Joe,
An acoustic instrument's undertone or overtone content provides it's timbre.
A loudspeaker's undertones or overtones are harmonic distortion.
Your "data" is a combination of the above along with room resonances and who knows what else.
Art
An acoustic instrument's undertone or overtone content provides it's timbre.
A loudspeaker's undertones or overtones are harmonic distortion.
Your "data" is a combination of the above along with room resonances and who knows what else.
Art
It's summer and a perfect time for outdoor testing, if you have a back yard. A 1 meter distance to the mic should obscure any background noise; put some pink through it (not Floyd...) and crank it up just shy of alerting the neighbors, who might notice Niagara Falls's sound appearing out of nowhere.
If you have a HiFi speaker - some of which have a notable flat frequency response - you can use that to reference your test setup. Sometimes I find "singles" in thrift stores and the like; I'm reminded they're useful to keep on hand if they have a nice flat response. A small Boston, Polk or Cambridge Audio speaker has a good chance at providing this.
I'd even say given what you're doing, this type of testing is something to get used to. Do it enough times and you can tell by ear if a speaker is "working right" at the least, if it's a good one at the most. These days, with things like a portable pink noise generator / amplifier (made from a SD card audio file reading ebay / alibaba amp and a 5V cell phone battery based recharger as a power supply) along with a spectrum analyzer app on your phone, or laptop with REW and mic, it's maybe 20 minutes to setup, test and teardown. No excuses are valid.
There will be times to come when you'll make some change (Driver, back cavity volume, horn length, driver coupling aperture, cavity damping material, crossover capacitor, etc) and want to know the results of that change - quantitatively - in a hurry.
If you have a HiFi speaker - some of which have a notable flat frequency response - you can use that to reference your test setup. Sometimes I find "singles" in thrift stores and the like; I'm reminded they're useful to keep on hand if they have a nice flat response. A small Boston, Polk or Cambridge Audio speaker has a good chance at providing this.
I'd even say given what you're doing, this type of testing is something to get used to. Do it enough times and you can tell by ear if a speaker is "working right" at the least, if it's a good one at the most. These days, with things like a portable pink noise generator / amplifier (made from a SD card audio file reading ebay / alibaba amp and a 5V cell phone battery based recharger as a power supply) along with a spectrum analyzer app on your phone, or laptop with REW and mic, it's maybe 20 minutes to setup, test and teardown. No excuses are valid.
There will be times to come when you'll make some change (Driver, back cavity volume, horn length, driver coupling aperture, cavity damping material, crossover capacitor, etc) and want to know the results of that change - quantitatively - in a hurry.
Holy **** JJ, how much time do you think I have? 🤣 I do like the idea of outdoor testing. I have a nice backyard to test in, but I live in town and my next door neighbor is close. Not that I ever think of that when I am playing guitar on the front porch, I try to be respectful. I am doing some testing tonight, hope to post later, stay tuned!
Hello all - check out "Another Man Down" by Heartsfield, this song has it all. Rocking song, great harmonies, great guitars, driving bass, even horns, so well mixed. I dare you not to love it!
Art - this thread is much more interesting when you are contributing.
I think my "data" is actually data. I mean if you look at the FR map as a world map, the bass increase looks like the size of China. The low end increase is shown clearly. I only accept data as truth when I validate it with my ears. I hear it. If it sounds good, it is good!
Now you make a good point about the room, but an acoustic guitar must put up with every room, that is the nature of it, must travel.
I think the "who knows what else" is valid, but I was very careful to record late at night, no low bass from trucks, furnaces...the undertones are real, I can hear them. Any other ideas about how this bass might record strong?
I ripped the chamber divider out of my guitar, put the soundboard back on, and played with the horns open. The volume and bass acoustically came right back, what a relief. I thought maybe it was not the 2" thick chamber, but maybe my guitar build sucked, thankfully was not the case.
Now the resonance on this chamber with the horns is complex, and crazy good/bad, just an experiment. Every time I hit a certain note (I think it was fourth string, fifth fret), the sound went crazy. Obviously a sympathetic vibration (or pathetic), sounded horrible. I mean a real quack, almost like acoustic feedback. Horrible and very interesting at the same time!
Then I put the chamber divider back on, but cut the two areas out where the amp will go, sounds great! The only problem is, will it sound OK with the amp inside, or should I just leave it external, as JJ suggests? Great to have options that work.
