Proline X

Performance Optimized Down Fire Sealed 10" Enclosure | Diamond Audio DMD-SH

Q: Why is this enclosure larger than Diamond Audio's recommendation?

Because the alignment is better. Diamond suggests 0.45 cubic feet, which computes to roughly Qtc 0.98 on the DMD102SH and above 1.14 on the DMD104SH - both underdamped with a pronounced lift near the corner frequency. At 0.80 cubic feet net the D2 lands at Qtc 1.003 and the D4 at 0.981, with 2 to 3 Hz more low-end extension on both. Diamond's own manual describes their enclosure table as a suggestion rather than a specification, and the extra volume costs about an inch of cabinet height.

Q: Why don't your Qtc figures match the ones in Diamond's manual?

Because Diamond's enclosure table does not reconcile with the Thiele-Small parameters printed on the same page. Their table lists the DMD102SH at Qtc 0.78 in 0.45 cubic feet. Running their own published Qts of 0.66 and Vas of 15.4 liters through standard sealed box math at that volume produces 0.98 instead. Every variant is off in the same direction by roughly 0.2 to 0.3.This is not a gross versus net volume convention issue, which some manufacturers do have. No reasonable interpretation of the volume closes a gap that large. We publish figures computed directly from the driver parameters, because those are what the driver will actually do in this enclosure.

Q: Should I choose the DMD102SH or the DMD104SH?

These two differ more than most dual-impedance pairs. The DMD102SH runs a Qts of 0.66 with 13.7 T of motor force and 7.9mm of Xmax, landing at Qtc 1.003 in this cabinet. The DMD104SH runs a Qts of 0.77 with 16.4 T and 8.8mm, landing at Qtc 0.981. So the D4 has the stronger motor and more excursion capability while the D2 has noticeably better damping. Check what load your amplifier is stable into first. If either works, choose the D2 for accuracy and control, the D4 for output.

Q: Why is the predicted F3 in the low 50s?

Because the driver's free-air resonance is 48 Hz, which is high. A sealed enclosure raises the system corner frequency above the driver's Fs, so no sealed box puts this driver into the 30s. The DMD-SH is designed for punch and midbass authority from a 3 inch mounting depth rather than for deep extension. In a vehicle, cabin gain rising below 50 Hz fills in considerably below the anechoic figure, so in-car response is meaningfully better than the number suggests.

Q: Where is the terminal cup located on a down fire enclosure?

Side mounted. Every Proline X Performance Optimized enclosure uses a side mounted terminal cup regardless of alignment, whether standard, wedge, or down fire. On this cabinet that keeps the connection fully accessible with the enclosure in its installed position, since the baffle faces the floor. The cup is our Proline X ABS and carbon fiber composite unit, recessed, with stainless hardware, copper ring terminals, and pre-wired 12 gauge OFC.

Q: Why are the corners square instead of radiused?

Down Fire cabinets are built with square corners as a series standard. The 3 inch top down corner radius used on other Proline X alignments does not apply here. A down fire box is a low, wide platform that sits flat against a floor or under a seat, and square corners maximize usable internal volume for a given footprint while keeping the cabinet stable on its mounting surface.

Q: How is this enclosure built?

V-groove and dado joinery, CNC-cut on ShopSabre routers from Langboard Elite MDF. Every panel joint is a machined interlocking groove that mechanically locks the panels before adhesive is applied, which is what keeps the cabinet airtight under sustained pressure cycling. The front baffle is a double layer at 1.5 inches, two bonded 3/4 inch sheets, standard across the Performance Optimized Series. Perimeter cross-bracing and pre-installed polyfill complete the build. Assembled and inspected in Tullahoma, Tennessee.

Q: Is the Diamond Audio DMD-SH subwoofer included with this enclosure?

No. This listing is for the enclosure only. Bring your own Diamond Audio DMD102SH or DMD104SH. The cutout and mounting depth are direct fit for either version.

