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Old 19th April 2005, 08:32 PM   #1
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Location: Il
Default frustrated with calcs

I can't seem to get a stable answer for a port length.

12" speaker
Qes = 0.38
Qms = 4.06
Qts = 0.347
fs = 25 Hz
Vas = 4.178 cu.ft.
Ze = 4 ohms
Xmax = 5.6mm
displacement = .12 cu.ft.

200 Wrms 600 max

wedge box

H = 16"
W = 14.75"
D1 = 9"
D2 = 12"

1.0 cu.ft box
0.82 after

Port dia. = 3"
tuning freq. = 42 Hz


What the **** is the length of the port?

I'll get anywhere from 8 in. to 11 in. I need a consistant calc.
or formula, plz.
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Old 28th April 2005, 12:09 AM   #2
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Default port length

I got 11.25" for a.82cuft box
if I'm supposed to minus the speaker vol from that its .7cu ft which gives me 13.69" long port. Assuming the normal flush one end and free end the other.
its not a flat response before rolling off its got about 2.6dB gain at 85Hz. IMHO i would go to a larger box and lower tuning freq.
there are differences from program to program partly due to more accurate modelling. Online ones are ok for approximations. Ive used WinISD(its free!!) most often but these numbers are from Bass Box Pro 6.
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Old 5th May 2005, 03:49 PM   #3
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Default made hanges

I have since canged box size and tuning freq.

tuning freq 29 Hz
2 in. ports per chamber non-flared

W = 14.75"
H = 16"
D1 = 18"
D2 = 21"

Port length 8 13/16" for ea.

sound about right?
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Old 5th May 2005, 05:58 PM   #4
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Default clarify

RE:
2 in. ports per chamber non-flared
Im assuming more then one 2" diameter port then, 1 flush 1 free end.

What internal volume do you have for the box before port ect.

(remember u have to minus port volume and speaker displacement in the final design).
from the numbers u gave me I wasnt getting close to your numbers unless you use 4 ports......
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Old 5th May 2005, 07:18 PM   #5
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It's actually two boxes in one (center divider)

W = 28.75"
H = 16"
D1 = 18"
D2 = 21"

.75" MDF

2 cu.ft. per chamber
2 ports per chamber
non flared straight tube

Using WinISD .05a7
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Old 5th May 2005, 07:40 PM   #6
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so 2 identical boxes/subs or like a 6th order bose?
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Old 5th May 2005, 07:55 PM   #7
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Box Front Angle = Degrees 79.4
Gross box volume = cu.ft. 1.881
Net box volume = cu.ft. 1.847
Port Length = Inches 9.4 (square)
square port dimensions H=2.507 W=2.507
Port Area = Inches2 6.283
Port Volume = cu.ft. .034

The calc I used only supports square ports
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Old 5th May 2005, 07:55 PM   #8
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sort of
going in my trunk

one big box with a center divider for seperation
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Old 5th May 2005, 07:55 PM   #9
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Default area too small

as per
min port area your port area is too small. Port area is your friend especially if you are looking to do better speakers and dont want port noise.
o square that makes all the difference then its not as bad but its still a bit small
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Old 5th May 2005, 08:10 PM   #10
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define gross/ net.
all I need are internal box volume after speaker displacement.
ports are by area shape doesnt matter. there is no major difference between square and round for your application. A single port per side will be more efficient as there is less surface area per port area. remember area for a circle thats same for port area pi r^2.

If you havent got any wood cut its usually alot easier to model what looks good(vol/ports) then define dimensions after that to give required volume. Thats how most programs are set up and people make boxes.
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