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Enjoy better sound from your in-wall speaker with Russound's Flexbox. Install one behind each speaker in your system to prevent sound from bleeding through walls, where it could muddy the sound of another room's speakers and distort the sound within your room. You'll get clearer, crisper audio throughout your home.

You can get the same improvement in sound for your in-ceiling speakers with the in-ceiling Flexbox. The Flexbox's sturdy-yet-flexible material allows for easy installation in new construction or existing homes.

Product Highlights:

  • back box for compatible in-wall speakers
  • flexible material for easy installation
  • reduces sound leaking into adjoining rooms
  • fire retardant material
  • cutout dimensions: 5-7/8"W x 9-3/4"H (speaker cutout must be equal to or smaller than this cutout to fit)
  • overall dimensions: 14-1/2"W x 16"H x 3-1/2"D
  • lifetime warranty

Russound Flexbox Reviews

Hands-on research

What's in the box?

Download owner's manual

  • FBW1-FR In-wall speaker back box
  • Installation sheet

Product Research



Overview: The Russound speaker back box is made of a proprietary composite material, and offers an innovative acoustic barrier that will reduce background noise, provide a moisture barrier, diffuse distortion, and improve sound quality for your in-wall speakers. It is flame retardant, and is sized to fit between the studs in 3.5" deep bays. It should be used for new construction, and is not designed for retrofit installations.

Speaker Wire: The back box does not provide a slot or hole for speaker wire. You must cut a small hole or slit in the material, and insert the wire.

Flame Retardant Standards: The speaker back box is flame retardant, and meets the ASTM E119 and UL 263/NFPA 251 (1-hour) and ASTM E84/NFPA70 standards. For fire rated installations, the hole where the speaker wire comes through should be sealed with fire-rated caulk (3M's Fire Barrier Sealant FD150+ or FD200+ is recommended.) Coating around the edge of the drywall side of the box is not required, but could be added to create a strong acoustic seal.


Dimensions: Width: 14.5", Height=16", Depth=3.5"

Material Thickness: 1" nominal thickness

Weight: 5.4 pounds

STC Rating: 32

Flame Spread: 23

Smoke Density: 30 (ASTM E84/NFPA 70)

Thermal Value: R4.2

Temperature Range: -40° F to 350° F

Fire Rating:

  • Class 1 Fire Rated
  • ASTM E119 / NFPA 251 and UL 263 for 1-hour fire rating

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team. They verify what’s in the box, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.