Road Test: JBL CBT 70J-1

Glenn Thompson is the director of Brisbane’s XConnect Services. Starting his career at Creative Audio, the Sydney Olympics was his first project as an engineering graduate. Glenn later contributed to Creative Audio’s Control Matrix product line before it was sold to Biamp and became Vocia. After stints of part-time work maintaining stadia audio systems, Glenn started XConnect, which provides engineering and integration services to venues including schools, churches, and stadia.

The JBL CBT 70J-1 is a passive, column speaker line array. It’s reasonably simple, with two physical controls to select between music or speech mode, and between broad and narrow dispersion. With 16 dome tweeters running straight down the middle of the column, the width of the HF coverage is impressively broad, at 150 degrees. This means that in small venues like school halls, you can mount a single JBL CBT 70J-1 above the middle of the stage and cover the entire space for speech. The narrowness of the vertical dispersion, at either 25 or 45 degrees, keeps sound from reflecting off the roof.

The horizontal dispersion stated at 150 degrees is a real 150 degrees. When you look at some loudspeakers specs that quote 150 degrees at 1KHz, you look at their dispersion graphs and find they’re dropping off dramatically at 4kHz at 90 degrees. I find you can stand well off to the side of a CBT 70J-1 and still have good, clean high frequencies.

Application

A school installation we completed recently saw us having to project into a covered-in area at the end of their otherwise open assembly area. The customer described it as their “acoustical nightmare.” Before we installed the JBL CBT 70J-1s, they were running their assemblies by bringing out a pair of standard powered 12 and horn boxes, with a fairly common dispersion pattern of 90 by 60 degrees. The slapback from the covered-in area was shocking. The real source of the problem is that they were throwing sound into the roof. I explained that the CBT 70J-1s would solve that, and after we installed and tuned them, there was no slapback whatsoever, which was quite incredible. Their pattern control and horizontal dispersion meant that we could cover the assembly area, at over 50 metres wide, with just two units.

We have installed CBT 70J-1s as a left-right into school halls designed for 500-600 people. The school with the covered-in area I mentioned can hold 1000, even though its usually used for 300. I find that the CBT 70-J1s provide exceptional coverage for speech. Now, you’re not going to run a rock concert with them, but they certainly achieve what I like to think of as the ‘golden target’ of 95dB and great intelligibility, and most jobs we achieve that with just two columns. Sometimes the horizontal dispersion can play against you depending on the space, but the CBT 70J-1s are brilliant for wide halls.

Brackets and Accessories

The 70J-1s are 8 ohm out of the box, but if you need to run 100V line, there’s a transformer module option that bolts onto the back. There is a low frequency extension unit available called the 70JE-1. It contains four 125 mm drivers that pattern control the LF even further while increasing output. They’re the same length as the main array which doubles the space you need, but if you’re mounting them on the side of a proscenium or onto a pillar, that doesn’t matter.

There are both flush mount and swivel-tilt installation brackets available. The brackets are easy to use and well thought out. The swivel-tilt bracket has angle guides on it for ease of installation, giving you five degree increments up to plus or minus 15 degrees to play with. There are ten M6 rigging points on the rear of the column if you want to fabricate your own brackets, which gives you a lot of flexibility.

With an aluminium grille and IP55 rating, you can happily install the 70J-1s outside and not worry about rust. To protect the cabling and terminals, they’re compatible with JBL’s MTC-PC2 and MTC-PC3 weather resistant panel covers. This is a major selling point for me, as while there are other speakers on the market that can do what the 70J-1s do inside, few can do it outside.

Reliability

I’m often visiting CBT 70J-1 installations for service and scheduled maintenance and I’ve never had an issue, which is notable when you consider the treatment they can receive in schools. I’ve installed a pair into a school hall with subs, and when I tuned them, the school said “We’ll never run them that loud.” Well, every time I’ve been there during a concert they’ve been much, much louder than I tuned them, and they’re still going strong.

Conclusion

I find the CBT 70J-1s provide a high-quality sonic result for both music and speech. They’re affordable considering what they’re capable of, and quite loud!

Product Info: jblpro.com

Distributor Australia: madisonav.com.au

Distributor New Zealand: www.jpro.co.nz

JBL CBT 70J-1 – The Specs

Components: Four 130 mm LF drivers, sixteen 25 mm HF drivers

Frequency Range (-10 dB): 60 Hz – 20 kHz

Coverage: Vertical (selectable via switch). Narrow Mode: 25° (2 kHz – 16 kHz) (±10°). Broad Mode: 45° (750 Hz – 16 kHz) (±10°). Horizontal 150° (500 Hz – 8 kHz, ±20°)

Nominal Impedance: 8 ohms

Max SPL: Narrow: (speech mode) 125 dB cont. av. (131 peak), (music mode) 120 dB cont. av. (126 peak), Broad: (speech mode) 123 dB cont. av. (129 peak), (music mode) 119 dB cont. av. (125 peak)

Enclosure: Fiberglass reinforced ABS cabinet, painted aluminum grille

Colours: Black or white

Insert Points: 10 M6 swivel (pan)/tilt (16 mm deep) insert points on back panel.

Dimensions (H x W x D): 694 x 170 x 237 mm

Net Weight: 9.5 kg

Outdoor Capability: IP-55 rated, per IEC529, when installed with optional MTC-PC2 panel cover. UV, moisture and 200-hr ASTM G85 acid-air/salt-spray resistant.