Cuban Mahogany and Lutz Spruce 00

[Darryl Young]

And the last one.

476 Hz:

476HzBeforeTuning.JPG

Oops, forgot this one earlier.

181 Hz:

181HzBeforeTuning.JPG

[Kevin Sjostrand]

Darryl, I have to admit I'm lost on this stuff.
So which one is the best one?

Kevin

[Darryl Young]

Kevin, there isn't a "best" when comparing these vibration modes. The soundboard vibrates at each of these frequencies. Now some influence the sound more than others. The first one shown above is a very good monopole pattern (the ring and a half mode) but that vibration mode pumps more air than any other mode so produces more sound than the other modes. So I guess you could say it's more important.

This is just a shot of how the soundboard vibrates with the soundboard thicknessed as is and the braces trimmed the way they are. So now I'll continue tuning/trimming the braces and see how the patterns change and see how the frequencies of the different vibration modes change......and see how the shape of the node lines change for the various vibration modes.

In his book, Gore provides frequencies for a few of the major vibration modes on really good sounding guitars. Gore believes that matching these frequencies will give you a similar sounding guitar. Of course that is easier said than done and I personally believe the shape and location of the node lines have some impact even if it only impacts the volume produced by a particular vibration mode. The best you can do is try to control the frequency of the 3 or 4 lowest modes.......but since they are the primary sound producers, that works pretty well (per both Somogyi and Gore). The main air resonant frequency is one of the importatant factors but of course it doesn't produce a pattern.

I'm learning this stuff as well. Even if I can't control things right now and they don't come out perfectly.......my thought is that documenting everything will at least allow me to learn from my experience and improve on the next build.

[tippie53]

the information can tell you how your top is moving. I like the match test , you hold a lit match about 8 inches from the sound hole and tap the area of the bridge , this should blow out a good match.
The patterns on the top will change when you add the bridge .

[Darryl Young]

And they will also change when you glue the top to the rim.

[turnertj]

Does a soundboard fully engulfed in flames have different resonant frequencies?

Darryl, what is your frequency generator?

[Darryl Young]

My setup is cheap. I use my computer for the frequency generator. I downloaded a free version of Prgrammable Analysis Software that I use for my function generator.

I use an old computer speaker as the amplifier. It works but barely has enough power.......meaning the patterns would form much faster if it had more power. For the speaker, I took a 4" speaker out of a box that went with an old bookshelf stereo I had sitting in the garage. You don't want too large a speaker as it you want to be able to vibrate at the anti-node (the part of the top that moves.......it's between the node lines). Sometimes you have to play with where you hold the speaker to get the patterns to form. I used to have to adjust the frequency up and down till I seen the sawdust start dancing.......but now using the iAnalyzerLite software on my iPhone it shows me the frequency to use.

I cut four styrofoam blocks into pyramid shapes and that is what I sit the soundboard on for testing. After the node lines start forming, I move the blocks so they are beneath a node line and adjust the frequency up/down a Hz or two till I get the most movement from the soundboard.

Here is a picture of my setup, hardly high tech.......

PS To clarify further, the Dell speaker amplifier is connected to the ear phone jack on my computer. There is an output on the Dell speaker phone that is normally used to connect the speaker on the other side for stereo sound. I connected the 4" handheld speaker to this output. The Dell speaker amplifier has it's own power supply so it is connected to a power outlet on the wall.

Also, measuring any of this doesn't make your guitar sound any different. It's only good as a tool to guide you on how to shape your braces and how far to go with shaving your braces. I think using this information for feedback can help you build a better or more consistent guitar........but you have to use them right as you could also build a consistently bad guitar! <smile> Gore gives some pointers on what to shoot for. Al Carruth's video on using Chladni patterns to tune soundboards gives other information that is helpful (but not defining).

FrequencyGeneratorSetup.JPG

[Darryl Young]

I'll see if I can post a Word document discussing Chladni patterns and the "Ring and a Half Mode".

FreePlateTuningTheory.docx

[turnertj]

Nice...thanks Darryl. The speaker doesn't have to be under the soundboard? It's just nearby?

[Darryl Young]

No, I have to hold the 4" speaker right above the soundboard (almost touching). Other setups are probably more powerful.