Jensen F12N, A and B

There are two, one purchased a seven years ago, A, in Sept. 2012 and its twin, B in Nov. 2019.  How time flies.

 

 

Gated response 200hz to 20khz   Near field response 10hz to 200hz

The near field response level is arbitrary.  Correcting the near field SPL to 1m would introduce an error as the pressure at a few mm from the cone and at the apex is very high and drops rapidly as the pressure exits the cone volume.  The response shape, however, is close to anechoic due to the high SPL at the apex and is thus highly unaffected by room acoustics.

What took so long to acquire the second unit wasn't the difficulty in finding one with a 1000 ohms field coil but there wasn't any need for a second unit.  The first one was purchased mainly to study the differences, if any, in a field coil speaker vs a permanent magnet.  Jensen made a C12N, identical to the F12N with exception of the magnet.  See this page   The problem making a comparison is that the originals are over 60 years old and the paper diaphragm certainly has been affected by time.

All data here was acquired with 10W to the field coil.  The reasons for this decision can be found on the original F12N page 

 

FIGURE 1

 

 

 

The responses in figs 2 and 3 were derived at 1/4 watt at 1/2 meter.  The similarity between the two in the band of 35hz to 250hz is incredible as is the rise between 2khz and 6khz.

FIGURE 2

FIGURE 3

 

 

     

Figs 4 and 5 are the near field responses measured at 4mm from the cone apex.

FIGURE 4

FIGURE 5

     

 

 

Fig 6 shows the alignments from BassBox Pro, Ver.6.  They are colour coded to coincide with the designs below, figs 7, 8, 9 and 10

FIGURE 6

 

 

 

 

The vents shown in Figs. 9 and 10 are normalized for a 3/4 inch tunnel length, the thickness of the baffle.

 

FIGURE 7 FIGURE 8 FIGURE 9 FIGURE 10

 

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