I know, I am terrible at doing that. I very much want to, but just not enough hours in the day. Now you have shamed me into doing it tonight! 
I have real dB measurements, that is a start. I have had it on my list for a while, now that I have the sound I want, I have no excuses! Heck a year ago I didn't even know what REW software was...
I have real dB measurements, that is a start. I have had it on my list for a while, now that I have the sound I want, I have no excuses! Heck a year ago I didn't even know what REW software was...Art - I though I posted these before. Just an open E chord being played with and with horns, and also "Stand Back" from my iPhone with and without horns. I just downloaded a new version of REW, and now the sweep icons are active, before some were grayed out, so hopefully I can do sweeps now. As much fun as playing the guitar is, I am a bit of a software geek, as I spend much time with my head in a CAD system, so it will def be fun to learn more about REW. 🔊 🙏
Hello Art - pulled out a connector on my speaker, thankfully I have about a dozen in stock, replaced, OK.
Attached are REW images. dB is 115 max, very powerful!
Let me know about FR, looks somewhat flat to me, and very similar to what I get with a nice Taylor standard acoustic guitar by itself, but louder.
So I am thinking, same FR but at a much higher dB level, good.
OK let me have it, am I missing something?
It is fun to learn REW, but I have a way to go, I know.
Also what about the sweeps? I am totally clueless regrading this. Thank you Art for being my mentor on this project!
Attached are REW images. dB is 115 max, very powerful!
Let me know about FR, looks somewhat flat to me, and very similar to what I get with a nice Taylor standard acoustic guitar by itself, but louder.
So I am thinking, same FR but at a much higher dB level, good.
OK let me have it, am I missing something?
It is fun to learn REW, but I have a way to go, I know.
Also what about the sweeps? I am totally clueless regrading this. Thank you Art for being my mentor on this project!
Why is the mic shown facing the small hole in the middle of the waveguide enclosing sound board? I thought what was best for now is to have the driver rear chamber sealed. You have a whole lifetime ahead to experiment with various "ports" into the upper chamber and / or the back of the guitar. For now to get a grip on what's happening with the two horns, make the chamber sealed - even blocking up the wire exit hole for connecting up the two speakers. There's still the experiment to do with sound absorbent material within that sealed enclosure -
I explained (I think - it's been so long) how to do the BedPlane measurement - put the guitar body at the head of the bed with the horn opening facing the foot of the bed. Place the measurement mic at the foot of the bed facing the horn openings. Take a measurement with REW doing a sweep, providing pink noise - anything that the frequency analyzer can display. Laying bare whatever the FR is now shouldnt be a source of embarrassment and can only lead to a better sounding horn design when finalized!
You can also do the measurement outside; one of Art's posts shows his SynTrip horn with a measurement mic on the ground pointing at it.
One tack with learning REW is to get a small HiFi speaker and measure it in the same way. This way you'll get some confidence in using REW when you can get the measurement to "make sense" against some average two-way HiFi speaker. I have a single small Boston speaker I keep for such purposes; I know what it's supposed to measure like. Is it measuring some insane way now, this time, this setup? Nope! Now I can go ahead with what I really want to look at, which a little confidence I havent made some sophmoric equipment / software application setup mistake...
You might want to get yourself "an amplifier" just for doing speaker measurements. This would be the kind of amplifier that has two RCA inputs, perhaps a volume control and a set of speaker connections - nothing else to do anything but flat frequency response voltage output from input, just to take another variable out of the measurement and the otherwise possible confusion thereafter.
7th and 9th chords, I can play an A7, G7, E7 and a D7 - but I dont know any 9ths. So you're better at guitar than me. I know how to use REW though and it's just a matter of practice with it, in learning how to measure a generic speaker. Like learning 9ths, it's just a matter of learning a few songs with a few of those, then it gets easy and straightforward. REW even easier - no finger dexterity needed!
