Page 1 of 3 >>
Audio Review: JBL CBT Series Loudspeakers
"If your church has a need for an asymmetrical coverage pattern, or simply has an unusually 'live' room..."
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.
Page 1 of 3 next page >>
John McJunkin is the CEO of Avalon Podcasting in Chandler, Arizona, which offers high quality podcast production and consultation services to a broad range of clients. He’s also the host of the Podcast Pro Tech & Tips Podcast at www.avalonpodcasting.com.
Post a Comment
ADD NEW COMMENT