This questions comes up often in audio forums and comments. People wonder whether so called soundproofing curtains are worth the investment and can actually provide a substantial sound barrier for cars, noise neighbors, or other loud disturbances.
The short answer is YES curtains do provide a substantial barrier for sound, but there are some sure signs that indicate if they will be successful.
A soundproofing curtain is one that adds a significant amount of sound blocking between partitions.
There are many curtains or window treatments that are marketed as sound blocking or sound proofing, but have little impact on noise! A low weight low density curtain will have little to zero soundproofing. True soundproofing curtains are dense, heavy, and often have an extra middle layer for the purpose of blocking sound. These middle layers can be made with vinyl or cloth materials. Curtains layered in other curtain material tend to be less effective. Luckily, curtains can be tested to scientifically give an accurate measure of there sound transmission.
The Science of Sound Blocking
Customers seeking soundproofing curtains should look for a curtain with a high STC rating. An STC rating guarantees that the curtains claims have been substantiated in a lab.
Sound Transmission Class (STC) is a number rating of how well a building partition attenuates airborne sound. In the US, it is widely used to rate interior partitions, ceilings/floors, doors, windows and exterior wall configurations. Partitions are tested at a range of frequencies to determine transmission loss. These transmission losses at different frequency are then standardized into an STC rating.
Curtains like other partitions can be tested under certified laboratory conditions to attain an STC rating. The STC rating roughly correlates to the number of dB that a material could be considered to block. A 10 dB noise reduction is perceived as a halving of the noise. An STC rating loses effectiveness at low frequencies. A material may be highly effective at blocking voices but be poor at blocking low-frequency train rumblings.
For a reference point interior walls composed of drywall, studs, and insulation have an STC rating of 33. The best curtains have STC ratings of around 20 to 30. For every increase of 10 in the STC rating, the sound passing through the unit is halved; the higher the STC, the better the unit is at blocking sound.
Just like anything there is a lot of variation between products. There are many products that are marketed as sound blocking or soundproof that don’t have any data to back up their claims. The final thing to keep in mind is that blocking sound isn’t always the solution. Sometimes the better solution is to absorb sound.
Sound Absorption vs Sound Blocking
Curtains can also be used as sound absorbers. A sound blocker helps block sound going across a partition. A sound absorber works to reduce echo or reverb in a space. They improve the acoustics or reverb of a room. Soundproofing material tends to be heavy and dense whereas sound absorbing material tends to be porous and light low density material. See our article Soundproofing vs Sound Absorption for more details.
In summary look for a product that looks like it is heavy and dense and that has an STC rating to validate their claim isn’t just marketing. If the product doesn’t have an STC rating it is probably not worth spending a lot of money on. Work with the company to make sure the curtain fits your noise problem.