I explained (I think - it's been so long) how to do the BedPlane measurement - put the guitar body at the head of the bed with the horn opening facing the foot of the bed. Place the measurement mic at the foot of the bed facing the horn openings. Take a measurement with REW doing a sweep, providing pink noise - anything that the frequency analyzer can display. Laying bare whatever the FR is now shouldnt be a source of embarrassment and can only lead to a better sounding horn design when finalized!
You can also do the measurement outside; one of Art's posts shows his SynTrip horn with a measurement mic on the ground pointing at it.
One tack with learning REW is to get a small HiFi speaker and measure it in the same way. This way you'll get some confidence in using REW when you can get the measurement to "make sense" against some average two-way HiFi speaker. I have a single small Boston speaker I keep for such purposes; I know what it's supposed to measure like. Is it measuring some insane way now, this time, this setup? Nope! Now I can go ahead with what I really want to look at, which a little confidence I havent made some sophmoric equipment / software application setup mistake...
You might want to get yourself "an amplifier" just for doing speaker measurements. This would be the kind of amplifier that has two RCA inputs, perhaps a volume control and a set of speaker connections - nothing else to do anything but flat frequency response voltage output from input, just to take another variable out of the measurement and the otherwise possible confusion thereafter.
7th and 9th chords, I can play an A7, G7, E7 and a D7 - but I dont know any 9ths. So you're better at guitar than me. I know how to use REW though and it's just a matter of practice with it, in learning how to measure a generic speaker. Like learning 9ths, it's just a matter of learning a few songs with a few of those, then it gets easy and straightforward. REW even easier - no finger dexterity needed!
Thanks for the thanks!
"Somewhat flat" frequency response could be construed as +/- 6dB on axis response over a given bandwidth, say that of a guitar, from 80Hz to 16,000 Hz.
Some of your sweeps show response dropping from near 115dB at 450Hz to only 70dB at 4kHz, a 35dB drop.
That is worse than I expected from the simulation in post #225.
That said, your notes don't mention any basic measurement protocol, such as signal voltage, mic distance to source, boundary conditions, so I have no clue as to what they are, or if they even are representative of the actual frequency response that would be heard in a normal situation.
Art
Both my mentors, excellent! JJ yes I agree with the sealed chamber, just proved yesterday what a disaster an unsealed chamber is on the other side. The chamber divider side had a port added to experiment, I also have a divider that is sealed, no problem, will test that.
I admit I rushed through REW last night, it was getting late. The good news is I like the software upgrade, and I am finally enjoying using it again, was fun.
I have tutorials Art supplied, and found many online, I really just need to print them out and read everything, get a better understanding of the software, and how to use it, then have fun actually using it and testing. I will get better with REW, that must happen, as the focus now is electronics in the guitar.
Also note that my FR is very similar to an acoustic guitar all by itself. When I measure a quality acoustic guitar, the dB levels are not even close to +/- 6 dB, maybe this is the nature of an acoustic guitar that is being strummed by itself (need to try the short horn). This is not a stereo or a full band, just a guitar,
As we discussed before, this is not just a reproducer, but a producer and reproducer together, so a bit unusual. Plus I wonder how the FR is affected by the strumming or finger picking. For instance sometimes I am doing two down stroke, then one upstroke, then one down stroke repeated over and over with different chords, offbeat rhythm. Obviously plenty of resonance, but attacking the strings at different times. There are not five other instruments playing, so this has to have some affect of FR and dB at given times. Yes? Thanks guys! Joe
I admit I rushed through REW last night, it was getting late. The good news is I like the software upgrade, and I am finally enjoying using it again, was fun.
I have tutorials Art supplied, and found many online, I really just need to print them out and read everything, get a better understanding of the software, and how to use it, then have fun actually using it and testing. I will get better with REW, that must happen, as the focus now is electronics in the guitar.
