Short answer: the KEF R5 for better sound quality, the Infinity Primus 360 for the lower price. The KEF R5 ranks #10 of 71 floorstanding speakers at $2999. The Infinity Primus 360 ranks #40 at $650, $2349 cheaper.
What the KEF R5 offers: 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. Watch for: 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.
What the Infinity Primus 360 offers: 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. Watch for: 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.
Buy the KEF R5 if sound quality matters more than the price. Buy the Infinity Primus 360 if the price matters more than sound quality.
Specifications Side By Side
| KEF R5 | Infinity Primus 360 | |
|---|---|---|
| Price | $2,999/pair Discontinued | $650.00 Discontinued |
| Ranked | #10 of 71 in Large Size Floorstanding Speakers | #40 of 71 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"H x 8-1/8"W x 13-7/8"D (990 x 208 x 330mm) |
| Discontinued | Yes | Yes |
| Weight | 59.5 lb each | 48.5 lbs (48.5 lbs / 22 kg) each |
| Woofer Cabinet | ported, rear | - |
| Frequency Response | - | 38Hz - 20kHz (±3dB, Manufacturer specified) |
| Crossovers | - | 350Hz & 3.3kHz, 24dB/octave |
| Recommended Power | - | 10-200W |
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The Two Speakers In Full
KEF R5: $2,999/pair Discontinued eBay
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.
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) |
| Dimensions | 40.4"H x 6.9"W x 13.5"D |
| Discontinued | Yes |
| 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) |
| Weight | 59.5 lb each |
| Woofer Cabinet | ported, rear |
- Links
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
Infinity Primus 360: $650.00 Discontinued eBay
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.
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. Discontinued.
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) |
| Crossovers | 350Hz & 3.3kHz, 24dB/octave |
| Dimensions | 39"H x 8-1/8"W x 13-7/8"D (990 x 208 x 330mm) |
| Discontinued | Yes |
| 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) |
| Weight | 48.5 lbs (48.5 lbs / 22 kg) each |
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