F-Holes vs. No F-Holes

on a semi hollow, the effect is mostly cosmetic, as there is a lot of timbre dominance by the "solid" core section of the guitar. on a full hollow, the f-holes change the natural resonance of the body, lowering it a bit and increasing what's known as the "Q" or peakiness of that resonance. in practical terms, that makes the guitar a bit more full bodied and also more susceptible to feedback at stage volume levels. that susceptibility to feedback is why acoustic/electric and hollow-body players often block the soundholes and f-holes, respectively, on their stage instruments - helps kill the peaky resonance. I'm not sure I've ever seen semi-hollow players (Gibby ES-335, Epi Dot ..., Tele Custom [barely a semi] ) have to do the same. The Guild Bluesbird is usually considered a chambered guitar, as are many new models of LP. No matter what is said about the tonal improvements from chambering, the main advantage is weight reduction.

for your guitar: I recommend you decide based on the appearance you like. the hollow "wings on the HS550" are not change the tone much, if any, with or without f-holes.

I'm not sure I've ever seen semi-hollow players (Gibby ES-335, Epi Dot ..., Tele Custom [barely a semi] ) have to do the same..

The Epiphone B.B. King Lucille is a semi-hollow body archtop with no f-holes and was designed by the great man himself. It's based on the Gibson ES-355 King played from around 1958 onwards. He used to stuff the soundholes with rags to prevent unwanted feedback. “I don't want feedback - unless I want it. And a lot of times with the S-holes if you really crank it up and the amplifier is close to you, you will get feedback. I'm no technical person, but I do know that. I know how to get feedback from Lucille when I want it. But only when I want it,” he told interviewer, Walter Carter.

Yeah, I agree (mostly) with Greg....
On a true hollowbody, the 'F-Holes' add additional vibration characteristics to the top.
They allow the top to vibrate more.... which can lead to unwanted feedback.

I have a hollowbody/electric with no F-Holes, and it sounds great.
It's not quite the same as a Carvin 550 though.
Mine has a spuce top/maple sides-back.

The Carvin 550 seems to be more of a 'chambered' style guitar body, and they say the arched-top is actually carved out of a thick piece of wood (choice of maples I believe, on a mahogany body?),
rather than a 335 neck-thru clone with hollow wings and a top 'cover'.

So, IMO the F-Holes on a so equipped Carvin 550 would be more ornamental than practical.

Which looks best to you????

Ken

Hmmmm - interesting question. I've never gone too deeply into the whole semi-hollow versus solid body argument - but what I do have is a cheapo copy of the type of Hofner bass sir Macca used to have in the early days of the Beatles, and has still used up to at least the year 2000.

Now that particular bass is as light as a feather, compared to all the other basses I've played - and it sounds reasonably OK unplugged, late at night in the spare room. It's definitely either hollow or chambered - I wonder would a couple (or even one) F-hole make it resonate more, unplugged? And what effect would it have on the sound when plugged in?

:D :D :D

Vic

Hey Vic :D

Well, the thing is.... no matter how many people will respond that they enjoy playing their hollowbody/electrics
unplugged (and I'm one of 'em :mrgreen: ),
they are not acoustic guitars.

That is to say; acoustics are specifically designed to be played 'acoustically',
while hollow bodied electrics are designed to be electric guitars.

They have their own sound, that's for sure.... mine is very dry and airy sounding.
The more maple (think T-Bone Walker's guitar), the 'drier' the tone.
Mine is maple with a spruce top (like a lot of acoustics have), so that adds to the airiness of the sound.
This Carvin has mahogany in it, so it will add a nice warmth to it (if that's what your after).

Although it has a spruce top (like a lot of acoustics), it's not built like an acoustic (if that makes sense).

So, to get a true 'acoustic' bass sound, one would need to play a stand-up bass.
(Although the new Harmony guitar company makes a remake of an old Harmony Hollowbody short scale bass that they claim sounds like a stand-up) (it can't really, unless maybe it is fretless, and still....)

LOL - That doesn't answer your question very well, does it? :roll:

Ken

LOL - That doesn't answer your question very well, does it?

