JBL PRX615M

Using advanced DSP and squeezing a 15‑inch driver into a compact cabinet, JBL's lightweight PA promises convenience, volume and clarity in abundance.

One of JBL's latest lines of self‑powered loudspeakers is the PRX600 range, consisting of four full-range models and two subwoofers, all with improved electronics, Crown class-D power amplifiers and the latest lightweight neodymium drivers. Compared with the previous PRX500 range, the new models are significantly smaller and lighter, and have a redesigned styling, being aimed equally at the portable sound and installation markets. The PRX615M is the second-smallest family member and is — along with its smaller sibling, the PRX612M — designed for use as either a main speaker or floor monitor, so its cabinet is shaped accordingly.

The Tech Spec

It would be easy to impress unknowing clients by simply quoting the power amp capability built into the PRX615M, and describing it as a 'thousand watt speaker' is actually true in terms of the built‑in Crown amplifiers. In common with the rest of the range, each power channel is rated at 500 watts, so in the case of the 615M that's 500 watts for the low-frequency and another 500 for the high-frequency section. On its own, this doesn't tell us much about the sound levels obtainable from this speaker, but does suggest that there's more than enough power available in the output stages.

The published figures for maximum SPL are 135dB when running full range and 1dB less in monitor mode. I didn't have the chance to take any measurements myself, but my subjective road‑test puts the 615M well up there in the 'loud' category. All the figures are available on the JBL web site, but in summary, we're looking at a ‑10dB frequency response from 45Hz up to 20kHz, or 54Hz to 18.5kHz at ‑3dB, depending on cabinet orientation and selection of full or monitor mode. The high-frequency coverage pattern is a nice wide 90 degrees side to side, with 50 degrees vertical; very much the norm for this type of speaker, and about right for the traditional, one‑speaker‑per‑side layout.

Inside the cabinet are, as you'd expect, two of JBL's own drivers, with a crossover frequency of 1.8kHz: a 265F1 neodymium 15-inch chassis unit that employs JBL's differential-drive design using dual voice-coils (a special design produced for use in two‑way, full‑range cabinets) and a one‑inch-exit, 2408H compression driver, which features a 1.5‑inch diaphragm and neodymium structure.

The Power Inside

Active speakers are the bees knees when it comes to ease of use, and the PRX615M make setting up and operation as easy as it can be. Everything is taken care of by the twin Crown power amps and their associated internal electronics; all you have to do is plug in a suitable signal, set the input level to match it, and away you go.

The class-D amps contribute to the overall low weight and have all necessary optimisation and protection circuitry built in. As full switching amplifiers, their power conversion is efficient compared to traditional designs, meaning that weight is saved on power supplies. Another plus point is that the amp section can safely rely on convection cooling, so there's no fan to use up additional power, draw dust into the unit or provide an opportunity for eventual mechanical failure. The outer surface of the amp module acts as the external heat sink and becomes quite warm during normal operation. It's good that there are no sharp‑edged cooling fins, meaning that there's no hazard to your clothes and skin during handling.

The rear panel includes the inputs and outputs you'd expect, plus preset EQs for monitor or PA applications, and a mic and line button that allows for direct microphone connection.The rear control panel is simple and neatly laid out, with the user controls being restricted to power, a rotary level control, and a pair of push switches for selecting 'main' or 'monitor' EQ settings and choosing mic or line sensitivity. There are two XLR connectors, one for signal input and one for link out, so that additional speakers or systems can be daisy‑chained. The input socket is one of those handy 'combi' types, and will accept either a three‑pin XLR or a standard jack plug (balanced or unbalanced).

The provision of a mic/line switch on the unit itself means that a mic can be connected straight into the speaker, making a simple PA for events that need nothing more elaborate. It's a useful feature, although only dynamic mics can be used, as no phantom power is provided. The 'link' output is full range, as the PRX series have the high‑pass filters for feeding the top cabinets in the subwoofers, when the two are used in combination.

Construction Sight

If I'm considering buying speakers to use for portable sound, I need gear that's well‑built and won't suffer when subjected to a bit of road rage. Taking a closer look at the PRX build quality, I was impressed with the fittings used and the overall standard of construction. For example, the front grille is held‑on by a combination of 'normal' screw fittings and long hex bolts, which should ensure that the grille neither works loose nor starts to rattle. I removed the grille (a sturdy, powder‑coated, 16‑gauge, dent-resistant punched steel) and found it to be backed with a thin, black, acoustically transparent lining material, which offers protection against moisture. It actually looks as if it would withstand direct rainfall for a time, though the makers don't claim this. I like the way the steel is on the outside, which protects the lining from tears and cosmetic damage.

The enclosures are built entirely from plywood, with 18mm sides and 25mm plates top and bottom (the previous PRX500 series had moulded end-caps). They are finished in JBL's trademark black coating known as 'DuraFlex', which I have found to be tough and good at resisting scuffs and scratches: my own five‑year old SRX700 speakers have the same finish and they still look very pretty after a fair amount of on‑the‑road use. I very much like the subtle and somewhat understated appearance of the PRX615M. Along with the rest of the PRX range, these speakers look entirely functional and very 'pro'. The standard 36mm pole-mount sockets on the bottom offer a choice of vertical mounting or a downward inclination. There are also M10 suspension points to facilitate install applications.

