Short answer: the Infinity Primus 360 for even on-axis response; the Klipsch Forte IV for heritage three-way output. The Primus 360 measures within about ±2dB on-axis, but its 93dB sensitivity spec runs 3-4dB optimistic versus a measured 89.4dB average. The Forte IV mates a 12-inch woofer and a 15-inch passive radiator to a horn-loaded midrange, yet it is recessed in the 1.5-4kHz presence region and can sound dull.
Buy the Klipsch Forte IV, since the Infinity Primus 360 is discontinued and only worth hunting down used.
Looking for alternatives? See the complete Passive Home rankings.
Specifications Side By Side
| Infinity Primus 360 | Klipsch Forte IV | |
|---|---|---|
| Price | $650 per pair Discontinued | $5,499.98 per pair |
| Ranked | #40 of 74 in Large Size Floorstanding Speakers | #42 of 74 in Large Size Floorstanding Speakers |
| Bass Extension (-10dB) | 37Hz (measured, Erin’s Audio Corner) | 39Hz (measured, Erin’s Audio Corner) |
| Bass Extension (-3dB) | 53Hz (measured, Erin’s Audio Corner) | 82Hz (measured, Erin’s Audio Corner) |
| Drivers | Two 6.5” mid-woofers, 4” mid-range, 0.75” dome tweeter | 1x 12” (305mm) fiber-composite woofer + 15” passive radiator, 1x 1.75” compression driver midrange on horn, 1x 1” titanium compression tweeter on horn |
| Sensitivity | 89.4dB (measured, Erin’s Audio Corner; 93dB manufacturer specified) | 93.8dB (measured average, Erin’s Audio Corner; manufacturer rates 99dB in-room / ~94dB anechoic) |
| Impedance | 8 ohms nominal, 3.5 ohms minimum (measured, Erin’s Audio Corner) | 8 ohms |
| Dimensions | 39” x 8.2” x 13” (990 x 208 x 330 mm) | 36”H x 16.5”W x 13”D (914.4 x 419.1 x 330.2 mm) |
| Weight | 48.5 lbs (22 kg) each | 117.3 lbs (53.2 kg) |
| Frequency Response | 38Hz - 20kHz (±3dB, Manufacturer specified) | - |
| Crossover Frequency | 350Hz & 3.3kHz, 24dB/octave | - |
| Recommended Power | 10-200W | - |
| Spinorama Preference Score | 4.97 | 3.78 |
| Spinorama Preference Score with Perfect Sub | 7.10 | 5.72 |
| DIY Kit | No | No |
| Woofer Cabinet | - | passive radiator |
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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 Forte IV: $5,499.98 per pair Amazon Crutchfield eBay
Pros: Three-way heritage design: a 1” titanium tweeter and 1.75” compression driver for the midrange mated to a 12” woofer, plus a 15” passive radiator for extra bass reinforcement. Genuinely resonance-free cabinet, a clear improvement over the notably boomy, resonant Heresy 4 in the same lineup. Surprisingly wide, expansive soundstage that beat both the Heresy 4 and a KEF LS50 Wireless 2 in direct comparison: images occasionally appeared several feet outside the physical speaker location. Deeper bass extension than the Heresy 4 (F3 of 82Hz, about 10Hz lower). Distortion measures well below 1% at 86dB and stays mostly within 1% even at 96dB. Comes as a factory-matched serial-numbered pair, backed by an unusually generous 10-year warranty. Mostly above 4 ohms impedance, so it’s compatible with AVRs, solid-state, or tube amplifiers. More neutral overall than other Klipsch models the reviewer has tested, making it a reasonable pick for listeners who already like the “Klipsch sound” but want something more balanced. Measured bass extension of 82Hz (-3dB), with a measured sensitivity of 93.8dB.
Cons: Contrary to the classic Klipsch reputation for being forward and bright, this model is actually somewhat recessed in the 1.5-4kHz “presence” region, which can make some tracks sound dull or lacking in detail. A peak around 6kHz reads as sibilant and “painful” when seated exactly on the tweeter axis; sitting a bit above that axis reduces it somewhat. Klipsch’s marketed 99dB sensitivity figure is an in-room rating that assumes 3-6dB of boundary gain: anechoic sensitivity measures closer to 94dB, which the manufacturer does disclose but can still mislead buyers comparing spec sheets. Radiation width isn’t consistent across all frequencies: a noticeable notch around 2-3kHz interrupts otherwise wide dispersion, which can cause a fundamental tone and its harmonics to image in slightly different places in the soundstage. Uses shallow low-pass crossover slopes (despite Klipsch’s steep-crossover marketing, which applies only to the high-pass side), likely contributing to some of the measured dips and possible cone-breakup artifacts. Some compression shows up around the midrange crossover point at very high output (102dB), though likely only audible at extreme volumes. At around $5500/pair, a significant investment, and still needs a subwoofer for material extending below about 50Hz.
Full Klipsch Forte IV review and specifications →
| Bass Extension (-10dB) | 39Hz (measured, Erin’s Audio Corner) |
|---|---|
| Bass Extension (-3dB) | 82Hz (measured, Erin’s Audio Corner) |
| DIY Kit | No |
| Dimensions | 36”H x 16.5”W x 13”D (914.4 x 419.1 x 330.2 mm) |
| Drivers | 1x 12” (305mm) fiber-composite woofer + 15” passive radiator, 1x 1.75” compression driver midrange on horn, 1x 1” titanium compression tweeter on horn |
| Impedance | 8 ohms |
| Sensitivity | 93.8dB (measured average, Erin’s Audio Corner; manufacturer rates 99dB in-room / ~94dB anechoic) |
| Spinorama Preference Score | 3.78 |
| Spinorama Preference Score with Perfect Sub | 5.72 |
| Weight | 117.3 lbs (53.2 kg) |
| Woofer Cabinet | passive radiator |
- Links
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- Head-to-Head Comparisons
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- Klipsch Forte IV vs PSB Imagine T65
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