Proline X

Professional Series Ported Dual 15" Enclosure | Sundown Audio U-Series v.1 15

Q: Do I need a subsonic filter?

Yes, at 23 Hz, 24 dB per octave. Below tuning a vented box stops loading the cone and excursion runs away toward DC. With the filter in place this cabinet puts the Sundown Audio U-Series v.1 15 at 28 percent of its usable travel at 3000 W.

Q: Would a sealed box be better for me?

The two alignments converge at the bottom of the band on this driver rather than crossing cleanly, so there is no meaningful subsonic advantage either way. Above 25 Hz the vent is the louder of the two for the same power. The Performance Graphs tab plots this cabinet, 3.06 cubic feet vented at 29.5 Hz, against Sundown Audio's recommended sealed box, 2.00 cu ft, so you can judge it yourself.

Q: How does the front port work?

It is a vertical slot beside the woofer, the full height of the cavity, 3.50 inches wide and 57.8 square inches. It runs 8.75 inches to the back wall and turns once along it for 29.23 inches; the fold costs about 1.5 Hz and the port is cut for it. The channel runs at 22.8 metres per second at 3000 W, 52 percent of its turbulence limit, and the mouth edges carry a 1/2 inch roundover so the air leaves the face at 16.8 metres per second against the 17 metres per second threshold where a slot starts to chuff.

Q: What does the price cover, and how does it ship?

76 lb, 44.00" W x 18.00" H x 16.00" D external. It ships as a UPS parcel; the price includes shipping in the 48 states. Every Professional cabinet is priced the same way, by its size: this one is 7.33 cubic feet outside. Delivery to the 48 states is inside the price; it ships as a 76 lb parcel and checkout adds nothing. The Performance Optimized 15 inch ported wedge is $499.99. The $194 difference is the larger box and the port this driver needs to run at its rating. Do not add polyfill; it ships dry on purpose.

Q: Is the U-Series v.1 15 included?

No. This is an enclosure only, cut for the Sundown Audio U-Series v.1 15 specifically: the 14.010 inch cutout, the 9.050 inch mounting depth allowance and the 3.06 cubic foot alignment all come from Sundown Audio's published parameters. It fits both coil versions; the alignment published here is the D2. Bring your own driver.

SKU: Pro 15D-P U15

QUICK SPECS

Alignment: 3.06 cu ft net vented at 29.5 Hz. F3 50.3 Hz anechoic, 0.21 dB passband ripple
Driver: Sundown Audio U-Series v.1 15 D2, 1500 W RMS, 30.0 mm Xmax, 37.90 Hz Fs
Build: Front-firing standard box, 2.25" three-layer baffle with the woofer flush-mounted in the outer layer, Sundown Audio logo acrylic, dado joinery, 57.8 sq in front slot port beside the woofer with one bend along the back wall, port and excursion gated at 3000 W
Cabinet: 44.00" W x 18.00" H x 16.00" D, 76 lb, threaded insert kit included

Shipping Included No freight charges at checkout on US orders. International orders are quoted live carrier rates at checkout.

Built in Tennessee CNC cut from 3/4" Langboard Elite MDF. V-groove and dado joinery.

Advanced Terminal Cup Built in-house. ABS/Carbon Fiber. Stainless steel hardware. Copper ring terminals.

$ 693.99

In Stock and Ready to Ship

Financing available. Choose Shop Pay Installments at checkout.

Complete Your System

Wavtech Link1500.1plus Amplifier - Compact 1500W Monoblock - Wavtech Amplifier for car audio systems

Wavtech Wavtech Link1500.1plus Amplifier - Compact 1500W Monoblock $ 699.99

Professional Series Ported Dual 15" Enclosure | Sundown Audio U-Series v.1 15

$ 693.99

Enclosure Type Ported

External Dimensions 44.00" W x 18.00" H x 16.00" D

Gross Volume 5.28 cu ft

Net Volume 3.06 cu ft

Tuning Frequency 29.5 Hz

Port Area 57.8 Square Inches

Weight 76 lbs

INSTALLER'S TAKE

I built this one for a pair of U-Series v.1 15 in a single shared chamber, which is how a dual ported box should be built: one volume, one port, both drivers loading the same air.

