Steevarino - Posted - 03/14/2010:  15:33:23

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I just got an order for a kind of guitar that I don't build. Should be interesting...

This customer has requested a round neck, left handed reso. guitar with f-holes. I guess I can handle the round neck OK. Although I have not yet built a round neck reso., but we do build mandolins and acoustic guitars, which have round necks.

No problem on the lefty part either, as I have made a few, including one in-process right now. It's the f-holes that have me stumped. So far, I have only used the round screened (or screenless) rings. I'm not all that crazy about the f-hole shapes I have seen on other reso. guitars I have seen so far.

I'm also wondering how to calculate the area of the opening, and hopefully keeping the aperture size similar the size of the round holes, as that is what I am used to building with, and I don't want to get in left field, tone and volume-wise.

So, can anyone help me? I don't really want to copy another reso. builders f-holes, but I guess it wouldn't hurt to get some inspiration from another type of instrument. I "Googled" f-holes (be careful with this) and found one that I like. It is part of a Gretch logo, as I recall. Other than that, I just got confused!

Any links or other info you can suggest would be greatly appreciated. I have also asked the customer for similar input.

Steve Smith
RedLineResophonics.com

SamCy - Posted - 03/14/2010:  19:28:29

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I have heard of two approaches for determining the area of the F-holes. The first would be to trace the shape on really fine grid paper and count the squares. Another suggestion was to set up a strong light and light meter at a fixed distance. If you used the round hole as a standard, you could adjust the shape of the F-hole until the readings matched. Checking the light through the round hole with and without the screen might give you an idea of just how much the screen reduces the effective area. It might even matter what gauge the wire in the screen is.

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Edited by - SamCy on 03/14/2010 19:47:20

Erik Waynesmith - Posted - 03/14/2010:  20:26:51

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quote:

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Originally posted by SamCy

Checking the light through the round hole with and without the screen might give you an idea of just how much the screen reduces the effective area. It might even matter what gauge the wire in the screen is.

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The wire gauge used in screened soundhole covers most definitely "matters" -- there's a substantial difference in the primary air resonance frequency of a reso body with U.S.-manufactured screened soundhole covers installed versus typical screened import covers due to the much finer wire gauge and wider mesh of the screening in Asian-made ones. You may also find the following info I'd posted on ResoNation in early 2009 of interest:

"Although it might not appear so at first glance, the fine-mesh heavy-gauge screening used in most U.S.-manufactured soundhole covers substantially reduces the effective surface area of the soundhole openings (by approximately 35 - 40%). FWIW, most low cost Asian-manufactured soundhole cover screens have a coarser mesh and smaller wire diameter, so their effective port surface area is reduced to a lesser degree by the screen wire; however, their screens are also more easily damaged due to the resulting structural weakness."

Erik Waynesmith - Posted - 03/14/2010:  20:42:07

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The way I now determine the surface area of non-circular soundhole openings in musical instruments is to simply draw the shape in a CAD program with a utility function that automatically calculates the enclosed area.

Before having access to the CAD software's enclosed area tool I'd determined the approximate area of non-circular soundhole openings by cutting the opening's shape out of a piece of aluminum then comparing its weight to a circular shape cut from the same piece of aluminum. If you have access to a precision scale, you could do the same thing using other materials which were less costly and/or easier to cut to the correct shape (such as a scrap piece of clear plexiglass).

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Edited by - Erik Waynesmith on 03/14/2010 22:25:45

Dukasyo - Posted - 03/15/2010:  05:44:04

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I like f-holes too. Good luck with your science experiment!

Tom Jr. - Posted - 03/15/2010:  07:10:32

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Steve this is a very interesting topic. Here is another question in the same area. Does the area of the hole need to be the same when another hole has a completely different shape (round versus f-shaped), does total soundhole perimeter matter, does location change the calculations for area/perimeter. The one that I built (photos in my album) are horse-head shaped. I am a land surveyor by trade and have the latest and greatest in measurement and calculation technology, including a CAD program. I can determine exactly how much area and perimeter is in something like this.
My process for getting the horse heads the right size was to scale a silhouette to several different sizes, lay them on the guitar top and the one that looked right was the one that made the cut.
For general f-hole proportions, eyeball some fiddles and basses too.
My favorite guitar in the world is a roundneck Beard which was my introduction to the reso world.

Steevarino - Posted - 03/15/2010:  07:33:00

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Good points, all. I appreciate the input. I'll have to check and see if any of the CAD packages I have access to will calculate surface area. If so, that would certainly be the easiest way. Cool trick about cutting out the shapes and weighing them, Erik! Makes perfect sense, in a more "Meat Space" sort of way.

Tom, I was wondering the same thing. Since f-holes are such a different shape from a circle, does this add to the mix? If I can figure out how to calculate surface area, I might compare the area of two f-holes on a mandolin to one oval hole on a similar mandolin. Surely, our mandolin (and other instrument) building ancestors must have crossed this bridge too...

