Folded Horn Acoustic Guitar Patent # 10,777,172

Most speaker drivers need something predictable to push against. In the simplest design, that's a sealed volume of air that's compressible by the rear of the speaker cone. More complex are the tuned enclosure types, where what the driver "feels" as push-back is frequency dependent.

I know it's desirable to have sound come out the hole in front of an acoustic guitar replica. I know anyone would want that in addition to the waveguide output. But I think it's going to be a tough row to get both.

If it were my work, I'd definitely start with the chamber behind the two drivers sealed. To determine the optimum volume, I'm sure it's just the first principles of speaker design along with the parameters of your chosen drivers. Then I would sacrifice - if necessary - those available chamber spaces (the two between the neck and the main speaker chamber) to achieve it. Perhaps the volume still works out even when filled with amplifier circuitry and batteries.

This will give the system more power handling capability than with the driver rear chamber open to the space between the two plates and sound hole. Also help quite a bit regarding feedback from the amplified system into the string sound pickup...obviously.

Since there is still a space between the guitar top and inner waveguide cover, the top will still be a membrane-o-phone like any ordinary acoustic. Sound would then come out the sound hole in the ordinary way. Since the horns go deep as you say, it's probably OK if the sound hole only produces treble tones, as it would due to the comparatively minuscule volume inside between the plates, vs and ordinary acoustic. Which might work out.

I'd run these ideas past the guitar building class instructor if you can get his time to talk about it. He should know something about how the thin acoustic section would work out.
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
Thank you JJ!. I can easily seal the the space behind the speaker, in fact I have a chamber divider that does not have an opening. When tested it sounded kind of muffled, but of course that was not with the complete guitar, so I will def keep it is an option and test with the real thing. One of the reasons I went with thick walls is that I want to screw the chamber divider on top of the waveguides, and also screw the soundboard on top of the side walls. This way I can easily disassemble and test, would be difficult with glue, but not impossible.

Since the guitar is so large, and the top chamber is 2" thick, it is almost exactly the same volume as a Martin Custom X Series guitar (approx. 700 sq. inches), so it is a full guitar even without the waveguides and electronics. I will get sound from both, but of course more from the waveguides. Also just because it is 4X louder does not mean I want to play it that loud, I usually find my self playing on about 7, not 10, very clean, rich sound. That said, if I want to get closer to an electric guitar, I can max the gain and also tone controls on the amp and piezo preamp and really rock it, many options, sometimes distortion is desired!

I have a soundboard with a hole, and one without a hole, so I can test different combinations. Thanks much for the help, keep it coming, and keep rocking! Joe
 
I guarantee the distortion is reduced.
You are comparing low frequency output potential, not harmonic distortion.
The louder the volume, the easier you can play, the less distortion.
Louder volume is not indicative of less harmonic distortion, guitar amps are typically designed to distort more at higher volume.
Buzzing strings from playing "too hard" is not distortion in a measurable sense.
 
Joe,

Your patent lists the speakers used as the Tectonic Elements TEBM406C20N-4B, I think that is a typographic error, the # is the TEBM46C20N-4B, or at least that's the one I find the specs for on line.

Your "Folded Horn Acoustic Guitar" can be modeled as a sixth order parallel band pass enclosure.
Although this alignment is a series of low frequency dips and peaks that average to around +6dB over a simple ported cabinet, above 1000Hz or so, the band pass attenuation drops level below the direct radiator.
Joes' BP6 approximation.png

Ported 25L.png


Though the sixth order parallel band pass is considerably louder, sometimes the "sounds like ****" phrase says it all. :cool:

Art
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
Art - wow, you really did read it! Good catch, there is a digit missing, never saw that, what do you think of the speakers? Also the sounds like **** is something I am trying to avoid of course, don't want anybody to misinterpret this. Playing an acoustic guitar too hard is something that happens often, because other instruments drown it out, and sometimes people just want to rock, even though they are not playing an electric guitar, for whatever reason. This allows people to play with less force, and get more volume, much more room to set the tone where it is desired and stay clean.