I played only acoustically tonight, very happy with the sound. Again, is it a Martin quality guitar? Hell no, it is my first build, but getting there.
When I hook up the electronics tomorrow night it will rock even better, Stay tuned!
Art - this thread is much more interesting when you are contributing.
I think my "data" is actually data. I mean if you look at the FR map as a world map, the bass increase looks like the size of China. The low end increase is shown clearly. I only accept data as truth when I validate it with my ears. I hear it. If it sounds good, it is good!
Now you make a good point about the room, but an acoustic guitar must put up with every room, that is the nature of it, must travel.
I think the "who knows what else" is valid, but I was very careful to record late at night, no low bass from trucks, furnaces...the undertones are real, I can hear them. Any other ideas about how this bass might record strong?
I ripped the chamber divider out of my guitar, put the soundboard back on, and played with the horns open. The volume and bass acoustically came right back, what a relief. I thought maybe it was not the 2" thick chamber, but maybe my guitar build sucked, thankfully was not the case.
Now the resonance on this chamber with the horns is complex, and crazy good/bad, just an experiment. Every time I hit a certain note (I think it was fourth string, fifth fret), the sound went crazy. Obviously a sympathetic vibration (or pathetic), sounded horrible. I mean a real quack, almost like acoustic feedback. Horrible and very interesting at the same time!
Then I put the chamber divider back on, but cut the two areas out where the amp will go, sounds great! The only problem is, will it sound OK with the amp inside, or should I just leave it external, as JJ suggests? Great to have options that work.
I played only acoustically tonight, very happy with the sound. Again, is it a Martin quality guitar? Hell no, it is my first build, but getting there.
When I hook up the electronics tomorrow night it will rock even better, Stay tuned!
If you were near me, I'd be round to yours like a shot, with my measuring mic and SW.
Running test tones and getting frequency amplitude etc plots for you, just for the fun of it🙂
Little thing called the Atlantic between us😂
My experience would be that regular acoustic guitars are pretty quiet and won't come anywhere near volume to load a room and excite room modes.
Amp that up with PA volumes and you might start to experience.
Larger venues and outside wouldn't be a problem.
There are room mode calculators. You put the size of your room in and get the typical frequency summations and cancellations.
Room modes are most a problem in certain sized rooms, where wavelengths are long at deep bass frequencies.
I have a huge one at 30Hz for example. DSP is my friend.
Won't be a problem for amped acoustic for those frequencies though 🙂
Might get screechy and overloading in the mid frequencies, female vocal is a common one.
Running test tones and getting frequency amplitude etc plots for you, just for the fun of it🙂
Little thing called the Atlantic between us😂
My experience would be that regular acoustic guitars are pretty quiet and won't come anywhere near volume to load a room and excite room modes.
Amp that up with PA volumes and you might start to experience.
Larger venues and outside wouldn't be a problem.
There are room mode calculators. You put the size of your room in and get the typical frequency summations and cancellations.
Room modes are most a problem in certain sized rooms, where wavelengths are long at deep bass frequencies.
I have a huge one at 30Hz for example. DSP is my friend.
Won't be a problem for amped acoustic for those frequencies though 🙂
Might get screechy and overloading in the mid frequencies, female vocal is a common one.
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Thank you Steve, can you post some pictures of those beautiful horns here? The horns (waveguides) in my guitar really make this guitar rock, they work better than I expected. I liked horns before, now I am a horn lover.
I have never tried the room mode calculators, adding it to my list, sounds fun.
Although I love the natural acoustic sound, I need to move beyond that thinking, and use a DSP...just need to fit inside my guitar. The amp outside the guitar idea is sounding better all the time, because once I cross that bridge, I can add all kinds of great devices, and stop worrying about packaging it inside the guitar, I am still on the fence.
I now have 25,000 hits, just like to follow that for fun, still pretty consistent.
I played my guitar again this morning with acoustics only, just to make sure I was not talking myself into anything last night, there were a few beers involved.
Man does it sound great, I am so thrilled. That 2" chamber divider space just did not cut it, having more volume in the chamber is everything. The two added chamber spaces are actually 5" deep and right below the sound hole, really did the trick.
I am attaching my PPT info just in case you do not see it before. Don't forget to turn your friends on to Heartsfield, Art did the sound for them for many years, what a great band. All their music is on iTunes. Note sure if they are popular in Sweden, so you are in the enviable position to hear them for the first time. Rock them through your horns, and let us know how it sounds please! I see you are on the Baltic Sea, beautiful I am sure!