It gets the full Professional treatment, a 2.25 inch three-layer baffle with both woofers flush mounted in the outer layer, and the port on the left of the face.

Wiring is where a dual bites you. These are two 2 ohm coils each, so you can land on 1 ohm with all four coils in parallel, 2 ohms as two series pairs in parallel, or 8 ohms with everything in series. Check what your amplifier is rated for before you wire it, not after.

Sundown Audio publishes no mounting hole locations for the U-Series v.1 15, so the inserts are not in the baffle when the box arrives. The insert kit is in the box: set the inserts where the woofer's own holes fall, with the drill bit and the 2.5 inch allen-head screws in the kit, and lay the gasket tape before the woofer goes down.

It ships dry. Do not add polyfill to a ported box. Set your subsonic filter at 23 Hz.

Product Details

Proline X Professional 15" Ported

A ported fifteen inch box for a pair of U-Series v.1 15, one shared chamber vented at 29.5 Hz

3.06 cu ft net Tuned 29.5 Hz F3 50.3 Hz 2.25" three-layer baffle Cut for the U-Series v.1 15 Built in Tennessee

3.06cu ft net

29.5Hz tuning

50.3Hz F3 anechoic

57.8sq in port area

Why this driver is vented at 29.5 Hz

This cabinet holds two U-Series v.1 15 in 3.059 cubic feet net, vented at 29.5 Hz through a 57.8 square inch port. F3 lands at 50.3 Hz with 0.21 dB of passband ripple. It measures 44.00 inches wide, 18.00 tall and 16.00 deep.

Threaded insert kit ships with this box. Sundown Audio does not publish the mounting hole locations for the U-Series v.1 15, so we cannot install the threaded inserts before it ships. The threaded insert kit comes in the box instead: inserts sized to the woofer, the correct drill bit, 2.5 inch allen-head screws, an allen key and woofer gasket tape. You set the inserts when you mount the woofer, and this box ships with two kits, one per woofer.

Both drivers share one chamber and one port rather than sitting in separate boxes, so the pair works against the whole volume and the port is sized for the pair rather than doubled. The port carries 57.8 square inches of area at 29.5 Hz, and the design power for the velocity and excursion checks is 3000 W for the pair. Passband ripple holds at 0.21 dB across the tuning, with F3 at 50.3 Hz.

What makes it Professional

Three-layer baffle, flush mount

Three layers of 3/4 inch Langboard Elite make a 2.25 inch front. The outer layer is routed to the flange, so the woofer sits flush with the face; the two layers behind it carry the mounting hardware and the load.

Sundown Audio logo acrylic

A glossy black acrylic insert with the Sundown Audio mark sits in the outer layer beside the woofer. It is standard on every Professional cabinet.

Threaded insert kit ships with this box

Threaded insert kit included, inserts NOT pre-installed: the manufacturer publishes no mounting hole locations, so the kit ships with the box for installation when the woofer goes in: 8 to 12 inserts sized to the woofer, the correct drill bit, 2.5 inch allen-head screws, allen key and gasket tape.

Port gated at 3000 W

The 57.8 square inch slot beside the woofer is sized so the channel runs 22.8 metres per second and the mouth 16.8 metres per second at the driver's rated power, under the 17 metres per second where a slot starts to chuff. The channel runs 8.75 inches along its wall and turns once along the back wall for another 29.23 inches, which is why a 29.5 Hz tuning fits a 16.00 inch deep box.

Why this is a Professional build

Every driver is run through the Performance Optimized wedge and down-fire before this chassis; the Professional box is where a driver lands when that smaller envelope, 30 inches wide and 18 inches deep with a triangular side port, cannot give it what it needs at its rated power. The U-Series v.1 15 did not clear the port gate there. The calmest wedge port that fits that envelope is 32.0 square inches at 26.0 by 11.12 by 17.86 inches, and its mouth runs 20.3 metres per second at 1500 W against the 17 metres per second line where a port starts to chuff. That port would stay clean to about 1054 W. The slot on this box reaches 57.8 square inches and holds the mouth at 16.8 metres per second at 3000 W.

