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Innovations: PMC QB1-A Active Studio Reference Monitor

Anger is an energy, as former Sex Pistols singer John Lydon famously said. And it’s true that dissatisfaction with an existing state of affairs can be a powerful motivation for change.

Anger is an energy, as former Sex Pistols singer John Lydon famously said. And it’s true that dissatisfaction with an existing state of affairs can be a powerful motivation for change.

In the case of PMC’s newest active professional reference monitor, the three-way QB1-A (launched at the recent AES show in Los Angeles), a major part of the inspiration for creating the product was disappointment. Maurice Patist, our U.S.-based president of sales and marketing, is constantly in and out some of the finest studios in the world, and has noted a consistent refrain among the top engineers and producers: dissatisfaction with the main studio monitors they were expected to use. He was regularly told that the mains were just there for loud playbacks to impress record company or advertising executives, while the critical listening and mixing was mainly being done on smaller near- or mid-fields.

PMC, of course, first appeared on the market with a large-scale reference monitor—the mighty BB5, still on sale and popular today — so we felt that we had already disproved this notion. But not all studios have space for a pair of BB5s. We became aware that there was a gap in the market which could be filled by a premium-quality, large-scale, active reference monitor, one with the excellent imaging, dynamics and performance of the BB5, but in a smaller housing, and which would be equally transparent and detailed whether used free-standing or flush-mounted to save space. Together with Maurice Patist, PMC’s owner and chief designer Peter Thomas toured studios worldwide, listening to what was currently installed, and considering what improvements could be made using PMC’s technology. After these extensive discussions and listening sessions, the QB1-A design project began.

As with all PMC products, the company’s proprietary Advanced Transmission Line (ATL) bass-loading technology is at the heart of the QB1-A. Peter Thomas’s contention has always been that this approach gives an extended, low-frequency response down below the lower limits of human perception, without the tonal compromises and detrimental effect on dynamics and vocal transparency that can be introduced by bass-reflex designs based on resonant ports. With ATL, PMC speakers can be used flush-mounted or free-standing— one of the original customer requirements for the QB1-A.

The PMC R&D team, steered by Peter and Maurice, made use of further feedback from key audio professionals around the world. Many users wanted their main monitors to offer both analog and digital inputs, so both were included in the QB1-A. A wired RJ45 remote was also added (already standard on all recent professional- division PMC monitors); it offers control of level, analog/digital input selection and custom EQ settings for individual engineers.

Digital signal processing was also included in the QB1-A. DSP is often frowned upon in hi-fi circles, and the PMC design team is aware that it is sometimes used to produce passable results from sub-standard loudspeakers with inferior components—but it has its place, if used to refine the performance of an already well-engineered design by a few percent at the end of the design process. In the QB1-A, DSP is used to manage the highly engineered crossovers and thereby extract the best possible performance from the three driver types.

The QB1-A also benefited from research conducted at the UK’s National Physical Laboratory. Working with the team at NPL, PMC developed a opto-acoustic technique, RAOS (Rapid Acousto-Optic Scanning), to more accurately measure the dispersion characteristics of loudspeakers and speaker components using lasers rather than measurement microphones. RAOS directly influenced the design of the QB1-A’s mid-frequency driver.

Nothing was left to chance with the QB1-A’s drive units. We maximized the performance of our hand-built 34 mm and 75 mm soft-dome drivers, and employed four of our patented flat-piston carbon-fiber bass units per speaker, engineered to a very high standard with outsize magnets to ensure a dynamic response. The finished designs exhibit respectable efficiency of 90 dB for 1 W at one meter. To ensure that everything runs comfortably within maximum tolerances, we designed proprietary Class-D amplification to supply more than 4800 W of power per channel with a high damping factor. This can be regarded as abundant over-provision, but it unquestionably makes for a faster, more dynamic monitor.

For high-level output with low distortion, the QB1-A’s transmission line had to be heavily damped with various types of bespoke, acoustically absorbent foam. To reduce acoustic and airflow turbulence, the line was also divided into sections with profiled wooden strakes (vanes) along the bottom, effectively using aerodynamic principles to create a more laminar flow. The cabinet was engineered to high standards, with a 36 mm thick Medite front baffle, and extra bracing and reinforcement to eliminate coloration and resonance.

Our starting beliefs with QB1-A were that most main studio monitors were underpowered and based on aging designs and technology that did not include the latest developments in the field of drive unit and cabinet design, minimal-intervention DSP management, and really good Class-D amplification. The QB1-A makes good on those deficiencies.

Keith Tonge is the creative director of the UK-based PMC.

PMC Loudspeakers


Capitol Studios and the QB1-A

Capitol Studios in Los Angeles initially expressed interest in the QB1-A for a possible upgrade of its mastering studios, but during the speaker’s development phase, plans expanded as part of a complete refurbishment and relaunch of the renowned studios. The new speakers would be installed in prototype form at the main Studio B at Capitol, on the understanding that a sale would follow on completion of the design if Capitol’s internationally renowned engineers were satisfied.

A qualified acoustic specialist with intimate knowledge of PMC’s designs and speakers, Maurice Patist is always closely involved in fine-tuning PMC systems at the installation stage, but the Capitol project proved to be a particularly detailed test of his expertise, as the existing soffits used by Studio B’s previous speakers were tapered, and could not initially accommodate the QB1-A prototypes. Partnering with Capitol Studios’ chief engineer and general manager Arthur Kelm, Patist thus oversaw the redesign and physical reconstruction of the soffits, carefully adding mass and bespoke acoustic elements. Capitol has decided to purchase QB1-As for Studio A also. As a British manufacturer, it’s a great honor to have one of our designs chosen for an iconic American studio.