Tonight I rock with the electronics after my wife goes to bed, can't wait!
I have never tried the room mode calculators, adding it to my list, sounds fun.
Although I love the natural acoustic sound, I need to move beyond that thinking, and use a DSP...just need to fit inside my guitar. The amp outside the guitar idea is sounding better all the time, because once I cross that bridge, I can add all kinds of great devices, and stop worrying about packaging it inside the guitar, I am still on the fence.
I now have 25,000 hits, just like to follow that for fun, still pretty consistent.
I played my guitar again this morning with acoustics only, just to make sure I was not talking myself into anything last night, there were a few beers involved.
Man does it sound great, I am so thrilled. That 2" chamber divider space just did not cut it, having more volume in the chamber is everything. The two added chamber spaces are actually 5" deep and right below the sound hole, really did the trick.
I am attaching my PPT info just in case you do not see it before. Don't forget to turn your friends on to Heartsfield, Art did the sound for them for many years, what a great band. All their music is on iTunes. Note sure if they are popular in Sweden, so you are in the enviable position to hear them for the first time. Rock them through your horns, and let us know how it sounds please! I see you are on the Baltic Sea, beautiful I am sure!
Tonight I rock with the electronics after my wife goes to bed, can't wait!
Needless to say, if I wasnt a half a continent away...
Is it possible to reduce the 1/2 thick dimension of the separator board? Like a sheet of the type they use on a traffic stop sigh? That times the large surface area would bring in some more cu in.
I'm really liking my self-powered "fake Transacoustic" guitar, with battery that recharges from a cell phone wall wart. I think once you get an amp in yours, you'll be hooked. If I had the 'nads, I'd post and link a recording with vocals, echoing through the guitar body, for all on social media to slaughter.
My suggestion of an outboard amp was to scoot things along; it's a formidable task to design something like the preamp - DSP effects - BT interface - power amp - battery - recharging circuit module I'm using. Probably took a team of engineers 6 months...for just the electrical, nevermind the mounting and packaging.
It's defective, BTW - someone made a design mistake which is probably why they're dumped on alibaba and the like. The internal mic is supposed to shut off when you plug in an external amp; it only comes on intermittently when the 1/4" plug is removed. Then it goes off again, when it's supposed to be functional. I've found where to make the wire jump to make it work all the time, but not a fix to make it work as intended. No schematics, of course. Plugging in an external amp also cuts off the internal driver.
Is it possible to reduce the 1/2 thick dimension of the separator board? Like a sheet of the type they use on a traffic stop sigh? That times the large surface area would bring in some more cu in.
I'm really liking my self-powered "fake Transacoustic" guitar, with battery that recharges from a cell phone wall wart. I think once you get an amp in yours, you'll be hooked. If I had the 'nads, I'd post and link a recording with vocals, echoing through the guitar body, for all on social media to slaughter.
My suggestion of an outboard amp was to scoot things along; it's a formidable task to design something like the preamp - DSP effects - BT interface - power amp - battery - recharging circuit module I'm using. Probably took a team of engineers 6 months...for just the electrical, nevermind the mounting and packaging.
It's defective, BTW - someone made a design mistake which is probably why they're dumped on alibaba and the like. The internal mic is supposed to shut off when you plug in an external amp; it only comes on intermittently when the 1/4" plug is removed. Then it goes off again, when it's supposed to be functional. I've found where to make the wire jump to make it work all the time, but not a fix to make it work as intended. No schematics, of course. Plugging in an external amp also cuts off the internal driver.
JJ - you are too far, one of these days...
I think I have created a Monster. First test with 5" chamber in two areas, with electronics.
But first, when I play acoustically, really really like it.
Now with improvements, I play amp volume on 3, piezo and mag pickups, holy **** that sounds great, and plenty of power.
Then I turn up to 5, I am like wow, this thing seriously rocks!
Then I turn up to 7 and I can't believe it, way way more power than I ever experienced, tone it up, sounds great! Be careful!
Then I put it on 10 and it squeals like a pig, way way too much power! I might be able play at this volume if nobody is home, and I better never take my fingers off the strings, this guitar turns into an electric guitar that I can not control. Don't play on 10! Let's rock!
I think I have created a Monster. First test with 5" chamber in two areas, with electronics.
But first, when I play acoustically, really really like it.
