Grandpa's old Harmony archtop.

[ricklt]

This old guitar was given to me when I was about 15. Learned to play on it. Grandpa and my dad had done a bad job of refinishing it, back when dad was a teenager. It has no value I know, but there is a ton of sentimental value. Having said all that, I am now trying to repair and refinish it correctly. Painting with nitrocellulose lacquer. Have a question though. This guitar had no back bracing at all. I read somewhere that if one was added to these guitars that it would improve sustain and volume. Can anyone verify that. I would be very grateful for any feedback. Enclosing photos.

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[Simon Barden]

Hi and welcome to the forum.

I'm no expert but I doubt that adding bracing to the back will increase the volume. The bracing on the top of the guitar is there to give it strength to help support the downward force of the strings. The design of that bracing will have an effect on the tone and sustain of the guitar but I suspect you are going to get the greatest volume with minimal bracing.

The arched top and back of the guitar already give a lot of structural strength compared to the flat surfaces of a normal acoustic and so whilst the top has a couple of braces (to help with the the string tension and downward force), the back doesn't need more support. An steel or classical acoustic guitar, has some bracing on the back to provide structural rigidity, but the arched back of the Harmony doesn't need it.

Did the guitar have a bridge soundpost fitted to it when you took the back off? I see something stuck to the top underneath the treble side of where the bridge goes. This would indicate to me that there had been a wooden post fitted at some time that connected the top and the back. This is a standard feature of instruments like violins and cellos and assists the back in vibrating to improve volume. It's not clear exactly how you'd wedge it in when you glued the back on, but if the post wasn't there when you opened it up, it could have come loose and been removed through an f-hole in the past. It's worth looking up details of construction methods for violins etc.

The design of jazz archtops is of its nature to reduce, rather than increase sustain. A lack of sustain was thought better to hear individual notes stand out when fast solos were played. Apparently sound waves travel through wood about 10 times faster in one direction than in the other (I think it's faster across the grain rather than with the grain). This is why jazz guitars have f-holes at the sides rather than a round soundhole near the neck join as it deliberately reduces the sustain of the guitar. I also suspect that the neck to rear bracing , rather than the mainly side to side bracing on other acoustics, was also found to reduce sustain.

The string break angle on the bridge does have an effect on the guitar's volume, but that is really going to be determined by the guitar's overall design. The steeper the break angle, the greater the downward force on the top and the more more the string vibrations will 'drive' it and increase the volume. It is possible to have to steep a break angle and you can 'over-drive' the top which doesn't sound nice. But the overall bridge/string geometry is determined by things like the neck angle and the amount of arch on the top of the guitar. It would be possible to remove the neck and re-set it at a steeper angle to the body. The bridge would then need to be set higher and so the string break angle would increase and so should the volume (slightly).

In hindsight, if the bridge had height adjustment, you could have raised it up significantly and seen whether the guitar's volume increased enough to notice. Of course you'd have a terrible action (and it looks like the guitar has a non-adjustable truss rod so it's probably not wonderful to start with) but you should have been able to tell from the open string levels. If it had, then you could have considered a neck reset. But as the guitar is all apart and you won't want to keep glueing it and un-glueing it, that may be a step too far.

Fit some decent thickness strings, I'd suggest a 0.013" set minimum. Heavier strings will get a bit more volume from the guitar but obviously playability suffers unless the action is really low.

So I think it is what it is, a fairly dead sounding jazz guitar, and you probably won't be able to improve the volume that much. Though I would look at using heavy strings and trying to fit a bridge soundpost.

[ricklt]

Thank you very much for your input. Will keep you posted on my progress

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[Kick]

I think your dad and granddad will be proud of you!

[ricklt]

More pics of Grandpa's old Harmony archtop. Have the back on it now. Sanding, trying to get it ready to finish. Want to try the Amber and Black sunburst. As close to original as I can with what I have to work with.

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[ricklt]

More

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[ricklt]

All I have right now.

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[JohnH]

What a wonderful thing to do!