What the price covers

Every Professional cabinet is priced the same way, by its size: this one is 7.33 cubic feet outside. Delivery to the 48 states is inside the price; it ships as a 76 lb parcel and checkout adds nothing. The Performance Optimized 15 inch ported wedge is $499.99. The $194 difference is the larger box and the port this driver needs to run at its rating.

What Sundown Audio recommend

Sundown Audio publish a vented box for the U-Series v.1 15 at 3.00 cubic feet on a basis they do not state, tuned to 35.0 Hz. This cabinet holds 3.06 cubic feet net and tunes to 29.5 Hz. They call for a port area of 48 sq in. The tuning sits lower than theirs, which trades a little output at tuning for reach below it.

The cabinet

44.00" W x 18.00" H x 16.00" D external. A windowed brace runs front to back beside the woofer, clearing the cutout by two and a half inches. The box ships dry: polyfill detunes a ported alignment. This is our dual 15 inch Professional envelope, built around the U-Series v.1 15's own frame and mounting depth, with both woofers on one face and the port on the left. It ships as a parcel.

Port mouth velocity peaks at 16.8 m/s against the 17 m/s point where a slot begins to chuff, and 22.8 m/s in the channel, both measured at the pair's design power. Both drivers must be the same model and the same coil: mixing them puts unequal loads on one shared chamber, and neither driver sees the airspace it was picked for. Sundown Audio does not publish the mounting hole locations for the U-Series v.1 15, so we cannot install the threaded inserts before it ships. The threaded insert kit comes in the box instead: inserts sized to the woofer, the correct drill bit, 2.5 inch allen-head screws, an allen key and woofer gasket tape. You set the inserts when you mount the woofer, and this box ships with two kits, one per woofer.

The numbers to respect

Set a 23 Hz subsonic filter, 24 dB per octave. Below tuning the vent stops loading the cone; with the filter in place the cone reaches 8.4 mm of its 30.0 mm at 3000 W.

Enclosure Specifications

Series	Proline X Professional
Driver-Specific Fitment	Sundown Audio U-Series v.1 15 D2 (D2)
Enclosure Type	Ported \| Front-Firing Standard Box
External Width	44.00 Inches
External Height	18.00 Inches
External Depth	16.00 Inches
Internal Volume (Gross)	5.28 Cubic Feet
Internal Volume (Net After Displacement)	3.06 Cubic Feet
Port Type	Vertical Slot Beside The Woofer \| Front Exit \| One 90 Degree Bend Along The Back Wall
Port Geometry	3.50 x 16.50 Inches, 57.8 Square Inches, 45.23 Inches Of Path
Port Area	57.8 Square Inches
Port Tuning (Fb)	29.5 Hz
Port Mouth	1/2 In Roundover On All Four Edges, 78.8 Square Inches At The Face
Port Air Velocity	22.8 m/s In The Channel, 16.8 m/s At The Mouth, At 3000 W (17.0 m/s Chuff Threshold)
Design Power Basis	3000 W RMS (1.2 x The Driver Rating) For Port Velocity And Excursion
Predicted F3	50.3 Hz (Anechoic)
Passband Ripple	0.21 dB (Anechoic)
Subsonic Filter	23 Hz High-Pass, 24 dB/Octave - REQUIRED On A Vented Enclosure
Driver Fs	37.90 Hz
Driver Qts	0.310
Driver Qes / Qms	0.340 / 3.100
Driver Vas	54.000 Liters / 1.907 Cubic Feet
Driver Sd	872.1 Square Centimeters
Driver Mms	355.70 g
Driver BL	30.70
Driver Re	3.8 Ohm
Driver Xmax	30mm (One-Way)
Driver Displacement	0.24 Cubic Feet (Published by Sundown Audio)
Driver Sensitivity	91.2 dB
Driver Power Handling	1500 Watts RMS
Driver Overall Diameter	15.590 Inches (Sundown Audio Spec)
Mounting Depth Required	9.050 Inches (Sundown Audio Spec)
Cutout Diameter	14.010 Inches (Sundown Audio Spec)
Flush Mount Recess	16.500 Inches In The Outer Layer
Material	Langboard Elite 3/4" MDF
Construction	ShopSabre CNC / Windowed Brace Front To Back Beside The Woofer
Joinery	Dado Joinery (CNC-Cut), Flat Panels
Front Baffle Construction	Three 3/4" MDF layers, 2.25" total \| Woofer Flush-Mounted In The Outer Layer
Baffle Layers	3
Acrylic	Glossy Black Sundown Audio Logo Insert, Outer Layer, Standard
Mounting Hardware	Threaded Insert Kit Included: 8-12 Inserts, Drill Bit, 2.5 In Allen-Head Screws, Allen Key, Gasket Tape
Voice Coil Configuration	D2
Terminal Cup	Proline X ABS/Carbon Fiber Composite \| Back Panel, Terminal-Cup Side \| 12g OFC Pre-Wired
Damping	None - Ships Dry. Polyfill Detunes A Ported Enclosure
Recommended Power	1050-1500 Watts RMS (Sundown Audio Rated: 1500W RMS)
Carpet Finish	Plush Black
Weight	76 lb
Shipping	UPS Ground Parcel, Included In The 48 States
Bundle Options	Enclosure Only (Bring Your Own Sundown Audio U-Series v.1 15)
Warranty	2-Year Limited (Enclosure)
Manufactured	Tullahoma, Tennessee, USA