The handle on the side is also a quality piece of hardware, very comfortable and secure, with a generous cup space that didn't rub or catch on my knuckles. The fit of hardware to body is very good, including the neat, recessed rubber feet that offer protection and prevent sliding in vertical or monitor positions. The cabinets didn't clunk, creak or rattle when rocked roughly on their sides or thumped from corner to corner on a hard surface, so I'd be satisfied that internal bracing and jointing is all it should be, and well up to this manufacturer's usual standards.

Shipping & Handling

As each PRX615M weighs under 20kg, handling the units is extremely easy, but personally I found that only having a handle on one side of the cabinet made picking it up a little awkward; it's actually easier to pick it up from the floor one‑handed. I imagine it's a design decision made to keep overall size down, and taking into account the ridiculously light weight of these speakers.

There's a large open port at the top of the rear panel, through which the high-frequency driver is clearly visible, and this serves as a useful extra handle of sorts. Still, for a two‑handed vertical lift I had to put one hand under the bottom of the cabinet — not more than a minor inconvenience with a speaker as light as this one, but I'd still like another handle. Packing the 615s into the back of a car or van is a piece of cake, and because of the speakers' straight sides, you can fit other gear neatly around them.

On The Road

As it happened, I had an opportunity to test out the PRX speakers in a theatre production of Footloose, involving 16 radio mics, two further off-stage mics and a five‑piece band. The theatre seats around 250, including rake and orchestra pit, and I was limited to a single speaker stack either side of the stage. I had been planning to use my JBL SRX700 system (a single SRX718 sub and a single SRX725 per side), as it had given very good results for previous shows, but I decided to give the PRX boxes an outing. The director had mentioned (several times) that she wanted a big, 'in your face' sound that would have the audience on their feet, but also that vocal clarity was equally important, especially as both dialogue and sung vocals would be running through the system.

Rigging the PRX cabs was a matter of deciding which of the pole-mount sockets to use, and simply lifting them into place, which was a job I managed single‑handedly and without any great effort, even though the poles were quite high. After trying the speakers in both mounting positions I opted to have them in vertical orientation, as the pole height put them almost level with the middle of the raked seating. Using the angled-down socket fired too much high-frequency straight into the front rows and pit in this particular venue.

In order to get the system up and running for a 'quick and dirty' test, I connected a full‑range stereo signal direct into the speakers, set the desk output level to yellow (quite hot), and cautiously turned up the input controls. From the outset, it was clear that these are very powerful speakers and that they produce an impressive amount of solid bottom end for their modest size. While the lighting guys were on their break, I ran a few CDs through the system and pushed the level a bit, and I knew that vocal clarity was not going to be any kind of issue for this show, nor would we be falling short of the mark in the 'in your face' department.

After a few more minutes playing with a wide range of recorded material, we connected some subs (a single JBL SRX725 each side) and started balancing everything. I experimented with a few different crossover points in my Dbx Driverack speaker optimiser, and settled on running the PRX615Ms full‑range, with a separate auxiliary feed to the subs filtered at 80Hz. This is lower than I would normally use with this size and shape of system, but with live sound it's a case of going with what works best on the day. The only further work needed was bridging the sub amps (1600W each side) just to keep up with the powerful 615Ms. I ran the Driverack's auto‑EQ just out of interest, decided to keep the settings (with a couple of manual tweaks for good measure), and we were good to go.

Sound Quality

The most striking thing about the sound of the PRXs is the clarity and sweetness of sound that's maintained all the way up to the highest levels we could cope with in the venue. The system easily broadcast all the vocals over the live band. Using head‑worn mics mightn't be the best vocal test, but it's certainly a challenge, especially when there are 16 on the go all at once. I found that the PRXs were absolutely up to the job.

They stayed crisp and effortlessly clear, very much on‑song for the whole performance, and I didn't notice the sound becoming any less focused, or need to drive the system harder toward the end of the show. After the eighth and final run, I was happy to note that the main desk faders were in exactly the same place as they had been for opening night.

Conclusion

The more I used the PRX615Ms, the more I appreciated how easy they were to work with. Most impressive of all was how good they sounded when the levels were really cranked up: the system sounded like a much bigger system that wasn't even trying!

I enjoy hearing other peoples' feedback on the sound of my setups (well, most of the time), and on this occasion I received several unsolicited comments from members of the crew, production team and also from the audience, about the high sound quality. The words I heard most often were 'clear' and 'loud', as well as one unprintable comment ending in "stunning”. I agree; the PRX615Ms are super‑efficient powerhouses, and they put their message across very forcefully. It's a shame I have to give them back, because I think I'd use them for just about every job currently in the diary.

Doing Double Duty

The punched‑steel grille is extremely tough, and the water resistant material behind it helps to protect from moisture.

The PRX615M is designed to be used as a main PA speaker or as a live‑sound monitor, and selecting the monitor setting adjusts the internal EQ accordingly. This is something that can be done elsewhere in the sound system, but it's very handy to have a single button to take the hassle out of doing it when using a basic setup. When laid on its side, the 615M sits at a nice, stable 45 degrees, and has a pleasingly low profile for a 15-inch cabinet. In fact, when the front grille is removed, you can see that there isn't much space between the driver chassis and the edge of the box, so the overall width is about as small as it's possible to fit a 15‑inch chassis inside of. This is one very compact and versatile 15‑inch active speaker!