hi there guys!
first of all, i'd like to explain that at this stage, the following discussion will be completely HYPOTHETICAL. while i do plan to make this guitar at some stage, when, i'm not sure. i would go to a luthier forum, but i want to design it from the perspective of the enclosure designer/audio engineer/physicist/driver designer/speaker enthusiast! so with that in mind, let your imagination go wild! but not too wild, stay on topic pretty please 🙂
i have been thinking about building an acoustic guitar using SPEAKER theory instead of just guitar builder/Luthier theory. by this i mean i want to think of the face of the guitar as the diaphragm/piston, the strings as the motor, etc to create something that is a little different. it doesn't need to sound anything like a traditional guitar by the end of it. it will be MY design with MY sound. 🙂
just for your reference, this is the "anatomy" of the basic acoustic guitar. just so we can all get our nomenclature correct 🙂
just a bit of history, I've so far had a play with trying increase the efficiency of the "diaphragm". my main method was playing with different materials as diaphragm and surround. my favorite so far is 0.5mm fine plywood with carbon fiber bracing and 0.25mm silicon sheet for the surround, but i also tried fiber glass diaphragm and rubber surround. the rear enclosure was quite small, only around 0.5 liters.
this gave it quite a percussive sound because while the diaphragm was quite sensitive, the surround was quite dampening and absorbed the sound quite quickly. this was not a good or bad thing, as it just coloured the sound, which is can be a good thing. it was about as loud as a regular guitar, but a fraction of the size.
anyway, what i propose is a rear loaded, horn loaded guitar. my reason is for ultimate efficiency, as there is not alot that would be a problem or sacrifice because it is a musical instrument. it doesn't need to be designed like a hifi system. distortion is a-o-k.
to simplify/complicate things for maximum efficiency, i propose a diaphragm for each string, with a horn for each diaphragm. this way, each diaphragm can be maximized for two main things:
*efficiency
*resonance
i think for this reason, some super thin 2-3 layer carbon fiber, for the diaphragm may be best. but i may find that each string may need a slightly different material. who knows till i try it!!
there is a pass band, and for each string this is the ACCEPTABLE pass band.
e - 82-246
A - 110-275
D - 146-365
G - 196-490
B - 247-617.5
E - 330-825
while the guitar is capable of going beyond the above pass bands, this should be good enough, especially for efficiency. the narrower the pass band, the higher the potential efficiency and DB output. they are still quite wide in my opinion, but are a good starting point for designing.
so what i want from you guys is, how would i go about designing the diaphragm to best suit a horn driver for a given pass band? i suppose i try t make the diaphragm resonance the lowest frequency it will create? i.e the low e string's pass band is 82hz - 246hz so i should make the diaphragm resonance around 82hz? when modeling this in hornresp, i assume that only the sd is the important thing? i ask that because for obvious reasons i cant input the t/s.
now that i have had quite a bit of experience with fiberglass fabrication, i feel comfortable taking on a project like this.
as i said, this is all hypothetical atm, but any thoughts guys, i would love it!! maybe if i get enough info, i may build it!
first of all, i'd like to explain that at this stage, the following discussion will be completely HYPOTHETICAL. while i do plan to make this guitar at some stage, when, i'm not sure. i would go to a luthier forum, but i want to design it from the perspective of the enclosure designer/audio engineer/physicist/driver designer/speaker enthusiast! so with that in mind, let your imagination go wild! but not too wild, stay on topic pretty please 🙂
i have been thinking about building an acoustic guitar using SPEAKER theory instead of just guitar builder/Luthier theory. by this i mean i want to think of the face of the guitar as the diaphragm/piston, the strings as the motor, etc to create something that is a little different. it doesn't need to sound anything like a traditional guitar by the end of it. it will be MY design with MY sound. 🙂
just for your reference, this is the "anatomy" of the basic acoustic guitar. just so we can all get our nomenclature correct 🙂
just a bit of history, I've so far had a play with trying increase the efficiency of the "diaphragm". my main method was playing with different materials as diaphragm and surround. my favorite so far is 0.5mm fine plywood with carbon fiber bracing and 0.25mm silicon sheet for the surround, but i also tried fiber glass diaphragm and rubber surround. the rear enclosure was quite small, only around 0.5 liters.
