Complete (almost) guitar - spectrum results

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gerryt
Kauri
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Location: Moray, Scotland

Complete (almost) guitar - spectrum results

Post by gerryt » Sun Sep 15, 2019 8:02 am

As I said in a previous post I'm in the home straight with my first falcate braced guitar. In other previous posts I described frequency test results I got at the closed box stage.

The guitar is OM sized and has a side soundport and small-ish arm bevel. The finish is on and buffed and the bridge is glued on. The neck is a bolt on but with a plain glue down fretboard extension (not glued on yet). It is made of somewhat unsuitable material for a falcate braced guitar with an adirondack spruce top and IRW back and sides.

So at the closed box stage I was getting T(1,1)1 as 107/8Hz, T(1,1)2 as 189Hz and T(1,1)3 as 231Hz.

With no side masses added and with the neck bolted on but without the fretboard extension glued down I got 113Hz, 187Hz and 232Hz respectively. Blocking the side soundport T(1,1)1 drops to 106Hz. Last time I'll be building with a soundport I think.

Adding 100g of side mass to each side I got 113Hz, 182Hz and 231Hz. Both of these last tests were done with no strings on. The frequencies are all a bit high I think you'll agree. But they don't fall on any notes and there's sufficient separation I think between top and back resonances.

Not ideal but it is what it is. The spectrum taken today showed lots of other peaks as well as the three main ones so I'm hopeful of a decent sound.

Am I right to be thinking that I should stop there and finish up the guitar and accept it for what it is? Or should I be chasing frequency drops for the three main resonances? I'm wary particularly of trying to drop the T(1,1)1 in case I drop it on to A at 110Hz. Or can I expect any changes when it's strung up to pitch?

Thanks again in advance!

gerryt
Kauri
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Joined: Tue Nov 30, 2010 3:31 am
Location: Moray, Scotland

Re: Complete (almost) guitar - spectrum results

Post by gerryt » Sun Sep 15, 2019 8:16 am

This is the frequency spectrum taken with 100g attached to each side
Freq_100g.jpg
Freq_100g.jpg (59.47 KiB) Viewed 680 times

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Trevor Gore
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Re: Complete (almost) guitar - spectrum results

Post by Trevor Gore » Mon Sep 16, 2019 9:12 am

String it and listen to it. With the added mass of saddle and strings the T(1,1)2 will drop and you may have to alter the side mass to hit 180 Hz for the T(1,1)2. You should end up pretty close to 180/226, which is not a bad place to be. With the sound port, the air resonance will always be higher than "normal".

gerryt
Kauri
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Joined: Tue Nov 30, 2010 3:31 am
Location: Moray, Scotland

Re: Complete (almost) guitar - spectrum results

Post by gerryt » Wed Sep 18, 2019 3:33 am

Thanks for the reply Trevor.

Yep pretty much resigned to the main air being as it is. And re the T(1,1)2 I wouldn't be disappointed to have to reduce the amount of weight to bring it to 180Hz after stringing up.

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