Cherry and WRC Parlour sprectra question

[Francis]

I'm working on a small parlour which is currently at the closed box stage - neck/bridge not fitted. Tried some tap tests at the bridge position using a phone app. Would like comments on the spectra please:


The guitar so far:

Soundboard is Falcate braced with CF top and bottom of all braces. Back is radially braced.

Other images of the build/bracing can be seen here: http://milsomguitars.weebly.com/heathers-parlour.html

[johnparchem]

Do you think the 209 Hz is the top? With a parlor I suspect the 239 Hz is the top resonance T(1,1)2 before the bridge and strings. Also the 239 Hz peak is taller than the 209 Hz. I wonder if the back resonance is lower than the top. Nice looking guitar.

[Francis]

John - I'm not sure - the back before closing didn't sound lower than the back - though I dodn't take any spectra at that stage.

[lamanoditrento]

What phone app are you using Francis?

[Francis]

Phone app is: Spectrum Analyze (found a link on this site - somewhere...)

Few more traces with a narrower range:


Red traces are front plate tapped at bridge position - yellow on back plate opposite the bridge position.
This is just finger tapping on the different points so db levels have changed each time...

[Francis]

Phone app: viewtopic.php?f=33&t=7261&p=80172&hilit ... yze#p80172

[kiwigeo]

Do you think the 209 Hz is the top? With a parlor I suspect the 239 Hz is the top resonance T(1,1)2 before the bridge and strings. Also the 239 Hz peak is taller than the 209 Hz. I wonder if the back resonance is lower than the top. Nice looking guitar.

I just did a quick tap test on my parlour with results as follows:

T(1,1)1 - 110.5Hz
T(1,1)2 - 207Hz
T(1,1)3 - (back) 269.6Hz (top not coupling with back at this stage).

[johnparchem]

Do you think the 209 Hz is the top? With a parlor I suspect the 239 Hz is the top resonance T(1,1)2 before the bridge and strings. Also the 239 Hz peak is taller than the 209 Hz. I wonder if the back resonance is lower than the top. Nice looking guitar.

I just did a quick tap test on my parlour with results as follows:

T(1,1)1 - 110.5Hz
T(1,1)2 - 207Hz
T(1,1)3 - (back) 269.6Hz (top not coupling with back at this stage).

Is that stung up or just closed?

[kiwigeo]

Do you think the 209 Hz is the top? With a parlor I suspect the 239 Hz is the top resonance T(1,1)2 before the bridge and strings. Also the 239 Hz peak is taller than the 209 Hz. I wonder if the back resonance is lower than the top. Nice looking guitar.

I just did a quick tap test on my parlour with results as follows:

T(1,1)1 - 110.5Hz
T(1,1)2 - 207Hz
T(1,1)3 - (back) 269.6Hz (top not coupling with back at this stage).

Is that stung up or just closed?

Bridge on strung up with strings damped.

[johnparchem]

I have found as much as a 20 Hz drop after gluing on the bridge and putting strings on a steel string. His 209 Hz is certainly in the range for a small body guitar for the T(1,1)2

[Steve.Toscano]

Did you close over those string holes in the top when tapping? One of your peaks could be an air freq coming from those holes if the phone is pointed at them...
Also i find i dont get good results with finger tapping, for a quick and easy tapper try an eraser on a skewer, just round over one end of the eraser to very blunt point.

[jeffhigh]

Upper bout soundport is going to raise the air resonance and consequently the others.

[Francis]

Many thanks for the responses guys. The bridge pin holes were open and the sound-port too. So will have another go closing these and make a 'tapper' rather than the Mk 1 finger tip.
TBC...

[Francis]

Following the above comments I've closed the bridge pin and sound port holes, made a tapper and re-recorded sets of data at shorter scale ranges to get more precise peaks -

The upper frequencies (209.95 and 236.87 Hz) have remained the same, the lower frequency has dropped from 123.82 to 118.43 Hz with the aperture closures.
Need to go away and read more from 'the book' to get a better understanding of these graphics.
Cheers Guys

[Francis]

Having a few problems with the phone app so downloaded a PC prog., to look at the spectra - notes on the images:
Front plate tap traces:

Back plate tap traces:


Comments welcome

[johnparchem]

That looks more normal, so it looks like your Main top is at 230 Hz, after it is bound with a bridge and strung up it may be around 210. That is where my small guitars end up. I do see that 209 ish peak in the white back tap test.