SKU: PO 10-S DF DMD

QUICK SPECS

Alignment: 0.80 cu ft net. Qtc 0.856 (D2), Qtc 0.981 (D4), computed from Diamond's published T/S
Driver: Diamond DMD102SH (DVC 2Ω) or DMD104SH (DVC 4Ω), 250W RMS / 500W max, 3.00" mounting depth
Build: Proline X V-groove and dado joinery, double-layer 1.5" front baffle, perimeter cross-brace, 12g OFC side-mounted terminal cup
Cabinet: 30"W x 15"D x 6.125"H measured in down fire position, square corners

Shipping Included No freight charges at checkout. What you see is what you pay.

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.

$ 249.99

In Stock and Ready to Ship

Financing available. Choose Shop Pay Installments at checkout.

Performance Optimized Down Fire Sealed 10" Enclosure | Diamond Audio DMD-SH

$ 249.99

Enclosure Type Sealed

External Dimensions 30" W x 15" D x 6.125" H (measured in down fire position)

Gross Volume 0.86 cu ft

Net Volume 0.80 cu ft

Weight 32.5 lbs

Front Panel Thickness 1.5"

INSTALLER'S TAKE

The DMD-SH 10 is a clean 3.00 inch shallow with an aluminum heatsink dust cap, die-cast frame, and a vented pole. Diamond says the motor and suspension symmetry are Klippel optimized, and the T/S they publish is consistent enough across variants that I believe it.

The two coils are genuinely different drivers here, more so than on most dual-impedance pairs. The D2 runs Qts 0.66 with 13.7 T of motor force and 7.9mm of Xmax. The D4 runs Qts 0.77 with 16.4 T and 8.8mm. So the D4 has the stronger motor and more excursion, the D2 the tighter damping. In this cabinet that is Qtc 1.003 versus 0.981. If you want accuracy take the D2, if you want output take the D4.

We build this at 0.80 net rather than Diamond's suggested 0.45. Their number puts the D2 near Qtc 0.98 and the D4 above 1.14, both underdamped with a lift at the corner. At 0.80 you get better control and 2 to 3 Hz more extension, and Diamond's own manual calls their enclosure table a suggestion rather than a specification. On a down fire cabinet the extra volume costs about an inch of height, which is worth it here.

Something you should know if you compare our numbers to the manual: they will not match, and the gap is bigger than a rounding difference. Diamond lists the DMD102SH at Qtc 0.78 in 0.45 cubic feet. Run their own published Qts of 0.66 and Vas of 15.4 liters through standard sealed box math at that volume and you get 0.98. Every variant is off in the same direction by roughly 0.2 to 0.3. That is not a gross versus net convention issue - no volume interpretation closes a hole that size. Their T/S table and their enclosure table appear to have been produced independently. We publish what the driver data actually gives.

Honest limitation: Fs is 48 Hz. That is high, and it means F3 lands in the low 50s no matter what you build. This is a driver for punch and midbass authority in a tight space, not for deep extension. Cabin gain below 50 Hz does the rest.

250 watts RMS, 500 max. Dual voice coil, final impedance set at the driver.

Product Details

Proline X Performance Optimized Down Fire 10" Sealed

Cut and tuned for the Diamond Audio DMD-SH 10

V-Groove and DadoLangboard Elite MDF0.80 cu ft NetKlippel Optimized Motor

0.80cu ft net

0.981system Qtc, D4

52.4 HzF3 rolloff, D4

6.125 incabinet height

Performance, Performance Optimized, and Micro

Proline X builds three tiers of Down Fire enclosure. The difference is not finish or materials, it is whether the cabinet was designed for a category or for a driver, and how much of the fitting work is already done for you.

