Short answer: the Q Acoustics 5040 for better sound quality, the Infinity Primus 360 for the lower price. The Q Acoustics 5040 ranks #25 of 56 floorstanding speakers at $1236.49. The Infinity Primus 360 ranks #32 at $650, $586.49 cheaper.
On the Q Acoustics 5040 side: C3 (Continuous Curved Cone) driver profile technology provides smooth midrange integration, controlled cone breakup, and improved bass damping. Set against that: Free-field frequency response exhibits a noticeable mid-bass scoop around 200Hz (~6dB lower than mean SPL).
The case for the Infinity Primus 360: 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. The tradeoff: Manufacturer-spec sensitivity of 93dB runs about 3-4dB optimistic versus the measured 89.4dB average.
Buy the Q Acoustics 5040 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
| Q Acoustics 5040 | Infinity Primus 360 | |
|---|---|---|
| Price | $1,236.49 | $650.00 Discontinued |
| Ranked | #25 of 56 in Large Size Floorstanding Speakers | #32 of 56 in Large Size Floorstanding Speakers |
| Bass Extension (-10dB) | 39Hz (measured, Erin’s Audio Corner) | 37Hz (measured, Erin’s Audio Corner) |
| Bass Extension (-3dB) | 70Hz (measured, Erin’s Audio Corner) | 53Hz (measured, Erin’s Audio Corner) |
| Dimensions | 38.1"H x 11.5"W x 14.2"D (967 x 293 x 361 mm) | 39"H x 8-1/8"W x 13-7/8"D (990 x 208 x 330mm) |
| Impedance | 6 ohms nominal (3.0 ohms minimum, measured by Erin’s Audio Corner) | 8 ohms nominal, 3.5 ohms minimum (measured, Erin’s Audio Corner) |
| Sensitivity | 91.5dB (measured average, Erin’s Audio Corner) | 89.4dB (measured, Erin’s Audio Corner; 93dB manufacturer specified) |
| Drivers | 0.88 in. decoupled dome tweeter, twin 5.0 in. C3 Continuous Curved Cone woofers | Two 6.5" mid-woofers, 4" mid-range, 0.75" dome tweeter |
| Weight | 39.7 lbs / 18.0 kg each | 48.5 lbs (48.5 lbs / 22 kg) each |
| Woofer Cabinet | ported, rear | - |
| Discontinued | - | Yes |
| 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
Q Acoustics 5040: $1,236.49 Amazon
Pros: C3 (Continuous Curved Cone) driver profile technology provides smooth midrange integration, controlled cone breakup, and improved bass damping. High voltage sensitivity (91.5dB SPL at 2.83V/1m) allows loud listening with low-to-moderate amplifier wattage. Cabinet features Point-to-Point (P2P) internal bracing and Helmholtz Pressure Equalizer (HPE) tubes to suppress internal standing waves and panel vibrations.
Cons: Free-field frequency response exhibits a noticeable mid-bass scoop around 200Hz (~6dB lower than mean SPL), causing an F3 of 70Hz (F10 of 39Hz) in open space and requiring boundary placement (11-22 inches from front wall) to reinforce upper bass output. Measurements indicate an enclosure resonance near 300Hz visible in sound power data. Minimum impedance drops to 3.0 ohms, demanding a stable 4-ohm rated amplifier despite high sensitivity.
Full Q Acoustics 5040 review and specifications →
| Bass Extension (-10dB) | 39Hz (measured, Erin's Audio Corner) |
|---|---|
| Bass Extension (-3dB) | 70Hz (measured, Erin's Audio Corner) |
| Dimensions | 38.1"H x 11.5"W x 14.2"D (967 x 293 x 361 mm) |
| Drivers | 0.88 in. decoupled dome tweeter, twin 5.0 in. C3 Continuous Curved Cone woofers |
| Impedance | 6 ohms nominal (3.0 ohms minimum, measured by Erin's Audio Corner) |
| Sensitivity | 91.5dB (measured average, Erin's Audio Corner) |
| Weight | 39.7 lbs / 18.0 kg each |
| Woofer Cabinet | ported, rear |
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Infinity Primus 360: $650.00 Discontinued
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 |
As an eBay Partner, we may be compensated if you make a purchase.
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