Analysed examples

Classical 

Spectrum tap tone classical

f air = 110 Hz

The peak of the air resonance stands out consistent with relative strong lows of this instrument. This was my second instrument before I applied any tuning of tops. This instrument is not bad but could be much better by making the top bracing lighter before assemblence. The result would be a more complex spectrum not dropping off as steep at the higher end. The insrument would have a better response on the high end of the spectrum, a more balanced tone and better lower end as well. It taught me that building a good classical guitar is possibly more challenging than building a good steel string instrument. Making the bracing lighter after closing the box is very difficult and not really an option.

OM 

Spectrum tap tone OM

109 (Air), 226 (Top)

The top and air resonance frequencies are coupled which is good.

The back is pretty stiff and not very active. This explains a higher air resonance frequency than for the OMC model below.

OMC

Spectrum tap tone OM Cutaway

Main resonance frequencies: 101(Air), 201(Back), 210(Top)

Analysing the spectrum shows that the main resonance frequency of the top is double the the air resonance frequency plus a semitone and the back has a peak resonance frequency a semitone less than the top. This is good. These values were created by measuring frequencies during construction and changing the weight of the bracing before mounting the back of the guitar. The result is a coupling between the various resonance frequencies. The spectrum shows a balanced tone because dominant peaks have been avoided. The relative lighter top results in more response for higher frequencies and together with the loser back a lower air resonance frequency. 

Selmer Maccaferri, ovale hole

Main resonance frequencies: 254(Top), 93(Air), 215, 138, (1397)

(Note: Scales are different from previous pictures)

This picture explains the very specific character of this type of manouche jazz guitar. A low air resonance frequency of 93Hz  is related to the small oval hole and a high response at the higher end of the spectrum is partly because of the very thin dome shaped top. The very stiff light top makes these instruments very responsive and capable of cutting through other instruments even in an acoustic setting. Check out manouche players like Django Reinhardt, Stochelo Rosenberg, Jimmy Rosenberg, Angelo Debarre and many others who really know how to use these instruments.