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JBL 7 Series

Active Monitors
Published February 2018
By Phil Ward

If you’re looking for a monitor that goes loud and low, and has excellent high-frequency performance, JBL’s new range might just fit the bill.

In much the same way that Tannoy are iconically associated with traditional studio monitoring in the UK, over the pond in the US, a similarly iconic status belongs to JBL. As the man originally behind both Altec Lansing and JBL, James Bullough Lansing was one of the founding fathers of the US audio industry and right up to the last decades of the 20th Century, monitors that carried his initials, or at least incorporated drive units that did, were probably as commonplace in studios as Yamaha NS10s subsequently became. As monitoring hardware diverged, however, into desktop, bedroom, nearfield, midfield and main sub-species, and choices expanded to include active speakers and numerous new entrants to the market, JBL’s preeminent position, just like Tannoy’s, began to fade. Having said that, JBL are still a major player across the live sound, pro audio and consumer audio sectors, and their two newest active nearfield monitor products, the 708P and 705P, are the review subjects here.

It’s been four years years since we’ve covered any JBL monitoring products; the last occasion being Paul White’s review of the LSR3 series in SOS February 2014. The LSR3 series is very much JBL’s entry-level proposition, and not only has technology moved on in the intervening years, the 7 series is also significantly more ambitious in terms of performance and functionality. There’s no mistaking the lineage, however, or that the 7 series are products of a US design ideology. There’s somehow an inescapable element of bling apparent in their blacker-than-black surfaces and perforated metal grilles. The asymmetric tweeter waveguide also dominates visually and gives the monitors a “look at me!” kind of vibe. So there’s nothing shy and retiring about the 7 series, but strangely, their electroacoustic fundamentals actually have something in common with the approach of the uber-cool Nordic style personified by Amphion monitors. I’ll explain why that’s so later on, but first I’ll attempt to describe the 7 series without getting tempted to wander off on too many tangents.

Knocking On Seven’s Door

The first thing to say about the 705P and 708P is that they are significantly different in terms of physical size. Where the 705P is a truly compact monitor that approaches ‘cute’ proportions and will fit in the smallest studio space, the 708P is actually towards the large size for nearfield monitoring. To my mind the size difference actually reflects a fundamental electroacoustic reality that many speaker manufacturers deny in pursuit of overpopulated product ranges that hit price targets. You see, the benefits that fundamentally arise from a physically larger speaker are extended low-frequency bandwidth and higher maximum level. But to make a genuinely significant and noticeable difference to both parameters simultaneously, a speaker really has to be quite a bit bigger (and more expensive). As a result, in a typical range of monitors designed to hit target prices, the fundamental performance differentiators between adjacent products in the range are likely to be, well, not huge. The published 705P and 708P specs provide some context for this quite nicely, and to make things easy I’ve tabulated the appropriate numbers in the ‘Number Crunching’ box.

So, with two monitors of significantly different dimensions (the internal volume of the 708P approaches four times that of the 705P), while the maximum volume level is significantly higher (+7dB) from the 708P, its low-frequency extension is greater by only 4Hz — that’s approximately the difference between low E and F on a bass guitar. It begs a question: unless you monitor regularly at very high levels, or have a very large room, why would you go for the 708P over the 705P? Perhaps the 708P incorporates some extra facilities and functions, or is better in other respects? Read on...

Class Act

Despite being so different in size, the 705P and 708P appear to incorporate the same Class-D power amplification. It is specified at 250 Watts for both bass/mid and tweeter sections, which seems slightly strange as, being compression and waveguide loaded, I’d expect the fundamental sensitivity of the tweeter to be at least 6dB or so higher than the bass/mid drivers and to require significantly less power. Perhaps tweeter amp headroom is required to accommodate the gain potentially available from the onboard EQ? It would be a strange monitor installation, however, that required more than a dB or so of extra tweeter gain.

Another aspect in which the 705P and 708P are the same is their cabinet construction. They both feature a relatively thin birch-ply chassis with what appears to be an injection-moulded plastic front panel. The enclosure is internally braced and the baffle is fabricated from ABS. The cabinets feel mechanically very well put together and respond well to the knuckle-tap test — they sound pretty dead.

