Soundhole And Neck-Through Design Questions

[GarrettS]

I have been designing a guitar for the past 12 months and I now have questions about Construction Design and Soundholes.

The goal is to make a guitar that is more ergonomic for me to play. It will be thick, very heavily contoured, and lighter by use of massive rear chambering. It will be more left-shifted by having a longer rear bout. It will be neck-through with ~4 cm thick top woods.

I thought to make a rear chamber with a carbon fiber backplate to cover it all.

Total solid thickness, excluding chambered-out areas, of top and back woods would be ~2.5cm (1"). 

Distance from face of guitar to back of horn: 7.5cm

This will leave a massive chambering less than 5 cm deep (due to curvature).

The neck thru will be 4 cm thick (not the full 7.5mm thickness (too heavy).

The neck thru will be sandwiched between the top wood and back wood.

The top wood will cover the neck thru.

the back wood will cover the neck thru.

The back wood will be notched to fit the neck through.

There will be one large carbon fiber back plate to cover the rear chamber.

Will this work? What's good about it? What's bad about it? What should I watch out for?

How will sound ports on the face of the body, through the top woods, affect the tone? Where should I consider placing them? 

Thank you.

Video describing it:

Side view sketch:

 

 

[Bizman62]

It certainly ca be done but there's several things you should make clear for yourself. Let's start with the ergonomics:

• 7,5 cm is less than the thickness of an acoustic guitar, hollowbody guitars might be in the ballpark and semi-hollows a bit thinner. So nothing revolutionary there.
• Acoustic and hollowbody guitars usually have the neck join at the 14th fret whereas a single horn Les Paul has that at 16th fret and the Strats and Teles at the 17th. Dual horns allow a better access to the higher frets but the lowest frets are as far away as with single cuts. So if the neck break angle is straight like on a Strat you'll struggle reaching the lower frets if the body is thick.
• That said a neck break angle is recommendable
• You mentioned a full size backplate. Notice that a belly carve can't be done - unless you laminate the carbon fibre backplate to shape!

If I understood correctly your design is like a semi-hollow with the neck being attached all the length to the top and the sides being carved out of a bottom block, a bit similar to this. Notice how you'd have to have a much thicker neck block to start with than just the 4 cm to get the neck break angle right:

 

I wouldn't worry about acoustic feedback or other tonal anomalies as modern pickups aren't too microphonic. A wolf note may even be tuned off by reshaping the headstock or heel, a bit similarly to how you'd tune xylophone sticks.

[curtisa]

19 minutes ago, Bizman62 said:

I wouldn't worry about acoustic feedback or other tonal anomalies as modern pickups aren't too microphonic.

I would probably advise the opposite. It's not that the pickups themselves will be microphonic. It's the natural resonances inside the hollow body itself that will be the bigger issue. Consider that to play an electro-acoustic through an amp or PA at high gain you typically install one of those rubber soundhole stopper plugs to reduce the chances of acoustic feedback. Hollow body electrics are no different and can suffer the same issue under high volume.

[Bizman62]

13 minutes ago, curtisa said:

I would probably advise the opposite. It's not that the pickups themselves will be microphonic

You're most likely right. I've never had any feedback issues with my hollowbody but I don't use much gain.

Also, we're talking about a semi-hollow with some extra space under the block and for what I've learned semi-hollows should suffer less from the natural resonances and such as the center block acts as a solid body.

[Drak]

6 hours ago, Bizman62 said:

You mentioned a full size backplate. Notice that a belly carve can't be done - unless you laminate the carbon fibre backplate to shape!

The way I understood it, the entire back of the guitar IS a belly carve...actually a full torso carve if I understood it correctly.

So the guitar 'custom fits' into the torso of the person, like a glove fits a hand.

And the back plate was going to be separately formed and molded to that 'full torso carve' shape, so it could be removed (screws, magnets, etc.)

I don't see any feedback issues, as the top is solid, and the top is what vibrates to create the howl of feedback.

Unless I misunderstood something there...