this gave it quite a percussive sound because while the diaphragm was quite sensitive, the surround was quite dampening and absorbed the sound quite quickly. this was not a good or bad thing, as it just coloured the sound, which is can be a good thing. it was about as loud as a regular guitar, but a fraction of the size.
anyway, what i propose is a rear loaded, horn loaded guitar. my reason is for ultimate efficiency, as there is not alot that would be a problem or sacrifice because it is a musical instrument. it doesn't need to be designed like a hifi system. distortion is a-o-k.
to simplify/complicate things for maximum efficiency, i propose a diaphragm for each string, with a horn for each diaphragm. this way, each diaphragm can be maximized for two main things:
*efficiency
*resonance
i think for this reason, some super thin 2-3 layer carbon fiber, for the diaphragm may be best. but i may find that each string may need a slightly different material. who knows till i try it!!
there is a pass band, and for each string this is the ACCEPTABLE pass band.
e - 82-246
A - 110-275
D - 146-365
G - 196-490
B - 247-617.5
E - 330-825
while the guitar is capable of going beyond the above pass bands, this should be good enough, especially for efficiency. the narrower the pass band, the higher the potential efficiency and DB output. they are still quite wide in my opinion, but are a good starting point for designing.
so what i want from you guys is, how would i go about designing the diaphragm to best suit a horn driver for a given pass band? i suppose i try t make the diaphragm resonance the lowest frequency it will create? i.e the low e string's pass band is 82hz - 246hz so i should make the diaphragm resonance around 82hz? when modeling this in hornresp, i assume that only the sd is the important thing? i ask that because for obvious reasons i cant input the t/s.
now that i have had quite a bit of experience with fiberglass fabrication, i feel comfortable taking on a project like this.
as i said, this is all hypothetical atm, but any thoughts guys, i would love it!! maybe if i get enough info, i may build it!
Adele - Rolling in the deep - Cover (Stroh Violin) - YouTube
http://en.wikipedia.org/wiki/Stroh_violin
not a horn but thought I'd put a plug in for Karlson anyhow
http://img86.imageshack.us/img86/9372/kbassvs6.jpg
http://en.wikipedia.org/wiki/Stroh_violin
An externally hosted image should be here but it was not working when we last tested it.
not a horn but thought I'd put a plug in for Karlson anyhow
http://img86.imageshack.us/img86/9372/kbassvs6.jpg
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similar to what i was thinking! but i was thinking one horn per string 🙂 but clearly there is a positive to doing it. i assume the negative is that it doesnt sound like a traditional violin and that it is more expensive to produce. 🙂
totally off topic but that youtube clip has the violin sounding remarkably like Darryl Way's mic'd up violin in the original curved air recordings.....so it can't be that far off.
In essence, this can not be done.
Not without making said "guitar" too large to carry, or be playable.
The dimensions of the "horn" required are simply too large.
Even if you managed to make a horn somehow, there is no compression diaphragm available to drive the horn. The closest available method would revolve around the original acoustic gramophones, that used a needle attached to a diaphragm that was placed at the throat of a horn. But again, even a gramophone sized horn is not particularly small, and would be actually large to reach what you spec'd for low E.
That's why they have piezo pickups in the bridge and lightweight portable amps these days? 😀
_-_-
Not without making said "guitar" too large to carry, or be playable.
The dimensions of the "horn" required are simply too large.
Even if you managed to make a horn somehow, there is no compression diaphragm available to drive the horn. The closest available method would revolve around the original acoustic gramophones, that used a needle attached to a diaphragm that was placed at the throat of a horn. But again, even a gramophone sized horn is not particularly small, and would be actually large to reach what you spec'd for low E.
That's why they have piezo pickups in the bridge and lightweight portable amps these days? 😀
_-_-
Make a Cornu guitar!
The bridge could be attached to a small diaphragm situated in a chamber much like a compression driver connected to a horn. The vibrations are small in amplitude but the force is substantial owning to the compression the strings under tension apply. A regular guitar or violin in fact uses the bridge and sound board to effect amplification via cavity resonance. Having a horn that could provide gain to amplify the lower notes would be a challenge though. One was is to coil the horn up much like the Cornu.
