The point of a line array is to restrict the directivity of the energy dispersion in such a way that it is "steered" to the right destination in the right quantities. In our example, we want some of the sound steered toward the folks sitting up front, and some steered toward those sitting in back. The trick is to try to get the same perceived loudness in the ears of both groups. A J-shaped line array accomplishes this with its shape. Presuming a slight incline from the front of the room toward the back and the line array suspended above and in front of the folks sitting up front, the bottom part of the array delivers lower amplitude to those in the front pews (downfill), and the upper elements of the line array deliver greater sound pressure level toward those seated in back. There's more to it than just this, however - when a substantial number of speakers are arrayed in a "stack" orientation, and in close proximity, phase and comb-filtering difficulties can negatively impact not only sound quality, but also loudness. Speaker developers have learned to use passive physical cabinet attributes to solve some of these issues, but electronic filtering and delays also figure into the delivery of consistent, phase-coherent, full-bandwidth sound with a reasonably flat response.
JBL's Constant Beamwidth Technology physically bends the array into a fixed arc (or with delays in the case of their straight arrays), and employs amplitude shading of the drivers from inside to outside with a Legendre function. Without getting too far out into the electronic and mathematical weeds, this is accomplished with analog circuitry, which naturally tapers frequency response and amplitude as necessary on a continuously variable basis, and without the time quantization error that would be introduced with digital circuitry.
Bottom line, this is some very clever science that facilitates small, passive line array speakers that can be used in smaller venues. And as JBL describes specifically what these speakers do, "asymmetrical vertical coverage sends a higher, more concentrated, sound level in the direction of the far area of the room and a lower, more spread out, sound level in the direction of the near area of the room."
I was sent a pair of CBT 70J-1 ?full-range speakers and a pair of CBT 70E-1 speakers for the extension of low end from 60 Hz down to 45 Hz. Considering the complexity of the system contained inside the cabinets, the setup and use of the system couldn't be much simpler. The speakers ship with plates and hardware for wall mounting, and the MTC-CBT-SMB1 bracket is available for mounting on a standard 35mm pole (but only the 70J-1 - the addition of a 70E-1 precludes speaker-on-a-stick use). Both speakers feature 10 standard M6 insert points, and the 70E-1s include a combining bracket to facilitate attachment to the 70J-1.
I set up both configurations at different times, and found the process very simple. In terms of connection to the amplifier, the inputs are two-lead terminal blocks intended to accept spade connectors. There are two rotary two-position switches on the 70J-1, one that toggles between full-bandwidth, flat response (for music) and a curve that accentuates high mids to enhance intelligibility of speech. The other switch toggles between two asymmetrical vertical patterns-narrow (25-degree) and broad (45-degree), the former of which is intended for long-throw applications, and the latter of which is preferable for mid-throw applications. These are relatively small speakers, particularly in terms of width, at 27.4 in. tall, 9.3 in. deep, and 6.6 in. wide.
The 70J-1 features four five-inch LF drivers and 16 one-inch HF drivers, all arrayed along a vertical line. This complement of drivers yields a broad frequency response, the upper limit of which is 20 kHz, and the lower limit is 60 Hz.
The 70E-1 is loaded with four five-inch drivers only, extending the lower limit to 45 Hz. The 70J-1 can handle 500W, and 1000W when the 70E-1 is attached. Maximum SPL is 127 dB, program (130 with the addition of the 70E-1), and the impedance of the 70J-1 and both speakers combined is 8 ohms.
I sent a broad array of program material through these speakers in both configurations and I was impressed with what I heard. The energy dispersion over the entire frequency range was very smooth and flat. Obviously, the removal of the notch filter that configures the speakers for speech adds a bit of a high-mid bump, but it's very intentional for the purpose of improved speech intelligibility, and it has that very effect indeed. The asymmetric dispersion pattern works just as advertised, with perceived SPL very consistent from the front of the room to the back.
Impressive Sound
As to SPL, these are far from the loudest speakers I've ever heard, and that's fine, as they're intended to provide even energy distribution, and not just brute force SPL. The 70E-1 extends the low-end punch below that of the 70J-1 by itself, but it does not deliver ground-shaking bass-it would be unfair to expect that of speakers this size. I did introduce a single 12-inch subwoofer to the system at one point, and with that extra low-end, I did get very solid SPL across the spectrum. As a matter of fact, it was sufficiently loud for rooms of the size for which this system is intended. The entire frequency range was represented clearly, with distortion only emerging at the very highest SPLs.
The one thing that really impressed me immensely was the stereo image the speakers presented-very distinct point sources for a very obvious spatial image. Obviously, this is accentuated in the high end, but the panning of various mix components is quite obvious on down through the mids as well.
The JBL CBT 70J-1 is a great-sounding speaker that delivers an asymmetrical pattern to grant the user control in a space where a larger-format line array would simply be too much, and helping to tame reverberation in particularly live spaces.
Considering its street price of just a little over $1,000.00, this speaker is an excellent value for the money. When combined with the JBL CBT 70E-1, low end is extended from 60 Hz down to 45 Hz, and while it doesn't shake paintings off the walls, it's good, tight, round bass. Augmentation of low end with a larger subwoofer or two truly delivers full bandwidth at very solid SPLs.
These speakers are well worth consideration if you have a need for asymmetrical dispersion and/or a particularly live room that needs some taming.
