Help with my spectrum

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AKEric
Gidgee
Posts: 5
Joined: Fri Sep 28, 2018 1:29 pm

Help with my spectrum

Post by AKEric » Tue Feb 05, 2019 2:16 pm

Hello to everyone,

I have completed the box of my first falcate braced guitar and would be grateful to you all for some input/advice on the resonances it has at this point.

Some details:
OM sized medium body.
14 fret body join.
Tzalam back and sides (752 Kg/m3).
Sitka top with a bit of bear claw figure (382 Kg/m3).
Sitka falcate braces. Primary & secondary max height of 6.5mm over the bridge plate.
Planning on a live back.
Can add side mass if needed.
Frequencies measured with no bridge or saddle.
Target for finished guitar T(1,1)1 = 90 Hz. …..............Measured at 95 Hz.
Target for finished guitar T(1,1)2 = 170 Hz. ….............Measured at 187 Hz.
Target for finished guitar T(1,1)3 = Not really sure?…..Measured at 235 Hz.

I have included the spectrum analysis for people to judge. Is it close to looking like it should?

The T(1,1)2 seems a little low for this stage of the game. Is this correct?

It seems like the T(1,1)3 is a little high, but I can't seem to find a reference to what it should end up at. I have not relieved the primary lower bout back brace too much at this point (see photo) and can do more as required. My feeling is that more needs to be taken out and the back and top are not fully coupled at this point; the back is not truly 'live' yet.

I would love some help on how to proceed in attaining my target frequencies.

Thanks,

Eric
#3 Box Spectrum.png
Completed Box Spectrum
Lower bout Back Brace.jpg
Lower bout brace

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Trevor Gore
Blackwood
Posts: 1408
Joined: Mon Jun 20, 2011 8:11 pm

Re: Help with my spectrum

Post by Trevor Gore » Wed Feb 06, 2019 9:11 am

Eric, check out Fig. 4.6-3 in the Design book, Section 2.4.1.2 and Appendix VI.

AKEric
Gidgee
Posts: 5
Joined: Fri Sep 28, 2018 1:29 pm

Re: Help with my spectrum

Post by AKEric » Sat Feb 09, 2019 5:22 am

Thank you Trevor,

Those references help considerably. I'm going to dive back into the books in more detail to proceed, but in your opinion, would you continue to relieve the back brace at this time, or wait until the bridge and saddle are attached? It's not nearly relieved as the books suggest to start with, but I want to proceed with caution so as to not go too far.

Thank you again.

Eric

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Trevor Gore
Blackwood
Posts: 1408
Joined: Mon Jun 20, 2011 8:11 pm

Re: Help with my spectrum

Post by Trevor Gore » Tue Feb 12, 2019 5:43 pm

AKEric wrote:
Sat Feb 09, 2019 5:22 am
...would you continue to relieve the back brace at this time, or wait until the bridge and saddle are attached?
I'd leave it at the moment. It gives you more options later.

AKEric
Gidgee
Posts: 5
Joined: Fri Sep 28, 2018 1:29 pm

Re: Help with my spectrum

Post by AKEric » Fri Feb 15, 2019 4:55 am

Thank you trevor, for your input.

Eric

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