Driving Force

Before describing what’s around the back of the 705P and 708P cabinets, and having already mentioned the tweeter waveguide, it probably makes sense to write a little about the drivers. Firstly, despite the larger waveguide on the 708P, the tweeter fitted to both monitors is the same 25mm-diaphragm 2049H compression driver. The use of compression HF drivers in nearfield monitoring is relatively unusual. However, such drivers are fundamental to JBL’s DNA, and contemporary high-tech compression drivers are far more sophisticated and capable than the primitive and inelegant units of old. The fundamental principle of a compression driver is to constrain the radiating environment adjacent to the diaphragm in order to create a better impedance match between the diaphragm and the air, increasing the radiation efficiency. The waveguide in front of the diaphragm then acts progressively to couple the radiation impedance at the throat to that of the wider environment, while at the same time defining the driver’s dispersion characteristics. Even a cursory glance through lists of past Audio Engineering Society technical papers will show that JBL have, over the decades, put a lot of work into developing waveguide loading for compression drivers. The result of a well-engineered compression driver should be high efficiency, low distortion and minimal compression, combined with tight dispersion control. With so much compression driver experience to call on, it’s something JBL ought to be able to pull off.

Moving on to the the 7-series bass/mid drivers, as perhaps more than hinted at by the model numbers, the 705P is fitted with a nominally five-inch unit and the 708P with a nominally eight-inch unit. Along with compression HF drivers, another strand of JBL DNA has always been an emphasis on high power handling, minimal compression and low distortion, and the 7-series drivers are clearly engineered to continue the tradition. For example, though the 705P driver appears relatively conventional in the construction of its magnet and voice coil, it still boasts an impressive 14mm peak-to-peak linear diaphragm displacement. The 708P bass/mid driver takes things further still by employing JBL’s proprietary ‘Differential Drive’ magnet and voice-coil technology to further reduce distortion and increase maximum linear displacement (although, ironically, the published specification doesn’t specify it). I’ve illustrated the concept behind Differential Drive in Diagram 1; put simply, it comprises twin voice coils and magnet gaps configured such that some of the negative characteristics of the conventional arrangement cancel out. There’s a JBL technical paper on Differential Drive that’s worth a look if you’re intrigued: www.jblpro.com/pub/technote/JBL_TN%201-33%20rev3.pdf.

Diagram 1: JBL’s Differential Drive technology makes use of two voice coils to reduce distortion and control excursion.Diagram 1: JBL’s Differential Drive technology makes use of two voice coils to reduce distortion and control excursion.Hidden behind perforated metal grilles, the 7-series bass/mid driver diaphragms are made from a paper pulp composite. (While many European speaker manufacturers make a marketing feature of diaphragm material, most don't put much emphasis on magnet and voice-coil systems, and it's interesting that JBL do.) The final feature on the front panel of the 7-series monitors is a generously flared and letterbox-proportioned reflex port. JBL say that the 7-series ports feature their patented ‘SlipStream’ technology that is claimed to reduce port turbulence and compression. It’s not easy to find any description of what SlipStream technology actually comprises. The JBL web site describes it thus: “The double-flared shape of the port is precisely calculated for greater low-frequency extension and reduced turbulence.”

Organ Grinding

Diagram 2: The output at the ports of the 705P (blue) and 708P (purple).Diagram 2: The output at the ports of the 705P (blue) and 708P (purple).Whatever SlipStream achieves, however, it does nothing to suppress an ‘organ pipe’ resonance in the 705P port, as I’ve illustrated in the FuzzMeasure response curves in Diagrams 2 and 3. The response curves result from placing a measurement microphone right in the mouth of the port and, for the sake of comparison in Diagram 2, I’ve overlaid the 705P and 708P. The lower port tuning frequency of the 708P is apparent, but it’s the different character at higher frequencies that’s of more interest. Where the 708P shows a relatively benign behaviour with no significant discrete resonances, the 705P port has an obvious problem at 740Hz. The resonant nature of the peak is displayed even more obviously in the Diagram 3 waterfall plot showing how it decays with time (the long decay of the primary port output is also revealed).

Diagram 3: The 705P’s port output.Diagram 3: The 705P’s port output.Organ pipe resonance occurs, as the name suggests, along the length of a port as a result of the same phenomenon that makes wind instruments work, and as such is distinct from the Helmholtz resonance that is the basis of reflex loading (the mass of air enclosed by the port ‘bouncing’ on the ‘spring’ of the volume of air in the enclosure). The problem with organ pipe resonance, apart from the potential audibility, is that the phenomenon is hard to fix because any lossy damping within the port will not only suppress the pipe effect but will also suppress the desired Helmholtz resonance. The million-dollar question on the 705P pipe resonance is, of course, that of audibility. Well, when listening to pink noise on the 705P, with the ports blocked by wadding or left open as intended, I could clearly hear a change in the mid-range as the wadding was removed, so in those circumstances, it’s audible. However, pink noise and music are different beasts, and with the constantly changing character of most music, it would be very hard consistently to pin down and identify the effect. It will be there, however, making a contribution to the overall aural signature of the 705P.