So, I think a neat experiment would be to take a Cornu BLH speaker and replace the driver with a custom bridge-coupled diaphragm. One would attach the neck/fretboard to the face of the Cornu. The Cornu is compact, lightweight, and has double length horns to help smooth the response. One could make a double layer Cornu and have 4 different length horns. I think a good diaphragm for this experiment would be to take an existing driver with a stiff suspension and mount the bridge to the cone. The outputs of the voicecoil would double as the pickup out for an amp! With a little photoshopping you can see what I mean... 🙂
The Cornu speaker has perhaps one of the largest horn expansion ratios of any BLH speaker (about 25:1) which gives it about +10 to +12dB of gain.
This would actually look kind of cool and be a total conversation piece.
The double layer Cornu looks like this before the guitar adaptation (which by the way appears to be foam core channel construction and for a Lowther - and whoever did this never posted or discussed it on the Cornu thread):
Given that the acceptable passband is 82Hz for the lowest notes, this is a very reasonably sized Cornu speaker of approximately 20 in x 20 in x 3 in deep. If you made it double layer then it could be 6 in deep to give it the holdability and feel of a regular guitar body.
The bridge could be attached to a small diaphragm situated in a chamber much like a compression driver connected to a horn. The vibrations are small in amplitude but the force is substantial owning to the compression the strings under tension apply. A regular guitar or violin in fact uses the bridge and sound board to effect amplification via cavity resonance. Having a horn that could provide gain to amplify the lower notes would be a challenge though. One was is to coil the horn up much like the Cornu.
So, I think a neat experiment would be to take a Cornu BLH speaker and replace the driver with a custom bridge-coupled diaphragm. One would attach the neck/fretboard to the face of the Cornu. The Cornu is compact, lightweight, and has double length horns to help smooth the response. One could make a double layer Cornu and have 4 different length horns. I think a good diaphragm for this experiment would be to take an existing driver with a stiff suspension and mount the bridge to the cone. The outputs of the voicecoil would double as the pickup out for an amp! With a little photoshopping you can see what I mean... 🙂
The Cornu speaker has perhaps one of the largest horn expansion ratios of any BLH speaker (about 25:1) which gives it about +10 to +12dB of gain.
This would actually look kind of cool and be a total conversation piece.
The double layer Cornu looks like this before the guitar adaptation (which by the way appears to be foam core channel construction and for a Lowther - and whoever did this never posted or discussed it on the Cornu thread):
An externally hosted image should be here but it was not working when we last tested it.
Given that the acceptable passband is 82Hz for the lowest notes, this is a very reasonably sized Cornu speaker of approximately 20 in x 20 in x 3 in deep. If you made it double layer then it could be 6 in deep to give it the holdability and feel of a regular guitar body.
Attachments
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The bridge could be attached to a small diaphragm situated in a chamber much like a compression driver connected to a horn. The vibrations are small in amplitude but the force is substantial owning to the compression the strings under tension apply. A regular guitar or violin in fact uses the bridge and sound board to effect amplification via cavity resonance. Having a horn that could provide gain to amplify the lower notes would be a challenge though. One was is to coil the horn up much like the Cornu.
So, I think a neat experiment would be to take a Cornu BLH speaker and replace the driver with a custom bridge-coupled diaphragm. One would attach the neck/fretboard to the face of the Cornu. The Cornu is compact, lightweight, and has double length horns to help smooth the response. One could make a double layer Cornu and have 4 different length horns. I think a good diaphragm for this experiment would be to take an existing driver with a stiff suspension and mount the bridge to the cone. The outputs of the voicecoil would double as the pickup out for an amp! With a little photoshopping you can see what I mean... 🙂
The Cornu speaker has perhaps one of the largest horn expansion ratios of any BLH speaker (about 25:1) which gives it about +10 to +12dB of gain.
This would actually look kind of cool and be a total conversation piece.
The double layer Cornu looks like this before the guitar adaptation (which by the way appears to be foam core channel construction and for a Lowther - and whoever did this never posted or discussed it on the Cornu thread):
An externally hosted image should be here but it was not working when we last tested it.
Given that the acceptable passband is 82Hz for the lowest notes, this is a very reasonably sized Cornu speaker of approximately 20 in x 20 in x 3 in deep. If you made it double layer then it could be 6 in deep to give it the holdability and feel of a regular guitar body.
