Modeled a couple boxes, let me know what you think. - AVS Forum
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post #1 of 10 Old 03-11-2008, 12:24 PM - Thread Starter
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I bought two of these. Dual VC subs from Fi, called the X (2in VC, as opposed to Q that has the 3in so should be a tamer version with better SQ?)

12 DUAL 4
Fs: 25.7 Hz
Re: 3.9 Ohms/coil
Qms: 4.01
Qes: .38
Qts: .35
Mms: 120g
Cms: 3.2mm/N
Sd: 480cm^2
Vas: 104.1 l
Spl: 88.6dB 1W/1m
Bl: 20.0 N/A
Xmax: 16mm
Rms: 300W
Sealed box: .9-1.3 cuft
Ported box: 1.6-2.2 cuft
Sub OD: 12.500
Cut ID: 11.125
Mounting depth: 5.750
Displacement: 0.10cuft

I wasn't sure if I want these in the same cabinet or not, and originally these were recommended to me by another member for an SVS clone (their tripple ported dual 12 sub). I may or may not do that later, but for now I want each in their own cab so I can use them under my mains for both aesthetics and speaker stands. Also I would like to run them in stereo once I get a good amp (or two monos).

Here's what I came up with as a best compromise for space v. curve.

Vented: 110L, 19hz, 1x 4in port of 20 inches.

Sealed:90L

SPL:



Group Delay:


This sub seems more cut out for vented boxes, though I'm still leaning sealed. It does drop a bit quick, but I'm assuming with room gain it'll even out a few dB. The difference in SPL between sealed v. ported doesn't look like a lot, though the group delay is insane for vented! I read as much as I could about it, though nobody has any concrete info on what Hz v. ms is audible, but I think i'd rather have the quick response of the sealed box down low. I like to believe I can hear that kind of stuff.

Whadya guys think?


Ps. looking for a good amp as well. Doesn't have to be 2ch, but it does have to be inexpensive. E-bay?
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post #2 of 10 Old 03-11-2008, 12:58 PM
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Quote:
Originally Posted by AlexE View Post

I bought two of these. Dual VC subs from Fi, called the X (2in VC, as opposed to Q that has the 3in so should be a tamer version with better SQ?)

No, it should be a cheaper version with lower power handling, not that won't sound good though.
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post #3 of 10 Old 03-11-2008, 01:04 PM - Thread Starter
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Originally Posted by armystud0911 View Post

No, it should be a cheaper version with lower power handling, not that won't sound good though.

It is a cheaper version with less power handling. And more accuracy at lower amplitude - no?

I don't imagine I could drive the Q as accurately in my room with the same power, that's what i was getting at.

So that aside, what did you think of the curves?
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post #4 of 10 Old 03-11-2008, 01:10 PM
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Your right, it does have a nice efficiency advantage


Personally, I'd reallly take the ported, however, your airspeed might be getting pretty intense there with just one 4" port, put the 300watts (or whatever it takes) into it and see what the airspeed is doing
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post #5 of 10 Old 03-11-2008, 01:25 PM - Thread Starter
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Actually I had a question about that. What represents the port air speed?

WinISD help doesn't work in Vista, even when I run the program in compatibility mode (otherwise it doesn't work for me period)
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post #6 of 10 Old 03-11-2008, 02:16 PM
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looks like airspeed peaks around 39m/s at 18hz
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post #7 of 10 Old 03-11-2008, 06:03 PM - Thread Starter
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Originally Posted by zero the hero View Post

looks like airspeed peaks around 39m/s at 18hz

When does it typically become an issue? I have 0 experience with DIY ported cabs.
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post #8 of 10 Old 03-11-2008, 08:55 PM
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Peak air speed in the port should be kept under 20m/sec when a pot is flared and good target to shoot for is around ...under 15m/sec. Over 30m/sec and you will have a giant puffer when material with content close to tuning arrives. I would run tests, to see what bothers you , modeling is only part ,testing is needed IMO to get a proper real world result.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #9 of 10 Old 03-11-2008, 09:04 PM
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It really depends though, winisd uses an average speed to determine the air velocity, this is not accurate at all, when you have a single large port, you will get much less chuffing due to the aerodynamics involved than if you were to have several smaller ports. A 6" port is very hard to chuff with a 15" driver due the how slow the air will be moving on the outside as opposed to the inside, if you were to do 3 4" ports, the chuffing would be more evident, even though you have more port area. An 8" port with an 18" driver is extremely hard to get to chuff even at high outputs down deep. You have to remember that when a sub is doing deep subsonic stuff, often times the chuffs aren't as audible because they aren't changing directions as fast creating less turbulence and noise. It is generally accepted that the threshold of audibility in a port is around 17.5m/s or 5% of the speed of sound, however if you look at what some manufacturers like SVS do, they REALLY push a long ways past this.
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post #10 of 10 Old 03-12-2008, 01:55 AM - Thread Starter
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So if a 6 is enough for a good 15, a 4 ought to work for my 12 "in real life"?

Also do both curves look OK? How far down should I be at 20-30 hz with a well matched 12" + enclosure? (very generally speaking of course) Everyone says that you don't want a perfectly flat curve, but both - especially the sealed look pretty steep to me.
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