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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 39 | Next

  1. Sp4 is nothing short of excellence!

    Posted by Unknown on 19th Aug 2014

    Haven't hooked my sp4 up to full power yet but its gonna be on a hifonics zrx3200.1D. Satisfied with what it can do. I only have it on 600 rms breaking it in.

  2. Ground Pounder!

    Posted by Graham from Canada on 26th Jul 2014

    I've been doing car audio for around 20 years, and I have to say the Fi SP4 has to be the most beastly sub I've ever put hands on. This sub replaces my BTL N2 and even before break-in it goes low with more authority. Looking forward to destroying the lanes with these two monsters!

  3. Thundering My Daily NEED...

    Posted by sherwin conarco on 25th Jul 2014

    Got My new SP415... One word... LOUD.. i hook it up on my Firland XL3000D mono amp and booommming like no tommorow... i put it on box 3.5cu ft tunned @ 32hz.. freaking catch up the low notes... its totaly awsome... MORE POWER to the Fi familly...

  4. your shits weak

    Posted by josh on 25th Jul 2014

    I have this sub wired at 1ohm on a Brutus 2400 and this thing quakes! Throbs n flexes everything hands down only fi from now on . Only flaw was the foam saround covered the screw holes but other than that this thing is freakin mean

  5. Ground Pounder!

    Posted by Unknown on 18th Jul 2014

    I've been into car audio for around 20 years, and I have to say these are hands down the most hard core subs I've ever had! The SP4's are in a league all their own!

  6. awesome daily driver

    Posted by Paul in md on 8th Jul 2014

    I haven't fully had the chance to break in the sub yet I have it ran Off of an aq3500 at 1 ohm and this thing moves air like crazy. About to add a bigger box and probably get another in the near future.

  7. wow!

    Posted by moredbsplease on 12th Jun 2014

    went from two 13w7s on a rf2500bdcp in ported box,to 3 15 sp4 in 4th order on the same amp for now and wow! is all i can say! i can't believe the difference in output every time i turn it up. can't wait to see what it does when i get the dc 9k hooked up. FI FOR LIFE!

  8. Ultra high quality sub!

    Posted by aem on 10th Jun 2014

    Everyone looking to buy, you will not be disappointed with this sub what so ever. Excellent craftsmanship and this monster gets L-O-U-D! Thanks FI for yet ANOTHER QUALITY SUB!!

  9. SP4's bang!!!

    Posted by Smoove on 2nd Jun 2014

    Did a 140.2 on an RF T5002 with 2 SP4 15's in a blowthough. I can't wait to see what to see what they on 2 RF T2000's.

  10. Perfection at it's best.

    Posted by Karkov on 29th Apr 2014

    No better sub on the planet.

Showing reviews 1-10 of 39 | Next