Short answer: the Monoprice Monolith M15-S, if you are buying new. The Outlaw Audio Ultra-X12 ranks higher than it (#6 vs #72 of 110 subwoofers, 4.2/5 vs 4.1/5) but is discontinued, so only consider it used; the Monoprice Monolith M15-S is still sold new at $999.
What the Outlaw Audio Ultra-X12 gets right: 12-inch ported with 350W RMS, 17Hz max extension earns Large Bassaholic rating.
Buy the Monoprice Monolith M15-S if you want one new; the Outlaw Audio Ultra-X12 is discontinued, so only look for it used.
Looking for alternatives? See the complete Subwoofers rankings.
Specifications Side By Side
| Monoprice Monolith M15-S | Outlaw Audio Ultra-X12 | |
|---|---|---|
| Price | $999 | $999 Discontinued |
| Ranked | #72 of 110 in Large Home Subwoofers (Over 75 lbs) | #6 of 145 in Medium Home Subwoofers (30-75 lbs) |
| Enclosure | sealed | ported, bottom |
| Output SPL at 15 Hz | 100.1 dB | - |
| Output SPL at 20 Hz | 105.6 dB | 108.3 dB |
| Output SPL at 25 Hz | 111.2 dB | 115.0 dB |
| Output SPL at 31.5 Hz | 115.2 dB | 116.1 dB |
| Output SPL at 40 Hz | 118.4 dB | 117.8 dB |
| Output SPL at 50 Hz | 119.3 dB | 121.4 dB |
| Output SPL at 63 Hz | 119.6 dB | 122.3 dB |
| Output SPL at 80 Hz | 118.9 dB | - |
| Output SPL at 100 Hz | 119.1 dB | - |
| Output SPL at 125 Hz | 118.9 dB | - |
| CEA-2010-A Average (40-80Hz) | 119.0 dB | 120.5 dB (avg of 3/4 bands) |
| Dimensions | 23.5"H x 16.7"W x 19.7"D (596.9 x 424.2 x 500.4 mm) | 21.3"H x 16"W x 23"D (539.8 x 406.4 x 584.2 mm) |
| Warranty | 5 | 3 |
| Country | United States | United States |
| Measurement Source | Manufacturer | Brent Butterworth |
| Weight | 80 lbs (36.3 kg) | 65.9 lbs (29.9 kg) |
| Drivers | 15" (381mm) driver | 12" (305mm) driver |
| Cabinet Color | - | black |
| Discontinued | - | Yes |
| Frequency Response | - | 19-179Hz, ±3dB |
| Amplifier Power | - | 350W RMS |
Related Speaker Comparisons
How Outlaw Audio Ultra-X12 compares with other leading options:
- Monoprice SW-15 vs Outlaw Audio Ultra-X12
- Outlaw Audio Ultra-X12 vs SVS 3000 Micro
- Emotiva X-Ref 12 vs Monoprice Monolith M15-S
- HSU Research VTF-3 MK5 HP vs Monoprice Monolith M15-S
- HSU Research VTF-15H MK2 vs Monoprice Monolith M15-S
Prices on this page were last checked September 23, 2026 at 11:24 PM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
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The Two Speakers In Full
Monoprice Monolith M15-S: $999 eBay
Pros: Published CEA-2010 specifications list 105.6 dB at 20 Hz and 119.0 dB through 40-80 Hz. The sealed enclosure with 15” (381mm) driver has the headroom for demanding film bass in a large room.
Cons: The 596.9H x 424.2W x 500.4D mm cabinet and 36.3 kg mass make this a serious placement and moving commitment. A sealed cabinet still needs careful placement and calibration to avoid room-mode peaks.
Notes: Product # 35141
Full Monoprice Monolith M15-S review and specifications →
| CEA-2010-A Average (40-80Hz) | 119.0 dB |
|---|---|
| Country | United States |
| Dimensions | 23.5"H x 16.7"W x 19.7"D (596.9 x 424.2 x 500.4 mm) |
| Drivers | 15" (381mm) driver |
| Enclosure | sealed |
| Measurement Source | Manufacturer |
| Output SPL at 15 Hz | 100.1 dB |
| Output SPL at 20 Hz | 105.6 dB |
| Output SPL at 25 Hz | 111.2 dB |
| Output SPL at 31.5 Hz | 115.2 dB |
| Output SPL at 40 Hz | 118.4 dB |
| Output SPL at 50 Hz | 119.3 dB |
| Output SPL at 63 Hz | 119.6 dB |
| Output SPL at 80 Hz | 118.9 dB |
| Output SPL at 100 Hz | 119.1 dB |
| Output SPL at 125 Hz | 118.9 dB |
| Warranty | 5 |
| Weight | 80 lbs (36.3 kg) |
- Reviews, Comparisons and Sound Samples
- These figures are manufacturer-specified rather than independently measured.
- Head-to-Head Comparisons
- Monoprice Monolith M15-S vs Rythmik F18
- Monoprice Monolith M15-S vs Monoprice Monolith M-15 V2
- Monoprice Monolith M15-S vs SVS PB-4000
- Monoprice Monolith M15-S vs HSU Research VTF-3 MK5 HP
- Monoprice Monolith M15-S vs HSU Research VTF-15H MK2
- Monoprice Monolith M15-S vs Rythmik FV15HP
- Monoprice Monolith M15-S vs Monoprice Monolith M-215
- Monoprice Monolith M15-S vs Reaction Audio PV-15X
- See all 15 comparisons
Outlaw Audio Ultra-X12: $999 Discontinued eBay
Pros: 12-inch ported with 350W RMS, 17Hz max extension earns Large Bassaholic rating. Innovative window-pane perimeter bracing design reduces resonance. Longer port than previous models. Second subwoofer output for multi-sub installations. Excellent value at $999.
Cons: Discontinued.
Full Outlaw Audio Ultra-X12 review and specifications →
| Amplifier Power | 350W RMS |
|---|---|
| CEA-2010-A Average (40-80Hz) | 120.5 dB (avg of 3/4 bands) |
| Cabinet Color | black |
| Country | United States |
| Dimensions | 21.3"H x 16"W x 23"D (539.8 x 406.4 x 584.2 mm) |
| Discontinued | Yes |
| Drivers | 12" (305mm) driver |
| Enclosure | ported, bottom |
| Frequency Response | 19-179Hz, ±3dB |
| Measurement Source | Brent Butterworth |
| Output SPL at 20 Hz | 108.3 dB |
| Output SPL at 25 Hz | 115.0 dB |
| Output SPL at 31.5 Hz | 116.1 dB |
| Output SPL at 40 Hz | 117.8 dB |
| Output SPL at 50 Hz | 121.4 dB |
| Output SPL at 63 Hz | 122.3 dB |
| Warranty | 3 |
| Weight | 65.9 lbs (29.9 kg) |
- Links
- Reviews, Comparisons and Sound Samples
- Independently measured by Brent Butterworth; the published figures above come from this ASR subwoofer measurement thread.
- Head-to-Head Comparisons