Short answer: both are discontinued, so this only matters if you are buying used. Used, the KEF R5 is the better pick: it ranks #40 of 188 floorstanding speakers by sound quality (rated 4.4/5), against #77 (rated 4.2/5) for the Infinity Primus 360. If you want one new, the Revel Concerta2 F35 ranks #30 at $900.
The KEF R5 is the more accurate choice. Slim three-way tower with the acoustic advantages of KEF’s coincident Uni-Q midrange/tweeter: horizontal and vertical off-axis responses track the direct sound smoothly, producing stable imaging and a well-behaved directivity index. Its measured preference score, a predictor of how neutral it sounds, is 5.78 against 4.97 for the Infinity Primus 360. The catch: The unusual gap between 77Hz F3 and 33Hz F10 indicates a gradual bass contour rather than flat deep-bass output; a subwoofer and roughly 80Hz high-pass are recommended for high-level playback.
The Infinity Primus 360 is the deeper-bass choice. Its bass reaches about 53Hz before falling 3dB, against 77Hz for the KEF R5. The catch: Manufacturer-spec sensitivity of 93dB runs about 3-4dB optimistic versus the measured 89.4dB average.
Buy the KEF R5 only if you find one used in good condition; both are discontinued, and it is the better rated of the two. For a new speaker, start with the Revel Concerta2 F35 instead.
Looking for alternatives? See the complete Passive Home rankings.
Specifications Side By Side
| KEF R5 | Infinity Primus 360 | |
|---|---|---|
| Price | $2,999 per pair Discontinued | $650 per pair Discontinued |
| Ranked | #40 of 188 in Large Size Floorstanding Speakers | #77 of 188 in Large Size Floorstanding Speakers |
| Bass Extension (-3dB) | 77Hz (measured, Erin’s Audio Corner) | 53Hz (measured, Erin’s Audio Corner) |
| Bass Extension (-10dB) | 33Hz (measured, Erin’s Audio Corner) | 37Hz (measured, Erin’s Audio Corner) |
| Sensitivity | Approximately 86dB/2.83V/1m (measured, Erin’s Audio Corner) | 89.4dB (measured, Erin’s Audio Corner; 93dB manufacturer specified) |
| Impedance | Approximately 3.5 ohms minimum near 150Hz (measured, Erin’s Audio Corner) | 8 ohms nominal, 3.5 ohms minimum (measured, Erin’s Audio Corner) |
| Drivers | 1” aluminum tweeter coaxial with 5” midrange; dual 5.25” woofers | Two 6.5” mid-woofers, 4” mid-range, 0.75” dome tweeter |
| Dimensions | 40.4”H x 6.9”W x 13.5”D | 39” x 8.2” x 13” (990 x 208 x 330 mm) |
| Weight | 59.5 lbs (27 kg) each | 48.5 lbs (22 kg) each |
| Woofer Cabinet | ported, rear | - |
| Spinorama Preference Score | 5.78 | 4.97 |
| Spinorama Preference Score with Perfect Sub | 7.40 | 7.10 |
| DIY Kit | No | No |
| Frequency Response | - | 38Hz - 20kHz (±3dB, Manufacturer specified) |
| Crossover Frequency | - | 350Hz & 3.3kHz, 24dB/octave |
| Recommended Power | - | 10-200W |
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The Two Speakers In Full
KEF R5: $2,999 per pair Discontinued eBay
Same family: the KEF R3 (bookshelf, rated 4.5/5), the KEF R7 (larger floorstanding, ranked lower, estimated 4.2/5), the KEF R11 (larger floorstanding, ranked lower, estimated 4.3/5) and the KEF R2c (center, rated 4/5).
Pros: Slim three-way tower with the acoustic advantages of KEF’s coincident Uni-Q midrange/tweeter: horizontal and vertical off-axis responses track the direct sound smoothly, producing stable imaging and a well-behaved directivity index. Erin measured deep low-frequency reach for the cabinet width (77Hz F3 but 33Hz F10) and less than 1% harmonic distortion at 86dB. At 96dB it remains clean when high-passed, and its mild response deviations are suitable for equalization because the radiation pattern stays orderly. Measured bass extension of 77Hz (-3dB), with a measured sensitivity of 86dB.
