Issue 91

Review: PSI Audio A21-M Studio Monitors

Pump up your critical listening setup with some PSI monitors.


19 September 2014

Studio monitors tend to be functional rather than audiophile, and often chosen on price as much as sound quality, but there is a better world out there. One where working with great sound can be a treat, where so tangible and detailed is the sound, mixing becomes a craft and less like blunt force trauma.

The high-end studio monitor market is led by dedicated audio manufacturers, both corporate and boutique, who continue the noble quest for better sound. Boundaries get pushed and gains are made in controlling the myriad parameters affecting the final sound delivered to the listener. PSI Audio is one of those companies, combining sophisticated electronics, strict objective measurements and critical listening to make a better monitor speaker. It is the Swiss way.


Based in Switzerland, PSI Audio’s parent company Relec has a decades-long history making speakers, many on an OEM basis, including a line of studio monitors for Studer in the ’90s. Since 2004 they’ve been making a range of studio monitors under the PSI brand, and Group Technologies has recently begun distributing them in Australia. The A21-M sits in the middle of the current seven-speaker range and it’s aimed at commercial studios, serious project studios, broadcast and surround sound applications.

PSI aims high. The speakers are almost completely hand-made, with unique features inside and out. The cabinets are made in Sainte-Croix, a Swiss mountain-town with a long history of creating finely detailed music boxes, automatons, and ornate gramophones. While not gilt-edged, I daresay that heritage helped influence the distinctive deep maroon, slightly sparkly finish on the cabinets in the range. They look great, but you can get black if the reddish tone clashes with the décor.

The A21-M is a front-ported, two-way design with the tweeter set well back inside a circular waveguide. A recessed light sits beside the tweeter to indicate power on, and flashes to let you know you’ve found full level. The eight-inch woofer is fully exposed, screw-heads and all. At first I thought it looked a bit unfinished compared to the rest of the cabinet but it grew on me. An optional black grille is available if fingers or flying objects are a concern. The dimensions are 250x400x300mm and weight is a solid 13.4kg. Some similar speakers are quite deep but these are a good size and easy to place. They look like modern furniture mounted above a mixing console; the finish catches the customer’s eye and the PSI logo on one side of the cabinet literally screams boutique.


The heart of these speakers’ quality is more than skin deep, with a few PSI-developed technologies responsible for their supreme sound. AOI (Adaptive Output Impedance system) continually adjusts the amp’s output impedance depending on the frequency content of the program. This optimisation of the damping rate allows for extremely fast acceleration and deceleration of the speaker cone without overshooting at the top or bottom. PSI claim this system lets the speaker get close to reproducing square waves. To the ear, the sound is fast and accurate. An interesting side-effect of this system is its ability to sense and correct potential cone distortions caused by other sounds in the same environment.

CPR (Compensated Phase Response) uses all-pass filters across several frequency bands to present a phase-coherent output over a wide frequency range. This explains the rock solid stereo image for monitoring and ensures maximum phase coherence in multi-speaker systems. 

While we’re on three-letter acronyms there’s also ALG (Acoustic Load Guide) that sees the tweeter set back in a little tunnel before flaring out at the front of the wave guide. The claimed benefits are wider frequency range, extended bandwidth and higher volume… and I hear them all.





    Group Technologies: (03) 9354 9133 or

  • PROS

    • Accurate sound
    • Distinctive finish
    • High volume ability

  • CONS

    • None if this is your price range


    These Swiss monitors are incredibly detailed, flat, and loud, without being clinically cold. About as good as you can get in a two-way monitor at the moment.


The rear panel wobbles a little because the amplifier and associated electronics are spring-mounted to avoid LF vibration at high volume. The rear panel gives you an XLR input, level trim and bass roll-off. Inside the amp module you get electronics designed and assembled by PSI with many hand-made components — PSI is especially proud of the hand-wound tweeter. 


Power comes from an analogue Class G amp delivering 120W for the woofer and 50W to the tweeter. Proprietary crossovers separate the drivers at 2.4kHz. They’ve got some great specs including 119dB max SPL at 1m, -6db down points at 38Hz and 23kHz, ±2dB tolerance between 44Hz–20kHz, and Total Harmonic Distortion is quoted at <1.4% between 90Hz and 12kHz.


When I fired up the A21-Ms with a few familiar tracks, the stereo image made a big first impression; wide and definite with a sense of almost seeing into the soundstage. Slightly mid-forward with amazing transparency, you get that feeling you’re hearing the tracks for the first time. These speakers will have you auditioning tracks just to hear what they sound like, as well as revealing sounds you hadn’t noticed before in more well-known works in your catalogue.

They starkly demonstrate the differences between recordings and easily highlight compression used in both recording and mastering. The details of distortion and reverb are clearly audible. The frequency response is wide and flat with not an ounce of flab in the bottom end. They look distinctive but don’t really have a sound of their own; they just reproduce what goes in with extreme accuracy. These are genuine studio monitors; no exaggerated or boomy bass, no scooped mids and no tizzy highs… just the truth. Starkly presented but beautifully delivered.

And they kick big butt when you turn them up. This is another side of these speakers; they run loud for this size box, they respond to the volume knob like a car with a high-revving engine, and they stay nice right up until just before the limit light (red line) comes on. They bite if it’s in the music and can sound brutal because of this accuracy rather than in spite of its absence. They can also sound big, like a good PA, if they’re up loud and you’re right in front of them. You can sit as close to them as you like but about one to two meters in front seems ideal. Their 90 x 90° dispersion presents a wide listening area. In a good room they would have the power and throw to work well at medium distances.


In use, you forget about how good they sound and start to appreciate them as a tool of trade. I loved them for tracking; their crisp transients and transparency get you right inside the sounds. The power and volume give you the dynamics and detail you need for tracking drums and other loud sources. The tweeter is a cracker at all volumes. And they’re perfect for giving the band a bit of a thrill on playback too.

Mixes I was already working on had good bits and faults equally well exposed. Early on, I was wrestling to control a harsh-sounding guitar band, but after a good tweak through the A21-Ms it all came together and I was very happy to hear how it sounded in the outside world. I proceeded with confidence; if you like the sound on these it will sound good anywhere. Once confident and familiar with them, both mixing and mastering benefited because I could hear everything I touched — these speakers reveal things to you. The only trouble I had with them was running them too loud, such a pleasure it was hard to stop, but with power comes responsibility, I suppose.

Quality touches abound. I like the silent off/on switching and it’s reassuring to know each speaker has been tested in PSI’s anechoic chamber and supplied with its own frequency plot. PSI aim to make the best monitors possible and to my ears these are as good as you can currently get. It’s not possible to be familiar with every speaker available, and personal choice comes into it sometimes, but these are right up there. There’s a price to pay for this sort of performance but it only takes a few seconds to hear what it buys. Used on a daily basis they are an ongoing pleasure. 


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