If possible, I would just make the entire (removable) back plate out of carbon fiber, why not?

I would think, over the years, with two separate pieces of wood, the possibility of deforming and gaps would be present.

With an entire piece of carbon fiber, that would hold it's shape over the long haul better than two separate pieces of wood would.

[Bizman62]

12 minutes ago, Drak said:

And the back plate was going to be separately formed and molded to that 'full torso carve' shape,

That's what I meant by "laminating the carbon fibre backplate to shape".

13 minutes ago, Drak said:

If possible, I would just make the entire (removable) back plate out of carbon fiber,

Do you mean like a cup, the top acting as a lid? If so, our thoughts follow similar paths - again.

[Drak]

Thinking about it a little more...

The removable back plate idea is stalling with me a little.

There would have to be a rational, reasonable justifiable reason why that idea should be implemented.

Instead of, I guess, a control cavity.

If I understood the reason behind it better, I might get on board with it.

But I can angle-grind a belly cut in about 1/2 hour and its done.

So an entire back-of-the-guitar contour would take a couple of hours, but then that part is done and over.

Even with integrating and grinding a bevel on the control cover, like @ScottR just did on his new build.

A thin removable (wooden) backplate, I think, would distort and warp over time, and maybe not that long a time.

I see future issues and problems with this, besides the pre-planning and work involved to execute it.

Maybe I'm just missing part of the concept...

Even a material that doesn't distort and warp, there's a fair amount of trouble, so I would want to know what the payoff is to justify it.

[curtisa]

The design idea (from my understanding) is to essentially make a semi-hollow guitar with a solid centre section plus a couple of openings at the side chambers. On a basic level that's nothing out of the ordinary compared to just about any guitar with an F-hole. The only real curveball is the heavily contoured profile the body has.

Like @Drak I'm not sure why the back needs to be removable as a massive single piece, but maybe that's an experimental or aesthetic choice that satisfies @GarrettS's personal requirements.

FWIW Warwick has done bowl shaped rear-contoured bodies on some of their basses, and @Andyjr1515 has incorporated similar design features in a couple of his builds (the 'sucked lozenge' profile was how he described it).

Tonally I don't really know how you'd predict what the effect would be on the plugged-in sound by porting the side chambers, especially on a guitar that has such an extreme concave shape. The pickups themselves would be residing within the solid centre section of the instrument. Whether that makes a difference or not I don't know. 

[Bizman62]

For what I understand the biggest issue will be the neck break angle in the neck-thru. Let me explain:

• the top will be 2.5 (1") thick and cover the neck-thru, a notch will be made into the bottom wood only
• that means that the bridge will be about 3 - 3.5 cm (1 - 1½") higher than the fretboard as the top of the neck will be glued to the bottom of the top.
• as the distance from neck joint to bridge is about 25 - 30 cm (10 - 12") the angle would be about 4.7 - 5.7 degrees. It's in the ballpark compared with e.g. Les Paul
• a ~5 degrees neck angle would require quite wide a block to be cut from. There's two ways to cut the block to a neck-thru, illustrated below:

The red lines illustrate using the edge for top of the body part, the pink lines show the angle been cut to both ends. The illustration is roughly in scale, the total length being 105 cm and the body part 4 cm thick. As the illustration shows about one third more wood width is required for the red lineup. A scarf joint in the headstock can be used to reduce that amount.

[curtisa]

What about the construction requires a neck break angle? Unless I missed something in the video or diagram, I don't see a need to complicate things by adding backwards neck angle to compensate for something in the layout of the instrument this early in the instrument's inception.

The bridge itself appears to be a headless trem of some type in the sketch, and earlier illustrations posted by @GarrettS elsewhere seemed to suggest a headless design as well. I'd assumed the sketch above was drawn headless because that was the intent, rather than to omit detail for clarity.

[Bizman62]

3 hours ago, curtisa said:

What about the construction requires a neck break angle?

The 1" thick top. The neck through will be carved into the body, under the top. Of course one could cut a step for the top but the structural integrity would severely suffer.

