Official Luthiers Forum!

I'm copying a response from a small but well regarded pick up company that specialize in acoustic guitar saddle transducers and "power bridges" that are direct replacments for many electric guitars that adds a pressure saddle tranducer that can be used for acoustic sounds and/or MIDI out if you buy their preamp with a MIDI card and cable. No MIDI for me yet but I can upgrade the preamp later if I want to pursue it.

My question was regarding the size of string slots for (width and heigth) for bass guitar strings and how the bridge angle may affect the larger bass string sitting on a fairly small saddle slot. These are 4 independent saddles that you place in the bridge slot wich "prevents cross talk" and allows each string to be individually intonated at the bridge.

Since I did not ask permission to review his advice or comments I have removed all references specific to the company or product as well as my personal contact information. My question appears below in blue (hopefully) and his response is black again but in italiacs for clarification.


Scooter B wrote:

I received my order of bridge transducers and the
preamp I ordered. They were well packaging in good condition and appear to have excellent instructions.

While I have not started building my acoustic bass guitar I do have a question regarding the string slot width and depth. The slots on these saddles seem to be sized for guitar strings more than bass strings. I would assume with your great reputation that this will not be an issue but I am doing a somewhat unique design that is a cross between a jazz guitar and acoustic guitar in a bass.
   
Basically there will be two struts from the neck that will run to the tail of the guitar but will not be in contact with the top, bottom or sides and will terminate in the tail. The bridge will be a jazz guitar style with the strings running through slots in the top behind the bridge and the ball ends terminating at the junction of the neck struts and tail inside the guitar.

My string angle will not be nearly as sharp as in a standard acoustic guitar or bass but closer to 11 degrees or so.

Do you think these string slots will securely seat the strings with this type of bridge design?




-=- Hi Scooter B,

This design will clamp the struts and the top together into a relatively
in-phase assembly (in the vertical plane) where the strings tie both of
them together. This produces a dominance in strut vibrations radiated by
the top if the struts are stiffer. You may get uneven response from this
arrangement because the struts will also vibrate in different ways
(sideways, torsionally, etc...) at different frequencies. Strings under
tension are ridgid coupling devices at low frequencies, but only in the
direction of pull. The string-clamped struts will exhibit a pendulum
action for some vectors of vibration and that can be a problem
resonance-wise. I suggest doing a patent search and discussing this
design with an experienced archtop guitar luthier to avoid surprises.



The 11 degree string break-angle is a bit shallow indeed, but Les Pauls
and similar instruments perform correctly with about 13-15 degrees of
break-angle. The string notches in our saddles have an included angle of
120 degrees when seen from a front view. They are designed for a 15 to
30 degree break-angle. It's also a matter of how hard the player is
picking.

With 11 degrees break-angle with a normal string action, medium-gauge
and picking at least an inch from the bridge, the strings will buzz
really hard on the frets from hard picking before the string gets pushed
out of the notch. In my experience. Heavy metal and Blues afficitionados
should have a full 20 degrees. Light Jazz players can live with about
10. Just my 2 cents....

Best regards,

Assuming that what he is saying is true (and he seems quite knowledgable) I have two theoretical questions.

Q1. How could I keep the strut neck through design for sustain and minimize wierd interactions from the struts with the top? I had hoped isolating the inner struts from the top and back would limit this interaction.

I was alraedy planning on using carbon graphite rods in the neck and another set in the struts. Also I plan on using a decent sized billet of hard wood to terminate the ball ends of the strings near the tail or as part of the tail. Something to add a little mass at the end of the struts as well as stabalize the struts laterally and front to back. This would have two tenon joints for the struts to lock into. This should also help with balance and prevent neck dive. I would think this arrangement along with the struts terminating into the tail block would significantly limit strut movement. Additional neck struts supports could be spaced out (like a ladder)if needed.

Q2
Regarding the string angle. One other idea I have tossed around is using several spaced holes between the struts that would allow me to sink threaded inserts and use matching neck mounting bolts to allow me to move this piece of hardwood closer or further from the bridge to try different bridge angles out.

Since this will be somewhat of a test bed of ideas I plan to allow some access to the inside of the guitar near the tail that will allow me to swap out electronics and move the "internal string retainer" that the ball ends terminate in even after the top and back are glued and finished. battery access will probably be located here and possibly volume/tone/blend controls. I generally am of the opinion that screws have no place in a nice acoustic guitar but I may make an exception if it is inside the guitar and increases my chances of a successful outcome. If one spot or string angle truly excels over the others I will probably go head and glue it on permanently in one spot.

I promise to take progress pics and post some clips if it sounds decent when I am done.

Sorry for the long post but it sounds like an interesting experiment.




Scooter B38918.7930555556

Bump and update. BTW I think this is some very nice service from this individual.

What I am going for is a warm blendable acoustic sound with the sustain
of an electric bass guitar.

-=- FYI, acoustic resonances shorten sustain by letting energy flow
rapidly from the string into the air. An instrument with less efficient
energy transfer to the air stands a better chance at having sustained
energy in the string. Then, it's mostly a matter of internal friction of
the vibration-coupled components. Substantial energy is taken up by the
neck which usually is a high-friction structure.


One other non traditional option I considered was mounting either a
small strip of spruce soundboard spanning the struts but thought I would
get too much potential for phase cancellations. What I had intended to
do was attach a thick cross member of hard wood that the ball ends would
actually terminate in and make it somewhat adjustable with several
predrilled holes and seated neck bolts so it is secure and adjustable
for different string angles. I could even mill some brass for something
like this to either span the struts or attach to the hardwood.


-=- A heavy anchoring point will improve sustain.

-=- Good luck in this project.

Best regards,
Scooter B38919.4908680556

I wish I could offer some advice, my friend, but this goes beyond my experience. It sounds like you're getting some good council, though, from your pickup supplier. He or she seems to have a good grasp of engineering principles and pitfalls. The passion hits all segments of guitar building, doesn't it?

Thanks for your input.

It sounds like in very general terms then that goals of longer sustain (through stiffer necks) and resonance or resonant energergy being transferred to the sound board are to some extent inversely proportional.

Of course there are other variables and perhaps some synergetic contributions from design and wood types that work well together. All the Olson guitars I have heard seem to have amazing sustain and of course amazing tone, projection resonance but them it is a guitar and not a bass.

It would seem I should either focus on the acoustic properties with the electric pick up being a secondary concern or focus on it being and electric sound and have the saddle tranducers as an added benefit to blend in more in the line of the chambered body electrics or thinline acoustic electrics.....

I suppose there is a reason this concept has not been mass produced yet. LOL