What Tools Would I Need to Capture Measurable and Quantifiable Metrics Of Different Types Of Resonator Guitar Coverplates

[Multicore]

Now that might be interesting - effectively measuring the impulse response of the guitar.

The idea is to use an impulse to get a wide spectrum input to see the resonances. I would use a frequency response to display it.

It could even be repeatable if the "mallet" were on a pivot being dropped from a controlled height onto a consistent location on the guitar. (just below the bridge, perhaps)

You could. When I was studying one of my guitars I learned that the absolute values aren't so important. The shape and relative position of peaks is the most interesting thing: center frequency, dB, and Q.

EDIT - I would be tempted to leave the strings open, since they form a significant part of the resonant structure of the guitar. Or at least try both open and muted.

It depends what you're looking for. OP was talking about comparing only the differences cover plate of the resonator cone make. I guess you could measure it both separately and assembled into the guitar and maybe identify which part produces which detail in the system response. For example with guitar you can damp the top and back separately to see which part is responsible for which peaks. ASR member @bluefuzz has a lot of knowledge and experience in this area.

But now I'm thinking that this approach may not be so helpful with a resonator. I would not be surprised to find that non-linear behavior is important in the characteristic sound.

 

[Multicore]

I might try placing the guitar very close to a speaker, maybe right up against the back, play a slow sine tone sweep, and see where the rattles appear.

The frequency range of an acoustic guitar’s fundamentals—its primary note pitches without harmonics—spans roughly 82 Hz to 1,318 Hz, covering the standard tuning (E2-A2-D3-G3-B3-E4)

Like this?

Measure the frequency response of an acoustic guitar body?

I have two Yamaha guitars, an FG830 budget-priced dreadnought and an LJ56 top of the line jumbo. I am interested to measure the practically relevant differences in the frequency response of the two. I have a UMIK-1 and some experience with REW. I also have the DAW Reaper which can record and...

www.audiosciencereview.com

 

[bluefuzz]

perhaps I am overthinking the human hand variable

As @Multicore suggests, you want an impulse response rather than a strum or single string note. This PDF from luthier Giuliano Nicoletti gives a good overview of how to measure an acoustic guitar using REW – the principles will be the same for a resonator although the methods of acting on the information thus obtained will obviously be somewhat different. You will also find discussion of these techniques on the Australian and New Zealand Luthiers Forum and in the works of Australian luthier Trevor Gore on who's work Nicolletti's book is based. Hope this helps.

It's interesting you think the coverplate makes a lot of difference. I have a biscuit bridge metal-body resonator and don't recall the guitar sounding much different with the cover on than with it off, although it's admittedly been a while since I tried. I find the quality and weight of the cone together with biscuit and saddle materials make more difference ...

 

[kemmler3D]

I don't know much about guitars per se but I agree with @Multicore that I'd want to know about nonlinear behaviour too... So in addition to exciting the guitar with a sweep, it would also be informative to play the same note at different volumes to see if the impact of the resonator changes depending on volume.

 

[Multicore]

I don't know much about guitars per se but I agree with @Multicore that I'd want to know about nonlinear behaviour too... So in addition to exciting the guitar with a sweep, it would also be informative to play the same note at different volumes to see if the impact of the resonator changes depending on volume.

An oscilloscope display of the waveforms can be useful for that. I saw it done in a study of pickups.

 

[Philbo King]

An option for single-string tests would be an E-Bow for exciting the string consistently.

Radiation patterns from a resonator (actually any instrument) vary in the spacial domain, so you might think about an array of identical mics that pick up sound from various directions at once. Perhaps a hollow hemisphere made of foam to mount the mics, while also attenuating room reflections.

 

[Timcognito]

This guy has whole series of videos of how measure and interpret DML panels with REW. There are several here is one. FYI

 

[RAMBLIN_RAWB]

Mute the strings and tap the bridge with a suitable mallet, e.g. a wine cork on a fondue fork. Average ten taps.

REW and a calibrated measurement mic will give you correct absolute members but you can get started with a spectrum analyzer app on your phone. It should reveal the main differences between different resonator builds. I use an Android app called Spectroid.

Show us what you find. It should be fun.

This is interesting and not something I thought of. I have my own theories on this, though, can you help me better understand why specifically mute the strings and specifically bridge taps?

 

[RAMBLIN_RAWB]

Now that might be interesting - effectively measuring the impulse response of the guitar.