LOVE IT! good starting point. 20inchs x 20 inchs is smaller then some of the guitars i've played, especially when it comes to acoustic basses, and only 3 inchs wider then my acoustic guitar! also, being a spiral inside, there is no reason it couldnt be a round shape instead of square, yes? or am i missing something? i take it the only reason they use a square design is for practicality? so that it can stand by itself and perhaps have a bit more strength?
well as i said, i am getting quite nifty with fiberglass, so i would most likely build the backing out of fiberglass, and have a nice timber facade on the front that that fiberglass horn spiral bolts to on the back. all i would do is get a big slab of wax, carve it to shape, and laminate fiberglass directly onto the wax. then i simply remove the wax or melt it out if its being difficult. so i could get all sorts of interesting shapes.
my knowledge of horns is limited (thus why i'm on here, i've never actually built or designed one) is there an advantage to narrowing the pass band per horn or should i simply have one large horn to guide all wave lengths? from an efficiency point of view? other then complexity of construction, are there any other problems with doing it like that?
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It can be made round but you will lose a little bit of the mouth expansion at the end which is where most of it is. One could oversize the horn to say a 26 or 27 in scale and trim the corner to round it and end up with effectively a 20 or 22 inch one.
Here is the plan for the channel to give you an idea. This is the full size 75cm version.
You could construct it with foam core for the channels which is the preferred route for ease of assembly. Then if you like fiberglass add a layer over the foam core like a surfboard. Cap with a nice spruce or mahogany top like a real guitar. The top piece will need to be bicker and strong to hold she freeboard and string tensioning device.
The diaphragm is where the hard work is. How to design one that efficiently couples the at ring vibration energy to drive the horns.
Can you post photos of your custom guitar with diaphragms that have carbon fiber bracing? I am thinking the design you have may be the way to go as the carbon fiber bracing is used to control the stiffness of the suspension and the silicone surround is just for the seal. I think a 5 in pro audio midrange driver with a fairly stuff suspension can be used - additional carbon fiber struts can be glued to the back of the cone and attached to the main board to adjust the stiffness.
Here is the plan for the channel to give you an idea. This is the full size 75cm version.
You could construct it with foam core for the channels which is the preferred route for ease of assembly. Then if you like fiberglass add a layer over the foam core like a surfboard. Cap with a nice spruce or mahogany top like a real guitar. The top piece will need to be bicker and strong to hold she freeboard and string tensioning device.
The diaphragm is where the hard work is. How to design one that efficiently couples the at ring vibration energy to drive the horns.
Can you post photos of your custom guitar with diaphragms that have carbon fiber bracing? I am thinking the design you have may be the way to go as the carbon fiber bracing is used to control the stiffness of the suspension and the silicone surround is just for the seal. I think a 5 in pro audio midrange driver with a fairly stuff suspension can be used - additional carbon fiber struts can be glued to the back of the cone and attached to the main board to adjust the stiffness.
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well, a dobro seems about halfway there,
maybe front-loaded horn,
with sealed glove reaching in from the outside to play,
like they use at the CDC?
Dobro
CDC | Public Health Preparedness Report - Public Health Laboratories (scroll to bottom)
or maybe a banjo with a back-loaded horn,
if you can accept the sonic compromises of a tightly-constricted, oblique throat?
might take the weight off your hands if it reaches the floor--
but I'd be more concerned about the psychological effects of playing the beast regularly
maybe front-loaded horn,
with sealed glove reaching in from the outside to play,
like they use at the CDC?
Dobro
CDC | Public Health Preparedness Report - Public Health Laboratories (scroll to bottom)
or maybe a banjo with a back-loaded horn,
if you can accept the sonic compromises of a tightly-constricted, oblique throat?
might take the weight off your hands if it reaches the floor--
but I'd be more concerned about the psychological effects of playing the beast regularly
it would be fun to try such a thing whether the outcome is great or not - my 1926 Orthophonic Victrola can sound great. There would need to be a workable diaphragm under the bridge to drive the throat. (or cheat with a fullrange speaker, magnetic pickup and concealed class D amp)
for non-horn, this technique from 1951 works well enough - just make sure to brace the upper bout region well 😀
for non-horn, this technique from 1951 works well enough - just make sure to brace the upper bout region well 😀
An externally hosted image should be here but it was not working when we last tested it.
