Soundboard Sonic Signature

[TallDad71]

Like many on this forum I have built beautiful instruments that sound amazing.
Like many in this group I have spent months on a guitar and wonder in sadness why it sounds like a shop bought guitar or worse.

Attached is the sonic signature of 3 guitars all the same model but different woods, large body steel string, X-Braced.

01 Classic - Well rounded mellow, gorgeous sound
02 Cocobolo - Very powerful, big and booming, but balanced, sound, great for fingerstyle, love it
05 Walnut - Lacking any real complexity in the sound or joy in the playing - built with a live back.

The three graphs were all generated using the same method, 20 taps to the bridge pins and bridge at slightly different angles, averaged.

The graph for the 05 Walnut is markedly different, less amplitude across the frequencies, T(1,1) monopole levels all shifted down a few Hz, but I also read, perhaps significantly, much less ability to generate tones in the 600Hz to 1500Hz range, which may be reflecting its lack of complex sound.

So my question, is this graph a smoking gun, can it be remedied?

I've worked on Chladni patterns for the guitars which show that the responses for the 01 Classic guitar (great one) are not symmetrical at mid frequencies 400Hz - 500Hz, here the lower bout treble side is less active than the bass. I will today investigate if the same is true for the weak guitar, maybe then start to think about how the soundboard could be stiffened in areas to better respond to mid frequencies.

Thank you for your thoughts.

[kiwigeo]

I've worked on Chladni patterns for the guitars which show that the responses for the 01 Classic guitar (great one) are not symmetrical at mid frequencies 400Hz - 500Hz, here the lower bout treble side is less active than the bass. I will today investigate if the same is true for the weak guitar, maybe then start to think about how the soundboard could be stiffened in areas to better respond to mid frequencies.

I've found that at the higher frequencies the Caldni patterns are heavily influenced by the pattern of the bracing

[TallDad71]

I expect you are right Martin
My Chladni experiments got interrupted by a garden party next door who were unhappy with my choice of music in the workshop, symphony in 453Hz!

Hopefully get a crack on investigating further this week.

[blackalex1952]

Would you mind listing the T,1 T,2 frequencies please. It might be good on this forum to have a standard for X and Y axis when posting Visual Analyser type images...I usually copy the graph, then use 'paint' to insert text above the peaks so that there is an immediate frequency read for every peak on my saved Visual Analyser images.-Ross

[TallDad71]

Would you mind listing the T,1 T,2 frequencies please. It might be good on this forum to have a standard for X and Y axis when posting Visual Analyser type images...I usually copy the graph, then use 'paint' to insert text above the peaks so that there is an immediate frequency read for every peak on my saved Visual Analyser images.-Ross

Hi Ross
If you think it might help here is a table with the frequencies taken from the graphs. The numbers in pink haven't been verified by use of Chladni patterns yet.

The specific mobility was also measured similarly for all guitars on the same day. Whether the calculations are correct I just don't know.

Cheers
Alan

[lamanoditrento]

Do you know what the bridge rotation is for each?

[TallDad71]

Do you know what the bridge rotation is for each?

They’re each around 2° The structural build, the stiffness of the x braces forwards of the bridge are all very similar. I wouldn’t have expected them to vary wildly anyways.

[blackalex1952]

in my limited experience, those monopoles seem rather low...Ross

[TallDad71]

in my limited experience, those monopoles seem rather low...Ross

Do you mean the ones for the 05 Walnut weak sounding guitar or in general across all three please?

[TallDad71]

in my limited experience, those monopoles seem rather low...Ross

The weak guitar does have lower monopole frequencies. I don’t quite know why. The soundboard was thicknesses according to equations as opposed to look and feel and sound. However the bracing was optimised by sound and feel the same as the others.

Could it be that the top was thinner than the other making it more responsive to lower frequencies and less responsive to higher ones?

[Trevor Gore]

The figures from the walnut guitar seem to imply it has a heavy bridge (relatively low T(1,1)2, relatively high stiffness). A heavy bridge would explain the lack of excitement in the sound, as it will be less responsive to higher frequencies. How heavy was the bridge?

[blackalex1952]

I've found the following to be a handy reference, and build to these resonances...it seems to work! I like my T1(2) to be higher, I don't really get excited, as a player, with those boomy dreadnought sounding steel string guitars. They seem to lack clarity between each note with low attack and lack projection. Heavy bridges slow soundboards down because, as we all know, inertia is the enemy of attack. I try to make my guitars have both attack and a rich tight bass, along with punchy shimmer in the mid and high frequencies...I also prefer OM sized instruments..there are too many dreadnought guitars and not enough smaller bodied more balanced guitars in this world! But I like jazz...so there!

download/file.php?id=13586&sid=39a9c931 ... c377d79b90 -Ross

[TallDad71]

The figures from the walnut guitar seem to imply it has a heavy bridge (relatively low T(1,1)2, relatively high stiffness). A heavy bridge would explain the lack of excitement in the sound, as it will be less responsive to higher frequencies. How heavy was the bridge?