Also note that my FR is very similar to an acoustic guitar all by itself. When I measure a quality acoustic guitar, the dB levels are not even close to +/- 6 dB, maybe this is the nature of an acoustic guitar that is being strummed by itself (need to try the short horn). This is not a stereo or a full band, just a guitar,
As we discussed before, this is not just a reproducer, but a producer and reproducer together, so a bit unusual. Plus I wonder how the FR is affected by the strumming or finger picking. For instance sometimes I am doing two down stroke, then one upstroke, then one down stroke repeated over and over with different chords, offbeat rhythm. Obviously plenty of resonance, but attacking the strings at different times. There are not five other instruments playing, so this has to have some affect of FR and dB at given times. Yes? Thanks guys! Joe
Joe,
A frequency response measurement compares an input signal to an output signal- an instrument does not have a frequency "response", it has a spectrum, or timbre.
The range of frequencies and levels which constitute an instrument's spectrum, or timbre can be displayed on a real time analyzer.
The sound spectrum of any instrument is affected as much by playing style as it's physical construction attributes.
To accurately reproduce the sound an instrument, the system must be reasonably "flat", yours is not, and may require around +/- 22 dB of equalization to even approximate an acoustic guitar's spectral response.
Art
You can find out. REW has a peak level reading in its plot. You can turn off the regular spectrum plot and show only the peak. Just take your mic and - as if recording the guitar - play it with REW doing a peak spectral analysis. Be careful not to bump the mic stand, clap or make any other sound besides the guitar (especially transient sounds).
Of course you'll have to fool with the REW spectrum settings, but it will give you an across the whole song frequency spectrum, showing all the frequencies made by the guitar. Try it once strumming, a second time (after reset of the spectrum, as it's cumulative) finger picking.
This information can in turn be used to design the reproducer; at least determine the most important frequencies. I mean if 16k shows up, but it's 40 db down in level from most of the other louder frequencies, probably dont have to worry about reproducing that one so much.
And when 4kHz is more than 40dB down from 440Hz (like in the measurement of the reproducer in #265) it's time to add a tweeter to the woofer
.
So I tried it with two guitars, one a nylon string the other a steel string with flat wounds. The Nylon is tuned to E, the Steel is tuned to D.
REW can analyze a recorded file, so I recorded me <ahem> playing the same tune on two different guitars. I recorded with my Tascam DR-05 on a camera stand at 32" height, about 2' in front of me sitting in a chair. SPL is relative. Here's the resulting spectrums -
(The RTA analyzer is set to 1/12th octave and 1/12 smoothing. When you open a file (.wav) with the RTA, it asks which channel and if you want to do a "peak" analysis. I selected left and peak, then watched it crank through the sound file. When I selected "both" at first, I just got two essentially identical analysis)
Not much sub-80 on that D tuned instrument - even though it's body is almost twice as deep as the Nylon guitar. Anyway - FWIW; you can quantize differences in instrument sounds: just dont get too attached to the result! Glad it's not possible to unravel this data and hear me play
REW can analyze a recorded file, so I recorded me <ahem> playing the same tune on two different guitars. I recorded with my Tascam DR-05 on a camera stand at 32" height, about 2' in front of me sitting in a chair. SPL is relative. Here's the resulting spectrums -
(The RTA analyzer is set to 1/12th octave and 1/12 smoothing. When you open a file (.wav) with the RTA, it asks which channel and if you want to do a "peak" analysis. I selected left and peak, then watched it crank through the sound file. When I selected "both" at first, I just got two essentially identical analysis)
Not much sub-80 on that D tuned instrument - even though it's body is almost twice as deep as the Nylon guitar. Anyway - FWIW; you can quantize differences in instrument sounds: just dont get too attached to the result! Glad it's not possible to unravel this data and hear me play
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Yes, thank you gents, response vs. spectrum that helps Art, more what I was looking for. I think of flat when considering a stereo, +/- 1 db flat to reproduce the existing sound would be great, especially when listening to Pink Floyd. There are other bands that I don't care how close the reproduction is, I don't want to listen at all, because the original music is terrible. Getting it right at the instrument is critical. I have heard my guitar sound not so great in the earlier days, when my electronics were "questionable", but today I am getting a sound that I only hoped I could get with this instrument. I need to get better with REW and get some better measurements, I know it is there. I may not have a good voice, but I do have a good ear.