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Stroh Cigarbox Guitar? - Cigar Box Nation
there should be some cheap acoustic phonograph reproducers on Ebay for those who wish to experiment with higher pitched instruments
http://api.ning.com/files/tBB6ozbRv...wWSJHZSHkA7*/photo44.JPG?width=640&height=478
the soundbox on the Stroh violin below must be similar to acoustic phonographs of its day - I first saw a Stroh on the original Gong Show - sounded very good
http://upload.wikimedia.org/wikipedia/commons/d/d4/Violon_de_jazz_a_pavillon.JPG
there should be some cheap acoustic phonograph reproducers on Ebay for those who wish to experiment with higher pitched instruments
http://api.ning.com/files/tBB6ozbRv...wWSJHZSHkA7*/photo44.JPG?width=640&height=478
the soundbox on the Stroh violin below must be similar to acoustic phonographs of its day - I first saw a Stroh on the original Gong Show - sounded very good
http://upload.wikimedia.org/wikipedia/commons/d/d4/Violon_de_jazz_a_pavillon.JPG
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Geez, sreten and I agree on something!
Mark this day down! 😀 😀
the big big problem is that the mouth size can never be large enough, so you can't make it work properly as a horn... horns have been around for a long time, as have stringed instruments. Just about every imaginable variation has been tried already. If there was a good one, we'd see examples of the idea, even if the implementation might be improved by things like carbon fiber moulding.
Perhaps a piccolo uke or mandolin might be built to the size of a dreadnaught guitar and made to function... perhaps.
Otoh, if you make it work, that would be something alright.
Mark this day down! 😀 😀
the big big problem is that the mouth size can never be large enough, so you can't make it work properly as a horn... horns have been around for a long time, as have stringed instruments. Just about every imaginable variation has been tried already. If there was a good one, we'd see examples of the idea, even if the implementation might be improved by things like carbon fiber moulding.
Perhaps a piccolo uke or mandolin might be built to the size of a dreadnaught guitar and made to function... perhaps.
Otoh, if you make it work, that would be something alright.
It is an engineering exercise. There is no reason why it can't work based on fact that a guitar or violin makes enough sound as a box resonator - a horn can only help. Think about how much vibration is required to make quite a loud sound in a woodwind like an oboe. Tiny reeds flapping ever so slightly. Think about how much energy a horsehair now imparts on a string as it is drawn across and that vibration is amplified by the bridge and sound board on a violin. Is take the same level of mechanical energy and transfer it to a diaphragm and then couple that to a compact horn. I know the Cornu horn works very well for taking a small vibration and amplifying it loudly. I don't understand all the negativity and naysaying. You haven't seen it simply because no one has tried to couple a guitar to a Cornu. Lest we forget the Victor gramophone where mechanical motion of a spinning plastic disc (or wax or clay) with grooves that vibrate a stylus coupled to a diaphragm and a horn is enough to play music for a room full of people. The OP will show all the naysayers that this can be done. As I said it is merely engineering from here on out. The physics are there and the size and form factor are there.
A couple of "marginal" postings have been removed. Don't let this thread turn into something where points have to be handed out.
It would be nice if it could fit on a regular human lap and has the correct rake, reach and neck width to be able to be used by players of various shapes and sizes. Should ideally be human body friendly and somewhat portable....
Efficiency is great and so is tone, but most of the sound of the guitar is in the player's hands. I am reminded of this every time I pick up a great guitar, they all sound lousy because of my playing.
Anywho, subscribed. Sounds like a fun project no matter which way it goes.
I'll throw my hat in the ring and ask to examine the B&W Nautilus spiral, it's somewhat similar to the shape of the guitar if not the dimension, so the lower bout could go across the thigh. Also IMO one big component tone is the harmonics coming out of sympathetic vibration between strings on a flattop, so not sure about the individual apertures for individual strings...
Efficiency is great and so is tone, but most of the sound of the guitar is in the player's hands. I am reminded of this every time I pick up a great guitar, they all sound lousy because of my playing.
Anywho, subscribed. Sounds like a fun project no matter which way it goes.
