ProAc Response Four or Operly Intelligence III?

Two loudspeakers that could not be more different share same electronics in this build - the ProAc Response Four, a 162kg five-driver three-way tower from 1993 still regarded as a Stereophile Class A benchmark, and the Operly Intelligence III, a horn-loaded design running a single full-range driver through both a direct and a reverse horn in a seamless monocoque cabinet. Both are driven by an identical YBA Signature chain, a CD player, preamplifier and stereo power amplifier, plus a Thorens TD 1500 turntable for vinyl, letting the same electronics reveal what two opposite loudspeaker philosophies actually sound like.

The system at a glance

Six components (counting either speaker option), an old-school five-driver dynamic design set against a horn-loaded full-range alternative, and French YBA electronics throughout. This is a system built for a listener undecided between two schools of loudspeaker design - the ProAc's five-driver, ribbon-wound-voice-coil dynamic approach versus the Operly's single-driver horn purity, with the electronics held constant so the comparison is honest.

Why these components work together

The Response Four is rated at 89 dB sensitivity into a straightforward 8-ohm load, with two 9-inch bass drivers using distinctive 3-inch ribbon-wound voice-coils chosen specifically for high dynamic output, an amplifier-friendly speaker despite its size and 355-lb shipping weight. The YBA Signature Stereo Power Amplifier is a fully symmetrical, dual-differential design delivering 200 watts into 8 ohms, engineered to cancel defects introduced by the power supply and minimise parasitic ground currents, headroom that lets the Response Four's ribbon-wound bass coils move with the speed and control Stereophile praised across multiple decades of reviews. The Operly Intelligence III takes the opposite engineering route entirely - a single full-range driver loaded by both a forward horn and a longer reverse horn, with the reverse horn's cutoff lowered by 10 Hz in this revised model, a configuration that trades multi-driver crossover complexity for genuine point-source coherence and, typically, considerably higher sensitivity than a conventional dynamic design. The same YBA power amplifier that gives the Response Four its control has more than enough reserve to run the far less demanding Operly without ever approaching its limits. Upstream, the YBA Signature CD player, a fully symmetrical 30.5kg design built around a machined-aluminium chassis, and the Signature Pre-Amplifier MKII, offering both MM phono and a built-in DAC supporting PCM up to 192kHz and DSD64, keep both speaker options fed by the same considered, uncoloured source, while the Thorens TD 1500 sub-chassis turntable, a direct descendant of the original 1965 design, adds an analogue option to either configuration.

How it sounds

With the Response Four in place, the system delivers exactly what decades of Stereophile reviews describe - a smooth, engaging treble and a full-range low end with genuine weight, all driven with the speed the YBA amplifier's symmetrical topology is built to deliver. Swap in the Operly Intelligence III and the character shifts toward horn-loaded immediacy and point-source coherence, trading the Response Four's multi-driver scale for the kind of unified, single-source presentation full-range horn advocates seek out, both readings arriving through the identical, uncoloured YBA electronics chain.