Box Tuning Troubles...

[grizzleyadams69]

im designing a box for my 15" BL. my dimensions of the box are 30 width x 16.5 height x 21 depth. port width 3.5 inches wide. shooting for 4 cubes after displacement @35 hz. with these dimensions plugged into the RE box calc, im at 4.1 cubes @34.5hz. the actual length from the port opening at the front baffle to the end of the port wall is 16.75 inches. but the calc says that the TOTAL port length is 22.75 inches (from the opening in the baffle to the back of the inside of the box). and the calc bases the tuning of the box on the total port length (22.75), not the length from opening in the baffle to the end of the port wall. it just doesnt sound right that it would base it off 22.75 inches of port and not the 16.75 inches. so my question is, is the calc correct and the box would be tuned at 34.5hz with 22.75 inches of "total" port length? im confused. and this is frustrating. i dont know how clear it sounds but i tried hard to make what im asking understandable. going to bed now, so ill be on tomorrow afternoon to clarify and answer questions u guys have for me. plz help me out!

[tibs]

is this a L port?

if so are you measuring from the middle of the port?

[Decaf]

heres a quick example

imagine the box is ur box... im guessing there isnt a L-port like in the box on the right

the port length is measured down the center of the port... so the port wall is obviously shorter than the total length the sub will "see" or "think"

lets say the left box port wall is 16" long... and the width of the port is 4".... the port length in that picture would actually be 16" + 2"(to get halfway thru the 4inch width) + 2"(to get to the port wall) + 2"(end correction factor... basically since u are using a internal wall as a port the sub thinks the port length is longer than it is, so you use ~1/2 the width of the port to figure out the actual tuning)

so a port wall for the right box would be 16" long, but total port length is 22"... 20" for box calcs that dont account for end correction

[shainemcconnell]

heres a quick example

imagine the box is ur box... im guessing there isnt a L-port like in the box on the right

the port length is measured down the center of the port... so the port wall is obviously shorter than the total length the sub will "see" or "think"

lets say the left box port wall is 16" long... and the width of the port is 4".... the port length in that picture would actually be 16" + 2"(to get halfway thru the 4inch width) + 2"(to get to the port wall) + 2"(end correction factor... basically since u are using a internal wall as a port the sub thinks the port length is longer than it is, so you use ~1/2 the width of the port to figure out the actual tuning)

so a port wall for the right box would be 16" long, but total port length is 22"... 20" for box calcs that dont account for end correction

^X2^

[grizzleyadams69]

heres a quick example

imagine the box is ur box... im guessing there isnt a L-port like in the box on the right

the port length is measured down the center of the port... so the port wall is obviously shorter than the total length the sub will "see" or "think"

lets say the left box port wall is 16" long... and the width of the port is 4".... the port length in that picture would actually be 16" + 2"(to get halfway thru the 4inch width) + 2"(to get to the port wall) + 2"(end correction factor... basically since u are using a internal wall as a port the sub thinks the port length is longer than it is, so you use ~1/2 the width of the port to figure out the actual tuning)

so a port wall for the right box would be 16" long, but total port length is 22"... 20" for box calcs that dont account for end correction

i read this thing like 5 or 6 times, and i think i understand it now. but what is this extra 2" of port "correction factor"? and whats the point of the box on the right? i thought we were just talking about the box on the left...

[Decaf]

end correction factor... basically since u are using a internal wall as a port the sub thinks the port length is longer than it is, so you use ~1/2 the width of the port to figure out the actual tuning... thats what end correction factor is

yeah i forgot to mention the box on the left... i was just gonna say its 16" + 2" + 2" + 10" (2nd port wall) + 2"(ecf)... the pieces of wood would have been 16" and 10"... but the actual port length is 32"... not 26"

*again these numbers are just an example and not to scale

*red lines are actual port length, black are pieces of wood, yellow is ecf

[grizzleyadams69]

end correction factor... basically since u are using a internal wall as a port the sub thinks the port length is longer than it is, so you use ~1/2 the width of the port to figure out the actual tuning... thats what end correction factor is

yeah i forgot to mention the box on the left... i was just gonna say its 16" + 2" + 2" + 10" (2nd port wall) + 2"(ecf)... the pieces of wood would have been 16" and 10"... but the actual port length is 32"... not 26"

*again these numbers are just an example and not to scale

*red lines are actual port length, black are pieces of wood, yellow is ecf

ok, so what would be the end port length for the first one?