Chladni and VA tests ???

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blackalex1952
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Re: Chladni and VA tests ???

Post by blackalex1952 » Sat Jan 02, 2016 1:27 pm

Yes, the floating bridge/archtop design, is probably more akin to a loudspeaker. On the Djangobooks forum there are interesting posts by a luthier Bob Holo who was an experienced loudspeaker designer before tackling the Selmeroids...he has some interesting opinions and has several tonal variations in his range of guitars.
"Everything I say on the topic is based solely upon inexperience and assumption!"

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sat May 27, 2023 8:02 am

kiwigeo wrote:
Sat Nov 28, 2015 8:30 am
Hi Alex,

Good to see you coming over to the dark side :mrgreen:

As John mentions your gain might be a bit high...the plots look a bit lumpy.

Can you give us a run down on your equipment and your method? ie VA settings, mic, computer, where youre holding mic, how your holding the guitar etc. Ditto for your chladni testing.

One thing you'll find with the Chladni testing....as you get into the higher frequencies you get some modes that appear complex and heavily influenced by the bracing.
I just got my speaker and amp set up to make Chladni patterns on my prototype Dreadnought
It’s strung up with a towel dampening the strings,, neck in vise and a triangle block with cork on top supporting the guitar below tail block.
Am I going to have null results like this?
After rolling from 20hz to 500ish, (had to stop due to family not happy about it) I wasn’t seeing all the higher frequency shapes,


These are all I got

I need more time vibrating concrete floor, walls my body, etc
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kiwigeo
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Re: Chladni and VA tests ???

Post by kiwigeo » Sat May 27, 2023 9:26 am

I sit my guitar in the cradle that's part of my Stewmac style binding channel routing jig. I generally take the strings off or if on I put a bit of foam between strings and upper end of fretboard.

You'll find that you'll need more energy to drive the upper frequency modes....many of the upper freq modes are also more complex than the main monopole modes....many of them heavily influenced by brace location.

I'm using a 50 watt Bradley tone generator and a 100mm speaker. I also use poppy seed rather than tea leaves.

Trevor may have some useful comments about your set up.
Martin

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Trevor Gore
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Re: Chladni and VA tests ???

Post by Trevor Gore » Sat May 27, 2023 10:53 am

Generally, you have to excite where you expect an antinode to be, which helps reduce the power requirement. Google up some pictures of Chladni patterns and that will give you an idea of where those are. There are pics in the book, too, of course.

The monopole at at 356 Hz is unusual. I suspect you are driving the air resonance at ~89 Hz with a signal two octaves higher in pitch.

The neck can be involved in some modes, so its best to have it free. Just support the body on a few (3) foam cones.

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sat May 27, 2023 12:10 pm

kiwigeo wrote:
Sat May 27, 2023 9:26 am
I sit my guitar in the cradle that's part of my Stewmac style binding channel routing jig. I generally take the strings off or if on I put a bit of foam between strings and upper end of fretboard.

You'll find that you'll need more energy to drive the upper frequency modes....many of the upper freq modes are also more complex than the main monopole modes....many of them heavily influenced by brace location.

I'm using a 50 watt Bradley tone generator and a 100mm speaker. I also use poppy seed rather than tea leaves.

Trevor may have some useful comments about your set up.
I’ll have to run it with out strings,, the reason it was set up like this is the neck is permanently connected.
I figured if the neck wasn’t clamped it would vibrate too.
Thank you.

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sat May 27, 2023 12:25 pm

Trevor Gore wrote:
Sat May 27, 2023 10:53 am
Generally, you have to excite where you expect an antinode to be, which helps reduce the power requirement. Google up some pictures of Chladni patterns and that will give you an idea of where those are. There are pics in the book, too, of course.

The monopole at at 356 Hz is unusual. I suspect you are driving the air resonance at ~89 Hz with a signal two octaves higher in pitch.

The neck can be involved in some modes, so its best to have it free. Just support the body on a few (3) foam cones.
The neck is permanently connected. It’s like a modern Spanish heel connection I’ve been doing to complicate my life more!
Will test without strings,
Yes sir, I had speaker over nodes snd etc, but I believe the strings like Martin mentioned are stopping the higher modes,
The t(1,1)1 is 97.7 but the G isn’t really wolfing
The t(1,1)2 is 180 , I believe your correct about the 359-360 octave drive
I just need more time to run the speaker, it’s vibrating my body and the house, wife shut it down

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kiwigeo
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Re: Chladni and VA tests ???

Post by kiwigeo » Sat May 27, 2023 1:51 pm

WilliamDavidReynolds wrote:
Sat May 27, 2023 12:25 pm
I just need more time to run the speaker, it’s vibrating my body and the house, wife shut it down

:lmao :lmao :lmao :lmao
Martin

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Trevor Gore
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Re: Chladni and VA tests ???

Post by Trevor Gore » Sat May 27, 2023 2:44 pm

Trevor Gore wrote:
Sat May 27, 2023 10:53 am
The neck can be involved in some modes, so its best to have it free.
WilliamDavidReynolds wrote:
Sat May 27, 2023 12:25 pm
The neck is permanently connected. It’s like a modern Spanish heel connection I’ve been doing to complicate my life more!
When I said free, I meant not clamped in a vise! Basically, try to mimic the conditions the guitar is in when you play it. The contact with fleshy parts of the body is a pretty soft support from the engineering point of view, so bits of foam as supports simulates that adequately.

Have fun, but don't antagonise the family!

