Fi Q 18 - Please make sure I don't mess up again - AVS Forum
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post #1 of 8 Old 07-01-2012, 06:22 PM - Thread Starter
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Okay, well after I purchased 2 Skar VVX 15s on a whim and built the box and realized that I made a horrible enclosure I tried to put some effort into designing a nicer response down low.

I already have a Behringer EP1500 (1100 RMS @ 4 Ohms...ish)

I have spent over 8 hours today modeling woofers in winisd and I think I found what I want and for a good price too.

Driver: Fi Q 18in Dual 2 Ohm VC

T/S:

Q18

DUAL 1 | DUAL 2

Fs: 32.4 Hz | 32.1 Hz
Re: 0.7 Ohms/coil | 1.4 Ohms/coil
Qms: 9.31 | 9.37
Qes: .48 | .48
Qts: .46 | .46
Mms: 341g | 347g
Cms: 0.73mm/N | 0.73mm/N
Sd: 1210cm^2 | 1210cm^2
Vas: 149.7 l | 149.7 l
Spl: 92.0dB 1W/1m | 91.9dB 1W/1m
Bl: 13.9 N/A | 19.65 N/A
Xmax: 28mm
Rms: 1500W
Sealed box: 4-8 cuft
Ported box: 6-10 cuft @ 28Hz
Sub OD: 18.500”
Cut ID: 16.750”
Mounting depth: 10.000”
Displacement: 0.24cuft

Here is my WinISD graph (Keep in mind I am not looking for a flat graph or response particularily low. I want to have maximum output at around 26hz. This sub is for music only and I listen to alot of music that peaks in the 20Hz range.. I am spoiled my output down low in my car and want to get close to it in my house.)

(Click on photo to go to imageshack and the click on pic again to enlarge it)
q18v.jpg


Now to simplify my build I want to use Sonotube. I want to use a piece that is 24inches in diameter and 5 feet high. This gives me 15.7 Cubic feet of gross volume. My port I figured I would use the cheap Quickrete brand of sonotube that Lowes sells. It is 12" in diameter. So my port will be 12 inches in diameter and the length will be 23 inches as shown below

q18box.jpg

Please let me know if there is anything you would change. THANKS!

Edit: Is 1100w rms a safe amount of power in this size box? When would I exceed xmax?
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post #2 of 8 Old 07-01-2012, 07:17 PM
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How big is your room? Lower frequencies can receive a boost from the room (just like a car, but it happens much lower in frequency), which is why a lot of people shoot for a shallow roll off, instead of flat or peaked response. Another thing to consider is the EP1500 doesnt do very well bridged at 4ohm when pushed hard, it is better suited to stereo 4 ohm at 400 watts per channel. If you could fit a pair of the large enclosures you are talking about, you could get a pair of Obsidian 18's for a little more then the price of one Q18. You could then build a pair of 20hz tuned boxes, a 10" x 26" port in your spec'd enclosure above would do the trick. Each will have a ton of output with only 400 watts, and xmax is never an issue. You could also try plugging the ports, as this box size is ideal for a sealed Obsidian 18. There are many benefits to running dual subs, and it definitely makes a difference for a music system.


Here's a comparo between Obsidian 18 ported and sealed in the above enclosure size with 400 watts
270
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post #3 of 8 Old 07-01-2012, 07:20 PM
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Quote:
Originally Posted by Jay1 View Post

How big is your room? Lower frequencies can receive a boost from the room (just like a car, but it happens much lower in frequency), which is why a lot of people shoot for a shallow roll off, instead of flat or peaked response. Another thing to consider is the EP1500 doesnt do very well bridged at 4ohm when pushed hard, it is better suited to stereo 4 ohm at 400 watts per channel. If you could fit a pair of the large enclosures you are talking about, you could get a pair of Obsidian 18's for a little more then the price of one Q18. You could then build a pair of 20hz tuned boxes, a 10" x 26" port in your spec'd enclosure above would do the trick. Each will have a ton of output with only 400 watts, and xmax is never an issue. You could also try plugging the ports, as this box size is ideal for a sealed Obsidian 18. There are many benefits to running dual subs, and it definitely makes a difference for a music system.
Here's a comparo between Obsidian 18 ported and sealed in the above enclosure size with 400 watts
270

i doubt he wants to wait 100+ days.
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post #4 of 8 Old 07-01-2012, 07:22 PM
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i doubt he wants to want 100+ days.

eek.gif I didn't realize they were that far out
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post #5 of 8 Old 07-01-2012, 07:41 PM
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I guess I could answer your actual question. Everything you have planned looks fine if that's the FR you're looking for. Cone excursion shouldn't be an issue as long as you dont actually watch movies with ULF content, but if you do, just turn on the amps 30hz HPF, which simply flattens out your peak, giving a -3db point of 26hz. This is also something you can try if you feel the low end is overpowering with your planned peaked response.

edit: you also should consider some kind of EQ to kill the massive inductance hump this driver has at 50hz
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post #6 of 8 Old 07-01-2012, 07:58 PM
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"I am spoiled my output down low in my car and want to get close to it in my house."

this is going to come as a disappointment, but physics is physics.

take the volume of your room in your home and divide it by the volume of your car.

that will give an approximation of how many multiples of what you have in your car, when placed in your home, you will need for the same effect.

e.g., if your room is 20x12x8, that is 1920 cubic feet. if your car is 4x6x4, that is 96 cubic feet. so the multiple is 1920/96, or 20 times. so if you are happy with one 12" woofer with 100 watts in your car, you will need twenty 12" woofers and 2000 watts in your home or an equivalent for the same effect.

sound is just moving air around. the more that you want to move, the more tool is required to move it.

Listen. It's All Good.
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post #7 of 8 Old 07-01-2012, 08:25 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

"I am spoiled my output down low in my car and want to get close to it in my house."
this is going to come as a disappointment, but physics is physics.
take the volume of your room in your home and divide it by the volume of your car.
that will give an approximation of how many multiples of what you have in your car, when placed in your home, you will need for the same effect.
e.g., if your room is 20x12x8, that is 1920 cubic feet. if your car is 4x6x4, that is 96 cubic feet. so the multiple is 1920/96, or 20 times. so if you are happy with one 12" woofer with 100 watts in your car, you will need twenty 12" woofers and 2000 watts in your home or an equivalent for the same effect.
sound is just moving air around. the more that you want to move, the more tool is required to move it.

I already know I am going to be disappointed as I meter 144db at 28hz. I just want to be less disappointed than I am currently tongue.gif

Well, I suddenly had a change of heart. I think I am going to build 2 12 cubic ft enclosures per Skar VVX as I do not want to go through the hassle of selling them and finding a used Q 18 which is pretty hard to find. The VVX's should actually have more output from 0hz up to 60hz so I think I will end up happy.
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post #8 of 8 Old 07-04-2012, 11:35 PM
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Quote:
Originally Posted by andale927 View Post

I already know I am going to be disappointed as I meter 144db at 28hz. I just want to be less disappointed than I am currently tongue.gif

Build two 12cu ft folded horns tuned to 26hz, they are the loudest box design you can choose. That is all you can do short of buying 20 subs and 20 amps to get similar numbers.
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