Sound post in an archtop?

[Archie]

As a thought:

1) Use a softer wood that will take some of the compression through the posts and not pass it all on to the back.
The only issue you have with dry fitting is that the posts will likely become somewhat compressed over time, so when you take the strings off, they will fall over. Unless you change one string at a time.

2) Glue some soft wood blocks on the back plate for the posts to sit in. They can perhaps take up some f the compression when the top is back under tension. Balsa wood blocks with a weak glue, just to position them.

3) You could then measure how deeply the posts compressed into the balsa wood and that can give you the amount of compression you're getting and thus the height needed for your posts. Cutting the posts then to that length is easy but holding them up whilst you re-tension the guitar, wont be because they wont have enough friction to stand up between the top and back.
You could use blue tac to hold them then scrape the blue tac off around the posts once under tension.

4) Actually just find a way to measure the compression between top and back plate (callipers? A measuring stick through the F-holes?), cut posts to suite and make little feet for the posts to sit in, so they stand up whilst you get the guitar under tension. Although easier said than done.

Best to fit under tension really but if you need access through the bridge pickup what can you do?

An interesting idea. Good luck.

[Tal_175]

Based on some of the past threads in this forum, I was under the impression that putting sound posts in archtop guitars was a trivial thing. I thought I was over-thinking and making up non-existing risks. But so far the posts haven't been very reassuring. I won't do it unless I get some definitive insights from people who have done this mod and they can convince me that the pressure on the back from the sound posts under the string tension won't be a problem or they have a proven solution. It is possible, for example, that the compression of the top under the string tension is miniscule therefore the pressure on the back plates from the sound posts is negligible.

ArchtopHeaven suggested some interesting approaches, but they are too experimental to try on my vintage Byrdland for my comfort. They are good research ideas that need to be tested on cheaper guitars

[6v6ster]

I wouldn’t do it. It really kills the tone. Especially on a finely tuned old archtop, don’t do it.

[pingu]

(I wouldn’t do it on a birdland either)

I have my laminated top jazz box half-filled with soft foam ( used to be fully filled but
i took half out)
at the moment which successfully inhibits feedback but it feels a bit too much damping at the moment ....

next I’m gonna try a different thing ....
squeeze in a piece
of the dense plastic foam ,
the kind used for shaping the inside equipment presentation and perfume cases etc
about 2” square and however deep
i’m just gonna pre- squeeze it and then put it in place (not glued in ) and let it expand naturally by itself ....

my hope is that it will dampen down the top somewhat but still let the guitar ring a bit
stuff it and see
let us know what you do with the bird

[wintermoon]

Doug's Plugs....

[Archie]

I wouldn’t do it. It really kills the tone. Especially on a finely tuned old archtop, don’t do it.

They have two big pickups routed and suspended in the top. I'm not sure the term 'finely tuned' get's you that far and to what lengths Gibson tune their Archtops; would be interesting to know. Perhaps the braces to some degree? Perhaps they think a top with two hum buckers doesn't need tuning?

I've always been interested to know how much they tune tops and on what models they do so. I had a Byrdland and the top didn't seem to have any real finesse but it was a 90's one, although singed by Jim Triggs.

What do you think Tal?

[Little Jay]

Here’s the sound post in my ES-125:



The post is mahogany, about 1” x 1”. I have slightly rounded off the edges and corners of the foot and top, to prevent it from denting the wood.

It is positioned off-center to the bass side, because of the stip covering the middle seam (my 1949 or 1950 ES-125 has a flat back braced like an acoustic).

When I placed it, there was an ever so small space between the top and the sound post, but not enough to make it move freely. After tensioning the strings a little bit I positioned it with a rod through the f-hole. With strings fully tensioned it doesn’t move at all.

It has been sitting there for 5 or 6 years now and I do not see any negative effects on the wood of the back. Inside nor outside, no denting or bulging or anything.

Now mind you, in this case it was necessary because my 125 is missing her parallel braces completely.

But I have not experienced a significant difference on the acoustic sound before and after. Actually, I much preferred the electric sound after placing the sound post, but in all fairness, I did a swap from humbucker to P90, round wound strings to flatwounds and a new bridge and tailpiece at the same time, so it’s hard to say what was responsible for what…..

Perhaps the sound post gave a slight reduction in acoustic volume, but even of that I am not certain. The change from rounds to flats could also have caused that.

What I do know, is that my ES-125 is much more feedback resistant and has a tighter bass response than 3 other ES-125s of fellow guitarists in my home town (when played on the same jam session on the same amp).

If I were you I’d do it and see how you like it, since it’s completely reversible anyway.

[Tal_175]

They have two big pickups routed and suspended in the top. I'm not sure the term 'finely tuned' get's you that far and to what lengths Gibson tune their Archtops; would be interesting to know. Perhaps the braces to some degree? Perhaps they think a top with two hum buckers doesn't need tuning?

I've always been interested to know how much they tune tops and on what models they do so. I had a Byrdland and the top didn't seem to have any real finesse but it was a 90's one, although singed by Jim Triggs.

What do you think Tal?

Mine is 1974. The top seems pretty resonant for a carved electric. I don't think Gibson tunes tops of electric archtops. Some builders believe top tuning is a calibration method that helps them achieve minimum top stiffness that is structurally sound. I don't see why minimum possible stiffness would be a goal for an electric archtop.

[Tal_175]

When I placed it, there was an ever so small space between the top and the sound post, but not enough to make it move freely. After tensioning the strings a little bit I positioned it with a rod through the f-hole. With strings fully tensioned it doesn’t move at all.

That sounds like a good idea. I was hoping you'd chime in as I know you put sound posts in some of your guitars.

[pingu]

good info Little Jay
I might do dat

is it difficult to get the length of
the post right ?

i imagine yes !

[Little Jay]

good info Little Jay
I might do dat

is it difficult to get the length of
the post right ?

i imagine yes !

Yes to get the length right was a fiddly proces with a lot of trial and error. I made a post just a little too long and sanded that to length little by little.

But I guess you could use something like this for measurement:

[sgosnell]

As the old saying goes, "measure twice, cut once".