— Speaker Coverage · Steerable column
JBL Professional CBT 70J-1 — SPL & coverage
Problem. A 20 × 12 m house-of-worship hall needs even, intelligible coverage out to a 12 m listener without a visible line-array or a forest of ceiling speakers. The design question is whether a single steerable column can hold usable SPL at the back of the room while keeping its vertical pattern off the ceiling and walls.
Answer. At 55 % drive, the JBL Professional CBT 70J-1 delivers roughly 106 dB SPL to a listener 12 m out, with a horizontal coverage half-width of about 44.8 m on the −6 dB axis. Both figures come from the cabinet's rated 131 dB @ 1 m output and its 150° × 25° (H × V) dispersion pattern.
02 / In depth
How this preset reads — the engineering view.
The CBT 70J-1 is rated at 131 dB SPL at 1 m, full output. SPL falls with distance under the inverse-square relationship — roughly 6 dB for every doubling of distance — which brings full-output SPL at a 12 m listener down to approximately 109 dB. Backing off to the preset's 55 % drive level lands at approximately 106 dB at that same 12 m listener: still well above the 85–90 dB range typical worship-music programme asks for, with headroom in hand.
The cabinet's 150° × 25° (H × V) nominal dispersion is what sets the ~44.8 m horizontal coverage half-width the planner reports. The wide 150° horizontal spread is built for covering a broad seating plan from a single column without side-fill cabinets; the narrow 25° vertical pattern is the steerable-column signature — it keeps energy off the ceiling and side walls, controlling reflections and slap-back in a hard-surfaced worship hall. The CBT 70J-1 is passive, so it needs a matched external amplifier channel sized to the cabinet's power handling — there is no onboard amplification to budget around.
Use the planner by dragging listener distance and drive-level to watch SPL move in real time — this is how you find the point where SPL at the furthest listener drops below your target and more drive, a second cabinet, or a different model is needed. The box-count figure the planner shows is a front-coverage area estimate only; SPL adequacy at your furthest listener is a separate check and the one that actually determines whether the design works.
The planner does not model room reverberation or RT60 (a hard-floored, hard-walled worship hall can add several dB of reverberant build-up on top of the direct-field figure above), zoning across distinct seating areas (balcony, side transepts, overflow rooms usually need their own coverage pass), subwoofer pairing for low-frequency music programme, the mechanical rigging or steering-angle configuration a real column install requires, or DSP/delay tuning between multiple cabinets or zones.
What this preset deliberately does not solve
- SPL figures are direct-field, free-field estimates from the rated 131 dB @ 1 m spec — they do not include room reverberation, which typically adds several dB in a hard-surfaced hall.
- The 44.8 m coverage half-width is a horizontal-dispersion estimate on the −6 dB axis; it assumes a clear, unobstructed line from cabinet to listener with no absorptive treatment factored in.
- This is a single-cabinet, single-zone calculation — multi-column steering, delay alignment, and subwoofer integration all sit outside what the planner reports.
How this preset differs from its siblings
Other steerable-column options in the catalogue vary meaningfully in rated SPL and dispersion, which changes both the achievable listener-distance SPL and the coverage half-width this planner reports — a column rated lower at 1 m or with a wider vertical pattern will show a shorter usable throw and less reflection control in the same room. The CBT 70J-1's 131 dB @1 m rating combined with its 150° × 25° pattern and passive format place it as a wide-horizontal, tightly-controlled-vertical option suited to broad single-column seating plans; this preset exists to show that specific combination at the 12 m distance and 55 % drive point rather than being folded into a generic column preset.
02 / What that means, drawn
Plan view, drawn to one scale in both directions. The room is 20.00 m deep by 12.00 m wide, with the cabinet on the front wall and the listener 12.00 m down the axis. JBL Professional CBT 70J-1 has a nominal horizontal pattern of 150°, so the covered shape is a wedge whose apex is at the CABINET, not a circle around the listener. The wedge is drawn at half that angle either side of the axis. At the listener's distance that wedge is 89.57 m across — 44.78 m either side of the axis. That width is the published figure, and it is the only coverage quantity this tool establishes. The room is 12.00 m wide there, so one cabinet covers the full width with 77.57 m to spare across the two edges combined. The wedge is the nominal beamwidth drawn with straight edges. It is not a measured -6 dB contour, and it is a HORIZONTAL quantity only: no vertical coverage, and no covered area, is claimed here. This cabinet's vertical pattern is 25°, and the difference between the two is exactly why a single circular figure would misstate the covered patch.
03 / Hydrated calculator
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Presets are a typology starting point. The brief wizard captures the room geometry, programme and constraints we need to translate this configuration into a real design.