Kind of funny, though, isn't it? Someone orders an instrument from you because they like how you build, and then ask you to build one a different way. Personally, I am surprised at how often this happens. I usually say no if the project is too far off the path, but this one involves a great guy, and a wonderful customer, so we become "Burger King" (have it your way). I just hope I end up with some nice f-holes AND a guitar that sounds the way I want it to!

Steve
RedLineReso.com

Stringnut - Posted - 03/15/2010:  17:28:14

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Careful Steve - If you don't watch out you'll be building arch top guitars before long. Have you given any thought to an 8 string reso yet? Just thought I'd throw that out there.

Dan

Steevarino - Posted - 03/16/2010:  15:33:25

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Dan --

I HAVE been getting some strange requests lately, but the only arch tops you will ever see me making would most likely be of the 8 string mandolin family variety, and that's not likely to be for some time yet. I can see doing an 8 string reso. I have worked on several, so I think I know what it would take. Plus, we are already talking about modifying our all new RLR spider to an 8-string model, to offer better support for the longer bridge insert.

I just stumbled upon a very nice pair of F-holes. I got them from Roger Siminoff's F-5 mandolin construction book, right here in my shop office. I'll zap a couple out in the next day or two, as well as a couple of my more usual round holes, put what comes off of the board on the old triple beam scale, and see what we get, weight-wise, and maybe adjust them a bit from there.

Steve
RedLineReso.com

Erik Waynesmith - Posted - 03/16/2010:  20:14:46

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quote:

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Originally posted by Tom Jr.

Does the area of the hole need to be the same when another hole has a completely different shape (round versus f-shaped), does total soundhole perimeter matter, does location change the calculations for area/perimeter.

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There's some 'pressure zone' and turbulence effects that occur near the edges of a soundhole opening which could make a non-circular hole shape with the same surface area as a circular one perform somewhat differently; however, unless the non-circular soundhole had a circumference several times greater than the circular hole (such as a narrow, elongated slot or a whole bunch of small holes) these edge effects will generally produce only minor variations in a reso's sound.

Soundhole locations can have a far more significant effect on a reso's bass response and projection than most people realize, due mostly to acoustic coupling between the cone and soundhole(s) at low frequencies; the impact of soundhole location can be particularly noticeable if the hole(s) are located in very close proximity to the cone.


FWIW, you could empirically verify two different soundhole shapes would produce the same air resonance frequency in a reso body before cutting holes in the reso by using a Helmholtz Resonator constructed from a rigid, airtight box having approximately the same enclosed air volume as the reso's body and the two soundhole shapes cut in opposite sides. By sealing first one then the other soundhole and exciting the box's air resonance using a speaker placed near the open soundhole (or simply humming different frequencies into it to determine the box's resonance frequency) it'd be possible to verify both soundhole shapes were producing the same resonance frequency.

Grizz - Posted - 03/16/2010:  20:22:18

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I am really learning something here. Do I need to know it, no, but it is interesting. To lighten the mood a little I think I have deduced why they are called "F" holes. Steve, maybe you should ask if he would accept "A" holes. Now guys please don't get angry with me I'm just havin some fun.

Mike

Erik Waynesmith - Posted - 03/16/2010:  21:03:02

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Although I'm not a big fan of f-holes on resos, here's a link to some that I think look pretty good: s4.hubimg.com/u/55231_f260.jpg

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Edited by - Erik Waynesmith on 03/16/2010 21:06:36

Steevarino - Posted - 03/16/2010:  21:09:23

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Mike --

You bring up a good point, but since this customer has already made a substantial deposit on the instrument, it would probably be better if I don't call him an A-hole... :)

Good stuff, Erik, as usual. Way over my head, but still good! What it made me think of while reading it was a small body wooden Dobro that I put together from old discarded stock parts a few years ago. Thinnish body, cutaway, 9 1/2" biscuit cone,and a sound hole arrangement they called the "shotgun" pattern, which was just a bunch of small holes drilled in a sort of a diamond pattern, which was actually somewhat interrupted on the cutaway side of the instrument.. The guy I put that guitar together for (a very accomplished player, by the way) has loved that guitar from the day he got it, and he's still crazy about it. If that crazy hole pattern gave a good sound, I'm thinking maybe I don't have all that much to worry about.

I do, of course, want the guitar to sound as good as possible though.

Steve

eastmountain - Posted - 03/19/2010:  19:48:50

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Since I'm new to resos, I probably think more about aesthetics than tone. Luthier Linda Manzer has some beautiful modern F holes for her archtop guitars. She also make some guitars with side ports on the body that can be opened or closed incrementally to change the tone. I wonder what that might do for tone on a reso.


I'm also fond of the Rickenbacker "cats eye" sound holes.

Once, I was making a mountain dulcimer and was trying to make a soundhole area that looked like a cluster of grapes. the top splintered between the holes and I had to abandon the design. Looking at the grape holes, I saw an image...as you might see figures in the shape of clouds. The "accident" became a dolphin, one of my favorite sound holes ever.

Grizz - Posted - 03/19/2010:  20:45:49

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quote:

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Originally posted by eastmountain

She also make some guitars with side ports on the body that can be opened or closed incrementally to change the tone. I wonder what that might do for tone on a reso.