[curtisa]

The more I read the OPs design hitlist the less clear I am about what the shape of this is meant to be. I originally thought the whole thing was meant to be some kind of hollowed-out bowl, convex on the front face of the body and concave on the rear. The 'thickness' of the body was to come from the distance from the outermost front face of the convex face to where the outer edges 'fold back' against the players' body. Now I'm not sure if the body was actually meant to be curved on the front and flat(ish) on the back, giving more of a potbelly shape.

Both bodies are effectively 7.5cm 'thick', but the construction of each are substantially different if they are to be hollow (cross-sectional rough-as-guts comparison sketch below):

Some more clarity from the OP would be helpful here. There are a number of figures quoted that I'm having trouble understanding how they work with each other (1" thick top and back, 4cm thick neck-thru, 5cm chamber depth...). Whether neck break angle is required here may be a little early to call.

Getting back to the OPs original call for things to watch out for, I would point out that if there is some kind of (headless?) trem to be installed in this as the sketch seems to suggest, there will be a minimum thickness of wood required around it in order for it to work correctly. 4cm is certainly what I'd call a minimum to make room for the springs and trem block on most typical headless trem assemblies available these days. You can make the block shorter to fit a slimmer body, but beyond a certain limit the leverage forces required by the springs to equalise the strings starts making the trem feel noticeably stiff and uncomfortable in use.

[GarrettS]

WOW! Thanks, everyone for the awesome responses! I wanted to reply earlier but there is so much to think about and respond to. 

@Bizman62 comment about the neck pitch changed my perspective. I realized that neck pitch will affect the forward tilt. More on this in the video below.

The removable back plate would fit snug and be attached with tiny magnets. The purposes are 1) to provide fast access to the bridge and controls, and 2) to cover the chamber.

I also considered 1/4 turn release latch with spring release latches, as in the drawing. Turn the knob, pull opposing latches, and open. Problems: Harder to construct than magnets, might break. Benefit: won't accidentally pop off and should be easy to remove by hand.

@curtisaIf I put any sound hole port(s) on the front, they will be set further away from the pickups to avoid feedback. Still undecided on this, but it would look cool, would reduce weight, and would provide a sound port for unamplified playing.

The bowl shape will be about what you've depicted in your blue crescents.

@Drak The point of the rear back plate is fast access to the bridge and all components, including the output jack. 

Here is a video about neck pitch:

 

Thank you ,everyone!

 

Edited July 27, 2021 by GarrettS

[GarrettS]

@curtisa The top is to be 1cm, not 1 inch!

[Bizman62]

6 hours ago, GarrettS said:

The top is to be 1cm, not 1 inch!

My fault, I somehow mixed the "total wood thickness" with "top thickness" and kept repeating that.

That said, a 1 cm top can easily be installed like shown in my last illustration, there'll be no weak spot. Heck, I'll draw it!

Anyhow, as you say the distance from the highest point on the top will be 7.5 cm apart from the lowest point at the horn, there's quite big a contour. Are you planning on bending the top over a carved bottom or just carve the shape? Both are valid options, it's more about the looks and simplicity to build. Same for the lower bout between the bridge and strap button.

[curtisa]

I think there's a misunderstanding with what there is to 'break' the neck angle from. Again, I still don't see a need to purposely design a neck with break angle in it to mitigate a high bridge (as you would for a guitar fitted with a tune-o-matic bridge for example).

You can design a guitar with a neck that deliberately angles backwards if you want. There's nothing here that says it cannot be done. But the strings still traverse a straight line from nut to bridge, and the proposed body design effectively stops at the bridge (sketch held up to camera at 02:00 in second video), so there's nothing left at that point to break the angle away from. The pickups still need to be positioned underneath the strings and the face of the guitar still needs to be at the same angle (more or less) as the strings for the pickups to be able to 'reach' the strings. The body itself is so contoured on front and back that neck break angle where it meets the body becomes completely irrelevant.

