Short answer: the PSI Audio A21-M. It ranks #19 of 68 powered bookshelf speakers by sound quality, rated 4.5/5, at $3720; the Devialet Phantom Ultimate 108dB ranks #29, rated 4.4/5, and costs $7998, so there is little reason to consider the other one.
What the Devialet Phantom Ultimate 108dB does well: Erin’s measurements show full bass output all the way down to about 20Hz, the lowest frequency measured, which is remarkable from a single cabinet about 34cm deep. Watch for: DSP limiting and compression take over near maximum volume, so the deep bass you hear at moderate levels shrinks when you push it; Erin’s 96dB distortion test ran into the limiter.
The case for the PSI Audio A21-M: ASR measured 39.6Hz -3dB extension and a 2.2dB response span from 300Hz to 5kHz, giving useful bass and broadly even mids. The catch: The measured tonal result is good rather than a clear advance over less costly competitors.
Buy the PSI Audio A21-M. It is rated higher for sound quality than the Devialet Phantom Ultimate 108dB and costs less, so the other one has nothing left to offer.
Looking for alternatives? See the complete Powered Home rankings.
Specifications Side By Side
| Devialet Phantom Ultimate 108dB | PSI Audio A21-M | |
|---|---|---|
| Price | $7,998 per pair | $7,440 per pair |
| Ranked | #29 of 68 in Large Size Powered Bookshelf Speakers | #19 of 68 in Large Size Powered Bookshelf Speakers |
| Bass Extension (-3dB) | <21Hz (measured, Erin's Audio Corner) | 39.6Hz (measured, Audio Science Review) |
| Bass Extension (-10dB) | <21Hz (measured, Erin's Audio Corner) | 33.2Hz (measured, Audio Science Review) |
| Dimensions | 10"H x 9.7"W x 13.5"D (255 x 246 x 342 mm) | 9.8"H x 15.7"W x 11.8"D (250 x 400 x 300 mm) |
| Weight | 24.5 lbs (11.1 kg) each | 28.2 lbs (12.8 kg) each |
| Drivers | Aluminum tweeter, aluminum midrange, two opposed aluminum woofers | 27mm handmade dome tweeter, 172mm cone woofer |
| Inputs | Wi-Fi, Ethernet, Bluetooth, Optical | XLR (balanced analog) |
| App | Yes (Devialet) | - |
| Bluetooth | Yes (5.3 with SBC, AAC) | No |
| Bluetooth Codecs | SBC, AAC | - |
| Wi-Fi | Yes (Wi-Fi 6, dual-band) | - |
| Streaming Services | Yes (AirPlay 2, Google Cast, Spotify Connect, TIDAL Connect, Roon Ready, UPnP) | - |
| Amplifier Power | 1,100W total | 335W total (280W woofer, 55W tweeter, Class A/B) |
| Maximum SPL | 108dB (manufacturer specified) | 110dB short term, 121dB peak (manufacturer specified) |
| Frequency Response | 14Hz - 35kHz (Manufacturer specified) | 38Hz-23kHz -6dB |
| Spinorama Preference Score | 6.73 | 6.07 |
| Spinorama Preference Score with Perfect Sub | 7.38 | 7.72 |
| Subwoofer Output | No | - |
| XLR Input | No | Yes |
| RCA Input | No | No |
| TRS Input | No | No |
| Optical Input | Yes | No |
| Coaxial Input | No | No |
| USB Input | No | No |
| HDMI Input | No | No |
| AES Input | No | No |
| Aux Input | No | No |
| Enclosure | - | ported |
| Crossover Frequency | - | 2.4kHz |
| Warranty | - | 5+1 years |
| Country | - | Switzerland |
Related Speaker Comparisons
How PSI Audio A21-M compares with other leading options:
- Yamaha HS8 vs PSI Audio A21-M
- Focal Solo6 ST6 vs PSI Audio A21-M
- Meyer Sound Amie vs PSI Audio A21-M
- PSI Audio A21-M vs JBL 708P
- Devialet Phantom Ultimate 108dB vs Genelec S360
Prices on this page were last checked September 23, 2026 at 11:24 PM UTC. Product prices and availability are accurate as of that date/time and are subject to change; the price and availability shown on Amazon at the time of purchase will apply to the purchase of this product.