	Performance	Performance Optimized	Micro Series
Fitment	Universal. Accepts any subwoofer that clears the published cutout and mounting depth.	Woofer specific. Cut for one named subwoofer, with cutout, mounting depth, magnet clearance and displacement drawn in CAD from that driver.	Woofer specific. Cut for one named subwoofer.
Footprint	Sized to the driver diameter. 24.5 by 13.5 inches on the 10 inch.	Shared 30 by 15 inch platform on most builds, with cabinet height as the variable. A few drivers need a wider or deeper platform.	Compact per driver footprint. 21.5 by 14.5 inches on the 10 inch.
Front baffle	Single, 3/4 inch.	Double, 1.5 inch, outer layer machined as a flush recess.	Double, 1.5 inch.
Driver mounting	Solid flange. You drill your own mounting holes.	8/32 threaded inserts, stainless machine screws included.	8/32 threaded inserts, stainless machine screws included.
Joinery	V-groove and dado, CNC cut.	V-groove and dado, CNC cut, perimeter cross brace.	Stack fab, dowel reinforced.
Published alignment	Modeled Qtc profiles across a range of drivers. No single response curve.	A real predicted Qtc and F3 for that exact driver, calculated from its own Thiele-Small parameters.	Target alignment described in the listing.
Carpet	Gray standard, black optional.	Plush black.	Plush black.
Warranty	1 year limited.	1 year limited.	2 years.

Feet ship with every tier, uninstalled on purpose. Mount them where your floor wants them for a down fire install, or leave them off and run the cabinet front firing or up firing. The orientation is yours to choose.

This page is a Performance Optimized enclosure. The airspace, the cutout and the cabinet height all come from the Diamond Audio DMD-SH 10's own published numbers. A Performance box fits your subwoofer. A Performance Optimized box was built for it.

Built Around the DMD-SH 10

Nothing about this cabinet is generic. The baffle is bored to the driver's 9.13 inch cutout, the internal height is set by its 3.00 inch mounting depth, and the 10.87 inch total diameter Diamond publishes sits inside a 30 by 15 inch footprint. The finished cabinet stands 6.125 inches tall measured in the down fire position, low enough for under seat and cargo well installs that will not take a conventional box.

The DMD-SH is a shallow mount design: an aluminum heatsink dust cap over a high strength paper cone, a die-cast shallow frame, a vented pole for cooler operation, oversized push terminals, a black spider with woven tinsel leads, and a wrap-around ABS mounting gasket. Diamond states that the motor and suspension symmetry are Klippel optimized. Effective piston area is 0.0359 square meters.

The two coil variants sit further apart than most dual impedance pairs. The DMD102SH, dual 2 ohm, runs a Qts of 0.66 with 13.7 T of motor force and 7.9mm of Xmax. The DMD104SH, dual 4 ohm, runs a Qts of 0.77 with 16.4 T and 8.8mm. The D4 carries the stronger motor and the longer travel, the D2 the better damping.

Net Volume, Not Gross

We build this cabinet at 0.80 cubic feet net out of 0.859 cubic feet gross, against Diamond's suggested 0.45 cubic feet. Their figure puts the D2 near Qtc 0.98 and the D4 above 1.14, both underdamped with a lift at the corner. At 0.80 net you get meaningfully better damping and 2 to 3 Hz more extension, and Diamond's own manual presents its enclosure table as a suggestion rather than a specification. On a down fire cabinet that extra volume costs about an inch of height.

True net, not marketing net. Internal volume is calculated from the machined cavity dimensions and the driver's published displacement, not estimated from external dimensions minus wall thickness.

In this volume the DMD104SH lands at Qtc 0.981 with F3 at 52.4 Hz and the DMD102SH at Qtc 0.856. The D2 is the more damped alignment of the two, the D4 the one with the motor force and the excursion behind it. Both figures are computed from the Thiele-Small parameters Diamond publishes, and they do not match the Qtc values printed in Diamond's own enclosure table, which run lower by roughly 0.2 to 0.3 across every variant. No gross versus net convention closes a gap that size, so we publish the figure that follows from the driver data.

Free-air resonance is 48.0 Hz on the D2 and 48.5 Hz on the D4. That is high, and it is the reason F3 lands in the low 50s in any sealed volume. This is a driver for punch and midbass authority from a 3 inch mounting depth rather than for deep extension.

