JBL MTC 300BB12 3 cu ft Back Box for 12-inch Control 300 Series Speakers

JBL Professional MTC-300BB12 - 3 cu ft Back Box for 12" Control Series 300 In-Ceiling Speakers

The JBL Professional MTC-300BB12 is a 3 cu ft backbox designed for the JBL Control 300 Series 12-inch in-ceiling loudspeakers. Its reinforced 16-gauge steel construction with 12mm MDF overlay eliminates resonances and delivers extended bass response in demanding commercial installations. It features conduit knockouts on the top and all four sides, a dual baffle mounting system , and an M4 stud platform for mounting a high-power 70/100V transformer (e.g., JBL MTC-300T150 ). It meets plenum ratings for air handling spaces, facilitating approval for corporate, retail, hospitality, and education applications.

Main features

• Construction : Extra thick 16 gauge metal with 12mm MDF inside to reduce vibration and staining.
• Volume : nominal external ≈85.0 L (3 ft³); internal volume ≈68.0 L (2.4 ft³).
• Knockouts/bulkheads : 5 holes of 22.1 mm diameter (one top and four sides) for conduit entry.
• Dual speaker mounting system :
  • Option 1: Fixing at 6 side points with #10 × 19 mm sheet metal screws (included).
  • Option 2: Fixing at 4 corners with M4 × 14 mm screws (included).
• Transformer platform : 4 M4 × 12 mm studs (center to center 70 × 67 mm ) for high power 70/100 V transformer.
• Dimensions :
  • Width : 587 mm
  • Depth (body) : 461 mm; 505 mm including side flanges
  • Height : 324 mm total ( 308 mm protruding above the false ceiling)
  • Ceiling cut : 378 × 378 mm (square)
• Weight : 20.6 kg (net); 23.1 kg (shipping).
• Approvals : suitable for plenum , in accordance with UL-2043 , UL-1480 , NFPA 90 and NFPA 70A .
• Included Accessories : 6 #10×19mm screws, 4 M4×14mm screws and 4 M4 nuts for optional transformer.

Compatibility

Official backbox for 12" Control 300 Series speakers:

• Control 321C / 321CT
• Control 322C / 322CT
• Control 312CS (12" subwoofer)

Matching square grid: MTC-300SG12 . Recommended transformer for high impedance lines: MTC-300T150 .

Product benefits

• Consistent sound quality thanks to controlled volume and the MDF lining, which attenuates internal resonances and improves bass extension.
• Flexible and secure installation with two speaker mounting systems and multiple knockouts for cable management.
• Regulatory compliance for plenum installation, simplifying building approvals and audits.
• Native JBL integration with Control 300 accessories and models, ensuring mechanical and acoustic compatibility.

Use cases

• Shopping centers, retail and hospitality with suspended ceilings and plenum air return.
• Corporate and educational: meeting rooms, auditoriums, hallways, and common areas.
• Enclosures requiring greater bass pressure and extension with 12" in-ceiling speakers.

Frequently Asked Questions

• Is a back box mandatory? Many projects require it by code or to control bass response and isolation; the MTC-300BB12 provides both.
• Which 70/100 V transformer fits? The inner platform is designed for the MTC-300T150 (150 W), attaching it to M4 studs.
• Can it be used with a square grille? Yes, the MTC-300SG12 grille is designed for the 12" models in the series.
• What cut size do you need? 378 × 378 mm .

Description for projects

JBL MTC-300BB12 Back Enclosure for 12" In-Ceiling Speakers (Control 300). External volume ≈85.0 L; internal volume ≈68.0 L. 16-gauge steel construction with 12 mm MDF internal liner. 5 x 22.1 mm knockouts (1 top, 4 sides). Dimensions: 587 mm (W) × 461/505 mm (D body/with tabs) × 324 mm (H; 308 mm above ceiling). Ceiling cutout 378 × 378 mm. Plenum rated (UL-2043/UL-1480; NFPA 90/NFPA 70A). Net weight 20.6 kg. 70/100 V transformer platform with M4 studs (70 × 67 mm). Includes hardware for both mounting systems. speaker.