Sonopan Soundproofing Panels Review: What the STC Ratings Mean
Updated
Sonopan soundproofing panels are 3/4 in. sheets of recycled wood fiberboard that you screw to the studs before the drywall goes up. The board by itself rates STC 27, and in maker MSL's 2x4 wall designs it reaches STC 50 to 58, but most of that comes from the insulation, resilient channel and drywall it's built into. It's a layer inside a wall, not a panel you hang on one.
What Sonopan is made of
Sonopan is a 4 × 8 ft fiberboard made from over 93% wood fiber, with under 5% starch and under 2% wax (MSL safety data sheet (opens in a new tab)). Both faces are pressed with cavities of different depths, and MSL says that helps it absorb "a greater frequency range" (architect brochure (opens in a new tab)).
| Spec | Value |
|---|---|
| Size and thickness | 48 × 96 in., 3/4 in. |
| Weight | 26 lb per sheet, about 0.8 lb/sq ft (26 ÷ 32) |
| Density | 14 lb/cu ft |
| Thermal value | R-2.45 |
| Use | Interior only, protected from weather before, during and after install |
At 0.8 lb/sq ft, a sheet weighs about a third of what 5/8 in. Firecode X drywall does at 2.2 lb/sq ft (USG (opens in a new tab)). The mass law gives you only about 6 dB each time you double the weight (NRC Canada, CBD-239 (opens in a new tab)), so the board's weight alone can't explain the assembly ratings.
Sonopan STC ratings: what the maker's tests show
MSL rates Sonopan alone at STC 27 (Sonopan FAQ (opens in a new tab)), close to the STC 26 of 1 lb/sq ft mass loaded vinyl (Johns Manville (opens in a new tab)). The numbers worth looking at are the wall ratings in MSL's architect brochure.
Watch out: MSL's brochure and technical documentation page (opens in a new tab) don't name a test lab or report number for these ratings, and the short comparison rows don't spell out every layer. We found no published independent lab report for a Sonopan wall, so treat these as the maker's figures. The brochure itself says results "can vary according to the physical properties" of the materials.
Against the building code, STC 50 is the minimum for walls between dwelling units, or 45 tested in the field (LADBS, IBC 1206 (opens in a new tab)). MSL's channel walls clear that on paper. The plain Sonopan wall at STC 43 doesn't.
Sonopan vs QuietRock and mass loaded vinyl
Of the three common add-on layers, Sonopan adds the least weight and the most thickness.
| Layer | Thickness | Weight | Maker's example |
|---|---|---|---|
| Sonopan | 3/4 in. | 0.8 lb/sq ft | STC 50 with resilient channel |
| QuietRock 510 (opens in a new tab) | 1/2 in. | 2.1 lb/sq ft | STC 49 on one side of a 2x4 wall |
| Mass loaded vinyl | 0.1 in. | 1 lb/sq ft | STC 26 alone (Johns Manville (opens in a new tab)) |
These numbers come from different test walls, so they don't rank the products. MSL's FAQ (opens in a new tab) says Sonopan is "less expensive and much easier to install than soundproofing glues," which is a maker's claim with no prices or test data behind it. The damped boards and Green Glue are covered in soundproof drywall panels.
How to install Sonopan
Sonopan goes on the framing like sheathing, then the drywall goes over it. Where the channel goes in the stack changes the rating by 2 points in MSL's designs.
- Insulate the cavity with at least R-12 in walls and R-20 in ceilings, and don't compress it (Sonopan FAQ (opens in a new tab)).
- Cut with a circular saw and a sharp blade, with a dust vacuum indoors and a mask (installation guide (opens in a new tab)).
- Add resilient channel first for the higher rating, or over the Sonopan for an easier install. Any screw that hits a stud through the channel shorts it out.
- Fasten the sheets to studs, joists or channel every 12 in., using 1-1/2 in. screws or narrow crown staples on wood and 1-1/4 in. drywall screws on metal. On ceilings, run the sheets continuously across the joists, never between them.
- Seal the perimeter and every gap with acoustical sealant.
- Hang the drywall with its seams offset from the Sonopan seams, using screws long enough to reach 3/4 in. into the framing. MSL recommends 5/8 in. Type X, and two sheets in extreme cases.
Where Sonopan works and where it doesn't
Sonopan makes sense for walls and ceilings that are open or getting new drywall anyway. As a surface panel you buy to fix noise without rebuilding, it does nothing.
New wall or ceiling
Good fit
Goes up before the drywall. Pair it with insulation and channel for the STC 56 to 58 designs.
Over old drywall
STC 56 estimated
MSL's renovation design adds Sonopan, channel and two drywall layers. That rating is an estimate, not a test.
Footsteps upstairs
Wrong product
Impact noise needs a floor treatment. MSL sells 7/16 in. SONOpanX for floors.
Echo in a room
No NRC published
MSL suggests leaving it bare for absorption but doesn't give an NRC. Use absorption panels instead.
Rule: Sonopan only counts as soundproofing when it's sealed inside a wall with insulation and drywall over it.
FAQ
Is Sonopan fire rated?
Not on its own. MSL says Sonopan "does not carry a fire rating itself" but is UL/C listed in rated designs such as U305 and U309, where the drywall provides the rating, so follow the exact design you need.
Can Sonopan go over existing drywall?
Yes. MSL's brochure allows fastening it over existing drywall, screwed through into the framing, with new drywall on top.
Is Sonopan the same as SONOpanX?
No. SONOpanX comes in 4 × 4 ft sheets 7/16 in. thick for floors and goes after impact noise. Sonopan is the 4 × 8 ft wall and ceiling board for airborne noise.
Is Sonopan dust safe to cut indoors?
Wear a dust mask, safety glasses and gloves. MSL's safety data sheet lists sawing dust as an eye and airway irritant and says to clean it up with a vacuum or by wetting it down, never by dry sweeping.
Does Sonopan block bass?
MSL says it absorbs "a wide range of noise frequencies, including low bass," but it publishes no low-frequency data, and it recommends resilient channel for party walls and ceilings where bass is likely. You'll find more answers in the soundproof panels FAQ.