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The Two Speakers In Full
Devialet Phantom Ultimate 108dB: $7,998 per pair Amazon B&H Photo Video eBay
Pros: Erin’s measurements show full bass output all the way down to about 20Hz, the lowest frequency measured, which is remarkable from a single cabinet about 34cm deep. The listening window is close to flat, with a -0.04dB per octave tilt and 0.80 smoothness, earning a 6.73 preference score on its own and 7.38 with an ideal subwoofer. Directivity is smooth, so room reflections keep the same tonal balance as the direct sound. Wi-Fi 6 streaming with AirPlay 2, Google Cast, Spotify Connect, TIDAL Connect and Roon Ready, plus Ethernet and optical inputs, makes one unit a complete music system. Measured bass extension of <21Hz (-3dB).
Cons: DSP limiting and compression take over near maximum volume, so the deep bass you hear at moderate levels shrinks when you push it; Erin’s 96dB distortion test ran into the limiter. Stereo means buying two units, which puts a pair well above conventional powered monitors that measure as well. There is no analog input or subwoofer output, and the rounded shape does not sit on a shelf or desk stand like a box speaker.
Full Devialet Phantom Ultimate 108dB review and specifications →
| AES Input | No |
|---|---|
| Amplifier Power | 1,100W total |
| App | Yes (Devialet) |
| Aux Input | No |
| Bass Extension (-10dB) | <21Hz (measured, Erin's Audio Corner) |
| Bass Extension (-3dB) | <21Hz (measured, Erin's Audio Corner) |
| Bluetooth | Yes (5.3 with SBC, AAC) |
| Bluetooth Codecs | SBC, AAC |
| Coaxial Input | No |
| Dimensions | 10"H x 9.7"W x 13.5"D (255 x 246 x 342 mm) |
| Drivers | Aluminum tweeter, aluminum midrange, two opposed aluminum woofers |
| Frequency Response | 14Hz - 35kHz (Manufacturer specified) |
| HDMI Input | No |
| Inputs | Wi-Fi, Ethernet, Bluetooth, Optical |
| Maximum SPL | 108dB (manufacturer specified) |
| Optical Input | Yes |
| RCA Input | No |
| Spinorama Preference Score | 6.73 |
| Spinorama Preference Score with Perfect Sub | 7.38 |
| Streaming Services | Yes (AirPlay 2, Google Cast, Spotify Connect, TIDAL Connect, Roon Ready, UPnP) |
| Subwoofer Output | No |
| TRS Input | No |
| USB Input | No |
| Weight | 24.5 lbs (11.1 kg) each |
| Wi-Fi | Yes (Wi-Fi 6, dual-band) |
| XLR Input | No |
- Links
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons
PSI Audio A21-M: $7,440 per pair B&H Photo Video eBay
Pros: ASR measured 39.6Hz -3dB extension and a 2.2dB response span from 300Hz to 5kHz, giving useful bass and broadly even mids. Its 7.72 ideal-subwoofer score supports serious monitoring, with analog phase compensation offering an alternative to DSP-based systems. Measured bass extension of 39.6Hz (-3dB).
Cons: The measured tonal result is good rather than a clear advance over less costly competitors. There is no built-in automatic room-calibration system, so placement or external correction still matters. The premium construction and analog circuitry should not be mistaken for proof of better audible performance.
Full PSI Audio A21-M review and specifications →
| AES Input | No |
|---|---|
| Amplifier Power | 335W total (280W woofer, 55W tweeter, Class A/B) |
| Aux Input | No |
| Bass Extension (-10dB) | 33.2Hz (measured, Audio Science Review) |
| Bass Extension (-3dB) | 39.6Hz (measured, Audio Science Review) |
| Bluetooth | No |
| Coaxial Input | No |
| Country | Switzerland |
| Crossover Frequency | 2.4kHz |
| Dimensions | 9.8"H x 15.7"W x 11.8"D (250 x 400 x 300 mm) |
| Drivers | 27mm handmade dome tweeter, 172mm cone woofer |
| Enclosure | ported |
| Frequency Response | 38Hz-23kHz -6dB |
| HDMI Input | No |
| Inputs | XLR (balanced analog) |
| Maximum SPL | 110dB short term, 121dB peak (manufacturer specified) |
| Optical Input | No |
| RCA Input | No |
| Spinorama Preference Score | 6.07 |
| Spinorama Preference Score with Perfect Sub | 7.72 |
| TRS Input | No |
| USB Input | No |
| Warranty | 5+1 years |
| Weight | 28.2 lbs (12.8 kg) each |
| XLR Input | Yes |
- Links
- Reviews, Comparisons and Sound Samples
- Head-to-Head Comparisons