Performance Graphs

Net airspace

3.06

cu ft

Tuning

29.5

Hz · Fb

Half power

50.3

Hz · F3, anechoic

Xmax at

14136

W RMS · 23 Hz subsonic

With NO filter

4649

W RMS · unfiltered

Port

16.8

m/s at the mouth · 3000 W

01Is this driver right for a ported box?

Efficiency bandwidth product places the motor before anything else is decided.

EBP = Fs ÷ Qes = 111.5

Sundown Audio U-Series v.1 15 D2 · EBP 111.5

Above 100 the motor is asking for a vent. The Sundown Audio U-Series v.1 15 D2 reads 111.5, so a ported load is the alignment it was designed around, not a compromise applied to it.

02What the box does to it

3.06 cu ft net against a 54.0 L Vas, vented at 29.5 Hz.

Fb = 29.5 Hz · F3 = 50.3 Hz · passband ripple 0.21 dB

Sundown Audio U-Series v.1 15 D2 · Fb 29.5 Hz, F3 50.3 Hz

Anechoic, before any cabin gain, with the 23 Hz subsonic filter already applied. The vent takes over below 30 Hz and the cone stops doing the work there, which is what holds travel down at the bottom of the passband.

03Perceived Ported vs Sealed

This cabinet, 3.06 cu ft net vented at 29.5 Hz, against Sundown Audio's recommended sealed box, 2.00 cu ft.

Ported Fb 29.5 Hz · the 2.00 cu ft sealed box runs Qtc 0.43, Fc 53 Hz

Ported · this cabinet, 3.06 cu ft, Fb 29.5 HzSundown Audio's recommended sealed, 2.00 cu ft net, Qtc 0.43

Shaded blue is where the ported alignment is louder for the same power, orange where the sealed one is. The sealed curve is Sundown Audio's recommended sealed box, 2.00 cu ft, not this cabinet with the port blocked: two different boxes, because that is the choice a buyer actually has. Across 25 to 60 Hz the vent is worth 8.8 dB at its widest and 5.5 dB on average. This is the anechoic picture, which is not what you hear in a car.

04Real World Ported vs Sealed

The same two boxes with cabin gain applied, 45 Hz corner, 18 dB ceiling.