Socket To Me

Moving around to the back of a 7-series monitor, be it a 705P or a 708P, you’ll find a mains input and power switch, balanced analogue and AES3 digital inputs (along with a digital ‘through’ output socket), and a HiQnet network socket that enables connection to JBL’s proprietary Intonato 24 monitor management and optimisation system. Intonato 24 hardware or software was not supplied for the review so we’re in no position to gauge how well it works.

The 7-series monitors feature both analogue and digital inputs, and there’s a menu with options for room and user EQ settings, plus delay correction and bass management.The 7-series monitors feature both analogue and digital inputs, and there’s a menu with options for room and user EQ settings, plus delay correction and bass management.Along with the connection sockets is a 65 x 20 mm display plus a rotary encoder and buttons for menu parameter navigation and selection. The menus and parameters available cover: input selection, input sensitivity and trim, user EQ, room EQ, frame delay and speaker delay, bass management, EQ presets, left/right select, network configuration and menu timeout.

These menu options are the same for both the 705P and 708P and many of them are self explanatory. A few of them, however, would probably benefit from a little description. Firstly, the user EQ menu provides low shelf (90Hz) and high shelf (2kHz) adjustment along with four bands of parametric adjustment. User EQ settings can be saved and recalled through the EQ presets menu. The room EQ menu provides another eight bands of parametric adjustment that can be used in addition to the user EQ, but are also brought into play automatically if the aforementioned Intonato speaker/room optimisation system is used. The frame delay and speaker delay options are intended to be used to compensate for, respectively, lip-sync issues in AV monitoring and to enable individual speakers in very large multi-channel installations to have delay applied to adjust signal arrival times. The delay parameters can also be saved to user presets. Finally, the bass management menu enables a high-pass filter to be engaged when 7-series monitors are used either in monitoring installations that incorporates a discrete LFE channel, or in stereo monitoring systems that incorporates a subwoofer.

In use, the 7-series setup menu user interface is perfectly adequate, however it’s a mild inconvenience that it is located on the back of the monitor and that any adjustments made to one monitor of the pair have to be duplicated on the other. It seems a shame, considering that the 7-series monitors are network equipped, that there’s no entry-level setup app available.

Diagram 4: The 708P’s off-axis output is remarkably consistent; shown here are measurements on axis (orange), 30 degrees off the horizontal axis (blue) and 45 degrees off the horizontal axis (green).Diagram 4: The 708P’s off-axis output is remarkably consistent; shown here are measurements on axis (orange), 30 degrees off the horizontal axis (blue) and 45 degrees off the horizontal axis (green).I wrote earlier that the 7-series electroacoustic concept has some similarities with the Amphion monitors. This is because both employ the dispersion control and increased sensitivity of a waveguide-equipped tweeter to enable a low crossover frequency (around 1700Hz on both monitors). The advantage is that the inherent dispersion narrowing of bass/mid drivers towards the top end of their range is avoided, and the system as a whole displays a more linear dispersion character. I’ve illustrated this in Diagram 4, which shows the 708P frequency response from 200Hz upwards with the microphone aligned on the tweeter axis, and both 30 and 45 degrees horizontally off axis. The curves show a remarkably consistent dispersion performance with little sign of the upper-mid-range off-axis droop that’s typical on two-way monitors with higher crossover frequencies. The 708P tweeter holds up well too, only showing a significant fall-off above 10kHz at 45 degrees. This is a genuinely strong dispersion performance from the 708P. I measured the 705P too and it was similarly impressive.

Listening In

I began listening with a 705P set up either side of my workstation and first impressions were, well, somewhat perplexing. As I became more attuned to the 705P its strengths became more apparent, but to begin with I was primarily conscious of its tonal balance. In comparison to my KEF LS50 reference, a monitor that for me is as tonally as neutral as they come, the 705P sounded recessed in the presence band (say, 1kHz to 5kHz) and over-cooked in the lower mids. Without adjusting the EQ, I actually found it difficult to get a firm grip on what I was hearing so, after experimenting a little with a Pro Tools EQ plug-in, I reached around the back of the 705P and started to take advantage of its parametric EQ. I settled on -3dB at 450Hz with a Q of 0.5, and +2.5dB at 3.25kHz, also with a Q of 0.5. With the EQ engaged, the 705P moved into more familiar territory in terms of tonal balance, but I was still aware of what I can best describe as a ‘thickness’ in the mid-range that to my ears significantly masked detail and flattened the stereo image. It’s a characteristic that hi-fi reviews of old would identify as a ‘boxy’ coloration. As to the cause, it’s very hard to say. There’s no obvious tell-tale features in the frequency response, and the enclosure construction feels rigid and non-resonant. My best guess is that the coloration is inherent to the bass/mid driver.

