Deformed F-hole

KrisH · #1 04-25-2009, 08:45 PM

Maybe someone can tell me why this happens. The F-hole on the bass side on my plywood upright has deformed. Meaning that the lower curve has lifted above the surface of the top a little bit. I've seen this happen on other instruments before, and wonder what causes it. Is it cause for concern? This developed over the winter. I kept it in a room that I tried to keep relatively well humidified, but it was a challenge sometimes.

fdeck · #2 04-25-2009, 11:01 PM

I'm not a luthier. But I suggest finding a way to look inside with a bright light and mirror, to make sure the bass bar is intact and fully attached.

I suspect that my ply bass spent more than a few years with a cracked bass bar, missing sound post, or both. It has a sunken top, and consequently deformed FF's. Since I fixed it, the top has not deteriorated any further.

**Matthew Tucker** · #3 04-25-2009, 11:56 PM

if you're talking about the outer edge of the FF lifting, look again, it's most likely the belly sinking under the bridge pressure. This is VERY common, and usually nothing to worry about, as long as it doesn't keep increasing. You can have a bass play fine for years like this.

That said, it could be a loose bass-bar inside, which isn't fun. Probably for your own peace of mind you need to take the bass in for a health check.

If it's the inner edge of the FF that is lifting, then i have no idea what it is.

KrisH · #4 04-26-2009, 05:46 AM

Quote:

Originally Posted by Matthew Tucker

if you're talking about the outer edge of the FF lifting, look again, it's most likely the belly sinking under the bridge pressure. This is VERY common, and usually nothing to worry about, as long as it doesn't keep increasing. You can have a bass play fine for years like this.

That's it -- sinking top, I can understand that. When I bought it (used) it had light strings on it. I replaced them with medium strings, with higher tension. Can it be that a bass is made with light strings specifically in mind? I had it checked out about 14 months ago, after I'd already replaced the strings.

Hammertime3 · #5 04-26-2009, 08:46 AM

My 41 Kay is the same way, but my bass bar seems intact. Both ends of the F hole are deformed, one up and one down. It was delaminated a little when I got it, but had it glued and now I will just live with it. Doesn't bother the sound at all. After all, that bass is almost as old as me, and not nearly as deformed!

Jake deVilliers · #6 04-26-2009, 01:20 PM

And here I thought you were talking about my brother-in-law!

**Matthew Tucker** · #7 04-26-2009, 04:44 PM

Quote:

Originally Posted by KrisH

Can it be that a bass is made with light strings specifically in mind?

Well not really. it just is what it is. My ply bass liked heavier strings too, and a higher action, all of which made the bass louder, but pushed the top down more. This is the problem with ply basses; by their very nature they don't tend to be loud, or bright, and if you're looking for that, you try all sorts of things to improve the tone, but in the end, a carved top is what you're after.

I have been doing Chladni analysis on my bass tops; just to look at really; i'm not sure what they mean yet. A carved top will give all sorts of resonances quite easily, you can see all the harmonics working away. But a ply top is REALLY hard to get even the most basic resonances showing.

Here is the original plywood top with the sunken top under the E foot, and the new carved top side by side

Here’s the mode two that leaps right out of the carved top:

But here’s the best mode two pattern I can coax out of the plywood:

(I realise that yes, the ffs are not cut from the carved top yet, and this affects things, but the upper bout of the ply vibrated like a piece of plasticene in comparison)

Here's the higher frequency mode five for the carved top:

but i couldn't even get it to show ANYTHING on the ply top!

You can probably see why this is also why ply basses work really well in some environments; they are naturally less resonant and prone to feedback amplified (some might disagree) and less finicky in the set up (others will surely disagree).

Why did you put heavier strings on?

moles · #8 04-26-2009, 05:48 PM

The description of the f-hole in the OP sounded a bit too familiar, so I just peeked inside mine...

Looks like I have a fair bit of separation on the south end of the bass bar. It's hard to say how much - I had to take my glasses off to get my eyeball right up to the f hole to look inside. It looks like it's solid up until about 6 - 8 inches south of the bridge anyway.

The top hasn't sunken any more than what it was like when I got the bass - but I guess this'll have to be addressed as soon as feasible.

So what's the process to get it back in order? I guess what I'm really curious about is whether the bass bar that's on it will be reusable, or if a whole new one would have to be made to fit the now (slightly) sunken top.

Damn, this is starting to add up. Maybe the moral here is "Don't look a gift-horse in the f-hole."

drurb · #9 04-26-2009, 06:33 PM

Quote:

Originally Posted by Matthew Tucker

I have been doing Chladni analysis on my bass tops; just to look at really; i'm not sure what they mean yet.

Fantastic and informative post! Thank you for taking the time to share that, Matthew.

fdeck · #10 04-26-2009, 06:39 PM

There's a bass bar thread in setup and repair right now.

**Matthew Tucker** · #11 04-26-2009, 06:51 PM

Quote:

Originally Posted by moles

So what's the process to get it back in order? I guess what I'm really curious about is whether the bass bar that's on it will be reusable, or if a whole new one would have to be made to fit the now (slightly) sunken top.

you can sometimes glue it back in place by opening the bottom seam to the lower blocks. But it depends on the condition of the top, really, and why the bar separated in the firstplace. If it separated because the ply is deteriorating (is yours a ply bass?), you have serious thinking to do. If its merely a bad glue job, you might have more luck just getting it glued back.

moles · #12 04-26-2009, 07:03 PM

Yessir - ply top. I don't see any signs of deterioration on the inside, but that doesn't say much - I wouldn't know what to look for (aside from obvious signs of splitting on the outer layers), and would defer that kind of judgement to a luthier...

It's going to have to have a big trip to the luthier one day soon anyway - so I can just get this done at the same time I suppose.

KrisH · #13 04-26-2009, 09:22 PM

Quote:

Originally Posted by Matthew Tucker

Why did you put heavier strings on?

Thanks for the info -- and a good reason to look for at least a hybrid for my next bass.

As for why I put heavier strings on -- the lights felt "floppy," and the action was higher than I wanted. When I lowered the bridge, I got buzz. So I switched to strings with more tension, and got clean tones with lower action. Just that.