Reducing neck-through stiffness for tonal reasons

[I-Am-The-Slime]

Hey guys and gals,

So, I've been thinkin'...

I'm working on a fretless neck-through single-cut that I plan to set up with piezo bridge pick-up only.

Current and previous discussions here in the Corner concerning body stiffness in relation to tone have been interesting and educational for me, specifically:

That really depends on the size of the chambers you are routing. If they are relatively small, you can leave just 1/8". For larger chambers, where the span across is 2" or more, it's safer to leave 1/4". Just to keep someone from caving it in later on.

A simple way to do chambering is to rout a pattern of straight slots, parallel and leaving 1/4" to 3/8" wall between them. Make the slots like 3/8" wide and deep enough to leave 1/8" of the top surface. That's simple to rout and work with.

If you make those slots parallel to the centerline, you are turning the center area of the body into a row of little parallel I-beams. As a rough guideline, think of what percentage of the volume of wood you are removing. You are weakening the body by about half of that percentage. That is, if you are removing 50% of the wood, you are weakening the beam by around 25%. The webs and the top and back surfaces are still carrying the bulk of the load.

If you cut the slots crosswise, perpendicular to the centerline, that weakens the structure much more. That's like cutting big holes in the web of an I-beam. The top and back surfaces are still carrying the bulk of the load, but because they are thin, they could buckle. In that case, removing 50% of the wood may remove 50% of the strength. You could have structural problems. The body could bend and collapse under the load of the strings. Which is not a good thing.

In general, you are trying to weaken the body somewhat. Not drastically. As a starting point, I'd suggest removing 30% to 50% of the wood volume from the center area of the body, leaving some ribs parallel to the centerline.

Making the center area of the body weaker like this allows it to flex more with the strings, adding extra background harmonics. Because the length of this weaker zone is roughly 1/4 to 1/3 of the overall scale length, these added harmonics will tend to be in the mid-range. This is what we call warmth.

The overall purpose of my structural tricks is to make the deep lows and the highs very clear, and then add harmonic warmth in the middle. The truss rod and the rigid neck/body joint make the deep lows clear. Careful mounting of the bridge and the nut make sure the highs are clear. Chambering the body brings in that mid-warmth and keeps the overall instrument from being too cold and sterile sounding.

although this^ was more about bolt-on than neck-through...

@Bruce Johnson, you rock I guess I'm kind of calling you out for more, but I assume you enjoy participating in these discussions almost as much as I like reading your comments. And of course I would love to hear anyone's thoughts on this matter! I'm not necessarily looking for an answer (which would probably be "g'ahead and find out "), more of a discussion or call for ideas...

So, in the pic below
A. is what we have in hand (actually, mine's not one piece but a sandwich, but we can get into the effect of wood on the tone later...)
B. is the channel for the piezo wires, that is going in regardless (GraphTech saddles)
C. is the position of conventional magnetic pickup routes
D. balls to the wall hog-out
E-K. etc. etc. Let your imagination run wild!

What d'ya think? More? Less? Under the bridge? Not? More on the bass-side? More on the treble? Something completely different? Ever seen something like this done before? Do I want to err on too soft or too stiff when using piezo's? What's best for metal?

Thanks for reading!

 

[MattZilla]

GENTLEMAN, BEHOLD: SCIENCE!

We shall build thirty of each design, all with maple necks, pau ferro fingerboards, medium frets, and the same piezo bridges, and we will convene in a year's time to evaluate the results and then we will determine the best neck thru constructed bass forrrr metulllllllllllllll! Dismissed!

 

[Slidlow]

I have built neck through with piezoelectric and have not done any lightening or hollowing. I have not encountered issues with lack of mid range or tonal issues. I am more inclined to leave the wood in place from what I know of sound wave propagation and refraction. My latest five string has a solid ebony neck with piezo and it has full range sound with inexpensive preamp. My next build is a six string with ebony neck, piezo and a Richter piezo preamp to see where upscale preamp brings tonal quality. Also the Richter preamp has individual string level control to better balance string output.
Regards

 

[I-Am-The-Slime]

Thanks for your comments @Slidlow !