Borrowing @Bizman62's sketch from earlier, if you extend the neck blank (exisitng lines drawn in burgundy colour) up through the body (new lines drawn in green) there is zero neck break angle required, yet the neck may still be angled backwards as much as you like (relative to other surfaces of the body):

Given that the proposed body is such an organic, free-flowing shape, to simplify design and construction of the 'business end' of the guitar (ie, the neck, strings, pickups and bridge) it will be far easier and simpler to keep the neck-thru section as basic as possible. The wings of the body either side of the neck-thru block can then ebb and flow as much as you like in 3D space, pseudo-angling the neck backwards through the contact points with the players' body.

[Andyjr1515]

Hi

Interesting project @GarrettS !   

As @curtisa says, I've done a number of builds that have some of the elements you describe and, if I have understood your description well enough. there may be stuff I can help with in terms of what I found did work and what I found problematic in some of the more unorthodox stuff I've played around with.

Overall my conclusion with guitar and bass design has been that:

- there are some fundamental geometric interactions and limitations that affect some decisions (and funnily enough, that includes neck angle  )

- there are some practical considerations

- there are some things that affect the sound and playability 

- there is a HUGE amount of stuff that doesn't affect any of the above and therefore is only limited by our imagination 

 

So there is nothing that so far is screaming to me 'that isn't going to work' and there's lots that says 'yup - that's interesting and could work'

I'll have a bit more time later today to consider some of the things you ask, but just for starters, this is the sort of thing that @curtisa is referring to above:

This is one of my lightweight basses.  Looks pretty conventional from the front:

 

Oh - and yes.  With increasing trouble from arthritis in my hands, I have done a fair bit of experimenting on my own guitars and basses of the angle that the body sits on the strap and its effect on the ease of access to the fretboard.  Ref your second video above, some of that might be of interest

 

I'll have a full read of the thread and watch your videos later today .

Andy

 

 

 

 

[Andyjr1515]

I've watched your videos a couple of times now, @GarrettS  and still don't see any major 'no-no's', based on my understanding so far. 

But having said that - because in this sort of thing context is everything, with suggestions that are right in one context being sometimes absolutely wrong in another - I'm not clear about a couple of things:

Question 1 - You make one or two references to acoustic sound and unamplified playing.  I'm not clear whether this is intended to be an electro-acoustic you are designing or a thinline electric?  If it is electro-acoustic, then the top needs to be much, much thinner (it is the vibration of the top that produces the tone with the back there largely to 'bounce' the sound forward). 

If it is planned as an electro-acoustic, then yes, feedback needs to be considered.  Also, the rigidity and positioning of the back plate/panel would need to be considered 

But if it is planned as a solid-topped guitar (and to me, a relatively rigid 1 cm top says that is what this is planned to be), then feedback, with or without a soundhole, is unlikely to be an issue.  Likewise, in this case the back panel becomes largely there to stop the hardware snagging your shirt

Question 2 - I'm not sure what cross-sectional shape you are planning for your top?  Is it planned to be flattish, or flat along a spine from fretboard end to tail end but curved either side of that, or 'contact lens' shaped

The answer to this question influences the bridge/pickup heights and - in some instances - the neck/body angle.

 

In the meantime, I'll drop in a few thoughts on some of your other questions in the next hour or so 

 

 

[GarrettS]

 

9 hours ago, Andyjr1515 said:

This is one of my lightweight basses.  Looks pretty conventional from the front:

 

Oh - and yes.  With increasing trouble from arthritis in my hands, I have done a fair bit of experimenting on my own guitars and basses of the angle that the body sits on the strap and its effect on the ease of access to the fretboard.  Ref your second video above, some of that might be of interest

I like the triangle soundhole. I like the curved back.

How thick is your neck through? looks like 3cm in that photo. Where are the strap buttons?  

 

@Andyjr1515 The objective is lightweight, ergonomic guitar.

Weight can be decreased by chambering and holes (like monkey grips, etc). Chambering with holes creates sound holes — holes that emit sound (bonus). 

