Some Questions about F-hole Design

[CarlM]

He (Gilchrist) does a great job of describing his perception of tonal generation and his methods of manipulation.

Do you have a link or source for an interview or article where he talks about this?

[hank]

Carl look under his Design/Tone here. http://www.gilchristmandolins.com/design/

[hank]

The fundamental difference between primary vibrating surfaces.

[hank]

Where I’m going on this is aperture shape and location can change the voice of the box. The instruments apertures are not only area specific to the box size but also guide the flexibility and range of motion of the plate. Sort of like a suspension bridge along its edge.

[sunburst]

Tops move in their normal modes of motion and do nothing else. Neither the shape nor size nor placement of the ports change that, the laws of physics support it, observation supports it, measurements support it, it has been demonstrated and published. Normal modes of motion involve the whole plate. Mode shapes are independent of port size, placement and shape. Stiffness and mass of the plate determine frequencies of the modes, so holes and braces can change mode frequencies, but not mode shapes. We can control plate stiffness and mass through carving and graduation to control mode frequencies, so we are not limited by the size, shape and placement of holes.
Air modes are different from plate modes.

[Spruce]

Cause that's how Loar did it. And it has been proven time and time again, there is literally nothing that can be aesthetically improved upon in the Loar designed F style mandolin. It is as perfect as perfect can be. Change anything even slightly, and you disrupt the balance of the universe.

(Thanks, Darryl...)

[fscotte]

That weird looking mando on the left is the red headed stepchild.

[hank]

Thank’s John. Are you saying that applies to all mandolin tops or all carved top mandolins or all F-5 shaped plates with the plate anchored 360 degrees to the rim or head block? A hybrid oval is the animal you describe but does the model still fits the unanchored neck area of the plate in the shortneck ovals? Does the manipulation of frequency also include amplitude or range of each cycle. An example is getting the reflex areas thin enough to allow enough move ment to get the bass woof without too much losing power. The coupling seems very different on an oval holed short-neck configuration. The bass comes in a more broad less pumped or percussive way.

[sunburst]

All tops, mandolin, guitar, banjo, everything, move in normal modes of motion. The shape of the rim has to be very different for there to be any particular difference in mode shapes. An F5 is not enough different from an A for the normal modes to be different. For that matter, a flat top guitar is not enough different for the mode shapes to be particularly different. A fingerboard attached to the top, a la pre-20s Gibson, has about the same mode shapes as one with an elevated extender. The mode frequencies may be different, but as I mentioned earlier, we have various ways to control mode frequencies.
The bass "woof" is mostly a result of good coupling between the top, back and air within the instrument. A thick top paired with a thick back might have as much "woof" as a thin top paired with a thin back. It comes down to coupling more than thickness per se.
If I have known what it is about oval hole mandolins that keeps them from having the kind of chop that an f-hole mandolins has, I've forgotten, but there is obviously some difference.

[flyingmotorsound]

Turns out that when we directly measure velocity of sound at the sound holes, it is highest at the edges of the opening. Therefore, increasing the total perimeter of a sound hole can increase the acoustic conductance (volume) of a top. Early violin builders discovered through trial and error that cutting narrower sound holes, while increasing the length (creating f-holes) produced louder instruments. But there was a balance. Elongating them too much weakened the top creating a less desirable tone (and a weak structure).

There is an excellent article about the evolution of f-holes and sound conductance. I can't post the PDF here but you can find it on Google Scholar or try Googling the DOI: 10.1098/rspa.2014.0905



http://www.jettinstruments.com

[Geoff B]

interesting...
I've done a lot of digging on this, and have some of my own personal opinions, but haven't much to contribute for the sake of humanity. I see some builder names I recognize and respect and generally agree with regarding design, modes of vibration, frequency coupling etc.
I would emphasize this though: if one wants to install a pickup (or work on the internal parts as mentioned before) in a completed instrument, it is very nice when things can fit through the soundhole(s). For a typical endpin jack that I run across, that means a circular cavity that can accommodate a hole roughly 9/16-5/8" in diameter somewhere in there. Usually in the the wide part between the points, sometimes in the larger circular portion of the f-hole. This does not preclude a more delicate f-hole shape, but it would create boundaries, in my own building, about future care/maintenance of the instrument and how the holes are designed and implemented.

[Mark Gunter]

I will of course defer to Dave's much greater understanding of such things, though my understanding was it was the different in area that caused the difference, the oval hole being about 25% smaller that the combined f-holes. I do miss Dave's enlightening contributions. A shame he was driven out by the flat-earthers.

cheers

"flat-earthers"?

Don't know about that. Dr. Cohen was invited to leave by Scott in a thread where he tended to disparage Roger Siminoff, not because of his scientific contributions but because of his attitude (the tenor of his responses) toward other contributors here. I remember it well, because I started the Siminoff thread that the exchange occurred in.

For myself, I don't think anyone would describe me as a "flat-earther" - but when I was a babe to this forum I was taken to task by Dave's lackey's here for such minor infractions as using the exact terminology you're quoting John on: "causes air to pump in and out of the f-holes".

