Monopole mobility again...!

[davidafterwork]

Hello all
I would really appreciate some feedback here as I have built a TG method guitar and not too happy with the sound. If someone could help me out with a few tips it would be great! Here goes..
The guitar is a 00 type 14 fret steel string
Response with strings on etc are as follows
97 Hz with target of 95
177 Hz with target of 180
235Hz with target of 226

I have measured a deflection of .16mm and a response of 170 Hz with sound hole muted
Now, can anyone send me a pic or write out the formula for specific mobility that would allow me to input these 2 measurements?? I know it’s in the book but I’m afraid I need to see it written out once so I can “get it”! as I’m pretty bad at excel... I have Excel eventually set up for thickness etc and now I want to put the specific mobility into the sheet so I can use it again.
I am going to do this test on my Martin 00 28 as well which sounds so good in comparison to mine so I am trying to get to the bottom of what is going on here...!
Thanks in advance for any help you guys can give
Dave

[johnparchem]

Not from only those 2 measurements. You would also need the weight of the load used for the deflection.

Do three calculations even with a calculator.

K is the stiffness K is N/M so get your load into Newtons then divide that by your deflection times 100000 (turning your deflection into meters)

get mass using the K and the plugged sound hole frequency. K divided by (2 * 3.141 * 170)^2

monopole mobility is just 1 divided by square root ( K * mass) multiply that by 1000 to get the units straightened out.

[davidafterwork]

Sorry my mistake! I used exactly 1 kg weight
Dave

[johnparchem]

No excel only a calculator

1kg = 9.81 N

I made a mistake the following is the correct calculation.
So in a calculator .. 9.81 / .16 = 81.75 X 1000 = K= 81750

mass = 81750 / (2 * 3.141 * 170)^2 = 0.07167 m(kg)

1 / square root (81750 * 0.07167) * 1000 = 13.064 In the range for a SS.

[davidafterwork]

John
Thtats really great that you took the time to respond in that detail...much appreciated and I will be saving that info for my next build!
I am slightly puzzled now in that I am not too impressed with the sound ( I tend to compare my sound to the Martin 00 28 ) but yet the figures appear good...
I am going to do the same test on my Martin and see what results I get
Can you see anything else obvious in my figures that might need to be addressed and what would your typical Monopole mobility figure be???
All input welcome and I will post the results of the martin test in a few days
Dave

[johnparchem]

Sounding good is somewhat subjective. What do you like with the Martin that is missing in your guitar? It would be interesting to do a bit testing on the Martin, both spectrum and specific mobility to see if you can associate any difference to what you are hearing.

[Dave M]

Have you checked your bridge rotation? This would show if you have overbuilt. Very common with early builds - certainly with me.

Section 4.4.2 in the black book.

Dave

[davidafterwork]

Thanks Dave. I am going to do all tests on mine and the Martin at the weekend and will be getting back to you all for a few tips to see what the most likely culprit is in my not too great sounding build!
Dave