Mid-range coloration notwithstanding, the 705P is a capable little monitor with great low-frequency extension for its size (albeit with a reflex port character that masks some LF detail), and an obvious ability to play loud without complaint. The wide mid- and high-frequency dispersion of the 705P is noticeable too; it’s tonally very consistent off axis. Lastly on the 705P, its tweeter sounds smooth and detailed and nothing at all like an old-school compression driver, which is a very good thing.

Substituting the 705P for the 708P, I was a little apprehensive. Historically, you see, I’ve often tended to prefer the smaller and less ambitious monitor in any review of two from a range, so having felt less than entirely convinced by the 705P, I wondered how well the 708P would perform. However, in a perfect illustration that past experience can not always be relied upon to predict future events, I liked the 708P more. I was still not entirely comfortable with its tonal balance as, in common with its smaller sibling, it seemed a little overcooked and slightly coloured in the lower mid-range, but the 708P imprints less of its own character on the sound than the 705P and is consequently a more immediately usable mix tool. In other areas too the 708P has some qualities over the 705P beyond its expected and obvious greater LF extension, greater volume level abilities and general ‘big speaker’ sound. It seems more revealing of detail both in terms of mix elements and stereo imaging — I felt happier that it would be usable without any need to spend time to learn its quirks, and that mixes would transfer more readily. I wonder if the low distortion levels that result from the 708P Differential Drive magnet and voice-coil technology is perhaps responsible?

One respect in which the 708P is similar to the 705P is in its high-frequency performance, the common tweeter meaning that both models share the same smooth, detailed and ‘un-compression-driver-like’ character. Both models have ported enclosures too, and although sounding less reliant on the port for bass than the 705P, the 708P still had a touch of port character in its presentation of kick drum and bass guitar. I suspect this is another area in which the extra linearity of the Differential Drive technique probably helps though. Finally, like the 705P, the 708P is noticeably consistent with listening position. That JBL expertise with waveguides and tweeter directivity really pays off.

Final Thoughts

When I first unpacked the 705P I had high hopes. I have a thing for compact monitors that are well put together and have some engineering tradition and integrity behind them. Overall, I found the 705P slightly disappointing — if JBL could fix its mid-range coloration things would be completely different, but as it stands, to my ears the 705P imprints too much of its own character on music for it to be an entirely satisfactory mix tool. The 708P, however, is a much more interesting prospect. It still has some quirks of tonal balance and slight coloration, but its no-nonsense, wide-bandwidth, low-distortion and high-volume personality seems to me exactly what JBL is about. I can imagine numerous dance or electronic music studios, where volume levels can get high and the workload is unrelenting, where the 708P would be in its element. If that’s your kind of scenario, you should add the 708P to the list of interesting monitors.  

Alternatives

The 705P and 708P inhabit a crowded sector of the monitor market so there are numerous alternatives around their respective prices. Models from Neumann, Dynaudio, Genelec, PSI and Barefoot all spring to mind.

Number Crunching

705P

  • Dimensions: 268 x 151 x 274 mm
  • Max SPL: 107dB
  • Internal Volume: 7.5L
  • LF Cutoff: 45Hz (-3dB)

708P

  • Dimensions: 441 x 250 x 312 mm
  • Max SPL: 114dB
  • Internal Volume: 27L
  • LF Cutoff: 41Hz (-3dB)

About The Author: Phil Ward’s loudspeaker career began in 1982 when he joined UK hi-fi company Mordaunt-Short in a junior design role. After leaving Mordaunt-Short in 1987 for a spell in audio PR, Phil joined Canon as Design Manager for the Japanese multinational’s range of consumer and custom install speakers, and then Naim Audio as speaker design and project manager. Since 2001 Phil has worked as a freelance consultant and writer across both the pro and consumer audio sectors. Phil plays electric and double bass and has recorded, produced and mixed numerous bands and artists. Phil's blog can be found at http://musicandmiscellany.com   

Published February 2018