Rockford Fosgate RFD2218 - Manual (Page 11)

5
B
UILDING AN
E
NCLOSURE
To work properly, the walls of the enclosure must be rigid and not flex when
subjected to the high pressures generated by the speaker's operation. For
optimum performance, we recommend using 3/4" MDF (Medium Density
Fiberboard) and internal bracing. The enclosure should be glued together
and secured with nails or screws. MDF is porous; therefore, it is suggested
to also seal the outside walls with polyurethane.
C
ALCULATING
V
OLUME
Calculating volume is merely a matter of measuring the dimensions in inch-
es and using the formula:
If two facing sides are of uneven length, add them together and divide by
two to take the average. Using this number will give you the volume with-
out the necessity of calculating the box in sections and adding the sections
together. The thickness of the baffle material reduces the internal volume so
this must be subtracted from the outside dimensions to determine the inter-
nal volume. The speaker itself also reduces the internal volume. The
amount of air displaced by each model is listed on the specification sheet
and should also be subtracted from the gross volume calculation.
Height" x Width" x Depth"
1728 cu. in./cu. ft
Box Volume =
(cubic feet)
S
UBWOOFER
C
ROSSOVERS
There are two operational types of crossovers, passive and active. Passive
crossovers (coils or inductors) are placed on the speaker leads between the
amplifier and speaker. An active crossover is an electronic filter which sep-
arates the audio signal fed to different amplifiers. For optimum subwoofer
performance, we recommend using an active 80-100Hz low-pass crossover
at 12dB/octave.