No.

But then again, I'm not about to take any kind of woodworking tool(s) to ANY of my guitars, on the simple basis of, "If you don't know what you're doing, leave it the hell alone...." and judging off all the shelves I've put up over the years, not one of which has less than a ten degree sloping downward angle, I don't know what I'm doing.

I was just curious, is all.....

Oh, and thanks for the PM about the hole in the Tele - I've had so many over the last week or so, I've still got about 10 to reply to!

:D :D :D

Vic

I'm not sure I've ever seen semi-hollow players (Gibby ES-335, Epi Dot ..., Tele Custom [barely a semi] ) have to do the same..

The Epiphone B.B. King Lucille is a semi-hollow body archtop with no f-holes and was designed by the great man himself. It's based on the Gibson ES-355 King played from around 1958 onwards. He used to stuff the soundholes with rags to prevent unwanted feedback. “I don't want feedback - unless I want it. And a lot of times with the S-holes if you really crank it up and the amplifier is close to you, you will get feedback. I'm no technical person, but I do know that. I know how to get feedback from Lucille when I want it. But only when I want it,” he told interviewer, Walter Carter.

Okay -- you caught me. I know about Lucille, but have always assumed BB really did it to keep out the sweat :wink: . as a Tele player, I'm sure you know how to make a solid body feed back as well -- especially a nice resonant one (even solid woods can resonate). covering the f-holes of a 335 is a pretty minor change -- esp because it's center block is massive. as Ken notes, it really is a solid guitar with hollow wings.

Okay, I'll admit that I know a lot more about solid body instruments than hollow-body/acoustic instruments...and without going too far off the OP's topic, I've got a question.

I understand that a full hollow electric instrument with F-holes can feed back on stage, and I've seen several guys tape off the F-holes to reduce or eliminate the feedback. BUT, I don't understand how the feedback is generated...at least on an instrument that only has magnetic pickups. I thought that, in reality, the vibrations of the strings themselves were the only thing transduced by the pickups and thus, the string vibrations are really the only thing producing the sound of an electric instrument. Of course, the body, neck and other aspects of the guitar will change how the strings vibrate and thus each has some effect on the sound...but I still don't quite get how the hollow body's resonance will cause feedback...

Anyone have a good explanation?

Yeah, there are a couple of things that can happen...

First, the vibrating string induces a current by passing over a magnet. As the string disturbs the field, voltage is produced... but as the string moves away from the magnet, the magnet wants to move towards the string. So the less stable the surface the magnet's mounted on, the more vibration will be introduced into the top plate of the guitar.

That's a small thing... at first. But now you've got a magnet making tiny movements towards (and away from) fixed strings - the ones that aren't moving. And that induces a current, just like they've been played at a very low volume. This is going to produce an amplified signal, and if it's at a resonant frequency you'll get feedback. By definition it's at a resonant frequency - it matches the vibrations of the top plate and the unplayed strings.

Most hollow bodies try to minimize this route with a sound post in the body, shoring up the support to keep the pickup in place.

The second mechanism is the Helmholz frequency. Air disturbed within a sound cavities produces pitch, just like you can get a pitch by blowing across the neck of a bottle. These tend to be pretty low (roughly the open A string). And they can generate sympathetic vibrations on other strings (and other parts) of a guitar, which is then amplified... which then reinforces the original vibration, and so on.

the pickup being supported by a vibrating top is one path for feedback, Tom. but I think it's probably a second order consideration, as stronger coupling mechanism usually exists between the strings and the top -- right at the bridge. on hollowbody guitars the bridge is usually designed to facilitate that coupling. and it's reciprocal: strings transfer vibrations to top, and top does the same back to strings. the latter is usually a main connector in the feedback path, which end-to-end looks something like this:

strings => pickup => electronics/cable/amp=> speaker cab => sound wave => top of guitar => strings (back at beginning!)

all those frequencies for which the phase shift around the loop is net some integer multiple of 360 degrees and the gain is unity (1) or greater are candidates for oscillation (a.k.a. feedback). the dominate one (greatest gain) wins. because there are a number of resonances in this loop (strings' vibrational freqs, Helmholz resonance of the body cavity <interacts heavily with top at low end>, top resonance, EQ, pup peakiness ...), there is a quite a bit of selectivity for particular frequencies where the loop gain can be greater than unity at the correct phase shift. changing any of these resonances (e.g. covering f-holes or sound hole, filling guitar with dirty laundry, depressing trem) can alter the phase and gain around the loop enough to either kill feedback (gain now < 1 and all frequencies) or enhance feedback (phase-gain stars have lined up!)

