Monitor Audio CSM Box - Back Box

A Sealed Enclosure That Gives Your In-Ceiling Speaker a Proper Air Space

The CSM-BOX is Monitor Audio's sealed back box for in-ceiling speaker installations, designed to give a compatible driver the same kind of controlled air space a bookshelf or in-wall speaker cabinet provides. Without a back box, an in-ceiling speaker fires directly into an open joist bay, where insulation, wiring, and the size of the cavity can all change how the speaker actually sounds from one room to the next.

This is a pre-construction accessory built for installers and homeowners planning ceiling speakers ahead of drywall or finishing work, not a retrofit solution for an already-finished ceiling. It replaces Monitor Audio's previous CMBOX, which has been discontinued.

Consistent Bass and Midrange, Regardless of What's Behind the Ceiling

Built from MDF (medium-density fiberboard) with an interior foam lining, the CSM-BOX creates a fully sealed enclosure behind your in-ceiling speaker. That sealed air load is what lets the speaker's driver behave the way its designer intended, rather than being shaped unpredictably by whatever happens to be on the other side of the ceiling, whether that's open attic space, mechanical ductwork, or a room below.

Better Sound Isolation Between Rooms and Floors

Beyond improving the speaker's own performance, the sealed design reduces how much sound bleeds upward or downward into the space above or below the ceiling. That matters most in multi-room installations, upper-floor bedrooms, or any room where you don't want music playing in one space to be clearly audible in another.

One Box, Multiple Compatible Speakers

The CSM-BOX ships with both Small and Medium Ring adapters, and either can be removed depending on which speaker you're installing. That flexibility lets a single back box accommodate a range of Monitor Audio's Creator Series, Basics, and All-Weather CI in-ceiling speakers, rather than requiring a different box for every model.

Is the Monitor Audio CSM-BOX Right for You?

• You're installing in-ceiling speakers before the ceiling is finished. The CSM-BOX is a pre-construction product, meant to be mounted between joists ahead of drywall.
• You want consistent sound regardless of what's above the ceiling. The sealed MDF enclosure removes the variability of an open joist bay from the equation.
• You care about sound bleeding between rooms or floors. The sealed design measurably reduces how much audio escapes into adjacent spaces.
• You're outfitting multiple rooms with different Creator Series or All-Weather CI speakers. The included Small and Medium Ring adapters let one box work with several compatible models.
• One honest limitation: this back box does not include a speaker, mounting hardware for the speaker itself, or wiring — it's strictly the sealed enclosure, and it's not designed for retrofitting into an already-finished ceiling.

Setup, Compatibility & What's Included

The CSM-BOX mounts between ceiling joists during construction or renovation, before drywall goes up, and is compatible with Monitor Audio's C1S, C2S, C1M, C2M, C2M-TX, C2M-CP, CSS230, C3M, C165, AWC265, and AWC265-T2 in-ceiling speakers, along with earlier 6.5-inch Monitor Audio in-ceiling models. Included in the box: the sealed MDF back box itself, plus removable Small and Medium Ring adapters to match your specific speaker's mounting ring size. The compatible speaker, speaker wire, and any mounting brackets or grille trim specific to the speaker itself are sold separately.

Key Features

Sealed MDF Construction with Foam Lining
Creates a controlled air space for more consistent bass and midrange, regardless of what's on the other side of the ceiling.

Reduces Sound Bleed Between Rooms
The sealed design helps keep audio contained to the room it's playing in, rather than leaking into the space above or below.

Removable Small and Medium Ring Adapters
Both included, so one box fits a range of compatible speaker models without needing separate hardware.

Broad Speaker Compatibility
Works with Monitor Audio's Creator Series, Basics, and All-Weather CI in-ceiling speakers.

Pre-Construction Installation
Mounts between joists before drywall or ceiling finishing goes up.

Successor to the CMBOX
Replaces Monitor Audio's previous back box model, which has been discontinued.

Specifications

• Type: sealed in-ceiling speaker back box
• Material: MDF (medium-density fiberboard) with interior foam lining
• Included adapters: Small Ring (removable), Medium Ring (removable)
• Compatible speakers: C1S, C2S, C1M, C2M, C2M-TX, C2M-CP, CSS230, C3M, C165, AWC265, AWC265-T2, and earlier 6.5″ Monitor Audio in-ceiling speakers
• External dimensions (H × W × D): 500 × 350 × 160mm (19 11/16″ × 13 3/4″ × 6 5/16″)
• Installation type: pre-construction (between joists, before drywall/finishing)
• Replaces: Monitor Audio CMBOX (discontinued)
• Sold as: each
• Price: $140 each (launch price; confirm current pricing before publishing)

Frequently Asked Questions

Do I actually need a back box for my in-ceiling speaker?

It's not strictly required, but Monitor Audio and most custom installers recommend one. Without a sealed back box, the speaker fires into an open joist bay, where insulation, ductwork, and cavity size can all affect bass and midrange consistency, and more sound can bleed into adjacent spaces.

Which speakers is the CSM-BOX compatible with?

It's designed for Monitor Audio's C1S, C2S, C1M, C2M, C2M-TX, C2M-CP, CSS230, C3M, C165, AWC265, and AWC265-T2 in-ceiling speakers, as well as earlier 6.5-inch Monitor Audio in-ceiling models.

Can I install this into an already-finished ceiling?

No. The CSM-BOX is a pre-construction product, designed to be mounted between joists before drywall or ceiling finishing goes up. If you're working with a finished ceiling, give us a call and we can help you find a retrofit-friendly option.

Does this include a speaker?

No. The CSM-BOX is sold as just the sealed back box with Small and Medium Ring adapters. A compatible Monitor Audio in-ceiling speaker is sold separately.

How is the CSM-BOX different from the older CMBOX?

The CSM-BOX is Monitor Audio's current back box, designed to replace the CMBOX across the same range of Creator Series, Basics, and All-Weather CI speakers. The CMBOX has been discontinued and is no longer in regular production.

Why Audio Advisor?

• 40+ Years of Expertise – Helping music lovers build better systems since 1981.
• 60-Day Money-Back Guarantee – Hear it in your own system with confidence.
• Real Product Experts – Friendly advice before and after your purchase.
• Free Shipping – On qualifying orders over $49.
• Flexible Financing – Convenient payment options available.