The attached file is a violin, I see +/- 15dB all over the internet for guitars and violins. I think I can get better with improvements, but why can't this type of curve be reproduced with all the different dB levels at different Hz? I am talking about a guitar by itself, or with voice, or another guitar. In a band I understand that would be different. Also a regular acoustic guitar is giving me the same type of curve, just 20 dB less SPL, like JJ, so it is not my unique guitar per say, it must be my measurement methods. If I measured a standard acoustic guitar with the same setup, and it looked totally different, that would make me wonder.
JJ you are getting about +/- 10 dB from 80 Hz to 1000 Hz, that is almost exactly what I am getting for my best measurement, plus mine was 20 dB louder or more across the board. Yes Art is correct I was also getting +/- about 20 dB in that range also with different setup, I need to figure out what is going on there.
Plus playing at 20 dB louder on an acoustic guitar is a whole different experience, it will be even better when it is in the guitar! You can play with such ease and get a big sound, really changes everything. It is a little hard now, because the body is close to me, but not in my hands, so still amp like for now.
I hope to get lots of pictures of Horn speakers and hear them at guitar building school this week, we shall see. I would not say this, because it would be very cocky, but I will think it: My instrument has all your products (guitars, speakers, horns and amps) in one product, that might make them think. OK Art, Waveguide (with a horn on the end), a real horn just can't fit, you would need to be a giant to play it! This whole process is pretty much two steps forward, one step back, but it is still progress. Thanks much guys, and don't forget my offer from earlier! Joe
The attached file is a violin, I see +/- 15dB all over the internet for guitars and violins. I think I can get better with improvements, but why can't this type of curve be reproduced with all the different dB levels at different Hz? I am talking about a guitar by itself, or with voice, or another guitar. In a band I understand that would be different. Also a regular acoustic guitar is giving me the same type of curve, just 20 dB less SPL, like JJ, so it is not my unique guitar per say, it must be my measurement methods. If I measured a standard acoustic guitar with the same setup, and it looked totally different, that would make me wonder.
JJ you are getting about +/- 10 dB from 80 Hz to 1000 Hz, that is almost exactly what I am getting for my best measurement, plus mine was 20 dB louder or more across the board. Yes Art is correct I was also getting +/- about 20 dB in that range also with different setup, I need to figure out what is going on there.
Plus playing at 20 dB louder on an acoustic guitar is a whole different experience, it will be even better when it is in the guitar! You can play with such ease and get a big sound, really changes everything. It is a little hard now, because the body is close to me, but not in my hands, so still amp like for now.
I hope to get lots of pictures of Horn speakers and hear them at guitar building school this week, we shall see. I would not say this, because it would be very cocky, but I will think it: My instrument has all your products (guitars, speakers, horns and amps) in one product, that might make them think. OK Art, Waveguide (with a horn on the end), a real horn just can't fit, you would need to be a giant to play it! This whole process is pretty much two steps forward, one step back, but it is still progress. Thanks much guys, and don't forget my offer from earlier! Joe
Any sound can be "reproduced" with a playback system with poor frequency response, it just sounds less like the original than if it were reproduced with a flat response.
This would be obvious to your good ear if you were to record the sound of your acoustic guitar, then play the recording back through your guitar shaped horn speaker set in the same place with the same relative mic position, record it and compare the two recordings through a reasonably flat speaker or headphone system.
If the guitar shaped horn speaker actually has the frequency response in #265, your good ear should notice how dull it sounds in comparison to the original.
Another way to skin the cat.
Given that you're a musician, you probably have the ability to record yourself playing guitar. Preferably an electric, either with mag pickups or piezo, as in an electrified acoustic. Record - with that guitar output directly plugged into the DAW (Audacity) - a whole song, save it as a .wav file and then do the cumulative "peak" spectrum analysis in REW. Save that picture.
