SR Technology STL1000

The STL250A is a two-way, active, bass-reflex box combining a 10-inch cone driver with a one-inch horn (dispersion angle is quoted as 90 by 30 degrees), and is designed to produce a full-range response, which may be dynamically modified by the built-in Physiocon analogue processor to match the response curve to the SPL. Both drivers are built by leading speaker manufacturer SICA. At low levels, our ears perceive sounds as being light on both bass and high end, so the processor puts in a type of 'smile' curve to increase the sense of power and loudness when used for low-power applications. As the level gets wound up, the processor attenuates the bass and high end to compensate, so that as well as maintaining a more consistent sound over a range of operating levels, the speakers are able to run louder with the processing switched in, owing to the fact that the bass end (which demands a lot of headroom compared with the mid range) is reduced when running the speakers hard.

The power amplifiers are so-called 'digital'— presumably meaning PWM — and are fed from traditional transformer PSUs. SR's TSS (Total Speaker Safety) protection system looks after both the amps and speakers, while at the same time allowing you to squeeze the maximum subjective level out of the system via some clever limiting. This clearly helps protect the components from damage due to over-enthusiastic use, but also claims to do so without any obvious gain-pumping effects, such as might be heard from more basic compressors or limiters. The crossover frequency between the two drivers is set at 2.5kHz with a brisk 24dB/octave slope to minimise the overlap between the cone driver and horn.

Being built from plywood rather than MDF or particle board, the ported cabinet is reasonably low in weight at 17.5kg and is shaped so that it can be placed on the floor at an angle to double as a monitor if required. The overall size is 320 x 340 x 475mm, which is in the same ballpark as one of my Mackie SRM350s. A finned heat sink on the rear panel helps cool the two amplifiers, which are rated at 200W for the cone driver and 50W for the tweeter. Ground Lift and Live/Monitor (which bypasses the Physiocon process when set to Monitor) mode switches are fitted on miniature toggles with both male and female XLRs for handling the signal input and output linking. A variable gain control is also fitted. Power comes in on the usual IEC connector with associated illuminated power switch, and the whole rear panel is recessed by 20mm or thereabouts to keep it from harm during transit, though the use of miniature toggle switches still makes me nervous, as I've broken a few in my time. Carrying handles are cut directly into the woodwork at either side, and there's a standard pole socket in the base of the cabinet for use with a speaker stand or a mounting pole screwed into a sub.

Capable of a maximum SPL of 122dB, the speaker covers a frequency range of 40Hz to 20kHz, though no limits are specified, so this isn't particularly meaningful. Frequency response is normally specified at the -3dB points, so if that's what's meant here, the spec is particularly impressive. The sensitivity of the drivers themselves is specified as 99dB for 1W at one metre, which is pretty efficient, though such figures are always open to interpretation, as all magnetic drivers are susceptible to power compression when driven hard.

Little bigger than the STL250A top box, the STW250A sub employs a single 10-inch speaker and is also rated at 250W RMS. This box measures 350 x 350 x 540mm and has pull-out side handles as well as a standard pole socket fixing in the top. Cosmetically and constructionally, it matches the STL250 and includes the filter circuitry necessary to pass on a high-pass filtered version of the input to the top boxes. Two sets of ins and outs are fitted, allowing a single sub to feed stereo tops, and there's a mini-toggle switch to select between mono and stereo operation. The outputs comprise two full-band links plus two with high-pass filtering at 120Hz. Other than a level control and mains inlet with switch, there's a ground-lift switch, which, like the mono/stereo switch, is a miniature toggle switch. The STL250A weighs in at a very manageable 19.5kg — not much more than the STL250A top box.

With a maximum SPL of 120dB, which is impressive from a 10-inch sub, the STW250A covers a frequency range of 30Hz to 120Hz (still with no limits specified) and has a fixed electronic crossover operating at 120Hz. Because the feed to the tops is rolled off below 120Hz, they are free to put more effort in the mid and top, allowing the system to run louder without stressing the components or running into low-frequency limiting. For applications requiring more in the way of subwoofer performance, the STL1100 system — a single STW600A 15-inch subwoofer teamed with two STL250A cabinets — would be a viable option.

This extremely lively venue has a small stage, which necessitated placing the speakers less than two metres from the performers and barely half a metre in front of the cardioid capacitor microphones used to mic the two guitars — one a nylon-strung classical model and one a steel-strung acoustic. I'm always nervous of miking acoustic guitars, as feedback can be a real problem, but I needn't have worried. With the mics around 250mm from the guitars, I captured a great tone and managed to get far more level than was actually needed before the feedback threshold. The subjective results were as good as I could have wished for and the whole concert ran without a flaw. The experience was more like listening to a studio monitor than a PA system, though the speakers were running at well below their maximum capacity.

To check out the system performance in a more typical band situation, I set up the whole system with subs and again played some commercial material through the system so that I could evaluate the quality of the low end, rather than just the quantity. As is often the case, I found that if the subs and the tops were set to the same level, the subs tended to be too loud, but a small adjustment soon corrected this. At low to moderate levels, the subs add the required depth to the sound and integrate quite seamlessly. In fact, it's only when you drive the system near to its limits that the subs start to sound a hint 'tubby', and even then they still hang in there and get the job done, which is remarkable for something so small and light. No doubt the contribution of the internal processing circuitry is significant when it comes to getting the most out of the system without allowing the components to become overly stressed.