I'll throw my hat in the ring and ask to examine the B&W Nautilus spiral, it's somewhat similar to the shape of the guitar if not the dimension, so the lower bout could go across the thigh. Also IMO one big component tone is the harmonics coming out of sympathetic vibration between strings on a flattop, so not sure about the individual apertures for individual strings...
Thanks for the tip to the Dobro and resonator guitars. You are right that is halfway there but not sure why the reference to the CDC glovebox on the front? It would simply work like a BLH with the sound coming partially out of the front of the Dobro cone or "biscuit" as it is called and the sound out of the back of the cone would go into a horn rather than the guitar body. If you look at pictures of the inside of the Dobro the back side has a driver chamber and little throat holes. So I agree that however they did the bridge coupling to a diaphragm in the resonator guitar is a great start. The cone is rather large in diameter and that is to effect the good HF as the direct radiator. Getting. Such a large diaphragm coupled to a manageable sized Cornu will be a challenge. If the biscuit were made smaller it would depend in the horn gain to produce all freq via horn amplification and felt less on direct radiator emission.
Romanian Horn Violin a Kindred Spirit - Cigar Box Nation
https://www.youtube.com/watch?v=mHZenlzydG8
http://youtu.be/S6bNKmjw2Fk
http://youtu.be/eMYm2zHfUms
here are new Stroh violin replicas at a very reasonable price http://strohviolin.com/index.php?act=viewProd&productId=8
https://www.youtube.com/watch?v=mHZenlzydG8
http://youtu.be/S6bNKmjw2Fk
http://youtu.be/eMYm2zHfUms
here are new Stroh violin replicas at a very reasonable price http://strohviolin.com/index.php?act=viewProd&productId=8
An externally hosted image should be here but it was not working when we last tested it.
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Freddi,
Thanks for the links. I see that there is no reason why a Cornu horn cannot be as good as a gramophone horn attached to the Strohcello. It sounds quite nice and the low notes seemed especially powerful. I hunk it is clear that this concept can work and that the Cornu horn will allow a flatter more compact horn than a huge metal bell hanging off the side of the body.
The photo of the Stroh violin with two different size horns confirms the same approach that the Cornu would use to have two length horns.
It appears that a bellows type metal (probably steel) diaphragm is the preferred cone material for the Dobro and the Stroh. Start there and attach Cornu horn.
Thanks for the links. I see that there is no reason why a Cornu horn cannot be as good as a gramophone horn attached to the Strohcello. It sounds quite nice and the low notes seemed especially powerful. I hunk it is clear that this concept can work and that the Cornu horn will allow a flatter more compact horn than a huge metal bell hanging off the side of the body.
The photo of the Stroh violin with two different size horns confirms the same approach that the Cornu would use to have two length horns.
It appears that a bellows type metal (probably steel) diaphragm is the preferred cone material for the Dobro and the Stroh. Start there and attach Cornu horn.
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The Cornu throat and compression chamber are much too big. A vibrating string has only a tiny fraction of the amount of energy as the electric motor of a dynamic driver. If strings are attached to a diaphragm in the design as is, it's basically going to flap around and the horn won't do anything.
That being so, the throat and chamber will need to be made much smaller. Perhaps the inner spiral could be extended. I would recommend looking at both Stroh fiddles (etc) and acoustic gramophones for the 'driver' design. Later gramophones used aluminum diaphragms that were actuated by a lever. You might look at 're-purposing' a blown midrange compression driver.
As has been pointed out, there's basically no way to get the full bass range of an acoustic guitar with a full size horn. It would be prudent to expect to settle for a midrange only instrument.
BTW, my other hobby is instrument building, and I've built dozens of experimental instruments and guitars, so I'm not just flapping my mouth off here...
That being so, the throat and chamber will need to be made much smaller. Perhaps the inner spiral could be extended. I would recommend looking at both Stroh fiddles (etc) and acoustic gramophones for the 'driver' design. Later gramophones used aluminum diaphragms that were actuated by a lever. You might look at 're-purposing' a blown midrange compression driver.
As has been pointed out, there's basically no way to get the full bass range of an acoustic guitar with a full size horn. It would be prudent to expect to settle for a midrange only instrument.
BTW, my other hobby is instrument building, and I've built dozens of experimental instruments and guitars, so I'm not just flapping my mouth off here...