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Old 3rd April 2013, 06:28 PM   #1
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Default Dual Lab12C Sub

Hey everyone! After becoming quite obsessed with the idea of building my own sub, I'm stoked that I've found this website! So, the plan is to build two subs each with two Eminence Lab12C's. First off, I have a very basic question. Is the volume of the port included in the total volume of the cabinet? I've decided on going with an internal volume of 8 cubic feet, a shelf port that is 20 inches wide, 2 inches high, and 18 inches long. Does that sound alright? I'm after a flat response down to 30Hz and decent performance at 20Hz, which WinISD says I will get with the above dimensions. Thanks in advance for any advice!
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Old 3rd April 2013, 07:11 PM   #2
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Yes, you have to calculate total internal volume less the volume of the ports and drivers, what in a pro 15" driver situation, can be about 10L extra and enough to change the alignment.
WinISD shows the volume of the driver is it's last page.
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Old 3rd April 2013, 07:33 PM   #3
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Now the alignment.
1. EMINENCE LAB12C, VB = 66.4 L, FB = 22.0 Hz
This is a decent alignment (for each driver) why should you need 8ft³ (~226.5L)?!
What gives +/-140L internal (142L = 5.0ft³) each dual speaker sub. Faraway from your initial calculations (if you want another alignment). In this case
Port 2"x8" (5cmx20cm) - length ~27" (for 70L).

Driver Volume Displaced 188.6 cu.in. / 3.09 liters
http://www.eminence.com/?s=lab12

Last edited by Inductor; 3rd April 2013 at 07:45 PM. Reason: driver displacement
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Old 3rd April 2013, 07:54 PM   #4
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Thanks for the tips! Having a port of 27 inches long would make the box very deep though, wouldn't it?
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Old 3rd April 2013, 08:16 PM   #5
_henry_ is offline _henry_  Australia
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You can fold it or use PVC elbow
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Old 4th April 2013, 01:20 AM   #6
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@McFinkle, yes but that was only a starting point. (And I don't like it to be fair with you.)
In terms of construction (_henry is here helping you) I would consider the use of the fold in the cabinet (wood) but I would try to pass without it with a PVC/ABS port. Tell me it's for home or PA?! Do you plan to wire the dual LABs in series or parallel? What crossover freq/EQ are you using, is it just a stand alone sub+amp?
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Old 4th April 2013, 02:20 AM   #7
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2. EMINENCE LAB12C, VB = 70.0 L, FB = 24.0 Hz
This alignment (Vb for each driver) has in consideration F3=30Hz (free-field/24Hz in-room). You have to add the volume for each driver and port system to the internal volume for it's final internal volume (wood thickness and all). Probably this one looks better. You can run infinite calculations before you build...

Port (2"x8"/5cmx20cm) length = ~22.5"
Volume each driver = ~3L
Volume for each port = ~8L
Volume for each driver/system (1x) = 81L
Volume (internal) for a complete system (dual) = 162L (162L = 5.7210ft³)
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Old 4th April 2013, 02:48 AM   #8
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3. EMINENCE LAB12C, VB = 74.0 L, FB = 23.0 Hz
This better protects the woofer from the amplitude of the movement of the cone at low frequencies with port tunned low (longer port).

Port (2"x8"/5cmx20cm) length = ~23"
Volume each driver = ~3L
Volume for each port = ~8L
Volume for each driver/system (1x) = 85L
Volume (internal) for a complete system (dual) = 170L (170L = 6.0ft³)

Port tunning: fine tune the ports between 23" and 25" length (24/22Hz) for this same int. volume (#3).

Last edited by Inductor; 4th April 2013 at 02:59 AM. Reason: port tunning
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Old 5th April 2013, 05:43 AM   #9
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Thanks for that! One last question.. Is it better to have the port orientated so that each driver is the same distance away from it? Like if the drivers are orientated above each other should the port run vertically?
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Old 5th April 2013, 04:36 PM   #10
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Quote:
Originally Posted by McFinkle View Post
Thanks for that! One last question.. Is it better to have the port orientated so that each driver is the same distance away from it? Like if the drivers are orientated above each other should the port run vertically?
If the difference was even measurable, it would be slight.

You may be interested in looking at this dual Lab 12 design:
FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

I have a pair I could sell empty if you don't want to bother building.
It is a higher tuning than you want, but is a very nice compromise between small size and good musical LF output.
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