Short answer: the PMC twenty.21 for better sound quality, the Ascend Sierra Luna Duo for the lower price. The PMC twenty.21 ranks #62 of 63 bookshelf speakers at $2000. The Ascend Sierra Luna Duo ranks #63 at $1624, $376 cheaper.
What the Ascend Sierra Luna Duo gets right: Adding a second Luna woofer improves efficiency and reduces distortion versus the standard Sierra Luna, and the RAAL ribbon tweeter carries over. Set against that: Amir called it “one of the worse measuring and sounding [speakers] I have tested out of near 100 this year” and stated he “can not in any form or fashion recommend the Ascend Sierra Luna Duo.” On-axis response shows significant midrange irregularities, off-axis performance is uneven, and the port design creates notable frequency response disturbances.
On the PMC twenty.21 side: Transmission-line loaded design with a proprietary PMC/SEAS SONOLEX soft dome tweeter and doped mid/bass driver, reflecting PMC’s high-end British studio-monitor pedigree. The tradeoff: Amir was blunt: “The PMC Twenty.21 is a failure in design,” asking, “Did different people design different parts of the speaker and never talked to each other?” On-axis response is highly problematic, and the lack of a tweeter waveguide causes severe beamwidth compression that makes the speaker highly room-sensitive.
Buy the Ascend Sierra Luna Duo if the price matters more than sound quality. Buy the PMC twenty.21 if sound quality matters more than the price.
If sound quality matters at all to you, skip both of these and look higher up the 63 bookshelf speakers instead.
Specifications Side By Side
| Ascend Sierra Luna Duo | PMC twenty.21 | |
|---|---|---|
| Price | $1,624 discontinued, superseded by Luna Duo V2 | $2,000 discontinued, superseded by twenty5.21 |
| Ranked | #63 of 63 in Medium Size Bookshelf Speakers | #62 of 63 in Medium Size Bookshelf Speakers |
| Drivers | Custom RAAL true ribbon tweeter, dual 4.5" long-throw dual compliant CURV woofers | 5.5" (140mm) doped mid/bass driver with cast alloy chassis, 27mm PMC/SEAS SONOLEX soft dome tweeter (ferrofluid cooled) |
| Sensitivity | 84.9dB (2.83V/1m, measured, Audio Science Review) | 83dB (1W/1m, manufacturer specified) |
| Woofer Cabinet | ported, front | transmission line, 1.72m effective length |
| Bass Extension (-3dB) | 85.0Hz (measured, Audio Science Review) | 68.8Hz (measured, Audio Science Review) |
| Bass Extension (-10dB) | 52.2Hz (measured, Audio Science Review) | 48.7Hz (measured, Audio Science Review) |
| Dimensions | - | 12.8"H x 6"W x 10.9"D (325 x 152 x 277 mm) (+6mm grille) |
| Weight | - | 11 lbs / 5 kg each |
| Frequency Response | - | 50Hz - 25kHz, +/-4.4dB (Manufacturer specified) |
| Impedance | - | 8 ohms |
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The Two Speakers In Full
Ascend Sierra Luna Duo: $1,624 discontinued, superseded by Luna Duo V2
Pros: Adding a second Luna woofer improves efficiency and reduces distortion versus the standard Sierra Luna, and the RAAL ribbon tweeter carries over. Flexible orientation lets it work vertically as a main/LCR speaker or horizontally as a center channel.
Cons: Amir called it “one of the worse measuring and sounding [speakers] I have tested out of near 100 this year” and stated he “can not in any form or fashion recommend the Ascend Sierra Luna Duo.” On-axis response shows significant midrange irregularities, off-axis performance is uneven, and the port design creates notable frequency response disturbances. Vertical directivity has an extremely narrow optimal listening window. The reviewer noted a stark contrast with the Revel M105, which showed clearly superior tonality and clarity.
Full Ascend Sierra Luna Duo review and specifications →
| Bass Extension (-10dB) | 52.2Hz (measured, Audio Science Review) |
|---|---|
| Bass Extension (-3dB) | 85.0Hz (measured, Audio Science Review) |
| Drivers | Custom RAAL true ribbon tweeter, dual 4.5" long-throw dual compliant CURV woofers |
| Sensitivity | 84.9dB (2.83V/1m, measured, Audio Science Review) |
| Woofer Cabinet | ported, front |
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- Reviews, Comparisons and Sound Samples
PMC twenty.21: $2,000 discontinued, superseded by twenty5.21
Pros: Transmission-line loaded design with a proprietary PMC/SEAS SONOLEX soft dome tweeter and doped mid/bass driver, reflecting PMC’s high-end British studio-monitor pedigree.
Cons: Amir was blunt: “The PMC Twenty.21 is a failure in design,” asking, “Did different people design different parts of the speaker and never talked to each other?” On-axis response is highly problematic, and the lack of a tweeter waveguide causes severe beamwidth compression that makes the speaker highly room-sensitive. Dual bass peaks indicate improper port tuning, with the port bump at 100Hz compounding rather than compensating for existing woofer peaks. Distortion is elevated throughout, spiking further at 96dB SPL near 200Hz from port noise. Initial listening was “screechy bright” enough to trigger the reviewer’s tinnitus, with harsh, lispy vocals and tubby, unnatural bass; only heavy manual EQ made it acceptable. At $2,000, Amir suspects the tuning was done “by ear” rather than with measurements.
Full PMC twenty.21 review and specifications →
| Bass Extension (-10dB) | 48.7Hz (measured, Audio Science Review) |
|---|---|
| Bass Extension (-3dB) | 68.8Hz (measured, Audio Science Review) |
| Dimensions | 12.8"H x 6"W x 10.9"D (325 x 152 x 277 mm) (+6mm grille) |
| Drivers | 5.5" (140mm) doped mid/bass driver with cast alloy chassis, 27mm PMC/SEAS SONOLEX soft dome tweeter (ferrofluid cooled) |
| Frequency Response | 50Hz - 25kHz, +/-4.4dB (Manufacturer specified) |
| Impedance | 8 ohms |
| Sensitivity | 83dB (1W/1m, manufacturer specified) |
| Weight | 11 lbs / 5 kg each |
| Woofer Cabinet | transmission line, 1.72m effective length |
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