SP4 Series – SP415 v2

$692.00 $519.00

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Handmade in USAEstimated despatch time of 10-15 business days

The SP4 v2 Series is the latest in the progression of Fi subwoofers geared towards thundering daily drivers.

SKU: SP415 Categories:

The SP4 v2 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 water jet and 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 open motor geometry, there is plenty of thermal capacity in the SP4. A single 10″ high grade magnet provides the Gauss while 4 Fi designed 10″ heavy progressive spiders keep things under mechanical control. Utilizing a special 144 tinsel count leadwire there are no losses with power transfer to the coil. The 2017 SP4 v2 Series is designed for monster daily driving systems requiring high linearity and extreme power handling. The SP4 v2 Series raises the bar for the industry…again.

  • Dual 1 and Dual 2 Ohm

  • Extra heavy aluminum basket

  • Wrap around gasket

  • Kraft pulp fiber reinforced cone

  • Dual layer wide foam surround

  • Standard heavy duty stitched lead or Hybrid stitched FOAD system

  • 144 tinsel count leads

  • FEA optimized motor

  • Open column motor design for increased cooling

  • 4” diameter 4 layer coil (Flatwind standard)

  • Single high grade magnet

  • Four progressive 10″ spiders

  • Water jet and machined in house at Fi
Weight 69 lbs





Dual 1, Dual 2



Thiele-Small Parameters

SP4 v2 12 SP4 v2 15 SP4 v2 18
Coils DUAL 1 | DUAL 2 DUAL 1 | DUAL 2 DUAL 1 | DUAL 2
FS 27.9 Hz | 27.9 Hz 27.6 Hz | 27.9 Hz 24.7 Hz | 24.9 Hz
RE 0.65 | 1.27 0.65 | 1.27 0.65 | 1.27
QMS 6.08 | 6.01 6.56 | 6.45 7.45 | 7.38
QES 0.47 | 0.47 0.52 | 0.52 0.60 | 0.59
QTS 0.44 | 0.44 0.48 | 0.48 0.55 | 0.55
MMS 386g | 376g 434g | 424g 555g | 544g
CMS 84.5 | 84.5 0.77 | 0.77 0.74 | 0.74
SD 480cm^2 | 480cm^2 810cm^2 | 810cm^2 1210cm^2 | 1210cm^2
VAS 27.4 l | 27.4 l 70.4 l | 70.4 l 153.7 l | 153.7 l
SPL 82.8dB | 82.8dB 86.4dB | 86.5dB 87.8dB | 87.9dB
BL 13.7 N/A | 19.1 N/A 13.7 N/A | 19.1 N/A 13.7 N/A | 19.1 N/A
XMAX 33mm (One Way) 33mm (One Way) 33mm (One Way)
RMS 3500W 3500W 3500W

Technical Specifications

SP4 v2 12 SP4 v2 15 SP4 v2 18
Overall Diameter 12.500” 15.625” 18.500”
Cutout Diameter 11.125” 14.125” 16.750”
Mounting Depth 10.00” 11.00” 12.250”
Driver Displacement 0.19cuft 0.21cuft 0.26cuft
Sealed Box 1-2 cuft 2-3.5 cuft 4-6 cuft
Ported Box 1.8-3 cuft 3-5 cuft 6-8 cuft

This is a complete list of options; not all options are available on all models.
See drop down selections for options available with each speaker model

P Chamfer: This is a chamfer on the end of the pole, it helps to bring the air down around inside of the motor and helps cool the coil better. It also helps relieve the pressure underneath the dustcap. We recommend at the bare minimum to get this option if you choose this series of woofers.

Hyper Pole: This is an extended version of the standard P Chamfer. It has 1.250” more pole and chamfer resulting in an increased compression ratio for better cooling.

Cooling: Self explanatory, the cooling channels are machined into the inside of the sub to help cool the coil FAR better. But there are some things that you sacrifice. There is less metal inside of the motor so it is a little weaker. If you are looking for a fart/burp only scenario for SPL we suggest that you do NOT get this option. Stick with only the P chamfer. Now if you are looking for a daily sub to beat on and you have less then 2000 watts then this is the option for you. 2000+ watts you need to look into the BTL series.

Flatwind: The flatwire coil option simply helps the power handling of the sub. The coil has more surface area to dissipate heat and will take more power then the regular round wire coil that comes in the ‘stock’ version of the sub. This option will also make the sub tend to be more prone to ‘peaking’. If you are looking to do an SPL install we highly recommend that you use choose the flatwound coil option. In testing it is louder then the regular roundwire coil and takes the thermal abuse much better.

BP: “BP” option which was a machined aluminum compression plug to the pole which helps channel all of the air under the dustcap around the coil for better cooling. To aid with this increased airflow we also added 6 axial cooling channels in the top plate. Along with increased thermal capacity comes the addition of an extra spider and a changed spider pack. All of these features increase power handling from 200-500 Watts depending on the application.

High QTS: This option is for users who intend on using the subwoofer in only a sealed enclosure.

Low QTS: This option is for users who intend on using the subwoofer in only ported enclosures.

Extra Spider: This option adds an additional spider to the spider pack to help with mechanical power handling and keeping the moving assembly under control.

I Heat Ring: This option is a machined aluminum ring in the gap that lowers the inductance of the voice coil which allows it to play up a little higher in the frequency range and have better overall transient response. Please note that you can NOT select low Qts and the I Heat Ring options together.

Internal Lead: This option is for 8 lead coit per coil, increasing the current flow from coil to terminals.

Inner Heat Sink: Its a machined aluminum ring in the gap that lowers the voice coils inductance (allowing it to play up higher and have a little better overall transient response). It also reduces the volume inside the magnet gap of the motor increasing air speed with the cooling as well as allowing the coil to kick off heat to a more receptive thermal mass rather than magnets.

Daily or SPL: Simply put, if you plan on listening to any type of music you MUST choose the daily option. If it is strictly for a fart/burp scenario then choose the SPL option. The reason we have these options is the gap tolerances between the two are different. The gap in the SPL woofer is much tighter and FAR less forgiving in comparison to the Daily option. The Daily option simply gives the coil more wiggle room inside of the gap to deal with the non-linearity tendancys that you can get into when you are using a sub in a daily driving scenario. Typically SPL applications deal with 1 note and it does not change, therefore we can make the gap much tighter and get all of the motor strength that we can out of it.

Spider Spacer: Adding this feature mirrors the spider layers and in turn reduces rock ratio helping keep the voice in line at extreme excursion.

Universal: This option gives you the choice to later chance the impedance of your voice coils. You can change from dual 2s to dual 1s and vice versa by reconing them. If you do not choose this option your motor(s) will be optimized per the coil resistance that you have chosen. (Dual 2s will forever be a dual 2 motor, Dual 1 will forever be a Dual 1 motor).

Dust Cap Type: Choose between a standard or a carbon fibre dust cap. See the examples below…





Subwoofers & Recones are dispatched via FedEx Ground. Small goods such as sticker packs, various apparel items are shipped via USPS. Upon dispatch of your goods, order status will be updated from “test/pack” to “shipped” which is accompanied with tracking details.


    Sp4s have neverlet me down in the past. These look twice as good as te last.

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