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Keith, that is Interesting. Take a look at this. I was on Franks site and came across this.

youtube.com/watch?v=EmCrVrkgEA..._embedded

Mike

eastmountain - Posted - 03/20/2010:  06:11:57

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Really cool. Thanks for the link, Grizz..

Grizz - Posted - 03/20/2010:  08:14:45

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I thought it was real interesting. But who is going to take their guitar apart to change them. Then you would have to take it apart and put it back together after each one is removed until you get the sound you want. I'd have to think long and hard about this one.

Mike

eastmountain - Posted - 03/22/2010:  07:45:26

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I had an idea... what if the "plugs" in the sound well holes were like the butterfly valve in a carburator? It would be crazy expensive but they could be made to adjust with an allen wrench on the back of the guitar. That would allow for easy sound changes, even from song to song.

Tom Jr. - Posted - 03/22/2010:  10:57:52

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Eastmountain, that is a very cool idea. Very off-topic but threads are made for hijacking right. I would love to experiment with the butterfly valve concept. There is a huge potential for buzzes and rattles from all the necessary connections and linkages but still a great idea. I had a buzz recently but with the weather changing, I thought it would smooth out with time and spring. Turned out to be a loose screw on my tailpiece button.
My brain is thinking while typing. How about a "Bixby Bar" concept with a spring loaded bar attached to those butterfly valves to immediately alter the sound. Could you keep your picking fingers rolling while hooking the bar with your pinkie?

El Dobro - Posted - 03/22/2010:  13:08:05

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F-holes. Hmmm. No one's asked you to install a Virzi yet, have they?

Steevarino - Posted - 03/22/2010:  13:22:50

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A Virzi in a reso. guitar. Now there's a thought! I wonder what it would do...? Come to think of it, I have a couple of Virzis floating around the shop somewhere. Worth a shot, I guess...

I like the butterfly valve idea. I'd even consider trying it, but the thing is, so far I have only built one reso. with a traditional soundwell. And come to think of it, that one had parallelogram shaped holes, not round ones. Overall, I'm more of a "ring and post" builder.

Still, you could use the same concept and have an internal baffle or two that could be adjusted from the outside. I'm sure this has been done already. Anyone got pictures of a set-up like this...?

Steve
RedLineReso.com

El Dobro - Posted - 03/22/2010:  13:34:54

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I believe Bob Wolfe and Paul Beard have messed around with adjustable internal baffling and I think it was adjustable from the outside.

The Virzi may be an interesting experiment in a resonator, a baffle that also vibrates.

SamCy - Posted - 03/23/2010:  23:17:35

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The adjustable baffle openings I have seen were rectangular with sliding "doors". The butterfly valve sounds like a neat idea, just a 90 degree rotation from open to closed. The opening need not be circular as long as it was symmetrical about the axis. It would even work on a 45 degree baffle if the axis were also set at 45 degrees, and the top of the butterfly were narrow enough or set far enough down to clear the underside of the top in the open position.

Erik Waynesmith - Posted - 03/24/2010:  05:33:14

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quote:

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I believe Bob Wolfe and Paul Beard have messed around with adjustable internal baffling and I think it was adjustable from the outside.

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That's correct; both Bobby and Paul have used adjustable internal baffling... but AFAIK only on prototype or test instruments, not for production resos.

quote:

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The Virzi may be an interesting experiment in a resonator, a baffle that also vibrates.

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FWIW, Tim Scheerhorn originally used a thin sheet of aluminum to make the baffles installed in his resos, but eventually switched to plastic when he realized that the aluminum was vibrating and adding an undesirable 'metallic' resonance to the instrument's sound.

The "Power Reflex" design Saga has patented for use in their imported Regal-brand resos consists of a circular wooden disc suspended underneath the cone to supposedly 'reflect' some of the sound. Since this wood plate is only held in place at its outer edge where it makes contact with four posts, and isn't thick enough to be totally rigid, it tends to vibrate sympathetically with sound coming from the rear of the cone in a manner similar to the Virzi resonator plates installed inside some violins and mandolins.

In my own reso design I use a removable "Resonance Control Plate" which is easily accessible from the back/bottom of a fully-assembled instrument (without having to disturb the cone or spider!). Plates made from different woods and/or with different shapes and thicknesses can be installed to adjust the resonance properties and tonal balance of a finished reso.

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Edited by - Erik Waynesmith on 03/24/2010 17:43:29

phil dean - Posted - 03/25/2010:  13:56:40

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How about these?

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Edited by - phil dean on 03/25/2010 14:04:54

Steevarino - Posted - 03/25/2010:  16:01:40

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Very nice F-holes, Phil. My current thinking is that I just might come up with my own version of an f-hole. I'll probably start with that pair I lifted from a set of F-5 mandolin plans, and maybe goof around with the size and shape of them until I come up with something that looks at home on my classic sized reso. body. Then I'll measure them, weigh them, all that stuff, and goof with them until I get something similar to the area of the screened hole openings.

That's my current thinking, anyway...

Steve
RedLineReso.com