Short answer: the KEF R3. It ranks #15 of 222 bookshelf speakers by sound quality, rated 4.5/5, at $1,544.56. The MartinLogan Motion XT B100 ranks #139, rated 3.6/5, at $1,359.98, $184.58 cheaper, not enough of a saving to outweigh the sound-quality gap.
The KEF R3 is the more accurate, deeper-bass option. A three way bookshelf speaker with KEF’s coaxial driver for stable imaging across seats and very low distortion, easy to run with a modest amp. Its measured preference score, a predictor of how neutral it sounds, is 6.20 against 3.83 for the MartinLogan Motion XT B100. Its bass reaches about 58Hz before falling 3dB, against 71.8Hz for the MartinLogan Motion XT B100. Watch for: The low-frequency alignment rolls gradually rather than delivering high-output sub-bass; KEF specifies 58Hz +/-3dB and Erin’s high-level data supports using an 80Hz subwoofer crossover.
The case for the MartinLogan Motion XT B100: Premium standmount speakers with a large folded-motion tweeter and high sensitivity that is easy to drive. The tradeoff: The measured response rises strongly at +0.84dB per octave and directivity-index consistency is a poor 4.34, so tonal balance and off-axis behavior are less neutral than the price implies.
Buy the KEF R3. It is rated higher for sound quality, and saving $184.58 with the MartinLogan Motion XT B100 does not make up for the sound-quality gap.
Still deciding? The full Passive Home rankings cover every ranked option.
Measured Differences
- Efficiency: the MartinLogan Motion XT B100 is rated at 93 dB sensitivity against 86 dB for the KEF R3, so it plays as loud with roughly a third of the amplifier power.
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Specifications Side By Side
| KEF R3 | MartinLogan Motion XT B100 | |
|---|---|---|
| Price | $1,544.56 per pair | $1,359.98 per pair |
| Ranked | #15 of 222 in Large Size Bookshelf Speakers | #139 of 222 in Large Size Bookshelf Speakers |
| Bass Extension (-3dB) | Approximately 58Hz (manufacturer specified; consistent with Erin’s measured roll-off) | 71.8Hz (measured, Erin’s Audio Corner via spinorama.org) |
| Bass Extension (-10dB) | 35.2Hz (measured, Audio Science Review) | 50.7Hz (derived, log-interpolated between spinorama.org -9dB/-12dB points) |
| Sensitivity | Approximately 86-87dB/2.83V/1m (measured, Erin’s Audio Corner) | 93dB |
| Impedance | 8 ohms nominal; suitable for Erin’s 4/8-ohm-rated amplifier | 4 ohms |
| Drivers | 1” tweeter coaxial with 5” midrange; 6.5” woofer | 1.25 x 2.4” folded-motion XT tweeter, 6.5” Kevlar woofer |
| Dimensions | 16.6”H x 7.9”W x 13.2”D | 14.5H x 8W x 12.5D in |
| Woofer Cabinet | ported, rear Flexible Port | - |
| Weight | 29.9 lbs (13.55 kg) each | 20.5 lbs (9.3 kg) each |
| Spinorama Preference Score | 6.2 (spinorama.org) | 3.83 |
| Spinorama Preference Score with Perfect Sub | 7.97 (spinorama.org) | 6.35 |
| DIY Kit | No | No |
| Enclosure | - | 2-way, rear-ported |
| Country | - | United States (design) |
Where the Ratings Come From
- KEF R3: Spinorama.org measurements and reviews by Erin’s Audio Corner and Audio Science Review.
- MartinLogan Motion XT B100: Spinorama.org measurements and reviews by Erin’s Audio Corner.
This comparison is generated from the ratings, specifications and measurements on each product’s own page, and it updates when that data changes. How we rank explains how each rating is decided.
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