Thanks for this Trevor. The bridge weighed in at 35 grams, so quite heavy, yesterday I spent some time feathering the edges and back in order to reduce the mass after studying your bridge designs. It hasn’t made a right fat load of difference to the tone to be honest, I haven’t yet studied the monopoles.

My investigation today is based around stiffening areas of the Tone bars and or x bracing in a bid to make the board board responsive to higher frequencies. This is a tricky job for two reasons, one because I’m not a trained gynaecologist and two because I have the largest hands of anyone I have ever met. If you think it’s simply not worth losing the skin on my lower forearm please speak now!

Have you and O’Brien rescheduled your class dates yet from July 2020, early days I guess?

[TallDad71]

I've found the following to be a handy reference, and build to these resonances...it seems to work! I like my T1(2) to be higher, I don't really get excited, as a player, with those boomy dreadnought sounding steel string guitars. They seem to lack clarity between each note with low attack and lack projection. Heavy bridges slow soundboards down because, as we all know, inertia is the enemy of attack. I try to make my guitars have both attack and a rich tight bass, along with punchy shimmer in the mid and high frequencies...I also prefer OM sized instruments..there are too many dreadnought guitars and not enough smaller bodied more balanced guitars in this world! But I like jazz...so there!

download/file.php?id=13586&sid=39a9c931 ... c377d79b90 -Ross

Love this.
I can almost hear your punchy shimmer in the mid frequencies.

I’m nearly two metres tall, so a dreadnought looks a bit like a ukulele in my hands!

[Trevor Gore]

The bridge weighed in at 35 grams, so quite heavy...

Yes, that's over double what mine typically weigh. Is it much heavier than the bridges on the other guitars?

Have you and O’Brien rescheduled your class dates yet from July 2020, early days I guess?

No, not yet. Still too many unknowns, unfortunately.

[TallDad71]

The bridge weighed in at 35 grams, so quite heavy...

Yes, that's over double what mine typically weigh. Is it much heavier than the bridges on the other guitars?

Have you and O’Brien rescheduled your class dates yet from July 2020, early days I guess?

No, not yet. Still too many unknowns, unfortunately.

The bridges are all identical, made of Ziricote, as they match the fretboards beautifully so that's not necessarily a factor between the three.

I guess the difference in mass in mainly down to the densities of the wood, compared to something like Padauk, there's always be a trade off of form over function I guess. My second build had a Padauk fret-board and bridge, it reminded me of a ginger bearded Scottish highland warrior fighting the Macdonalds, to be fair it sounded a bit like one too!

Hopefully the pandemic will blow away in another 12 months or so, and that will be the major unknown gone. Until then, thanks for your help.

[blackalex1952]

I’m nearly two metres tall, so a dreadnought looks a bit like a ukulele in my hands!

You gotta look good!
Nobody, when talking about bridge weight, refers to the weight and stiffness of the bridge plate as well. The soundboard, sandwiched in between the plate and the bridge, act as a single brace with mass. The X braces pass underneath the ends of the bridge, activating it,which in turn activates the top, so to me, all these factors are where the string vibration enters the soundboard and is primarily distributed to the rest of the sounboard. Do these three guitars all have the same X brace angle? Also, how are your finger braces set up and carved..ie any difference between the two steel string guitars?
RE, my lucid description of the sound I'm looking for in my guitars, I sort of get there, but I have a DREAM! Just like us all, one way or another!
Cheers! Ross

[TallDad71]

I’m nearly two metres tall, so a dreadnought looks a bit like a ukulele in my hands!

You gotta look good!
Nobody, when talking about bridge weight, refers to the weight and stiffness of the bridge plate as well. The soundboard, sandwiched in between the plate and the bridge, act as a single brace with mass. The X braces pass underneath the ends of the bridge, activating it,which in turn activates the top, so to me, all these factors are where the string vibration enters the soundboard and is primarily distributed to the rest of the sounboard. Do these three guitars all have the same X brace angle? Also, how are your finger braces set up and carved..ie any difference between the two steel string guitars?
RE, my lucid description of the sound I'm looking for in my guitars, I sort of get there, but I have a DREAM! Just like us all, one way or another!
Cheers! Ross

There is one teeny weeny difference! I have a Stonebridge guitar on which the long arms of the X-Brace have not been graced, just tapered.
I tried the same for this soundboard in the hope that the top would still have a good range of very stiff and very loose areas so would still respond to a great range of frequencies.
Currently reading chapter 22 of the GG Build book, titled, you did everything right, why might it sound so bad. Very useful insights.