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sun May 28, 2023 3:42 am

WilliamDavidReynolds wrote:
Sun May 28, 2023 3:10 am
Trevor Gore wrote:
Sat May 27, 2023 2:44 pm
Trevor Gore wrote:
Sat May 27, 2023 10:53 am
The neck can be involved in some modes, so its best to have it free.
WilliamDavidReynolds wrote:
Sat May 27, 2023 12:25 pm
The neck is permanently connected. It’s like a modern Spanish heel connection I’ve been doing to complicate my life more!
I’ll set it up and post pictures.
When I said free, I meant not clamped in a vise! Basically, try to mimic the conditions the guitar is in when you play it. The contact with fleshy parts of the body is a pretty soft support from the engineering point of view, so bits of foam as supports simulates that adequately.

Have fun, but don't antagonise the family!
I’ll set it up, post pictures,
My comment got typed in Trevor’s quote,
Admin please delete previous post. ^^

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TallDad71
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Re: Chladni and VA tests ???

Post by TallDad71 » Sun May 28, 2023 7:16 am

WilliamDavidReynolds wrote:
Sat May 27, 2023 8:02 am
kiwigeo wrote:
Sat Nov 28, 2015 8:30 am
Hi Alex,

Good to see you coming over to the dark side :mrgreen:

As John mentions your gain might be a bit high...the plots look a bit lumpy.

Can you give us a run down on your equipment and your method? ie VA settings, mic, computer, where youre holding mic, how your holding the guitar etc. Ditto for your chladni testing.

One thing you'll find with the Chladni testing....as you get into the higher frequencies you get some modes that appear complex and heavily influenced by the bracing.
I just got my speaker and amp set up to make Chladni patterns on my prototype Dreadnought
It’s strung up with a towel dampening the strings,, neck in vise and a triangle block with cork on top supporting the guitar below tail block.
Am I going to have null results like this?
After rolling from 20hz to 500ish, (had to stop due to family not happy about it) I wasn’t seeing all the higher frequency shapes,


These are all I got

I need more time vibrating concrete floor, walls my body, etc
Have you tried using FFT by studio six? Fire it up on your phone and record a dozen finger taps on the soundboard. The frequency response curve will help you identify the which Hz to focus in on. The peaks are the anti nodes. You will have a peak around 90hz and many others.

Your family will still think you mad but you can reduce the time spent by 90%
Alan
Peregrine Guitars

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sun May 28, 2023 1:51 pm

TallDad71 wrote:
Sun May 28, 2023 7:16 am
WilliamDavidReynolds wrote:
Sat May 27, 2023 8:02 am
kiwigeo wrote:
Sat Nov 28, 2015 8:30 am
Hi Alex,

Good to see you coming over to the dark side :mrgreen:

As John mentions your gain might be a bit high...the plots look a bit lumpy.

Can you give us a run down on your equipment and your method? ie VA settings, mic, computer, where youre holding mic, how your holding the guitar etc. Ditto for your chladni testing.

One thing you'll find with the Chladni testing....as you get into the higher frequencies you get some modes that appear complex and heavily influenced by the bracing.
I just got my speaker and amp set up to make Chladni patterns on my prototype Dreadnought
It’s strung up with a towel dampening the strings,, neck in vise and a triangle block with cork on top supporting the guitar below tail block.
Am I going to have null results like this?
After rolling from 20hz to 500ish, (had to stop due to family not happy about it) I wasn’t seeing all the higher frequency shapes,


These are all I got

I need more time vibrating concrete floor, walls my body, etc
Have you tried using FFT by studio six? Fire it up on your phone and record a dozen finger taps on the soundboard. The frequency response curve will help you identify the which Hz to focus in on. The peaks are the anti nodes. You will have a peak around 90hz and many others.

Your family will still think you mad but you can reduce the time spent by 90%

I have the tap measurements in REW and VA, I started with my peaks. But wasn’t finding them, ran from I believe 20-50hz and ran up to 500 wasn’t very long before I got cut off, worried about neighbors too. Going to have wife take kids to park, and put a note on front door for the cops to call me if they end up reading it.

WilliamDavidReynolds

Re: Chladni and VA tests ???

Post by WilliamDavidReynolds » Sun May 28, 2023 2:29 pm

Trevor Gore wrote:
Sat May 27, 2023 2:44 pm
Trevor Gore wrote:
Sat May 27, 2023 10:53 am
The neck can be involved in some modes, so its best to have it free.
WilliamDavidReynolds wrote:
Sat May 27, 2023 12:25 pm
The neck is permanently connected. It’s like a modern Spanish heel connection I’ve been doing to complicate my life more!

When I said free, I meant not clamped in a vise! Basically, try to mimic the conditions the guitar is in when you play it. The contact with fleshy parts of the body is a pretty soft support from the engineering point of view, so bits of foam as supports simulates that adequately.

Have fun, but don't antagonise the family!
Did some stuff today,

First thing was check bridge rotation, got 1.3 degrees,
Then put 10grams of post adhesive on second from tail back brace, which brought top down from 180 to 174, the back went from 223-224 down to 209.
Took it off, I’m chasing the air T(1,1)1 to change it
Slotted the bridge pins and that changed my monopole from 180 to 178.18
Bound the sound hole with 1.26 thick mahogany I originally was going to bind it with, so it was 98mm and now 95.5ish, the Air went from 98 to 96.8,

There has been 128 grams and 138 gram steel weights bolted inside through these tests, they didn’t effect the air and only shifted the Top and back not an entire hz, which I was thinking it’s not enough, also maybe the structured sides being off more mass than usual would require more weight to effect the top, idk, but it’s a blast working through the steps trying to shift frequencies around.
All and all it’s pretty much fine except a pumping, it happens when I play it like I normally do which is bass player problems, if I just ease off and focus on playing it gently it is clear.

Going to put 3 grams and then a six gram ball of poster adhesive on the brace and see what weight brings the back and top dead on three semi tones apart, I believe maybe the back and top need to be in sync more, as my back is the thickness of a live back but braced like a Dreadnought , like you do for non active backs

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