Top deflection under saddle?

I am new to mandolin, purchased an Eastman MD304 about 3-4 weeks ago at a shop
several hours away that has a good rep. As I learned basic chords I noticed buzzing
at the G string and that the strings were way high at the nut and took it to another shop
that is very reputable and much closer, they adjusted the action by lowering the strings in
the nut and raising the saddle. Buzzing gone and much easier to fret. However there
is very visible deflection in the top under the bridge, is this normal and how much is too
much? Also it seems like the G strings are buzzing again a little like the action has gotten lower again and I'm wondering if its because the top is continuing to deflect.
The shop making the adjustments thought the neck had the correct amount of relief.
I have several acoustic guitars in a little music room where the humidity is kept between
45-50 % year round and thats where the mandolin lives.
I hate to drive 4 hours to have the shop it came from tell me " thats normal"
suggestions?

“That’s normal” is especially egregious when it comes from a medical person.
Anyhow, perhaps you might keep tabs on possible sinkage by measuring the action height, over the next weeks, maybe at the end of the fretboard, and/or post a photo of the suspect area with a straightedge across the dimple. Buzzing can also be anywhere beyond the string, from as trivial issues as loose tuner buttons.
Hopefully you will get more specific guesses here.

Agree, post a photo. There are some very talented luthiers on the Cafe who are likely to chime in. IMO, there shouldn’t be top sinkage on a new mandolin, if, in fact, that’s what’s happening. Should be covered by warranty if the mandolin’s a new instrument.

Not sure Im attaching the pictures correctly, I tried attaching two.
One at the 12th fret showing a Dava delrin pic thats 1.10 mm thick,
this just raises the G string at this position a little bit, my guess is
the action is a little low, I don't think it was this low right after they
raised it. The second picture is an attempt to show the deflection and it does
not really do it justice , it is visible because the shop I took it to for adjustment could see it. The owner has seen many, many hundreds of mandolins if not more in his life time go thru his shop, he inspected the interior to look for loose bracing and found none.
I purchased it new from an Eastman Dealer, looks like I'm just going to have to drive down there in a couple weeks when time allows. I bought where I did because they were the only shop I could find that hand one and I wanted to play it first.

By “deflection of the top” are you looking at the gap under the bass side of the bridge?

As for ”correct amount of relief”, on a mandolin, that should be “none”, or as near as.

I am looking at a slight depression in the top of the mandolin that just does not show well in the picture.
The depression is directly under the point that the bridge contacts the surface of the top and extends roughly
3/4 '' front and back of bridge and 1/2" either side of bridge. If more relief isn't the solution , and the neck
is straight, and subsequently to raising he action via the saddle height adjustment and then couple days later the
action has again lowered, then either the top continues to deflect down or the screws holding the saddle up are some how
turning on their own allowing the action to lower, given the tension on the saddle I'm not sure how that could be the case.
I have owned several arch top guitars with similar bridge / saddle set ups and not seen any thing similar, also
had no problem adjusting those to get the action I desired.

The necks on all my mandolins have zero relief and I’m sure most people would have theirs set up the same way. I’ve never heard of an adjustable bridge winding itself down - it’s hard enough to lower the bridge with the strings loosened let alone up to tension. Unless you’re experiencing some wide swings in humidity, it can logically, only be an issue with the top.

If it were mine, I’d start by carefully/accurately monitoring the gap between the strings and, say, the 12th fret to see if the action is reducing and by how much. I suppose that the mandolin could be going through some sort of settling in period if it’s new but it’s something I would want to monitor closely.

Call the dealer, explain the situation, forward pictures, and mail it off.

Quote:

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Originally Posted by Ray(T)

. I’ve never heard of an adjustable bridge winding itself down - it’s hard enough to lower the bridge with the strings loosened let alone up to tension.

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I beg to differ, if you bridge is set up very well you should be able to lower it under full tension with your fingers. I can even raise one of mine with my fingers under full tension.. Your bridge saddle is binding on the posts.

Quote:

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Originally Posted by pops1

I beg to differ, if you bridge is set up very well you should be able to lower it under full tension with your fingers. I can even raise one of mine with my fingers under full tension.. Your bridge saddle is binding on the posts.

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Tell that to the luthiers who built them!

A little deflection from the bridge pressure is normal. In fact, if there isn't any deflection, to me that's a sign the top is overbuilt. An oval hole may act a bit differently. I've built about half a dozen, all x braced, and they hold up fine.
Another factor is that it's the time of year when the furnace is on and humidity changes. As things get drier, the action will lower because the whole top is changing.

Well I removed the mandolin from the wall , room humidity 47%, temp 69 , and put it in its case with for a couple days with
some small case humidifiers, the action on the G string at the 12th fret has raised ever so slightly such that the same pic that raised the
G string slightly now has a gap and does not touch the strings. The very slight top deflection is still visible but the the G string now plays
cleanly in first position which is where it did not before. I have two hygrometers in the room one says 44% and one says 49%.
I got to 47% above by averaging the two. While the room humidity works fine for my guitars looks like its too low for the mandolin.
I am going to buy a case hygrometer , a Caliber lV, and let the mandolin live in its case. I may try to raise the room humidity
after I find out what the case is averaging, how ever here in upstate NY on 20 degree or colder days I'll have condensation on
my thermal paned windows all the time at anything approaching 50 % humidity.

Wow, glad that’s all the issue was, but sorry you have to go to the extra trouble, I’m able to keep my house at 50% +/- with a whole house humidifier in winter and a couple of floor dehumidifiers in summer. All of mine seem to sound best at 40-50% without the issue you’re describing.

How did 1920's Gibsons survive wood and coal burning stoves with no humidity control?

Careful owners, given the number that survived. They weren’t particularly inexpensive for the time. $177 for a new 1919 F4, $88.65 for an A4. Average wage was $0.56 per hour.

Quote:

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Originally Posted by MandoMack

How did 1920's Gibsons survive wood and coal burning stoves with no humidity control?

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My grandparents' house, built in the early 1890s, had a coal furnace and radiators. My grandmother always kept a roasting pan of water on top of one of the radiators, I suppose to protect the furniture from the winter's dryness. Any 1920s Gibsons in that house would have been OK. (Too bad there weren't any.)

Most of those houses were also drafty and not insulated much, if at all. They didn't dry out like a tight insulated house made later.