Now with improvements, I play amp volume on 3, piezo and mag pickups, holy **** that sounds great, and plenty of power.
Then I turn up to 5, I am like wow, this thing seriously rocks!
Then I turn up to 7 and I can't believe it, way way more power than I ever experienced, tone it up, sounds great! Be careful!
Then I put it on 10 and it squeals like a pig, way way too much power! I might be able play at this volume if nobody is home, and I better never take my fingers off the strings, this guitar turns into an electric guitar that I can not control. Don't play on 10! Let's rock!
I just ordered some AAA Sitka Spruce soundboard material and bracing. I will build this to compare with my existing Birch soundboard. Since the guitar is so large, I need to order two sets, and use three of them horizontally instead of the traditional method of two vertically. That is OK, Harp soundboards are built this way. 🤔
Playing my guitar, acoustics only, sooo good, it feels like the neck just found its correct position, after two weeks, the fingerboard is starting to feel right at home in my hands, wow!
Plugged in, WTF! What is that annoying little buzz? Then it got louder, pulled the piezo, that is it.
Played with the mag pickup only, actually pretty good!
But I must have mag and piezo both, that really brings out the tone, with all this power.
Went to piezo only, worse! The damn connector is failing, oh well, **** happens. It actually came apart. Seeing how I have taped this thing on for so long, big surprise, eh?
I have spare, getting late, will install tomorrow, and will buy two more.
It makes me think about sound guys, and how something can go wrong live, it must be an OH **** situation I am sure.
Like Dicky Betts said when I saw him in a small bar, about 10 feet away from his amazing playing when a "technical glitch" happened. That's show business!
Plugged in, WTF! What is that annoying little buzz? Then it got louder, pulled the piezo, that is it.
Played with the mag pickup only, actually pretty good!
But I must have mag and piezo both, that really brings out the tone, with all this power.
Went to piezo only, worse! The damn connector is failing, oh well, **** happens. It actually came apart. Seeing how I have taped this thing on for so long, big surprise, eh?
I have spare, getting late, will install tomorrow, and will buy two more.
It makes me think about sound guys, and how something can go wrong live, it must be an OH **** situation I am sure.
Like Dicky Betts said when I saw him in a small bar, about 10 feet away from his amazing playing when a "technical glitch" happened. That's show business!
I am getting used to the mag pickup only, tone not as good, but I can still jam.
If I put this this mother on 10, feedback bad.
If I put it between 7 and 8, great!
I drop D and play open chords up and down the neck, love it.
Then I let a well strummed D ring out, and this guitar is half way between almost endless sustain (60 seconds, I timed it) and feedback.
I mean WTF, wow! Remember, this is a very light but strong soundboard. I lightly touch it, I can fell the vibration like a damn drum skin, not kidding! And the sustain keeps going, and the possible feedback just fades away.
This guitar is a ******* sonic machine, and I am only getting started, now that the damn thing works. Lets rock, oh lets rock!
If I put this this mother on 10, feedback bad.
If I put it between 7 and 8, great!
I drop D and play open chords up and down the neck, love it.
Then I let a well strummed D ring out, and this guitar is half way between almost endless sustain (60 seconds, I timed it) and feedback.
I mean WTF, wow! Remember, this is a very light but strong soundboard. I lightly touch it, I can fell the vibration like a damn drum skin, not kidding! And the sustain keeps going, and the possible feedback just fades away.
This guitar is a ******* sonic machine, and I am only getting started, now that the damn thing works. Lets rock, oh lets rock!
Hehe, I won't derail this thread with my horns. It's beautifully focused on the guitar / horns.
Here's a link to a few pics of my 5 way horn system though.
https://fosworld.wixsite.com/magna-audio/home
That's pretty ordinary. Remember EVH was soaking his pickups in wax in his early days, in a DIY attempt to reduce uncontrolled feedback from his electric. Which I'd bet was a way to make them respond to only magnetic flux changes from the strings influence in their magnetic field - not mechanical vibrations.
Unsure of your arrangement of the mag pickup. Clamped in place at the soundhole? Freely sticking through a cutout in the top, but physically mounted to the dividing board? My guess would be if it's mounted onto the top, it's going to pickup vibes from the top mechanically; i.e. "microphonic". Mounted onto the dividing board may give a completely different response in regards to feedback. I cant say worse or better; you'll have to try to empirically find the best pickup position / mechanical mounting.
