JBL MTC 300BB8 1 cubic foot back enclosure for Control 300 Series, 8-inch drivers

JBL Professional MTC-300BB8 - 1 Cubic Foot Back Box for Control Series 300 with 8" Drivers

The JBL Professional MTC-300BB8 is a large-format backcan enclosure designed specifically for JBL Control 300 Series 8-inch in-ceiling speakers such as the Control 328C/328CT . Its 16-gauge steel construction and 12mm MDF interior liner reduce resonances and improve bass response, delivering solid acoustic support in demanding commercial installations. The MTC-300BB8 is approved for use in air handling (plenum) spaces per UL-2043 and UL-1480, and complies with NFPA 90 and NFPA 70A, facilitating regulatory compliance in corporate buildings, retail, hospitality, and education environments. It features incorporated 22.1mm (0.875") knockouts (one top and four sides) that simplify conduit and cable routing. Its optimized dimensions (310 mm ceiling cutout, 380 mm outer diameter, and 268 mm overall height) facilitate integration with JBL installation accessories.

Main features

• Compatibility: Designed for 8" Control 300 Series , particularly Control 328C/328CT .
• Construction: 16 gauge steel with 12mm internal MDF for resonance control and bass extension.
• Regulations: Plenum rated (UL-2043, UL-1480) and compliant with NFPA 90 and NFPA 70A .
• Knockouts/Busholes: 5 x 22.1mm holes (one top and four sides) for conduit.
• Volume: nominal external volume ~28.3 L (1 ft³); internal volume ~20.1 L (0.71 ft³).
• Key dimensions: outer diameter 380mm , inner diameter 273mm , ceiling cut-out 310mm , overall height 268mm (259mm above false ceiling).
• Weight: 5.2 kg (net); 7.9 kg (shipping).
• Included accessories: 4 #10 × 0.75" (≈19 mm) sheet metal screws for securing the speaker to the enclosure.
• Related accessories: MTC-TB6/8 (tile bridge) and MTC-RG6/8 or MTC-SG6/8 gratings depending on the project's aesthetics.

Product benefits

• Consistent acoustic enhancement: 12mm MDF and volume control control internal resonances and enhance the system's bass extension.
• Professional and clean installation: Five 22.1 mm knockouts facilitate conduit routing and cable organization.
• Code Compliance: Plenum-rated certifications simplify approvals for buildings with plenum air return.
• Guaranteed integration: dimensions and cutting pattern aligned with the Control 300 series and the MTC-TB6/8 tile bridge.
• Durability in demanding environments: high-gauge steel (16 gauge) for intensive use in fixed installations.

Use cases

• Offices, retail, and hospitality with suspended ceilings and plenum requirements.
• Educational centers, auditoriums, and conference rooms that require sound uniformity and discreet aesthetics.
• Corporate and commercial installations requiring greater bass control in 8" ceiling speakers.

Frequently Asked Questions

• Which speakers are compatible? Primarily the JBL Control 328C/328CT (8"). See the compatibility guide for other models and accessories.
• What is the cutout size in the roof? 310 mm diameter.
• Is a tile bridge necessary? For modular suspended ceilings, MTC-TB6/8 is recommended to distribute the load and minimize vibrations.
• Hardware included? Yes, four #10 × 0.75" (≈19 mm) screws are included to secure the speaker baffle to the enclosure.
• Does it meet plenum standards? Yes, suitable for air handling spaces according to UL-2043 and UL-1480; and NFPA 90 and NFPA 70A.

Description for projects

JBL MTC-300BB8 Back Enclosure for 8" In-Ceiling Speakers (Control 300). 16-gauge steel construction with 12 mm MDF interior lining. External volume ~28.3 L; internal volume ~20.1 L. Dimensions: OD 380 mm, ID 273 mm, ceiling cutout 310 mm, overall height 268 mm (259 mm above drop ceiling). 22.1 mm Knockouts: 5 locations (1 top, 4 side). Plenum rated (UL-2043/UL-1480); NFPA 90 and NFPA 70A compliant. Net weight 5.2 kg. Includes 4 #10 × 0.75" baffle mounting screws.