expect tonal balance will be out of whack. I can't get my head around the relationships between design and frequency response. No matter how much I read, nobody can explain things in a way I can translate into design thoughts. All I know is that a well designed speaker cone - a relatively simple shape - can handle a broad range of frequencies. No need for dipole/triple etc. analysis there.

Dan Gleibitz said:

Makes sense. The thoughts behind the tapered/sculpted soundboard are about increasing air movement due to the thin edges (think the flexible strip around the outer diameter of a speaker cone) while maintaining a mass in the center behind the bridge (the magnetic driver in the speaker). I imagine there's a trade-off there between response (lighter) and sustain (heavier)?

And yeah, I expect tonal balance will be out of whack. I can't get my head around the relationships between design and frequency response. No matter how much I read, nobody can explain things in a way I can translate into design thoughts. All I know is that a well designed speaker cone - a relatively simple shape - can handle a broad range of frequencies. No need for dipole/triple etc. analysis there.

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It depends what frequency range you're after....I worked with speaker drivers quite a lot when I was doing re-cone work for audio companies..mainly big PA stuff JBL, Electrovoice,Tannoy,Bose,Turbosound ect: and on the bass end 18" 15" 12" the cone's were all heavy duty stuff with 4 inch dia voice coils and very flexible surrounds and spiders..but the mids to high cones were much thinner and lighter with 2" dia voice coils and more rigid surrounds and spiders and very thin metal diaphram dust caps some made of Titanium to reproduce the high frequencies..The HF drivers (Tweeters) had 1" voice coils with diaphrams made of all sorts of materials Plastics, Aluminium, Kelvar, and Titanium etc: some were rigid and some very soft to the touch like a bubble...So I suppose if you made a perfect sound board it would have all these features thick and heavy and flexible in some areas thin and rigid and light in other areas..and may be a bit of titanium here and there .. great if you're building Church pipe organ size instruments or Pianos but I suppose it's too much to ask for in a simple single instrument like a uke..thats why we have Bass ukes, Baratones, Tenors and Sopranos.

True, but we're not really looking for 10hz to 10,000hz+ like a studio setup. The ukulele sits in the midrange, with a relatively narrow band of note frequencies between ~196 and ~1200hz for tenors. I suppose there are all kinds of harmonic interactions at different frequencies though...

The other thing that keeps me up at night (seriously, I'm weird), is that if I was to build a soundboard driven entirely from a ring in the middle like a speaker it would suffer from cancellation. I figure a significant amount of the top movement comes from the string lengthening and shortening as it vibrates, amplified by the leverage of the saddle. Unlike a speaker where all sides are excited simultaneously, I reckon this would cause each side of the bridge to move out of phase. So a stringed instrument seeking to avoid this would need to be stiffened between the bridge and the mid-brace. Which is what I see when I look at a fan braced ukulele.

Hence the curved 'keyhole' shape I have in mind. I think (and bear in mind I dropped out of uni physics in semester 1) it would provide the support needed to stop this cancellation, prevent bellying under pressure, and maximise the amount of movement in the top. I'll sketch it up for criticism one of these days. Or maybe just build it.

Ultimately you have to build it, peer review it and blind test it, preferably double blind. No one said this stuff was easy.
Alternately do what virtually everyone else does and stick to well trusted designs. That way you can sit on a beach for weeks at a time quaffing champagne.

Michael N. said:

Alternately do what virtually everyone else does and stick to well trusted designs. That way you can sit on a beach for weeks at a time quaffing champagne.

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Quaffing ??? ...I had to look this up https://www.youtube.com/watch?v=jiBWWPbYZjo and I don't fancy doing this with "Dom Perignon" unless someone else is paying for it.:cheers: