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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 29 | Next

  1. sp4 15

    Posted by keith miller on 13th Mar 2014

    good looking monsterous beast. I knew it was a good choice in a sub purchase but all my expectations were exceded and then some. Whomever is looking to buy or thinking of buying from fi you wont be disappointed at all.

  2. Amazing Product

    Posted by Unknown on 11th Feb 2014

    Well it took a month to get to me. Initially I was a little doubtful on how it would perform....not anymore, received the product modified my box & put it in my car....I'm pushing it with a RF T2500BDCP rated at 3445 watts on 1ohm. This monster sub takes it all & beg for more lol. I love this sub, will never buy any other sub FI rules.

  3. Ground pounding beast!

    Posted by Ryan on 21st Jan 2014

    Currently running my loaded SP4 in a 31hz tuned enclosure off of 1,925 watts RMS and this monster destroys the lows! Forget flexing, my doors wobble...
    Awesome sound quality and I'm getting a LOT more out of my setup than my previous driver (RE SXX15D2) on the same power. Can't wait to match it up with an equally beast amp!

  4. The Best

    Posted by Unknown on 1st Jan 2014

    The sp4 15 is my upgrade from 3 fosgate p2 12s on 1100 watts. Idk how to explain but on the same 1100 watt amp, this sub is heard from blocks.... This woofer is nasty. It will eat everything you give it. And it loves the lows. I can't even concentrate on driving with this thing slapping. I can't image what it can do with 3k....

  5. This subwoofer is amazing

    Posted by Unknown on 29th Dec 2013

    I upgraded from 12's to a single 15 and this thing shakes my whole truck like no other sub I owned. I like the way you can customize it and add carbon fiber.

  6. Monster 15.

    Posted by Unknown on 21st Dec 2013

    The sp4 15 is fantastic for the price. Hits the lows and doesn't roll off at 50 Hz like most 4 inch coil 15s. Best bang for the buck in the 3000 watt range hands down.

  7. Insane

    Posted by Trevor on 16th Dec 2013

    I have it hooked up to 1 ohm on an aq2200d right now in Chevy Cruze and it just gets nasty. This sub is a monster and fi is awesome! Thank you guys!!

  8. sp4 monster

    Posted by seth on 20th Nov 2013

    I recently upgraded from a BL 15 to a sp4 15, and the difference between the two is crazy. The sp4 destroys the lows and in my 30hz tuned box plays down to 18-20hz. By far the bet sub I've ever purchased. If you want one nasty 15 the sp4 is it.

  9. amazing

    Posted by Joe on 2nd Nov 2013

    This Is hands down the best sub I've ever heard and I'm only breaking it in with 1700

  10. Awesome subs!!

    Posted by Unknown on 9th Oct 2013

    Have 4 15" sp4s on two AQ 3500.1d amps and it just gets down right nasty I love it best subs for the money for sure!

Showing reviews 1-10 of 29 | Next