Cons: The unusual gap between 77Hz F3 and 33Hz F10 indicates a gradual bass contour rather than flat deep-bass output; a subwoofer and roughly 80Hz high-pass are recommended for high-level playback. Erin measured a minimum near 3.5 ohms around 150Hz, although most of the curve remains above 4 ohms, so amplifier quality still matters. Sensitivity is approximately 86dB/2.83V/1m. At 102dB, compression reaches roughly 1dB around 150Hz, showing the limits of the twin 5.25-inch woofers. This original model lacks the Meta version’s MAT rear-wave absorption. Discontinued.
Full KEF R5 review and specifications →
| Bass Extension (-10dB) | 33Hz (measured, Erin’s Audio Corner) |
|---|---|
| Bass Extension (-3dB) | 77Hz (measured, Erin’s Audio Corner) |
| DIY Kit | No |
| Dimensions | 40.4”H x 6.9”W x 13.5”D |
| Drivers | 1” aluminum tweeter coaxial with 5” midrange; dual 5.25” woofers |
| Impedance | Approximately 3.5 ohms minimum near 150Hz (measured, Erin’s Audio Corner) |
| Sensitivity | Approximately 86dB/2.83V/1m (measured, Erin’s Audio Corner) |
| Spinorama Preference Score | 5.78 |
| Spinorama Preference Score with Perfect Sub | 7.40 |
| Weight | 59.5 lbs (27 kg) each |
| Woofer Cabinet | ported, rear |
- Links
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
Infinity Primus 360: $650 per pair Discontinued eBay
Same family: the Infinity Primus 150 (bookshelf, rated 3.4/5).
Pros: A three-way tower from 2005 (two 6.5” mid-woofers, a 4” mid-range, and a 0.75” dome tweeter, 8 ohms nominal) that holds up remarkably well by modern measurement standards: on-axis linearity is within about ±2dB, and the listening window stays consistent out to roughly ±30° horizontal and ±10° vertical off the mid-range axis. Horizontal directivity is well controlled out to about ±75° before tonality starts to drift, meaning the reflected sound in a room stays close in character to the direct sound: a speaker that takes EQ well without fighting itself. Harmonic distortion measures low at both 86dB and 96dB, and multitone distortion stays under the reviewer’s 3% threshold. Silky, smooth midrange with a rich lower-midrange/upper-bass character. No mechanical issues or surround degradation found in a 20-year-old pair, and a second unit measured within about 1-1.5dB of the first, suggesting good long-term consistency for the design. Measured bass extension of 53Hz (-3dB), with a measured sensitivity of 89.4dB.
Cons: Manufacturer-spec sensitivity of 93dB runs about 3-4dB optimistic versus the measured 89.4dB average. Bass output drops off fairly quickly below about 50Hz in-room (F3 53Hz, F10 37Hz), so a subwoofer is needed for real low-end extension. Resonances show up around 170Hz, 220Hz, and 350Hz. On-axis, the lower treble can sound a bit bright or sibilant when the speaker is aimed directly at the listener; toeing out about 10-15° (rather than the more extreme 30°) gave the best balance, and some sidewall acoustic absorption further tamed a 4-5kHz peak. Placed close to the rear wall, bass gets boomy: pulling the speakers out about a foot resolves most of it, with roughly 1.5 feet from the wall as a good compromise between bass character and typical room aesthetics. Straying beyond about 25° above or below the mid-range axis introduces audible suckout. No longer in production, so it’s a used/secondhand purchase only.
Full Infinity Primus 360 review and specifications →
| Bass Extension (-10dB) | 37Hz (measured, Erin’s Audio Corner) |
|---|---|
| Bass Extension (-3dB) | 53Hz (measured, Erin’s Audio Corner) |
| Crossover Frequency | 350Hz & 3.3kHz, 24dB/octave |
| DIY Kit | No |
| Dimensions | 39” x 8.2” x 13” (990 x 208 x 330 mm) |
| Drivers | Two 6.5” mid-woofers, 4” mid-range, 0.75” dome tweeter |
| Frequency Response | 38Hz - 20kHz (±3dB, Manufacturer specified) |
| Impedance | 8 ohms nominal, 3.5 ohms minimum (measured, Erin’s Audio Corner) |
| Recommended Power | 10-200W |
| Sensitivity | 89.4dB (measured, Erin’s Audio Corner; 93dB manufacturer specified) |
| Spinorama Preference Score | 4.97 |
| Spinorama Preference Score with Perfect Sub | 7.10 |
| Weight | 48.5 lbs (22 kg) each |
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