(link to larger version, 156K)
Basically, the difference is that there is a string leading from the strap-button on the guitar lower bout, across the top of the guitar face, and joining to the strap at your left shoulder. This gives an improved playing position over straps using strap buttons on lower bout and neck heel or straps just tied off at the guitar nut (in my opinion), by putting the guitar bridge in a more natural position for finger-picking and the guitar face turned slightly upwards, and it also stops the strap slipping around on (or off!) your shoulders. The pressure from this string also holds the guitar close against your body and stops it moving around. For those who usually prefer to play seated (particularly classical or fingerstyle players), this gives more of that kind of stability than you would otherwise get from a strap.
How and why this came into being
The first steel-string guitar I bought had a heel-button on it for the strap. This worked OK, but I never felt I had as much control over the guitar as I would have liked. Electrics are thin and sculpted so they mould to your body well, whereas an acoustic guitar is large, flat-backed and unyielding. I didn't know there was much in the way of alternatives though, so I just carried on regardless.
Then I got my first new guitar, a Regal steel-body resonator. This had no heel-button on it, and I felt that drilling into the guitar of a nice guitar would be kind of sacrilege. So I put a bootlace around the neck above the nut and tied the strap to that, as is the usual way of securing straps on a heel-button-free guitar.
I immediately found the problem with this, namely that the bootlace gets in the way of your chording hand.
This was seriously annoying. I'd had exactly the same problem before on my old classical though (the guitar I'd learnt on), and to solve it on that, I'd tied the lace off on the central section of the slot-head. So a solution became apparent - tie the string off between the first and second pairs of tuners on the headstock. Job done.
I quickly found that this was not quite the perfect answer. Whilst my hand was free, the extra angle on the strap meant that the strap kept slipping off my left shoulder. Also the angles and guitar balance meant that the guitar bridge was further off to the right than was comfortable for a good playing position, and the resonator was very tail-heavy so it kept sliding round and trying to point its nose in the air! A better bit of engineering was needed, which would hopefully have the effect of pulling the strap down on my left shoulder, whilst also improving the playing position. And that's where I came up with the idea of this rig.
Putting it together
So, how to make this. All you need are two longish bootlaces, a short length of sturdy pipe and a slide toggle. (Oh, and obviously you need a guitar strap and a short bit of lace to attach it to the neck.) The bit of pipe needs to be as long as the the guitar strap is wide - this has to sit across the strap where the string meets the strap at your left shoulder, because if you just tie the string off directly to the strap then the strap gets crumpled. Use anything you like, so long as it won't bend or snap - I've made mine from cutting down a spare heavy-duty Rawlplug. Since the string goes round it, you'll want to file the ends to avoid sharp edges.
Put one lace through the pipe, round the strap, back through the pipe again, then tie the ends together with a reef knot (called a square knot if you're American). Wrapping the lace round the strap gives enough friction to keep this in place, but it can still be slid along the strap to adjust it. To make this look nice, roll the lace round so that the knot is hidden inside the pipe. I found that tying the lace in a knot after that (see the picture) kept it more stable by stopping the lace from moving around, but your mileage may vary. You then have a dangling loop of bootlace which you can tie things to.
At the lower-bout strap button, thread the other bootlace through the slide toggle and through the hole in the strap, then tie the lace off here (ideally using a bowline) so that there's a loop of bootlace holding the slide toggle (note that you don't want any lace left on one side of the knot, as it'll just be hanging loose). This stops the toggle slipping around when you adjust it. You may even want to take both bits of lace through the toggle and just rely on the knot to keep it in place - that's my preferred solution (see picture). Make sure that the toggle stays on the side of the guitar, because if there is enough slack for it to get round to the face of the guitar then (a) it's difficult to adjust, and (b) it could scratch or dent the soft wood on the face of the guitar.
Finally, thread the lace (the long bit left) through the dangling loop of the other bootlace, and back down through the slide toggle. Finish it off with a knot on the end so that it can't slide back through the toggle.
The double length of lace here makes it easier to adjust it. You can get away with a single lace from the tube down to the strap button, but I found this was too difficult to adjust accurately.
Adjusting the strap
Now you're all done, you just need to set it up how you like it. There are three main things that you can tweak: (1) the main strap length, (2) the location where the lace and strap are joined (ie. where the bit of pipe sits, by your left shoulder), and (3) the length of bootlace.
Strap length adjustment needs no extra information for anyone who's ever played a guitar. Go for the low-slung rock god look, the up-around-the-armpits Paul Simon look, or anything in between.
In general, the further towards the guitar nut the lace and strap join (for the same strap and lace length), the more neck-up the guitar will hang. Besides normal adjustment, this can also be very useful when you're playing in pub sessions with little elbow-room, as you can use the strap to hold the guitar in a near-vertical position.
Shortening the lace will have two main effects, firstly pulling the guitar into your body more and lifting the face, and secondly pulling the guitar leftwards across your body, so adjust the lace length to get the guitar bridge in the best playing position for you. Note that pulling the lace tight effectively reduces the main strap length (because the strap is pulled down a long way at your left shoulder), so you'll need to play about with both strap and lace lengths until you find something that works for you. Also note that shortening the lace increases the pressure on your left shoulder which could become uncomfortable if playing a long gig.
Some people have asked whether the neck will warp from this. I seriously hope not! Guitars have been strung by the headstock since the early days, so I think if there was a problem with this then we'd know. Everyone knows the urban legend, but I don't know of anyone who has personally seen a guitar neck warped by a strap tied to it.
Does it make it more difficult to put the strap on? Yes, slightly, because you have to thread yourself through the gap between the strap and the lace, but you soon get the hang of it. And if you're too drunk to put the strap on, you're too drunk to play!
If anyone finds this useful, or if you've got an idea for improving this, please let me know. No patents or anything, so if you're a strap maker and you want to sell straps with this design then feel free, just so long as you credit me with the idea.