I would argue that the sound post -- usually located near the bridge, has much more effect on string-bridge-top coupling than coupling through the pups.

WOW! Thanks so much for all the info! PLEASE, keep it coming. I'm not overly worried about feedback. I've been playing for 40+ years now, and these days, the volume isn't that extreme. Years ago I was playing a "jobbing" gig, that somehow turned into a "Hard Rock Karaoke" gig! (long story...) I was playing a very old ES150 (with NO sound posts at the time) and made it through the gig! LOL
My question is really about the difference, if any, to the sound.
Again, Thanks for all the input.
Cheers,

Thanks for answering my question gents...sorry for hijacking the thread a little bit there Ron D.

Greg, I don't disagree that coupling is the strongest at the bridge... but that's true of all hollow body guitars, whether there are F holes or not. So I disagree that hollow body feedback is primarily caused by string/bridge/top coupling.

If feedback occurs when there are soundholes, but doesn't occur when there aren't, it's a matter of comparison: what's changed?

And that boils down to what the soundholes DO... by introducing an opening to the cavity, they allow Helmholz resonance. In the case of F holes, they also interrupt the structural connection between the center of the top and the adjacent sides, allowing the center of the top to 'float'. Since those are the two big differences, one (or both) must be responsible for the feedback.

Placement of F holes are often on either side of the pup, allowing a lot more motion in relation to the strings. Strings move on all guitars, but all guitars aren't prone to feedback - just the ones where the pup can move relatively freely in relation to the strings. And Helmholz frequencies must be a big source - because commercial soundhole covers don't stuff the cavity - they simply cover the hole, eliminating motion of the air 'plug' that creates the Helmholz frequency.

Nice explanation of the relationship between frequency gain and feedback, though :)

you answered your own question: Helmholz resonance. re-read my post. we agree about that, though treat it a bit differently. even if one merely tapes over the holes, H-res will begin to change in Q and freq, while not yet affecting the compliance of the top. and any slight change in the H resonance will have an effect.

certainly "loosely mounted" pups can add to the problem, but I put that as a secondary -- more likely second order --contributing factor.

as to why certain guitars (hollow or not) are prone to feedback: it's to do with the system loop gain-phase at each frequency. if the frequency selective mechanisms don't happen to coincide, gain is leveled across frequencies, and the guitar is more feedback resistant. strings have a much higher Q than a suspended pup, and are far more likely to support a resonance (because they are designed too!), than a vibrating top and pup "system." so removing the string vibration is usually the key to killing inadvertent FB.

here's easy experiment to help track down the linking mechanism: start with guitar/amp setup just into feedback. lightly mute the strings. no feedback? then the strings are actively in the FB path. still FB? then it could be pup vibrating in the top (strings are still a positional reference.) returning to no FB case: still muting strings, now up the amp volume (loop gain) until FB starts again. difference between that and the point of FB onset for unmuted strings is the difference in contributions between pup-vibrating-in-top coupling and coupling of strings through bridge (+ nut/neck + tailpiece) ... though it could also be a highly microphonic pups and string "reference" is irrelevant. almost forgot: with initial setup also try this: touch the pups to see if damping their motions significantly kills the FB. I'm guessing we might wager differently on that :wink:

top mounted piezos and other "direct contact" pup types do what you describe to a much greater degree than magnetic pups. my T5 in switch position 1 (includes Expression magnetic body pup to grab top vibrations directly)does this quite well even with muted strings -- though unmuting usually shifts the oscillation to a freq of one of the strings.