This is an attempt to analyze and compare the difference between these two speakers.  Designs 1 and 2, red, orange, are the C12N using the T/S parameters as measures by LMS and  manufacturer's specs, resp.

Despite some differences in these parameters, the greatest being the voice coil inductance, Le, the two are very much identical.  The higher inductance given by Jensen accounts for the steeper roll-off at high frequencies.  The C12N doesn't perform well in a vented box until the volume approaches 8 cubic feet.  In a smaller vented box of about 4 to 5 cubic feet, it'll probably sound much like a juke box, ideal for one who wants to duplicate that sound.  There's a 3 dB rise between 70hz and 150hz. Based on that, only the closed box designs were considered.

The F12N gives a lower bass response due to the lower Fs which, in turn, is probably due to some 40 or more years of use.  Keep in mind, the C12N is designed for guitar while the F12N was primarily used in electric organs. 

The F12N will perform quite well in a vented box of very reasonable volume.  This, again, is based on their being over 40 years old.  How one would perform 40 years ago is anyone's guess.  Only a time machine would help in that determination.  Anyone got a De Lorean equipped with a flux capacitor?

 

 

C12N Thiele-Small parameters as measured on LMS C12N Thiele-Small parameters supplied by Jensen F12N optimized closed box F12N optimized vented box F12N extended bass (practical)

 

 

 

 

 

 

 

The F12N (left) and C12N (right).  For a larger pic, left click on the appropriate image.

 

     

 

 

 

 

 

Of the following 4 spectrograms, the first two are for the C12N and the F12N with a fundamental of 100hz. The second two are for the C12N and the F12N with fundamental of 1000hz.

These spectrograms were generated with about 1 watt to the speakers, generating an ear splitting 98 dB at 1000hz. Fortunately, it took but a couple of seconds to capture each of these spectrograms. At 100hz, the SPL was some 10dB lower

Comparison of the first pair shows that at 100 hz, the two speakers are very similar.  This may be due to the cone moving in unison, like a piston, little to no cone break-up.

 

C12N   f=100hz

 

F12N   f=100hz

 

 

 

The second pair is quite different.  the C12N, with it's stiffer and thinner cone will transmit traverse waves much easier and will also flex easier, Hence the numerous spikes at higher frequencies.

The F12N has a somewhat thicker cone and feels softer, thus damping traverse waves of higher frequency but creating more at frequencies an octave below and above the fundamental.

The moving system of the C12N is about 7 gm heavier than that of the F12N, thus having a higher moment of inertia, a reluctance to move when a force is applied.  This will cause the cone to move slightly later than the force applied to the coil.  By the same token, that extra mass will create a higher momentum, causing the cone to continue moving in the same direction despite the opposite force applied to the coil.  This crates a traverse wave, similar to that seen when one end of a garden hose laid flat and straight on the ground is whipped with the hand.  A hump will move towards the other end of the hose.

Listening to pink or white noise fed to both and switched between them, the C12N does have a brighter sound.

 

 

C12N   f=1000hz

 

F12N   f=1000hz

 

 

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