Then, play that recording back, but this time through your horn guitar's amplifier - with whatever control settings you want that makes it sound good - through your guitar body horn speaker arrangement. Record that using your USB measurement mic, preferably ~1M from the horn openings, with both the guitar / horn body and mic on a bed or carpeted floor, at the same loudness as an acoustic guitar would make. You could even do that part outdoors. Do the cumulative "peak" spectrum analysis of that recording in REW and save that picture.
Compare the two spectrums. Show them here. Show the amplifier control settings; Bass, Treble, Presence, etc. The difference will be the frequencies the amplifier / horn system aggravates and diminishes.
Given that you're a musician, you probably have the ability to record yourself playing guitar. Preferably an electric, either with mag pickups or piezo, as in an electrified acoustic. Record - with that guitar output directly plugged into the DAW (Audacity) - a whole song, save it as a .wav file and then do the cumulative "peak" spectrum analysis in REW. Save that picture.
Then, play that recording back, but this time through your horn guitar's amplifier - with whatever control settings you want that makes it sound good - through your guitar body horn speaker arrangement. Record that using your USB measurement mic, preferably ~1M from the horn openings, with both the guitar / horn body and mic on a bed or carpeted floor, at the same loudness as an acoustic guitar would make. You could even do that part outdoors. Do the cumulative "peak" spectrum analysis of that recording in REW and save that picture.
Compare the two spectrums. Show them here. Show the amplifier control settings; Bass, Treble, Presence, etc. The difference will be the frequencies the amplifier / horn system aggravates and diminishes.
OK thanks gents, I get it, have more work to flatten the FR. I attached a measurement that is a little better than the last, about +/- 15 dB (minus a few peeks), so flatter, but I know it still needs improvement. Maybe measurement alone (JJ) can improv some, maybe poor methods. Again, the two different horn lengths is also sounding better. Plus I just received a new Fishman pickup today, mag pickup and mic combo, will try that. My Guild is a pretty good guitar, but not great, I will try the Martin and Taylor with news strings who knows? I obviously have some minor EQ on my amp and preamp, so that of course could help. I adjust that by ear, but I can adjust as I measure and see what happens.
My question is I have a Taylor acoustic just by itself measured, and it is +/- 25 dB. This is a nice new guitar, what gives? It sounds great, so when being recorded, does the FR get adjusted during mix to flatten? Please advise and thanks! Joe
who knows? I obviously have some minor EQ on my amp and preamp, so that of course could help. I adjust that by ear, but I can adjust as I measure and see what happens.My question is I have a Taylor acoustic just by itself measured, and it is +/- 25 dB. This is a nice new guitar, what gives? It sounds great, so when being recorded, does the FR get adjusted during mix to flatten? Please advise and thanks! Joe
It's fine. Most musical instruments, especially the equally tempered kind, dont make sound at every frequency, so it is to be expected that one would see large sound level variations between the notes played and not played.
By playing a whole song however, there's more notes than in just a single chord, plus all the pick clicks, slaps, hammer ons, strums etc that initiate the individual note rings. These tend to fill out the spectrum where the pure tones dont exist. That's why I suggested recording a whole song, then analyzing the whole recording using REWs file input to the spectrum "peak" function. That will - pretty much - show the frequency spectrum the guitar can make.
Looking at the spectrums I posted, a reproducing speaker has gotta cover at least the 100 - 1K range, cause one can see that's where most of the sound output is. But even though the 1k - 10k range apparently tapers off in level, it's still conveying additional information about how the guitar sounds. The compromise is, how much of that 1 - 10k range would be needed in addition to the 100 - 1k range, for it to still sound good? 2k? 5k? How many guitar amps go all the way out to 20kHz?
Your horn speakers will only cover a section of the spectrums I posted. Let's see what that is, one way or another. Pink noise from REW, frequency sweep from REW, or a recording of you playing a song on your Taylor played back through them, analyzed by REW.
Most guitar amps are designed for electric guitar, and have a fairly large (+3 to +10) on axis peak in the 2 to 6kHz range, followed by a steep drop.
Electric guitar amps, speakers and effects add lots of additional harmonics (distortion..) which would sound "harsh" or "buzzy" with a flat response speaker.