I see dB is about 108 max, sounds about right. What do you think of the dB min/max over the frequency range, and any other comments are welcome. Thanks so much for modeling this! Joe
 
What do you think of the dB min/max over the frequency range, and any other comments are welcome. Thanks so much for modeling this!
The TEBM46C20N-4B simulations are not at all exact to your design, but show the difference between using the drivers front loaded compared to the way you have employed them.
Looks like your sixth order parallel band pass may "sound like ****" ;)
That said, the acoustic guitar sound may fill in some of the holes, and you are making a sound producer, not reproducer, guitar players often like the sound of phase shifters...

Cheers,
Art
 
So, I have owned a couple-few Gibson guitars and one of the remarkable aspects is when you tune the instrument to standard pitch, it "becomes alive"; this was noted on an acoustic and a SG, both of which I kick myself for not still having today.

Those combs in the acoustic response. If Gibson could do it (without a computer simulator), perhaps you can too! Unfortunately, I have no idea how they did it, what with SG meaning solid guitar, but they did and the effect was obvious. A hunk of wood with a long stressed member attached that happens to resonate in harmonics of standard pitch notes!

What I'm talking about is if each of those comb points corresponded to a musical note at standard pitch, maybe that wouldnt be a bad thing after all for a sound-producer. Maybe even two different horn lengths within the body, for more comb points covering more notes.

Now - if you believe me - get to work on those subsequent patents :) And everything else.
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
I believe you! I still say this guitar is doing things that I can not communicate well, or model well. The entire body resonating like I have never felt before has to be a very good sign of music to come, especially when I am still playing a guitar thru a guitar. When they are together, and the tone controls are in a favorable position, it has quit the potential for big rich acoustic sound. I am still in the wondering stage concerning the big flexible Birch soundboard, not sure why it would not be loud with all that vibration/movement, plus Birch should add an interesting tone. Can't wait for the Chicago School of Guitar Making next month! The second related patent (Acoustic Waveguide Guitar) has been accepted and is being reviewed by the Patent Office now, takes forever for them to grant, they are busy. Buy the way I have a third patent I have not mentioned yet, does not relate to this product, but it is a guitar (actually I could combine them, but not sure it is practical). It is U.S. Patent # 11,232,770 Floating Soundboard Acoustic Guitar. It is 100% acoustic, no electronics, not sure how well it will work. was granted earlier this year (attached). Thanks! Joe
 

Attachments

  • Katzenberger Floating Soundboard Acoustic Guitar Patent # 11,232,770.pdf
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It is U.S. Patent # 11,232,770 Floating Soundboard Acoustic Guitar. It is 100% acoustic, no electronics, not sure how well it will work. was granted earlier this year (attached). Thanks! Joe
It will work exactly the opposite as you propose in the patent.
The 29 bolts, rubber grommets and 58 nuts will add considerable weight and dampen the sound board, reducing it's sound output level. The isolation from the guitar body will reduce resonance, further attenuating the sound produced compared to a standard instrument.

One only has to listen to the reduction in sound rubber motor mounts provide to hear how vibration suppression reduces both direct and transmitted sound, or how drum dampening gell absorbs energy each time a drum is hit, reducing resonance and overtones.
 
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Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
This patent is an experiment, I almost abandoned it. I did not put much work into it, as you can see it is the same guitar but with a Floating Soundboard and components. If it fails, I don't care, but is still certainly worth a try. I agree and understand there will be no resonance transferred to the body, and the soundboard will be dampened, but it will be very free to move a great amount compared to a standard guitar soundboard. The strings and bridge force the soundboard to vibrate of course, and the soundboard is not attached on the sides, so it is free to move very easily, and create large amounts of SPL due to its size, and the amount it is free to move, like a speaker. The rubber is not hard rubber like an engine mount, but very light and soft rubber, that moves very easily. Plus I am considering plastic bolts (material not specified), they don't need to offset much force, and very light. Drum dampening gel is used on a drum that is still attached on the sides, a double whammy, no float.

Similar in some ways to a resonator guitar, but a resonator is still attached, and does not move much. Do I like to play a slide on a resonator and get a cool but very tinny sound, sure. Would I want to do this more than 3 or 4 times a year, nope, the tone is "an acquired taste".

There are examples of newer floating soundboards on YouTube, one in particular I thought was very cool. Hard to judge the sound through laptop speakers.
All of these are tied to the sides, and are not free to move that much. Mine moves in the "Z" direction, nothing to stop it other than very light rubber and the force of the string/bridge vibration (constant change of direction). I believe the force of the strings is about 175 lbs. You can move a light sound board with that kind of force very easily. These guys never got a Patent, I searched. I have the 20 Year Utility Patent, granted earlier this year.