Thanks JJ, yes mounted on the soundboard hole, I will try other locations, like that idea. I agree feedback on 10 is normal, I want it to have enough power to feedback, but only at high volumes, so this is perfect. Turning it down gives it great sustain, which can actually be controlled by how much I do, or do not, touch the soundboard.
Talk about feeling the vibration, this soundboard feels like it is dancing under your fingers, if it is touched slightly, it is doing some great things that I did not even consider.
If this was played from an external amp, it might be hard to control, but since the power is all in the guitar itself, it is completely controllable with my arms and hands, I mean talk about being one with your instrument. This weekend was truly a musical joy for me. The long journey is finally paying off, I have been working on this for years.
Steve - I love your horns, beautiful, I bet they sound fantastic! I really like that you are using Baltic Birch for the material, right in your neighborhood. Keep rocking!
Talk about feeling the vibration, this soundboard feels like it is dancing under your fingers, if it is touched slightly, it is doing some great things that I did not even consider.
If this was played from an external amp, it might be hard to control, but since the power is all in the guitar itself, it is completely controllable with my arms and hands, I mean talk about being one with your instrument. This weekend was truly a musical joy for me. The long journey is finally paying off, I have been working on this for years.
Steve - I love your horns, beautiful, I bet they sound fantastic! I really like that you are using Baltic Birch for the material, right in your neighborhood. Keep rocking!
I cut the chamber divider to include the two top openings in the upper chamber, all the difference, wow. The 2" upper chamber was just not enough. These two 5" deep areas added to the chamber is great!
Then I took the back off of them to see if they would be good ports, NOT, terrible, keep them sealed!
When I play acoustically only, really great!
With electronics, crank up to 7, rocking! 8 even better, 9 do I dare? love it but close to feedback.
10 feedback bad!
Easy to play knowing this, love the power!
My only problem is the second string 8th fret, 370 Hz feeds back every time I hit it, no solution yet!
Must be the new natural frequency of the guitar, any ideas? Let's Rock! Joe
Maybe make this divider Swiss Cheese'd instead of removing entirely. That way the air can circulate through, but the mechanical structure is still (mostly) intact.
Try gluing a connecting wood block to the magnet of each driver, so they push against each other instead of the wood frame. That'll change things, it's anyone's guess if it'll effect the 370 Hz problem.
The EMC engineers in my group once told me about the "sausage effect". Squeeze down on a high radiating part of the frequency spectrum, and the energy just squishes over to another set of frequencies. The problem is when you dump a bunch of energy into a container, it's going to find a way out - some of it in an undesirable form, transforming itself if necessary to do so.
I'll guess there's just no way you can do "10" with a sound hole magnetic pickup mount. Pickup has to be mounted to the most rigid part of the body structure, rather than the relatively "flappy" top.
Try gluing a connecting wood block to the magnet of each driver, so they push against each other instead of the wood frame. That'll change things, it's anyone's guess if it'll effect the 370 Hz problem.
The EMC engineers in my group once told me about the "sausage effect". Squeeze down on a high radiating part of the frequency spectrum, and the energy just squishes over to another set of frequencies. The problem is when you dump a bunch of energy into a container, it's going to find a way out - some of it in an undesirable form, transforming itself if necessary to do so.
I'll guess there's just no way you can do "10" with a sound hole magnetic pickup mount. Pickup has to be mounted to the most rigid part of the body structure, rather than the relatively "flappy" top.
Thank you JJ, I will def try that with the speakers. I hit this note going up and coming back on the fretboard playing Blackbird, highly annoying!
Love the sausage effect, only guys who work with this everyday can come up with such a real world solution.
I also really really like your idea about mounting the mag pickup elsewhere, maybe not on the soundboard itself, but just below it mounted mechanically to the chamber divider?
My soundboard is vibrating like a complete bitch, and I love it, but I know it affects the mag PU as you say. Thank you my friend!
Love the sausage effect, only guys who work with this everyday can come up with such a real world solution.
I also really really like your idea about mounting the mag pickup elsewhere, maybe not on the soundboard itself, but just below it mounted mechanically to the chamber divider?
My soundboard is vibrating like a complete bitch, and I love it, but I know it affects the mag PU as you say. Thank you my friend!
I usually play in my water closet while my wife sleeps, due to many doors and one floor away. It is 8 feet by 6 feet.
Today I jammed in my dining room, which is 12 feet by 18 feet, with 10 feet high ceilings in this old house.
