The PSI Audio A21-M Studio Red is a Swiss-made, fully analogue two-way active studio monitor for demanding nearfield and midfield work. With a powerful 210 mm woofer, PSI-designed tweeter, Class G/H low-frequency amplification, AOI driver control and CPR phase-response technology, it combines deep bass extension, high SPL capability and highly stable stereo imaging in a compact professional monitor.
 
The PSI Audio A21-M Studio Red is a reference-grade active monitor for engineers who need more headroom, bass authority and room coverage than a typical compact nearfield can provide, but do not want the physical scale of a large three-way midfield system. Handmade and individually calibrated in Switzerland, it is designed for recording, mixing, mastering, post-production and critical listening in professional control rooms.
The A21-M follows PSI Audio’s fully analogue monitor philosophy. There is no DSP in the signal path and no digital crossover processing. Instead, PSI uses custom analogue electronics, dedicated amplifiers, purpose-designed drivers and measured crossover integration to achieve the monitor’s accuracy. This results in direct transient response, minimal system latency and a coherent, predictable presentation for decisions about EQ, dynamics, spatial detail and low-frequency balance.
 
The two-way system combines a 210 mm woofer with a 25 mm tweeter. PSI Audio’s current technical data lists a 172 mm woofer diaphragm and a 27 mm tweeter diaphragm within their respective driver assemblies. A newly developed waveguide supports controlled high-frequency dispersion and helps maintain phase-coherent reproduction at the listening position, including through the critical crossover region. The bass-reflex cabinet provides useful low-frequency extension while maintaining a relatively compact footprint for a monitor capable of serious midfield output.
 
The A21-M is specified from 38 Hz to 23 kHz at −6 dB, with a tolerance of ±2 dB from 44 Hz to 20 kHz. This extended bandwidth enables reliable judgement of kick drum fundamentals, bass guitar, synthesizer low end, sub-harmonic build-up and the overall relationship between low-frequency weight and midrange clarity. In many rooms it can function as a complete main monitor without a subwoofer. Where deeper extension, more low-frequency headroom or immersive-system bass management is needed, it can be combined with an appropriate PSI Audio subwoofer and AvAA acoustic-treatment solutions.
 
PSI Audio’s CPR system, Compensated Phase Response, is designed to keep phase behaviour controlled through the crossover. This supports a stable, sharply focused image, reliable depth perception and strong transient definition. The A21-M’s AOI technology, Active Output Impedance, actively controls driver behaviour to reduce resonance and improve low-frequency definition. Together with the high-power amplification and carefully integrated waveguide, these technologies help the monitor remain clear and accurate at both low and high playback levels.
 
The woofer is driven by a 280 W Class G/H amplifier, while the tweeter receives 55 W of Class A/B power. The A21-M reaches 106 dB continuous SPL, 110 dB short-term SPL and 121 dB peak SPL at one metre. Its 80° horizontal by 30° vertical dispersion is designed to provide a useful listening area while limiting unnecessary energy toward the ceiling and desk. This makes it highly suitable for typical nearfield-to-midfield control-room geometry, with a recommended listening distance between one and three metres.
 
Rear-panel adjustment supports practical integration in real rooms. Input sensitivity can be calibrated to the monitor controller and interface gain structure, while frequency and placement compensation help optimise the monitor for stands, consoles or wall distance. A balanced XLR input makes it easy to connect professional monitor controllers, interfaces and analogue monitoring chains.
 
The Studio Red version has the same acoustic design as the other A21-M finishes but provides PSI’s distinctive red front-panel look. Every monitor is individually measured and calibrated in an anechoic environment, supporting consistent matching for stereo pairs and future multi-speaker or immersive expansions.
 
The A21-M belongs first in Studio Monitors and is an especially strong main-monitor option for professional mix rooms. Its precise analogue architecture and high-resolution active design also give it credible appeal for high-end active stereo listening, but the primary product story should remain reliable professional monitoring and mix translation.
 
Key features
Swiss-made active 2-way nearfield and midfield reference monitor
Studio Red finish
Fully analogue signal path with no DSP
Handmade and individually calibrated in Switzerland
210 mm woofer with 172 mm diaphragm
PSI-designed 25 mm tweeter with 27 mm diaphragm
Bass-reflex enclosure
Controlled waveguide for accurate listening-position response
Class G/H amplifier for woofer
Class A/B amplifier for tweeter
280 W LF + 55 W HF potential peak amplifier power
Frequency range: 38 Hz–23 kHz at −6 dB
Frequency tolerance: ±2 dB from 44 Hz–20 kHz
Crossover frequency: 2.4 kHz
CPR compensated phase-response technology
AOI active output-impedance technology
ALG overload protection
Dispersion: 80° horizontal × 30° vertical
Continuous SPL: 106 dB at 1 m
Short-term SPL: 110 dB at 1 m
Peak SPL: 121 dB at 1 m
Typical listening distance: 1–3 m
Balanced XLR input
Rear-panel input-sensitivity and placement calibration
Suitable for stereo, surround and immersive-monitoring systems
5-year warranty, extendable by one year upon registration
 
Applications
Main-monitor duties in small to medium control rooms
Nearfield and midfield mixing
Mastering, critical listening and professional music production
Editing, post-production and broadcast suites
Accurate low-frequency assessment without a mandatory subwoofer
Drum, bass, electronic and orchestral production
Stereo imaging, depth, reverb-tail and transient evaluation
High-SPL monitoring where compact two-way speakers normally reach limits
Surround and immersive systems
High-resolution active stereo playback for professionally minded audiophile listeners