REL Acoustics S/850 vs KEF Reference 8b

Short answer: the REL Acoustics S/850. It ranks #110 of 212 subwoofers by sound quality, rated 3.7/5, at $3,999; the KEF Reference 8b ranks #157, rated 3.4/5, and costs $8,999.99, so there is little reason to consider the other one.

The REL Acoustics S/850 is the better-sounding pick. Front-firing 12 inch carbon and aluminum driver plus a down-firing 12 inch passive radiator, driven by an 850W RMS Class D amplifier (1,000W peak). The catch: No independent measurements yet, so its output can’t be compared with ranked subwoofers; the rating is estimated from the measured REL Acoustics R-528, an older 12 inch REL that averaged 112.8dB in the CEA-2010 bands but fell to 92.7dB at 25Hz.

What the KEF Reference 8b does well: Flagship Reference series subwoofer featuring dual opposing 9-inch drivers in a force-cancelling sealed enclosure, eliminating mechanical cabinet vibration. The tradeoff: Flagship $8,999.99 price tag is aimed strictly at reference luxury installations, and the 77.2 lbs (35 kg) piano-gloss cabinet requires delicate handling.

Buy the REL Acoustics S/850. It is rated higher for sound quality than the KEF Reference 8b and costs less, so it is the default pick unless a specific strength of the other one matters more to you.

About the ratings: neither speaker has been measured yet, so both ratings are estimated from measured siblings and predecessors (likely ranges: REL Acoustics S/850 3.4 to 4.0; KEF Reference 8b 3.2 to 3.6). Treat this verdict as provisional.

Still deciding? The full Subwoofers rankings cover every ranked option.

Specifications Side By Side

Related Speaker Comparisons

More worthwhile head-to-heads for REL Acoustics S/850:

• Paradigm XR11 vs REL Acoustics S/850
• Sigberg Audio 10D vs REL Acoustics S/850
• Sigberg Audio INKOGNITO 12 vs REL Acoustics S/850
• REL Acoustics S/850 vs REL Acoustics S/550
• REL Acoustics S/550 vs KEF Reference 8b

Prices on this page were last checked October 11, 2026 at 4:59 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

REL Acoustics S/850: $3,999.00 Estimated REL Acoustics eBay

Older model: the REL Acoustics R-528 (ranked higher, rated 3.7/5). See every REL S and Reference Series generation.

Same family: the REL Acoustics S/550 (smaller subwoofer, ranked lower, estimated 3.5/5), the REL Acoustics Carbon Special Black Label (larger subwoofer, estimated 3.9/5) and the REL Acoustics 212 Black Label (larger subwoofer, estimated 4.2/5).

Pros: Front-firing 12 inch carbon and aluminum driver plus a down-firing 12 inch passive radiator, driven by an 850W RMS Class D amplifier (1,000W peak). REL rates it at 19Hz at the -6dB point. High level Speakon, RCA and LFE RCA/XLR inputs, and REL’s Airship wireless option, make it easy to blend with stereo and theater systems.

Cons: No independent measurements yet, so its output can’t be compared with ranked subwoofers; the rating is estimated from the measured REL Acoustics R-528, an older 12 inch REL that averaged 112.8dB in the CEA-2010 bands but fell to 92.7dB at 25Hz. At 42.5 kg it is very heavy, and it costs far more than measured 12 inch subwoofers with more output.

Full REL Acoustics S/850 review and specifications →

Released	Sep 2025 (1 year ago)
Amplifier Power	850W RMS (1,000W peak)
Cabinet Color	black, white
Country	United Kingdom
Dimensions	16.1”H x 19.2”W x 21.3”D (410 x 488 x 540 mm)
Drivers	12” (305mm) driver, 12” passive radiator
Enclosure	passive radiator
Frequency Response	19Hz (-6dB, manufacturer specified)
Warranty	3
Weight	93.7 lbs (42.5 kg)

• Links
  • REL Acoustics S/850 Website
• Reviews, Comparisons and Sound Samples
  • No independent measurement review is linked for this model; it is ranked from hands-on listening and comparison against similarly priced speakers.
• Head-to-Head Comparisons
  • REL Acoustics S/850 vs REL Acoustics S/550
  • REL Acoustics S/850 vs Sigberg Audio INKOGNITO 12
  • REL Acoustics S/850 vs Sigberg Audio 10D
  • REL Acoustics S/850 vs Paradigm XR11

KEF Reference 8b: $8,999.99 Estimated KEF eBay

Pros: Flagship Reference series subwoofer featuring dual opposing 9-inch drivers in a force-cancelling sealed enclosure, eliminating mechanical cabinet vibration. Driven by twin 500W Class-D amplifiers (1,000W total) with extensive DSP boundary compensation and balanced XLR plus RCA inputs, extending clean bass down to 24Hz (±3dB).

Cons: Flagship $8,999.99 price tag is aimed strictly at reference luxury installations, and the 35 kg piano-gloss cabinet requires delicate handling.

Full KEF Reference 8b review and specifications →

Amplifier Power	1000W
Cabinet Color	Piano Black High Gloss
Country	United Kingdom
Dimensions	15.7”H x 14.4”W x 16.9”D (398 x 365 x 429 mm)
Drivers	dual 9” drivers
Enclosure	sealed
Frequency Response	24Hz - 140Hz (±3dB) (manufacturer specified)
Maximum SPL	110 dB
Warranty	5/2
Weight	77.2 lbs (35.0 kg)
XLR Input	Yes

• Links
  • Official KEF Reference 8b Website
• Reviews, Comparisons and Sound Samples
  • No independent measurement review is linked for this model; it is ranked from hands-on listening and comparison against similarly priced speakers.
• Head-to-Head Comparisons
  • KEF Reference 8b vs REL Acoustics S/550
  • KEF Reference 8b vs Bowers & Wilkins DB2D