Down Fire Construction

Cut with V-groove and dado joinery on our ShopSabre routers from Langboard Elite 3/4 inch MDF, a dense 48.5 lb/ft³ board with a 200 psi internal bond and 410,000 psi MOE. Every panel joint is a machined interlocking groove that mechanically locks before adhesive is applied, which keeps the cabinet airtight under sustained pressure cycling. Corners are square on Down Fire cabinets.

Double Baffle, Flush Recess

The front baffle is 1.5 inches, two bonded 3/4 inch sheets, with the outer layer machined as a flush recess so the driver bolts to the inner layer. That recovers 3/4 inch of internal clearance. Mounting is into 8/32 threaded inserts, stainless machine screws included.

Side-Mounted Terminal Cup

Proline X ABS and carbon fiber composite cup with stainless hardware and copper ring terminals, pre-wired in 12 gauge OFC. Side mounted so it stays accessible with the baffle facing the floor.

Perimeter Cross-Bracing

Perimeter cross-bracing ties the long spans together on a wide, shallow cabinet where panel area is the main resonance risk. Polyfill is pre-installed.

Down Firing Into the Floor

The driver fires downward into the floor and the cabinet couples to the surface it sits on. No standoffs are required; the cabinet sits flat. The sealed rolloff meets rising cabin gain below 60 Hz, so in-car response extends well below the anechoic figures quoted above.

Power and Warranty

The DMD-SH 10 is rated 250 watts RMS and 500 watts maximum. Both variants are dual voice coil, so the final load is set at the driver. Confirm the result against your amplifier's minimum stable impedance before powering the system.

The enclosure carries a 1 year limited warranty. Bring your own DMD102SH or DMD104SH; the driver is purchased separately.

Cut for the Driver, Not the Catalog

One cabinet, one driver, one alignment worked out from the published parameters instead of a table of round numbers. Machined, assembled and inspected one at a time in Tullahoma, Tennessee.

Specifications

Series	Proline X Performance Optimized Down Fire
Compatible Driver	Diamond Audio DMD102SH (DVC 2Ω) or DMD104SH (DVC 4Ω)
Enclosure Type	Sealed \| Down Fire Geometry \| Floor-Coupled
Firing Direction	Down Firing, Driver Fires Toward Floor
External Width	30 Inches
External Depth	15 Inches
External Height	6.125 Inches
Dimension Reference	All External Dimensions Measured In Down Fire Position
Internal Volume (Gross)	0.859 Cubic Feet
Internal Volume (Net)	0.80 Cubic Feet
Diamond Suggested Sealed Volume	0.45 Cubic Feet Gross (We Build Larger, See FAQ)
Target System Qtc (DMD104SH)	0.981 (Computed from Published T/S)
Predicted F3 (DMD104SH)	52.4 Hz
Driver Fs	48.0 Hz (D2) / 48.5 Hz (D4)
Driver Qts	0.66 (D2) / 0.77 (D4)
Driver Qes / Qms	0.71 / 9.0 (D2) \| 0.85 / 8.0 (D4)
Driver Vas	15.4 Liters (D2) / 15.8 Liters (D4)
Driver BL	13.7 T (D2) / 16.4 T (D4)
Driver Mms	130.5 g (D2) / 125.0 g (D4)
Driver Cms	0.084 mm/N (D2) / 0.086 mm/N (D4)
Driver Sd	0.0359 m²
Driver Xmax	7.9mm (D2) / 8.8mm (D4)
Driver Sensitivity	85.8 dB (D2) / 85.2 dB (D4)
Driver Power Handling	250 Watts RMS / 500 Watts Max
Total Driver Diameter	10.87 Inches (Diamond Spec)
Mounting Depth Required	3.00 Inches (Diamond Spec)
Woofer Opening (Cutout)	9.13 Inches (Diamond Spec)
Standoffs	None Required
Material	Langboard Elite 3/4" MDF
Construction	ShopSabre CNC / Perimeter Cross-Brace
Joinery	V-Groove and Dado (CNC-Cut)
Panel Thickness	3/4 Inch
Front Baffle	Double-Layer 1.5" MDF (Two 3/4" Sheets Bonded)
Corner Profile	Square (Down Fire Series Standard)
Driver Mounting	8/32 Threaded Inserts \| Stainless Steel Machine Screws Included
Terminal Cup	Proline X ABS/Carbon Fiber Composite \| Side Mounted
Internal Wiring	12 Gauge OFC, Pre-Wired
Damping	Polyfill Pre-Installed
Carpet	Plush Black
Voice Coil Configuration	Dual Voice Coil, Final Impedance Set At The Driver
Bundle Options	Enclosure Only (Bring Your Own DMD102SH or DMD104SH)
Weight	28 lb
Warranty	1-Year Limited (Enclosure)
Built In	Tullahoma, Tennessee, USA