I do not have great knowledge about room acoustics, but I can tell you the difference was tremendous. It filled the room with sound, just different, not sure how to describe it, but much better. My guitar in the small room sounded pretty damn good, would feedback if both piezo and mag pickups were on 8 (not always) or 9 (always).
With my piezo and mag both on 9, no feedback! With my piezo on 10 and mag on 9, still no feedback. With both on 10, squeal!!!
I would never want to play at that level anyway, but a good test.
Any insights on room acoustics that might help me? Would be greatly appreciated.
Man this guitar was rocking today, so happy, just beautiful.
The last time I sent info to about (40) companies, asking them if they might be interested in my guitar, the hope was maybe they could help me build it. Crickets. OK I had 4 out of 40 responses, 10%, expected, but nothing great.
Now I can say I have built this, it works, I have proof, any interest? I will be sending this out soon. What will happen????
I need a professional studio to record me, to post on YouTube, not me fumbling around with my damn iPhone, what a joke, will do it!
Art - I found your Keystone Sub dimensions online, it is in the public domain, but I would like to ask your permission to use this. If not acceptable, I will remove from this sight, see attached and please advise.
I find my horns to be pretty much Juniors of great folded horn speakers, but from a ratio standpoint, they are legit. I just wish I could make the guitar body twice as thick, would be a killer. Then of course it would be larger than a Guitarron played in a Mariachi band, totally unplayable, need to work with realistic dimensions. My guitar now is a joy to hold and play, any larger, it would be toast, can't go there. Let's make the Acoustic Guitar rock!
Today I jammed in my dining room, which is 12 feet by 18 feet, with 10 feet high ceilings in this old house.
I do not have great knowledge about room acoustics, but I can tell you the difference was tremendous. It filled the room with sound, just different, not sure how to describe it, but much better. My guitar in the small room sounded pretty damn good, would feedback if both piezo and mag pickups were on 8 (not always) or 9 (always).
With my piezo and mag both on 9, no feedback! With my piezo on 10 and mag on 9, still no feedback. With both on 10, squeal!!!
I would never want to play at that level anyway, but a good test.
Any insights on room acoustics that might help me? Would be greatly appreciated.
Man this guitar was rocking today, so happy, just beautiful.
The last time I sent info to about (40) companies, asking them if they might be interested in my guitar, the hope was maybe they could help me build it. Crickets. OK I had 4 out of 40 responses, 10%, expected, but nothing great.
Now I can say I have built this, it works, I have proof, any interest? I will be sending this out soon. What will happen????
I need a professional studio to record me, to post on YouTube, not me fumbling around with my damn iPhone, what a joke, will do it!
Art - I found your Keystone Sub dimensions online, it is in the public domain, but I would like to ask your permission to use this. If not acceptable, I will remove from this sight, see attached and please advise.
I find my horns to be pretty much Juniors of great folded horn speakers, but from a ratio standpoint, they are legit. I just wish I could make the guitar body twice as thick, would be a killer. Then of course it would be larger than a Guitarron played in a Mariachi band, totally unplayable, need to work with realistic dimensions. My guitar now is a joy to hold and play, any larger, it would be toast, can't go there. Let's make the Acoustic Guitar rock!
The second string 8th fret, 370 Hz feeds back every time I hit it, no solution yet! Holy God, the rest of the guitar is completely rocking beyond my wildest dreams, and then I hit the 370 Hz, FEEDBACK.
I try it on the third string up higher, same 370 Hz, ouch, ouch! I need to EQ out if possible! Everything else is great, one last struggle!!! Stay tuned!!
I try it on the third string up higher, same 370 Hz, ouch, ouch! I need to EQ out if possible! Everything else is great, one last struggle!!! Stay tuned!!
Joe,
Not sure what you are asking permission to use, but the Keystone Sub is a tapped horn with the driver located in the mouth of the horn, and you have made front loaded horns with a sealed compression chamber roughly 5 feet from the mouth.
Room acoustics have little to do with the guitar's resonant feedback frequency you are experiencing, but a narrow band parametric EQ filter could be used to notch it out.
Not sure what you are asking permission to use, but the Keystone Sub is a tapped horn with the driver located in the mouth of the horn, and you have made front loaded horns with a sealed compression chamber roughly 5 feet from the mouth.
Room acoustics have little to do with the guitar's resonant feedback frequency you are experiencing, but a narrow band parametric EQ filter could be used to notch it out.