Flatness across 25–60 Hz: ported 7.6 dB spread, the 2.00 cu ft sealed box 3.3 dB

Ported, in-car · 7.6 dB spreadSundown Audio's recommended sealed, 2.00 cu ft net, in-car · 3.3 dB spread

Cabin gain lifts both boxes by the same amount, so the gap between them does not change: what changes is the shape each one ends up with. A car pressurises below roughly 45 Hz, which fills in the sealed box's shallower rolloff and over-drives it where the ported box is already flat. Across 25 to 60 Hz, the band kick and bass fundamentals occupy, this alignment holds 7.6 dB of spread against 3.3 dB for Sundown Audio's recommended sealed box, 2.00 cu ft. The sealed curve is flatter on paper; the ported one trades that for output. The two alignments converge at the bottom of the band rather than crossing cleanly, so there is no meaningful subsonic advantage either way here. Cabin gain here is a house assumption, not a measurement of your vehicle.

05The watts that reach Xmax (in this enclosure)

Travel scales with the square root of power, so there is one wattage that puts the cone exactly on Sundown's published 30.0 mm. The two traces are the same cabinet with the subsonic filter switched on and switched off.

P_Xmax = 14136 W with a 23 Hz subsonic · 4649 W with none → the filter is worth 3.0×

14136 W · subsonic at 23 Hz, 24 dB/oct4649 W · no subsonic filterXmax 30.0 mm one-way, published

Each trace touches the limit and no further, because each is drawn at the exact power that puts the cone on 30.0 mm. With a 23 Hz subsonic that takes 14136 W, reached first at 23 Hz. Take the filter away and the same cabinet reaches 30.0 mm on 4649 W — the filter is worth 3.0× the safe power. A vent unloads the cone below tuning, so there is nothing holding it once the box stops loading: on a sealed build a subsonic filter is an improvement, here it is required equipment. The unfiltered trace is still rising where this chart stops at 20 Hz, so treat 4649 W as a bound rather than a floor. Every wattage on this page is a MECHANICAL limit, not an electrical one. It is the power at which the cone runs out of linear travel in this cabinet, and nothing more. What the voice coil can dissipate as heat is a separate ceiling set by the driver, not by the box — Sundown rate this one at 1500 W RMS, and that is the number that binds first here: heat stops you before travel does, so treat 1500 W as the ceiling and the travel figures above as headroom. Final wired impedance, amplifier output and how long you hold the level are all electrical questions this graph does not answer.

Woofer Details

Sundown positions the U series as the direct replacement for the Z v.3 that ran from 2011 to 2016, at a lower price, and as SA series character with far more power handling. At 9.05 inches it is much shallower than the mega platform 15s beside it. This cabinet takes two of them in one shared chamber, so both drivers see the same air and the same port. Each opening is cut for 9.05 in of mounting depth and a 14.01 in cutout, taken from Sundown Audio's published figures rather than measured off a sample.

Driver	Sundown Audio U-Series v.1 15
Coil Options	Dual 2 Ohm or Dual 4 Ohm
Voice Coil Diameter	3 in, 2.36 in winding height, 4 layer
Coil Former	Black Aluminum
Dust Cap	Wide Flange
Surround	Double Stitched, Cast Aluminum Bolt On Retaining Rings
Lead Wires	Stitched On, Doubled XL Tinsel
Basket	Cast Aluminum
Motor	Double Stacked 8.66 in Y35 Ferrite, One Piece Bumped T Yoke, 5 mm Aluminum Shorting Ring
Motor Diameter	9.68 in
Cooling	High Velocity Pole Vent, Ten Rear Air Gap Vents, Vented Frame Spacer Ring, Top Plate Cooling Channels
Power, RMS	1500 W
Peak Power	3000 W
Sensitivity	91.2 dB (D2), 90.2 dB (D4), SPL (1W/1m)
Mounting Depth	9.05 in
Cutout Diameter	14.01 in
Frame Outside Diameter	15.59 in
Driver Displacement	0.24 cu ft
Driver Warranty	2 Year Limited, Authorized Dealer Purchase, Original Owner

Materials

Material

Built From a Spec Sheet, Not a Sales Sheet

Every Proline X Professional Series enclosure is CNC-cut from Langboard Elite MDF, 3/4" (18mm) panels produced to published mill specifications. Most enclosure manufacturers source generic MDF without published data. We can tell you the internal bond rating, the modulus of elasticity, the modulus of rupture, and the face and edge screw holding strength for every panel in this enclosure, because we chose the material based on those numbers, not on price or availability.

