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Your Price:
$464.00 (You save $111.00)
67.00 LBS
Estimated build time of 10-15 business days
Calculated at checkout

Product Description

All US steel machined in house at Fi.

The SP4 Series is the latest in the progression of Fi subwoofers geared towards thundering daily drivers. Starting with a monster 4" voicecoil for increase thermal capacity, we built the rest of the sub around that. With a proprietary US made steel machined in house on one of our CNC machines, there is no shortage of motor force in the FEA derived design. With a solid pole and the optional cooling systems, there is plenty of thermal capacity in the SP4. Two high grade magnets provide the Gauss while 5 Fi designed 10" progressive spiders keep things under mechanical control. Utilizing a special 280 tinsel count leadwire with FOAD lead attachment ensures that there are no losses with power transfer to the coil. The upgraded 2014 SP4 Series is designed for monster daily driving systems requiring high linearity and extreme power handling. The SP4 Series raises the bar for the industry...again.


SP4 Series: Currently in 15” and 18”
Dual 1 and Dual 2 Ohm (custom options available)
Extra heavy aluminum basket
Wrap around gasket
Kraft pulp fiber reinforced cone
Single layer wide foam surround
FOAD Bolted Leads
280 tinsel count leads
FEA optimized motor
High Flux density design
4” diameter 4 layer coil (Flatwind standard)
Double stack magnets
Five progressive 10" spiders
Optional Cooling Systerm
Machined in house at Fi
And many other custom options


Fs: 27.6 Hz | 27.9 Hz
Re: 0.65 Ohms/coil | 1.27 Ohms/coil
Qms: 6.56 | 6.45
Qes: .52 | .52
Qts: .48 | .48
Mms: 434g | 424g
Cms: 0.77mm/N | 0.77mm/N
Sd: 810cm^2 | 810cm^2
Vas: 70.4 l | 70.4 l
Spl: 86.4dB 1W/1m | 86.5dB 1W/1m
Bl: 13.7 N/A | 19.1 N/A
Xmax: 33mm | 33mm
Rms: 3000W | 3000W
Sealed box: 2-3.5cuft | 2-3.5 cuft
Ported box: 3-5cuft | 3-5cuft
Sub OD: 15.625” | 15.625”
Cut ID: 14.125” | 14.125”
Mounting depth: 11.250” | 11.250”
Displacement: 0.21cuft | 0.21cuft

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Product Reviews

Showing reviews 1-10 of 51 | Next

  1. Perfect sub. 5 Star Review

    Posted by on 2nd Apr 2015

    Not my first time buying these subs. To this day these are my favorite sounding subs. I will continue to buy and use FI products because of their quality. Nothing really bad to say honestly....

  2. very well built sub 5 Star Review

    Posted by on 6th Mar 2015

    I haven't hooked them up yet but man they sure are beastly subs!! Way better than any other sub I've bought in the pass and I had a lot of other "top brands". I should have both hooked up in a week or so and can't wait. I'm happy I went this direction

  3. Always happy with my purchase 5 Star Review

    Posted by on 18th Feb 2015

    This would be my second SP4 15 and I will be starting a full build in a much larger vehicle than my pickup. Even though being in a pickup with a barely put together box, this one 15" was noticeably louder than any other 15 i have come in contact with. Would highly recommend, especially paired with the soundquebed q3500.

  4. amazimg 5 Star Review

    Posted by on 12th Feb 2015

    Just installed and a great product from the care in the shipping to the power it puts out looking too by another soon

  5. added some power since my last review 5 Star Review

    Posted by on 15th Dec 2014

    Finally have 2 RF T2k's on my SP4's
    1:17 of the vid things float

  6. Outstanding 5 Star Review

    Posted by on 27th Nov 2014

    Great Sub. I hooked it up to 2 cresendo s1500s I want to try pushing more power in her and seeing what happens. But all around, killed my 2 15 in power acoustik mofo's out of the water.

  7. amazing 4 Star Review

    Posted by on 10th Nov 2014

    I have it running on a boundaries 2200 for now and can say it sounds great. Plan on getting a second one soon!

  8. Holy S**t!!! These subs are no f**king joke! 5 Star Review

    Posted by on 4th Nov 2014

    It's been 14 years since my SPL competition days... I built a 9.5 cu ft. ported box 1.5" thick MDF with all-thread bolts, etc... tuned to 32hz for 2 of these 15's in my suburban ( walled w/ all seating ) and holy s**t! these produce some serious SPL and sound amazing doing it. Might be in the high 140's. ( just a guess ) Only running on one amp wired at 2.6 ohms ( Dual 1 ohm version ) with roughly 2200 watts as a test, and I am afraid to strap the two amps together and run 8k to them! I am VERY impressed! Well built! Love the bolts to attach speaker wire or in my case 4GA wire!

  9. This is the real deal 5 Star Review

    Posted by on 19th Oct 2014

    I went from a re audio mx to this it's twice as loud and better sound quality it slams. Only got 2200 watts going to it and it is still very loud and low rattles house Windows when I pull in driveways. Couldn't imagine it on 3000+ watts, it's worth the wait and the money.

  10. great 5 Star Review

    Posted by on 7th Oct 2014

    When I got the boxes and open them I was surprised how they came in wooden frames. These subs deffitenly pound and still not broken in

Showing reviews 1-10 of 51 | Next