I decided to also go with a Richter buffer and EQ. Andreas has been very helpful in discussion. I will update the thread I started on piezo setups once I get the new gear

I expect that setup should give excellent tonal variety but I'm still intrigued about dialing in body stiffness. If nothing else, chambering the neck should have some effect on weight... Just a bit worried about going too far.

Cheers

 

[Slidlow]

Thanks for your comments @Slidlow !

I decided to also go with a Richter buffer and EQ. Andreas has been very helpful in discussion. I will update the thread I started on piezo setups once I get the new gear

I expect that setup should give excellent tonal variety but I'm still intrigued about dialing in body stiffness. If nothing else, chambering the neck should have some effect on weight... Just a bit worried about going too far.

Cheers

What I would consider is removing a block from the center after the neck and before the bridge and leaving maybe 3/8 to 1/2 inch thickness top and bottom. Rule of thumb with frequencies is higher propagate more readily through softer materials and lows through more dense materials. Another option is to leave the neck block intact and remove pockets from the body wings. Having said that personally I haven't found any coring of the body on basses worth while except to reduce weight. I have tried various ways since the early 1980s and have pretty much returned to solid materials.

 

[MPU]

Bruce Johnson has one opinion about chambering.
Headless four string ”Brucefied”

 

[I-Am-The-Slime]

Bruce Johnson has one opinion about chambering.
Headless four string ”Brucefied”

Yeah, the quote in the OP is Bruce commenting on your thread

Cool thread BTW! I didn't want to hijack, so started this new one...

 

[Arie X]

well you certainly don't want to reduce body stiffness to the point that the instrument becomes unstable. you risk folding up the thing, and diminishing transmission of string energy to the bridge. the instrument will not likely hold a set-up for very long as well as a host of other problems. you certainly aren't going to enhance tone with a body that is designed to dampen string energy right from the start as such it seems like you're looking for a crash course on acoustic bass design.

what's your max string tension on this thing? what are your woods?

 

[MPU]

Yeah, the quote in the OP is Bruce commenting on your thread

Cool thread BTW! I didn't want to hijack, so started this new one...

I tried Bruce’s truss rod and it really made an audible difference. I have no doubts that other Brucifications will work too. If I was making a thru neck I’d chamber it something like on bolt on neck body. I trust Bruce and his tests.

 

[Bruce Johnson]

Hey guys;

I'm thrashing away on a couple of necks for a client right now. I'll write up my recommendations in a little while.

 

[I-Am-The-Slime]

what's your max string tension on this thing? what are your woods?

Thanks for your comments!

As far as string tension goes, I have no idea of the numbers but I'm working on a four string 34" and am not sure yet whether it will get flats or rounds (or tapewounds?) but they will likely be standard gauge... hope that helps

The woods are walnut, maple, and purpleheart. I'll post a pic of the neck when I get home.

Hey guys;

I'm thrashing away on a couple of necks for a client right now. I'll write up my recommendations in a little while.

No worries, no rush, just chewing away at my fingernails in anticipation

 

[I-Am-The-Slime]

Here is the neck in question

 

[Bruce Johnson]

Oh, man, a hippy sandwich in 3D! Groovy.

 

[I-Am-The-Slime]

OK, so this is what I'm currently thinking. The neck stringers will be untouched and only the walnut, purpleheart, and maple "tone block" will be excavated.

FWIW, the wings are also chambered (single-cut, walnut top and back)

 

[I-Am-The-Slime]

Holey neckbeam, Batman!

This is what I ended up going with. I used a forstner bit to hog out the neck, but did not go all the way through, leaving a 1/4" "spine" in the middle. The two holes on either side of the chamber are for doweling the wings for glue-up, they go all the way through and were used to accurately drill the corresponding holes on the wings. Then there's a hole to lead the piezo PU wires to the control cavity.

Obviously we'll never know the influence on tone without a non-hogged control neck (and multiple replicates ) but it should save some weight in any case!

Progress on this build will be documented here: Winter 2017 Build Off - First scratch build: walnut, maple and purpleheart sandwich