4 Fi audio btl 4 15"s dual 2's. These are in perfect condition. I had all 4 on 1 ct sounds team 7k amp with a limitless lithium 100 ah hr batt and a 300 amp alt. I planned on adding alot more power but...life has kinda gotten in the way. They have about 10 hours of play time. They are not even broken in, they are still extremely stiff. I am parting put the whole car. Unfortunately i need to change paths and downgrade to something smaller. I am not looking for trades at the time. I have original boxes that they came from fi with the wood crates inside. I would prefer not to ship if possible. These were only made for one year and they are discontinued now, fi still offers recone kits tho if you ever need one. I do not see these coming up for sale ever tbh. Let alone 4 like new. I would like to sell all 4 at once it possible. Thanks for looking and feel free to message me with any questions.
Only issue is that the gaskets have a little paint on them.

Down below are the specs from fi's website.

Why a 4” coiled BTL? Well, because we can. New for 2019 is the first 4” coiled sub in the BTL Series. The BTL4-Ferrite is the latest in the progression of Fi subwoofers geared towards thundering daily drivers. Utilizing a favorite 3 stack ferrite magnet design using US steel cut on our water jet and finish machined on our CNCs, there is plenty of motor force in the FEA derived design for both daily and SPL use. Utilizing a solid pole and a venturi aided pole profile, the forced cooling keeps thermal temperatures under control. A classic 3 stack of ferrite magnets provide the Gauss while 4 Fi designed 10″ heavy progressive spiders keep things under mechanical control. Utilizing a special 144 tinsel count leadwire that is double sewn to the spider pack, there are no losses in power transfer to the coil (available in either standard stitched with terminals or the hybrid stitched with bolted termination.

Working in ported, 4th or 6th order applications the 2019 BTL4-Ferrite Series raises the power handling and thermal performance of a classic line to new levels . As always, the BTL is “Built To Last”.


BTL-4 18
Coils DUAL 1 | DUAL 2
Fs 24.8 Hz | 25.0 Hz
Re 0.7 | 1.4
Qms 7.61 | 7.59
Qes .56| .55
Qts .53 | .52
Mms 567g | 554g
Cms 0.73M/N | 0.73M/N
Sd 1210cm^2 | 1210cm^2
Vas 151.0 l | 151.0 l
Spl 88.0dB 1W/1m | 88.1dB 1W/1m
Bl 14.3 N/A | 20.2 N/A
Xmax 33mm (One Way)
Rms 3500W

Overall Diameter 18.500”
Cutout Diameter 16.750”
Mounting Depth 9.50”
DriverDisplacement 0.10cuft
Sealed Box 2.5-4 cuft
Ported Box 5-7cuft @ 33Hz

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
4” diameter 4 layer coil (Flatwind standard)
3 Stack high grade magnet
Four progressive 10″ spiders
Water jet and machined in house