The design is to be flat along a spine, from fretboard to bridge contoured, arched back along the sides, and with a deep with a deep forearm contour, .

Arching the lower side puts the controls further out of the way of my right hand, when strumming. Because I tend to anchor my fingers, a lower height on the lower side should make it easier to maintain a nice break in the wrist when picking. This should help me pick faster with palm muting while I anchor my fingers.

Although anchoring is considered "wrong", a lot of guys do it, and especially guys who play with downward pick slanting, including Zakk Wylde, Michael Angelo Batio (who is left handed), Yngwie Malmsteen, and John Petrucci. I practiced for almost a year not anchoring and eventually went back to anchoring.

Contouring the upper side reduces mass. A deep forearm contour makes room for my forearms and also helps me get that favorable break in the wrist.

 

NOTICE: The Solidworks Designer Cut her hand and has not been very responsive. I may need to hire someone else. Contact me if interested. 

Edited July 28, 2021 by GarrettS
Trim quote

[Andyjr1515]

Thanks for the extra info @GarrettS

OK - in general terms, my thinking and experimentation is very much like yours.  Over a number of builds, and then a series of lightweight builds (c 5.25lbs - 5.75 lbs for 6 string electric and the above full-scale bass at 6.5lbs) I came to a number of conclusions:

- You can basically build a neck.  This can hold the bridge, and the pickups, fretboard and tuners -  and pretty much everything else is optional

- The body is a convenient place to hang the electrics and strap buttons but, functionally, it doesn't actually need to do much else

- So the freedom to what you do with the body is immense

So yes - the centre of the body of that bass is around 30mm.  But even that was for the luxury of having full size pots and conventional fixing of the pickup.  This one was pretty much neck thickness  for the whole thru-neck body:

 

And yes - this had a slot routed in the top (similar to your thoughts of routing a slot for the back) to slot over the through neck) - so yes, your thoughts are entirely feasible.

Other things I noted from your outline spec, and these, of course, are only my own judgements (and never assume I know what I'm talking about) - 

- left shifted by 18.5cm.  Yes - haven't measured it but a Les Paul or ES335 must be about that much?  As long as you have the reach it's not an issue.  Remember, a Bass is 34" scale length!

-  25mm thickness of the solid middle bit.  Yes - as long as you can sort how to fix the pickups, there doesn't need to be any wood underneath them

- 1cm top wood.  As I say, I think that at that thickness, it is unlikely that you will have the top wood vibrating enough to cause feedback issues.  On the same logic, of course, it won't be enormously acoustically loud.

This one below is heavily chambered as well as having the back carve but has a pretty much standard electric unplugged sound - maybe just a little louder - and sounds just like any other 2 humbucker plugged in.  This has a playing weight of 5 1/4 lbs...and that is in spite of the back being weighty english oak:

If I'd just routed the chambers all the way through instead of keeping a back on it, it would be been pretty much the concept that you have in mind - a top and sides but hollow at the back.   Functionally and sonically, it would have worked just fine, which is why I don't think there is much wrong with your design thinking  

 

[GarrettS]

"The body is a convenient place to hang the electrics and strap buttons but, functionally, it doesn't actually need to do much else"

The body shape largely affects that balance and positions the guitar. My design aims to get it further away from my body and more to the left.

As for the router person, she offered to do the CNC toolpaths, too, then decided that that's all she'd do, then quit.

MakerNexus shop teacher, Jeannie Llewellyn, decided to take the project on, came to my house to gather details, hit on me, ignored me, wrote up a plan to do the prototype and CNC for the project using foam and basswood, made excuses, ignored me for weeks, tried to invite herself over again and, failing that, she sent a cryptic text:—

Quote

Garrett, how about I just model the guitar you want and you can enter it into zither GotY?

At that point, my confidence in her was lower.  

She later followed up to text me at 1:45 AM that "the retainer ran out".

The next day, I text replied asking what that meant. She read the text and ignored it.

I issued Venmo a request for refund.

She then rushed to send out some 3D image that does not match what is spec'd, and of course, reneged on the deal.