Langboard Elite is produced in the United States. The specifications below are pulled directly from Langboard's published mill data and are verifiable. This is the same panel stock used in our full Proline X lineup.

Specifications

Langboard Elite MDF: Published Mill Data

Property	Value	Why It Matters
Panel Stock	Langboard Elite MDF	Named, verifiable panel source, not generic "high-density MDF"
Thickness	3/4" (18mm)	Industry standard for subwoofer enclosures; panels below this flex under pressure
Density	48.5 lbs/ft³	Higher density = less porosity, better screw retention, reduced resonance
Internal Bond	200 psi	Measures resistance to delamination under sustained internal pressure. The most enclosure-relevant spec on this sheet
Modulus of Rupture (MOR)	4,200 psi	Bending strength before the panel breaks, relevant for larger unsupported baffle spans
Modulus of Elasticity (MOE)	410,000 psi	Stiffness under load; higher MOE means less panel flex under bass pressure, less resonance
Face Screw Holding	325 lbs	How firmly the panel surface holds a screw; critical for baffle joint integrity over time
Edge Screw Holding	250 lbs	Panel edge retention, relevant for every joint that isn't face-to-face

Internal Bond

200 psi: The Number That Actually Matters for Enclosures

The internal bond rating measures how well the MDF panel resists delamination under sustained pressure applied perpendicular to the face. In a subwoofer enclosure, every bass transient generates a pressure pulse that pushes outward on every panel simultaneously. A panel that begins to delaminate internally loses stiffness gradually. The symptoms are slow: a box that starts to sound softer, less defined, less punchy over months of use. 200 psi internal bond is the spec that determines how long this enclosure holds its acoustic integrity under daily use at real power levels.

Stiffness

410,000 psi MOE: Less Flex, Less Resonance

The modulus of elasticity measures panel stiffness, its resistance to bending under load. A stiffer panel flexes less under the pressure generated by a high-excursion driver at volume. Panel flex is a source of acoustic coloration: the panel itself begins to radiate sound at its own resonant frequency, adding distortion to the output. 410,000 psi stiffness combined with V-groove and dado joinery means the panels stay rigid and the bracing controls resonance at the structure level, not the panel level. The bass you hear comes from the driver, not the box.

Screw Holding

325 lb Face / 250 lb Edge: Joints That Stay Locked

Screw holding strength determines how firmly the panel grips a fastener at the face and at the edge. This matters most at the baffle joint, where the front panel meets the side panels and where the driver is mounted. A panel with low screw holding strength allows fasteners to loosen over time under vibration, leading to air gaps at the joint and loss of acoustic seal. 325 lb face screw holding strength means the baffle hardware stays put. Combined with dado joinery and adhesive, the front panel on a Proline X Professional Series enclosure is not going anywhere.

Sourcing

Named Panel Stock: Not "Premium MDF"

The phrase "premium MDF" or "high-density MDF" appears on marketing copy for enclosures across every price point, from $40 to $400. It is not a specification. It is a description with no defined standard. Langboard Elite is a named, sourced, mill-documented product with published data. We name it in our copy because naming it holds us accountable to the spec. You can look up Langboard Elite independently, verify the numbers on this page, and confirm you are getting what we say you are getting. That is the point.

Why Proline X?

Most enclosures are built to a price point. Proline X is built to a spec. Every box starts with published-data MDF, gets CNC-cut to exact internal volume, and is assembled by hand in our Tennessee facility. The difference shows up in the measurements, and in how the box holds up two years into daily use.

CNC-Cut to Spec

Panels are machine-cut on ShopSabre CNC routers and joined with V-groove and dado joinery. Consistent geometry, no hand-cut variance, no gaps at the joints.