Double Bass Soundpost fit for new bass- changes in RH

[BassinCT]

Greetings, folks!
In August, I purchased a new hybrid bass (with a very responsive and seemingly flexible top) and have recently noticed that the area above the soundpost is bulging slightly- more of a ridge that runs along the grain than a circular bump and not pronounced enough for a photograph to capture. When I tuned all of the strings down by a m3rd, the bulge almost goes away completely. At the moment, there appears to be no bulge forming on the arched ply back, but I want to keep it that way.

When fitting a new bass with a soundpost in the summer, would a luthier fit a post as usual and recommend keeping an eye on things? Or is the post fit differently in anticipation of inevitable RH changes, settling, etc.?

I understand how RH changes impact a single piece of wood, but am a bit confuzzled about how an arched wooden box expands and contracts. Would the bulge be more pronounced when things dry out in three months? I have searched the TB archives and the internet for information about this but haven't found exactly what I'm looking for. Most of the queries are related to plywood tops- so if any luthiers wouldn't mind chiming in, I'm all ears. Thank you!
RB

 

[RSBBass]

First there are many people here who no far more than I do. if they say differently do what they say. That said I see no harm coming from the advice I am giving. I would be concerned about a ridge forming in the top near the sound post. It sounds like it may be too tight. If tuning the instrument down removes the ridge I would do so and take the bass to a good technician very soon.

 

[DoubleMIDI]

Show it to a luthier.
If you cannot doth is soon, buy solo strings of the same kind and tune them to orchestra pitch. That way you can play the instrument for a while until you can let a luthier check your instrument. (And put the original string set on the bass about a week before you go to the luthier. The bass top needs some time to adjust to the new top pressure.)

 

[Ortsom]

A bulge in a solid top is not good and might develop into a soundpost crack.

The development of the bulge is probably not caused by RH changes, but rather by using strings that have too high a tension for this very responsive and seemingly flexible top. SP placement, diameter, length & fit will also contribute, so once again: best take it to a luthier (in the condition with the bulge, otherwise he doesn't see it, but the bulge will probably come quickly after tensioning-up). But as you say yourself, reducing tension makes the bulge go away, so if these are starks, maybe the instrument wants weichs. Or maybe reinforcement in that area.

 

[BassinCT]

Thanks for the replies! At the moment, it is already wearing EP weichs. With the strings tuned down a bit, a slight ridge can still be felt, which makes me think that the post may need to be re-fitted. I have put in a call to a luthier for an appt to get it checked out- I hope to strike a balance here for the health of the top.

If this turns out to be a problem, I will inquire about having a sound post patch installed to reinforce the area.

Back to the humidity- If left it alone (not my plan), how will a tight post fitting be effected by a drop in RH this winter?
Thanks everyone!

 

[KUNGfuSHERIFF]

The right post fit will get tighter as the weather gets cooler and drier, and you house's climate control will likely make the air dryer still.

Your hybrid will be more stable than a fully carved bass because the ribs and back plate won't move as much, but there will probably be a measurable change, especially because your bass is still a baby.