Short answer: the Klipsch Heresy IV for sensitivity and output; the Infinity Primus 360 for flatter measured response. The Heresy IV hits 94.5dB/2.83V/1m in anechoic measurement, well under Klipsch’s 99dB in-room claim but still excellent, though its 77Hz F3 and rolloff near 100Hz mean a subwoofer is required. The Primus 360 stays within about ±2dB on-axis, its 93dB spec measuring closer to 89.4dB.
Buy the Klipsch Heresy IV, since the Infinity Primus 360 is discontinued and only worth hunting down used.
Still deciding? The full Passive Home rankings cover every ranked option.
Specifications Side By Side
| Infinity Primus 360 | Klipsch Heresy IV | |
|---|---|---|
| Price | $650 per pair Discontinued | $3,198 per pair |
| Ranked | #40 of 74 in Large Size Floorstanding Speakers | #72 of 74 in Large Size Floorstanding Speakers |
| Bass Extension (-10dB) | 37Hz (measured, Erin’s Audio Corner) | 50.0Hz (measured, Erin’s Audio Corner) |
| Bass Extension (-3dB) | 53Hz (measured, Erin’s Audio Corner) | 77Hz (measured, Erin’s Audio Corner) |
| Drivers | Two 6.5” mid-woofers, 4” mid-range, 0.75” dome tweeter | 1” horn-loaded tweeter; 1.75” horn-loaded midrange; 12” woofer |
| Sensitivity | 89.4dB (measured, Erin’s Audio Corner; 93dB manufacturer specified) | 94.5dB/2.83V/1m (measured, Erin’s Audio Corner) |
| Impedance | 8 ohms nominal, 3.5 ohms minimum (measured, Erin’s Audio Corner) | Approximately 4 ohms minimum (measured, Erin’s Audio Corner) |
| Dimensions | 39” x 8.2” x 13” (990 x 208 x 330 mm) | 24.8”H x 15.6”W x 13.3”D |
| Weight | 48.5 lbs (22 kg) each | 45 lbs (20.4 kg) each |
| Frequency Response | 38Hz - 20kHz (±3dB, Manufacturer specified) | - |
| Crossover Frequency | 350Hz & 3.3kHz, 24dB/octave | - |
| Recommended Power | 10-200W | - |
| Spinorama Preference Score | 4.97 | 2.27 |
| Spinorama Preference Score with Perfect Sub | 7.10 | 5.02 |
| DIY Kit | No | No |
| Woofer Cabinet | - | ported, rear |
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The Two Speakers In Full
Infinity Primus 360: $650 per pair 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. 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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Klipsch Heresy IV: $3,198 per pair Amazon Crutchfield eBay
Pros: Very high 94.5dB/2.83V/1m sensitivity in Erin’s anechoic measurement (well below Klipsch’s 99dB in-room claim, but still excellent) and strong short-term output from a 12-inch woofer plus horn-loaded midrange and tweeter. The compact, furniture-grade Heritage cabinet is easier to place than most high-efficiency designs, and dynamics at moderate levels can sound lively. A stable four-ohm-capable amplifier can produce substantial SPL with relatively little voltage. Measured bass extension of 77Hz (-3dB), with a measured sensitivity of 94.5dB.
Cons: Erin measured a 77Hz F3 and response rolling away near 100Hz in-room, so a subwoofer is required for modern full-range reproduction. The impedance dips to about 4 ohms, reducing the practical amplifier advantage implied by its sensitivity. Pronounced directivity mismatch at the driver transitions, impedance/response resonances and elevated distortion spikes around the crossover remain audible concerns that EQ cannot fully solve. At 102dB Erin measured roughly 1.5dB midband compression; at 96dB distortion rises around crossover. Performance is difficult to justify at the price, and Erin explicitly did not recommend it.
Full Klipsch Heresy IV review and specifications →
| Bass Extension (-10dB) | 50.0Hz (measured, Erin’s Audio Corner) |
|---|---|
| Bass Extension (-3dB) | 77Hz (measured, Erin’s Audio Corner) |
| DIY Kit | No |
| Dimensions | 24.8”H x 15.6”W x 13.3”D |
| Drivers | 1” horn-loaded tweeter; 1.75” horn-loaded midrange; 12” woofer |
| Impedance | Approximately 4 ohms minimum (measured, Erin’s Audio Corner) |
| Sensitivity | 94.5dB/2.83V/1m (measured, Erin’s Audio Corner) |
| Spinorama Preference Score | 2.27 |
| Spinorama Preference Score with Perfect Sub | 5.02 |
| Weight | 45 lbs (20.4 kg) each |
| Woofer Cabinet | ported, rear |
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