Short answer: the Monoprice Monolith M15-S ranks #62 of 97 subwoofers at $999; the Outlaw Audio Ultra-X12 ranks #36 at $999. Close enough in price that the ranking gap is the deciding factor.
What the Outlaw Audio Ultra-X12 gets right: 12-inch ported with 350W RMS, 17Hz max extension earns Large Bassaholic rating.
One note: the Outlaw Audio Ultra-X12 is discontinued, but it still ranks #36 of 137 subwoofers, ahead of most of what is still sold new, so it is worth considering used.
Buy the Monoprice Monolith M15-S if the price matters more than the ranking. Buy the Outlaw Audio Ultra-X12 if the ranking matters more than the price.
Specifications Side By Side
| Monoprice Monolith M15-S | Outlaw Audio Ultra-X12 | |
|---|---|---|
| Price | $999 | $999 Discontinued |
| Ranked | #62 of 97 in Large Powered Home Subwoofers (Over 75 lbs) | #36 of 137 in Medium Powered 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 | 102.3 dB |
| Output SPL at 25 Hz | 111.2 dB | 109.0 dB |
| Output SPL at 31.5 Hz | 115.2 dB | 110.1 dB |
| Output SPL at 40 Hz | 118.4 dB | 111.8 dB |
| Output SPL at 50 Hz | 119.3 dB | 115.4 dB |
| Output SPL at 63 Hz | 119.6 dB | 116.3 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 | 114.5 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) | 21.25"H x 16.0"W x 23.0"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 |
| Power Output (Watts) | - | 350W RMS |
The Two Speakers In Full
Monoprice Monolith M15-S: $999
Notes: Product # 35141
| 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 |
- Head-to-Head Comparisons
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- Monoprice Monolith M15-S vs HSU Research VTF-15H MK2
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- Monoprice Monolith M15-S vs Monoprice Monolith M-215
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- See all 15 comparisons
- Links
Outlaw Audio Ultra-X12: $999 Discontinued
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.
| CEA-2010-A Average (40-80Hz) | 114.5 dB (avg of 3/4 bands) |
|---|---|
| Cabinet Color | black |
| Country | United States |
| Dimensions | 21.25"H x 16.0"W x 23.0"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 | 102.3 dB |
| Output SPL at 25 Hz | 109.0 dB |
| Output SPL at 31.5 Hz | 110.1 dB |
| Output SPL at 40 Hz | 111.8 dB |
| Output SPL at 50 Hz | 115.4 dB |
| Output SPL at 63 Hz | 116.3 dB |
| Power Output (Watts) | 350W RMS |
| Warranty | 3 |
| Weight | 65.9 lbs / 29.9 kg |
- Buy Used
- Head-to-Head Comparisons
- Links
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Product prices and availability were last checked August 9, 2026 at 6:57 AM UTC 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.