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Your Price:
$464.00 (You save $111.00)
71.00 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 58 | Next

  1. Best subs on The market 5 Star Review

    Posted by on 16th Aug 2015

    Great product worth the wait. I have two of these in my tahoe and they pound.

  2. clearest bass I have ever heard 5 Star Review

    Posted by on 13th Aug 2015

    Well built sub, worth every pennie. Hard hitting and very clean

  3. Sp4 15 5 Star Review

    Posted by on 13th Aug 2015

    This is by far the best sub I ever owned this thing is a monster and will tale one hell of a beating. Hit 144.3 db with the SP4 15 and the Crescendo BC3500 on stock electrical. Still got more to do.

  4. nasty lows 5 Star Review

    Posted by on 25th Jul 2015

    These subs get surprisingly loud for how low they hit. I hit 150.2 db @ 30 hertz with 2 of them with all my settings down somewhat cuz they're still new and breaking in. The sp4s have an awesome look to them and an even better sound. I'm definitely going to be getting other Fi products for my other car now

  5. great sub 5 Star Review

    Posted by on 8th Jul 2015

    This sub is amazing from hitting all the lows to spl in general definitely would recommend for any one who loves bass #beastmode

  6. Best Sub Ever 5 Star Review

    Posted by on 7th May 2015

    I just recently purchased and received my first Sp4 15" and I got to say the wait was all worth waiting for I am completely in love am running it with a Rockford Fosgate Power T3000.1bd rated at 3,612 @ 1ohm. And it takes it like a champ I am very impressed with the over all craftsmanship, performanceI and of course the great customer service Fi Audio has. I been running it for about a month and is still getting broken in and louder and louder with the Low. I will definitely be a Fi Audio customer for years to come

  7. satisfied customer 5 Star Review

    Posted by on 26th Apr 2015

    Very satisfied with this sub and it's worth every dollar. This is my third fi sub so excellence was expected but, I was not ready for this much.

  8. 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....

  9. 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

  10. 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.

Showing reviews 1-10 of 58 | Next