On the other hand, I've read many of Dave's archived posts here, and read several articles he'd recommended as well as a bit of his own published work, and can certainly see why folk would miss his enlightening contributions here. Some of the most informative and erudite people can sometimes have a tendency to denigrate their fellow humans. I had difficulty keeping my own acid tongue out of a recent discussion with a real-life "flat-earther." An amazing conversation it was. That conversation began with, "Did you hear about Paul McCartney?" "What about him?" "He was in an automobile accident." "When?" "Oh, a long time time ago." Can you extrapolate which twists and turns may have taken us from there to a story about a flat earth beneath a dome around which the sun revolves?

[Mark Gunter]

I'll go on record here as apologizing for my snarky comment, viz., "lackeys". I have no interest in disrespecting the cafe or any of its members. I love this site and the many good and talented people who post here; we all benefit immensely from it, and this discussion on apertures is another good one.

[fscotte]

Dave brought illumination to how it all works. And with it, lots of old "facts" and ideas about how mandos create sound, were discounted. It was common knowledge to believe that sound waves travel through the mandolin starting at the bridge, filtering through the top, etc.. .. well Dave and his studies proved otherwise.

[billhay4]

Dave and his studies proved otherwise.

Not exactly. Dave is merely one of many people who study acoustic science.
Bill

[fscotte]

I don't recall anyone from this forum doing what he did.

[billhay4]

Look, I don't mean to denigrate Dave's work. It is quite good. However, there is an entire academic field of acoustical studies. Dave is not trained in physics, but in chemistry and that is what he taught. But, it is obvious that he switched his attention to acoustics long ago. Well, maybe "switched" is the wrong word; he added acoustics to his fields of interest.
He has done good work in that area of interest. Much of his work has been in response to, and designed to supplement, the work of others in the field. This is ofter the way science works, especially when you're just making your chops.
I do, however, mean to denigrate unabashed adoration of Dave, and the suggestion that he is the be all and end all of acoustic science.
Bill

[Mark Gunter]

Really, this thread shouldn't devolve into a discussion of Dave Cohen IMHO. The discussion of top plate apertures has been interesting. I truly wish I hadn't responded to Graham's remark; hopefully someone will have something to add to the actual topic soon.

[Dave Cohen]

My degrees are in physical chemistry, and some of the work was theoretical chemistry. As such, much of my course work overlapped w/ that of physicists, including most of the math courses and some of the physics courses - both undergraduate and graduate.

One thing I have not done is talk about other people behind their backs, nor will I ever do so.

[Mark Gunter]

Dave, thank you for chiming in - and my apology for the "lackeys" comment.

[hank]

“In the Land of the blind the one eyed man is king.” Come on Bill, Dave has had a boatload of patience in his explanations of cause and effect in a phenomom none of us can see or fully understand. Thank you both for being here.

[dang]

Having read both threads, I never read Dave’s posts as attacking Roger, but rather as defending science. As I masters trained biochemist I think in similar terms, science is always a debate for the best ideas, and if yours stand the test of time you win.

But we shouldn’t be discussing locked threads, though there does seem to be some sort of relationship between Roger and the cafe (remember that whole rebranding of the “advertisement” for straight up strings as a white paper?)???

[gweetarpicker]

The lowest air resonance peak on the frequency response curve of a mandolin is typically higher for an f-hole mandolin than an oval hole mandolin due in part to the different shape of the holes. I read a paper by an MIT student that found the majority of the air flow passes through the near-the-edge area of the soundhole. I picture the air fluttering against the hard sharp edge of the soundhole while the air in the center void of the big soundhole is comparatively static. This line of reasoning implies that a f soundhole has the same effect on the lowest air resonance as a larger in area oval hole soundhole. In fact, the combined area of the two soundholes in my F5 is fairly close to the area of the single oval soundhole of my F4 (the air volume of the body of both instruments is almost the same as well); however, the lowest air resonance peak on the F5 is much higher. The long slender f-holes might also have less of an effect on the "with grain" stiffness of the top (plus the tone bars help with stiffness as well) compared to an oval hole. This might be one factor in the higher top mode wood frequencies reported for f-hole mandolins. The coupling between the air resonance and the plate modes of the f-hole mandolin contribute to the mid-range bark.


www.vintagefrettedinstruments.com

[billhay4]

science is always a debate for the best ideas

Not exactly. It is a debate followed up by experiments to test the ideas. And the ideas must be testable to be considered science. Periodically, the results of these experiments are compiled into new theories or paradigms which are then subjected to the same process of debate and testing.
I see no winning in this process, merely a never-ending process, an evolution of human understanding if you will.
Bill

[dang]

...Periodically, the results of these experiments are compiled into new theories or paradigms which are then subjected to the same process of debate and testing.
I see no winning in this process, merely a never-ending process, an evolution of human understanding if you will.
Bill

I wasn’t being that specific, and if you want to discuss scientific method I will do that all day, but in the loose jargon I was using I would say those new theories and paradigms you mentioned would now be the “best idea” and they “win” for a time. Of course experimentation and tests occur.

The evolution of understanding is WAY different then the rather pragmatic evolution of design, the only test that mandolins have had to pass over the years in order for the design to be considered successful is an economic one. Sure that correlates with some physical properties, but it doesn’t have to, and the explanations seem to fall short.

Otherwise wouldn’t these scientific explanations allow us to produce the “best” sounding mandolins in mass quantity?