Performance Graphs

Net airspace

0.80

cu ft per chamber

System Qtc

1.00

sealed

Half power

49.6

Hz · F3

Xmax at

249

W RMS · no filter

With 25 Hz subsonic

251

W RMS · +1%

Amplifier

250

W RMS recommended

This enclosure holds 0.80 cu ft net per chamber. In it the Diamond Audio DMD104SH runs a system Qtc of 1.00 with half power at 49.6 Hz, and the cone reaches its 8.8 mm travel limit at 249 W, below the driver’s 250 W thermal rating, so travel is what stops you here, not heat. Run a subsonic filter at 25 Hz and that becomes 251 W — +2 W, or 1 percent more power for the same 8.8 mm of travel.

01Is it a sealed driver?

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

EBP = Fs ÷ Qes = 57.7

D4 · EBP 57.7

At 57.7 the DMD104SH sits in the transition band, not the sealed band. That is not a mismatch: a transition motor works in either alignment, and sealed buys a smaller box and a gentler roll-off at the cost of some low-end output. Stage 02 shows what this airspace actually does with it.

02What the box does to it

0.80 cu ft against a 15.8 L Vas.

α = Vas ÷ Vb = 0.70 · Fc = Fs√(α+1) = 63 Hz · Qtc = 1.00

D4 · Qtc 1.00, Fc 63 Hz, F3 49.6 Hz

The box lifts resonance from 48.5 Hz free-air to 63 Hz and half power lands at 49.6 Hz, anechoic, before any cabin gain.

03The 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 8.8 mm — and a bigger one once a subsonic filter stops it wasting travel below the passband.

P_Xmax = 249 W unfiltered → 251 W with a 25 Hz subsonic

D4 · 249 W, no filterD4 · 251 W with subsonic at 25 Hz, 24 dB/octXmax 8.8 mm one-way

Every trace touches the limit and no further, because each is drawn at the exact power that puts that coil on 8.8 mm. Unfiltered that is 249 W, reached first at 45 Hz. It sits under the 250 W the driver can take thermally, so the enclosure sets the ceiling, not the voice coil. The dashed traces are the same driver behind a subsonic filter at 25 Hz, 24 dB/oct: stopping the cone wasting travel below the passband lets it take 251 W before hitting the same 8.8 mm. That is 1 percent more amplifier for the price of one filter setting.

Param	Value	Unit	Note
Fs	48.50	Hz	free-air resonance
Qts	0.770		D4
Vas	15.80	L	equivalent compliance
Sd	359.0	cm²	effective piston area
Xmax	8.8	mm	one-way linear travel
Pe	250	W	continuous RMS
SPL	85.2	dB	1 W / 1 m, derived from T/S

Driver parameters as published by diamondaudio.com product page. Curves computed against this enclosure’s actual net airspace.

Materials

Material

Built From a Spec Sheet, Not a Sales Sheet

Every Proline X Performance 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 Performance 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.