It could even be repeatable if the "mallet" were on a pivot being dropped from a controlled height onto a consistent location on the guitar. (just below the bridge, perhaps)

EDIT - I would be tempted to leave the strings open, since they form a significant part of the resonant structure of the guitar. Or at least try both open and muted.

the mallet could be the cork as stated above, though the control could be teh drinking perpetual motion bird...though may have to set it up with a motor

 

[RAMBLIN_RAWB]

An option for single-string tests would be an E-Bow for exciting the string consistently.

Radiation patterns from a resonator (actually any instrument) vary in the spacial domain, so you might think about an array of identical mics that pick up sound from various directions at once. Perhaps a hollow hemisphere made of foam to mount the mics, while also attenuating room reflections.

e-bow is a good idea but expensive! Ill see if anyone in my area has one I may be able to borrow!

 

[Multicore]

This is interesting and not something I thought of. I have my own theories on this, though, can you help me better understand why specifically mute the strings and specifically bridge taps?

slide a rag or cloth between the strings and the fret-board. you're trying to listen to the resonances of the body, not the vibrations of the strings.

Make a mallet with an eraser or cork skewered on the end of a chop stick or something. gently hit the bridge with it. you'll here the sound of the guitar body resonate briefly like a drum. give it some taps and listen. when you've got your percussion technique down, measure the frequency response with your phone. the spectrum analyzer app on my phone has a feature to hold the peak in each frequency bin and that works great. hold the mic about a 12 or 18 inches away from the bridge.

 

[Multicore]

This is a bit different but you see how he uses a mallet, microphone and spectrum analyzer. Since he's looking for frequency, calibrating the intensity of the hit isn't important. Probably won't be for you either.

 

[kemmler3D]

For a standardized pluck / strum you don't necessarily need anything motorized or fancy... just a device that can hold a guitar pick and move at the same speed at the same position, repeatably.

This could be as simple as a weight with a guitar pick attached (I guess sliding on a rail of some kind) that you lift to the same height and drop each time.

We all like to see a little over-engineering around here, but don't over-think this and prevent the project from moving forward, either.

 

[RAMBLIN_RAWB]

Thank you all so much for the direction and the brainstorm'n! Keep em' comin'! This is a bit tricky because I will be changing out coverplates to test the impact different styles of coverplates have on the voice/expression of the resonator guitar throughout the tests. I'm looking forward to the challenge! I cannot thank you enough!

 

[RAMBLIN_RAWB]

For a standardized pluck / strum you don't necessarily need anything motorized or fancy... just a device that can hold a guitar pick and move at the same speed at the same position, repeatably.

This could be as simple as a weight with a guitar pick attached (I guess sliding on a rail of some kind) that you lift to the same height and drop each time.

We all like to see a little over-engineering around here, but don't over-think this and prevent the project from moving forward, either.

Haha, I heard and excellent advice! I'm keepin tabs on the overthinking. I envision the guitar on its back having a control strum/pick mechanism. I feel having a human hold it, pick and strum in front of a mic has too many variables that can throw off the tests? I am new to all this so the aforementioned variables are assumptions at best.

 

[kemmler3D]

Haha, I heard and excellent advice! I'm keepin tabs on the overthinking. I envision the guitar on its back having a control strum/pick mechanism. I feel having a human hold it, pick and strum in front of a mic has too many variables that can throw off the tests? I am new to all this so the aforementioned variables are assumptions at best.

I think the frequencies a resonator emphasizes will be mostly the same if the guitar is played a little differently, so I don't think it's a showstopper for a person to play it if you're just looking for a general sense of how they vary.

If you want to quantify the difference, or measure very small differences, then I think it's a good idea to play the guitar mechanically to eliminate that variable.

 

[bluefuzz]

.though may have to set it up with a motor

That should not be necessary. Did you read the Nicoletti PDF I linked to a few posts up? The techniques described therein have been used for decades by some luthiers, especially in the violin community, and have now become more-or-less standard practice for many guitar builders. They are all you need to get a frequency response. No need to reinvent the wheel.

Some luthiers use a piece of magnet wire (such as that used to wind guitar pickups) looped over a string to make a consistent 'pluck'. Pull on the wire until it breaks, the force required will be very close to the same every time. But this is a more a test of the power response of the instrument an not necessary to measure frequency respose or timbre which is what you seem to be interested in ...

 

[RAMBLIN_RAWB]

Hey Everyone, just want to say thanks so much for all your insight and expertise. Life happened, everything is okay and I look forward to reviewing all of this and getting back to all of you asap. Kindest Regards to you all and can't wait!