Acoustic guitar amps are generally designed to be distortion free, and the better ones have fairly flat frequency response to at least 10kHz, or use tweeters to extend to 15-20kHz.
Most all acoustic guitar players seeking more level, but wishing to retain an acoustic sound prefer a flat response sound reinforcement system.
If the pickups, microphones and guitar all "sound good", relatively minor equalization is usually required of a flat response system.
Art
Shout out to Chicago School of Guitar Making/Specimen Products. The three day guitar building class was excellent.
Ian (the owner) reminded me of two guys from this DIY Audio site. First thing he said when he saw a port in my chamber divider was "put a cork in that port".
Horns especially need to have 100% sealed enclosures, I can do that - JJ!
He also said my soundboard would be tone dead, throw it away, and build one from Sitka Spruce. I was afraid of that, and I can do that!
Another: why not bend the wood and add instead of CNC subtract - Art! I could do that for a small number of guitars, but if this goes to production, that would be very labor intensive, go CNC and hit the button, let it run at night, I am standing by my method.
The body with speakers (most important part): very nice, that will work! After a few days he said Joe you are flying very close to the sun with this design (music producer and music reproducer in the same product). I said you like flying close to the sun don't you, he said yes I do, very very interesting, build it!
I am slowly working on him to be more involved, and I am going back to take more classes. My goal is to have him build one guitar with any changes he wants, I will license it. Have him build the amp. He builds tube amps (which I love) and says have it be lithium battery powered but not in the guitar, can get real sound and power, and replace years later when technology is better. Still UNPLUGGED, play anywhere, my goal.
His horn speakers sounded wonderful. Could hear every instrument, crisp, clean, warm, just awesome. 95 dB and only on volume level of four. Says his goal is to be anywhere in the room and not really know where the sound is coming from, it is everywhere. Let's Rock!
Ian (the owner) reminded me of two guys from this DIY Audio site. First thing he said when he saw a port in my chamber divider was "put a cork in that port".
Horns especially need to have 100% sealed enclosures, I can do that - JJ!
He also said my soundboard would be tone dead, throw it away, and build one from Sitka Spruce. I was afraid of that, and I can do that!
Another: why not bend the wood and add instead of CNC subtract - Art! I could do that for a small number of guitars, but if this goes to production, that would be very labor intensive, go CNC and hit the button, let it run at night, I am standing by my method.
The body with speakers (most important part): very nice, that will work! After a few days he said Joe you are flying very close to the sun with this design (music producer and music reproducer in the same product). I said you like flying close to the sun don't you, he said yes I do, very very interesting, build it!
I am slowly working on him to be more involved, and I am going back to take more classes. My goal is to have him build one guitar with any changes he wants, I will license it. Have him build the amp. He builds tube amps (which I love) and says have it be lithium battery powered but not in the guitar, can get real sound and power, and replace years later when technology is better.
Still UNPLUGGED, play anywhere, my goal.His horn speakers sounded wonderful. Could hear every instrument, crisp, clean, warm, just awesome. 95 dB and only on volume level of four. Says his goal is to be anywhere in the room and not really know where the sound is coming from, it is everywhere. Let's Rock!
For some reason I'd imagined your soundboard to be removable and tied to the body like the drum skin of a banjo. You know, with the adjustable bolts all around the periphery. Not to tighten the soundboard per-se, but just to clamp it to the body. Must've been so you could play with various ports in there, which perhaps now is no longer necessary! Patent that - "Guitar with replacable soundboard having different tonal..."
JJ - the soundboard is removable with small screws. Ian did not like that I made it from Baltic Birch, which is laminated in different directions. He wants Sitka Spruce which is very traditional, quarter sawn, and all grain in one direction. I think this traditional method is proven and likely best. I will try both for a great comparison. If mine sucks, OK. I will know it with proof. If it is OK, also good, we shall see. I am not surprised by this. I need to get Sitka Spruce boards made for a damn cello, since my guitar soundboard is so big, cut it down and brace it. 🔊