As I get older I keep forgetting my math formulas and data required to feed my speaker building addiction. So I made myself a one-page sheet derived from a JBL document of some of the important stuff I should remember... Which I think should also be useful for many other members here. Someone may like to make a "sticky" out of that. Be my guest and do it for the benefit of all. Richard
LITERS FEET^3 INCHES^3 METERS^3 MILLIMETERS INCHES METERS
___________________________________ _____________________________
1.00 = .035315 = 61.02 = .001 1.00 = .039 = .001 Liters = Cu. Ft. x 28.32
28.32 = 1.00 = 1,728 = .02832 25.40 = 1.000 = .0254 Cu. Ft. = Liters / 28.32
1000.00 = 35.315 = 61,024 = 1.00 1000.00 = 39.370 = 1.000
TO FIND SOUND WAVE LENGTH: divide velocity of sound by frequency (Hz)
SOUND VELOCITY = 344 m/s, 1130 ft/s or 13,560 in/s
AREA OF CIRCLE = Pi 3.1416 x (radius squared) Note: radius = 1/2 diameter; OR .25 x Pi 3.1416 x Dia. squared
TO FIND THE DIAMETER OF A CIRCLE WITH EQUIVALENT AREA:
2 x square-root of (area divided by 3.1416)
example: area of 9" (23 cm) tube = area of 8" (20 cm) square duct calculated:
(US Units) (area) 64/3.1416 = 20.372, square root = 4.5135 x 2 = 9.03" (diameter)
(Metric Units) (area) 400/3.1416 = 127.324, square root = 11.284 x 2 = 22.568 cm (diameter)
VOLUME OF CYLINDRICAL DUCT = circular area x length; logically it should be outside circular area ?
VOLUME DISPLACED BY JBL LOUDSPEAKERS: 8" (20 cm) = .05 cu ft (1.4 L.), 10" (25 cm) = .1 cu ft (2.8 L.),
12" (30 cm) = .15 cu ft (4 L.), 15" (38 cm) = .2 cu ft (6 L.), 18" (46 cm) = .3 cu ft. (8.5 L.).
JBL LOUDSPEAKER MOUNTING HOLE AND BOLT CIRCLE DIMENSIONS:
mounting holes: (Always double-check with specific driver data sheet)
8" = 7-1/16" (18 cm), 10" = 9" (23 cm), 12" = 11-1/16" (28 cm), 15" = 13-31/32" (35.5 cm),
18" = 16-13/16" (42.7 cm).
bolt circles: (Always double-check with specific driver data sheet)
8" = 7-5/8" (19.4 cm), 10" = 9-3/4" (24.8 cm), 12" = 11-9/16" (29.4 cm), 15" = 14-9/16" (37 cm),
18" = 17-3/8" (44 cm).
* Document taken from JBL FAQ Speaker Building Q & A, with some additions such as Metric conversions.
Richard
EDIT: Sorry but I just can't get the three data columns at the top to be separated so they would look more appropriate. Tried but need help on that.