Innovations: The Manufacturer’s View: Genelec’s 8351 acoustically coaxial compact three-way loudspeaker

Today’s recording and mixing environments are shrinking in size and becoming more uneven in their frequency responses, resulting in more coloration and larger differences between rooms.
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Figure 1. For size comparison shown are Genelec’s 8260 (left) and 8351 (middle and right).

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Today’s recording and mixing environments are shrinking in size and becoming more uneven in their frequency responses, resulting in more coloration and larger differences between rooms. The rooms used for applications, ranging from dialogue recording to full-scale multichannel mixing may even be repurposed over the course of a day, week or longer. Adding to the problems are the constraints of tighter budgets and increasing quality requirements for the end product. The solution to these problems is a monitoring system that has high neutrality for accurate recording, editing and mixing, along with high SPL capability when required. Genelec’s compact, acoustically coaxial three-way monitor, 8351, addresses these customer problems with innovative technology in acoustically novel ways and provides the performance required in these types of environments.

A Unique Three-Way Problem Solver: Three-way active monitors are the optimum design in many ways. The driver characteristics (linearity, output capacity, directivity) can be optimized more precisely. The best performing crossover frequencies can be chosen based on the acoustical requirements, and waveguides can enhance directivity and performance.

A three-way is typically needed for those applications where the highest quality of audio is required; it is necessary to hear subtle acoustic details even at high SPL; and control of directivity is essential.

Three-way Coaxial Enclosure: Much like our undertaking with the 8260 several years ago, we felt it would be quite important to maintain the overall outward appearance of the 8351 enclosure. That is to say, the ratios of width, height and depth needed to remain consistent to the 8000 Series product line. When considering all the factors we mention, notwithstanding reliability and performance, the size reduction created the greatest challenge and iterative thinking. The issue was, how to reduce cabinet size and still get nocompromise performance throughout the entire desired audio spectrum, in particular the low-end?

It was clear from our experience with the 8260 co-ax mid/tweet driver that it would serve as the anchor for the mid and high frequencies. The innovative solution to the low-frequency dilemma was to acoustically conceal woofers seated in the enclosure front, under a large Directivity Control Waveguide, creating a large continuous front baffle surface for mid and high frequencies, while the two woofers lay beneath and acoustically along two sides of the DCW. This Acoustically Concealed Woofer (ACW) technology is the cornerstone to enabling a compact enclosure with outstanding coaxial directivity. The result is that the Genelec 8351 inherits performance from the 8260 and size from the 8050. The enclosure dimensions are reduced to 80-percent of the 8260 (Figure 1), with dimensions at 17 3/4 x 11 1/4 x 11 inches.

Directive woofers: The use of two unique custom Genelec-designed oval woofers was chosen as they maximize and yield a total cone surface area close to a single 10-inch woofer. These two 8.5-inch x 4-inch woofers spaced in the 8351 front baffle form a highly directive low-frequency radiating system. This unique feature gives the 8351 the ability for directivity control on par with physically larger studio monitors. In order for our customers to minimize console top reflections, we suggest they place the 8351 vertically, enhancing vertical directivity (Figure 2). If side walls are close, you can mount the 8351 horizontally, reducing low frequency interaction with the walls. (Figure 3)

Easy to place in the tightest spaces: Again, we can see the 8351 locates tweeter, midrange and the woofer pair radiations co-axially. This eliminates coloration for off-axis listening positions at the crossover frequencies. Having the same sound character in both horizontal and vertical orientation makes fitting the 8351 three-way monitor into a room easier than ever. Genelec’s coaxial design also allows the 8351 listening distance to be very short. The minimum recommended listening distance is 0.5 m (1.5 ft). There is no recommended maximum.

How Low can you go?: In order to further optimize low frequency performance, a flowoptimized reflex port, common to all 8000 Series products, opens to the back of the enclosure and minimizes the woofer displacement. This enables the 8351 to radiate clean audio down to its LF -1.5 dB point of 38 Hz (-6 dB@32 Hz).

Amplifiers and Signal Processing: An analog input up to +24 dBu is AD-converted for all the signal processing. Digital audio in AES/EBU format is supported up to a sampling rate of 192 kHz, with a bit-accurate AES/EBU thru output provided. The audio signals are processed internally at 96 kHz sampling frequency. The system has controlled acoustical response up to about 45 kHz. For amplification, the 8351 uses low-noise Class D topology for the woofer and midrange drivers. A discrete component ultra-linear Class AB amplifier powers the tweeter. All three amplifiers are designed and built by Genelec and drive the 8351 to a short term SPL of >110 dB@1 m (>123 dB peak/pair@1 m).

SAM for Smart Monitoring: The 8351 is also a member of the Smart Active Monitoring (SAM) family of products. With the inclusion of the 8351, the Genelec SAM family now includes 10 two-way, three-way and subwoofer products addressing all professional monitoring applications. Genelec’s control network enables control of all aspects of the system at the main listening position. It enables automatic calibration and aligning of all monitors and subwoofers in a room, accounting for level matching, time-of-flight and room response optimization.

Manufacturing in Iisalmi, Finland: All 8351s are manufactured by Genelec in Iisalmi, Finland. The MDC coaxial driver and the ACW woofers are hand-assembled and tested in Genelec’s Iisalmi factory. Each 8351 is 100-percent tested for all aspects of performance. The final computer-based automatic calibration ensures high performance and tight acoustic match before leaving the factory.

The 8351 was a multi-year project involving many engineers attempting to solve a true audio paradox: How to increase the outward performance of an audio monitor, while at the same time reducing its footprint. We are indeed proud of the final outcome and feel quite certain customers will experience the true commitment and values placed into it.
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Aki Mäkivirta serves Genelec as Research and Development Director, Ilpo Martikainen is Genelec’s Chairman of the Board and Will Eggleston is US Marketing Director.