When you write your own and don't use a Patent Attorney, it only costs $900 and your time, much easier to get many and see what hits. Only 10% are successful, but that is not going to stop me from trying. Get creative, get innovative, fail, learn, have balls, enjoy inventing and design. Sometimes crazy ideas actually go somewhere though unintentional means. Let's Rock!
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
I did a sand movement vibration analysis, pretty crude, but telling. I could not get good pictures due to being Blond on Blonde :cool: See attached and let me know what you think please Art, JJ and all. Horns and speakers do not surprise me, matched dB levels, but most extreme turns? I think I may have some problems there, which can be fixed, what do you think? Thanks! Joe
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
JJ - I just put the 1/4" chamber divider with a hole over the speakers on the folded horns, then thought about your suggestion, and put the other chamber divider on top of that, the one without a hole, and the tone was better than I ever heard! I think you are correct, back of speakers need to be closed, but why two chamber dividers (1/2" thick total) sounds better, I do not know, but I like it!
 

Joe K

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2021-08-14 12:12 am
Indianapolis, IN.
I had a big musical moment today, and I have JJ and Art to thank for that:

JJ suggested that I need to close the back of the speaker area. Wow, I tried that before and had some results that I thought were not great, but totally my mistake. I think I had the tone settings wrong at the time. At this point in the project, the more I stop thinking like a mechanical engineer and design engineer, and start thinking like an Audiophile (which I am not, but learning), the better things get. JJ made me realize having the opening through the chamber divider was like having a speaker cabinet with the back off, bad idea! I decided the chamber divider with 1/4" thick Baltic Birch was not stiff enough, given its large size. I glued two together, made them 1/2" thick, closed the back, and put a small port in it (calculated from some old JBL speakers, same ratio), and wow the distortion went way way down (the chamber divider is also the back of the speaker cabinet).

I already had the volume increase by 20 dB, great!
I already had the bass go through the roof with two five feet long folded horns (captures 1/4 wavelength of about 80 Hz), great!

I just did not have a good feeling about the tone. It did not sound like ****, but it just was not good enough.
When I covered the back, it was very clear to me the speakers now had the air pressure to work like speakers in a cabinet. It was also very clear to me they stopped driving too hard, speaker excursion was distorting the sound, and preventing me to do anything without thinking it sounds like something close to ****! A little reverb, much master, not too much gain, low bass due to horns providing this, not too much mid/high, preamp maxed out...

When that happened I started playing an old favorite song that is blues/jazz, many 7th and 9th chords up and down the fretboard. When I did it before it sounded OK, when I did it today, I was absolutely stunned at how good it sounded! It amazes me how such a "small" change can have such a large affect on the sound, wow! Maybe Art can model this again with these changes? 🙏

I know I can't play like Wes Montgomery, but this is the type of sound I am looking for. Not just an acoustic guitar sound, but also a sound that resembles a big Gibson hollow body electric sound, I think it is possible, blows me away!

Also need to consider potting the piezo, the guitar did not feedback when playing, but if you leave you hands off it, and try your best to get it too feedback, it will. I am pretty sure a mic just can't be used in this situation, it would be a feedback machine. 🔊

I must say the speakers I found online from Art back in the day are pretty stunning, above 1000 watts!! (see attachment). Wow, you are in a different league my friend! I can't remember the calcs, but I think at about 60 Hz your folded horns needed to be 6-1/2" feet to capture 1/4 wavelength, and yours are 7 feet or more, sweet! This is the type of speaker I have been trying to put in my guitar. Can I do it, no! But I sure can use it as a scaled down target. I just don't have the room for all the gradual horn taper, so more like a waveguide, but the guitar works, the damn thing works! Let's rock! Joe
 

Attachments

  • Art Welter Sub Woofer With Folded Horn.pdf
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a sound that resembles a big Gibson hollow body electric sound
One would think magnetic pickups and steel strings would go a long way to getting that. Then you could make - er sandwhich within - a thin steel plate in the divider board, to shield any magnetic fields coming off those speakers, in being so close to the pickups. Of course, this plate would be electrically grounded to the guitar cord shield.