Glass is a dense reflective material that can work as a sound barrier material if it’s used correctly.
A single standard glass pane 5 mm thick (7/32”) is STC 20 on average. Satisfactory results STC 35+ can be achieved by having 2 double glazing panes 9 mm thick and 7 mm thick with an 11 mm gap in between. The thicker the glass pane the more reduction can be obtained.
Sound booths are usually designed with insulation sound barrier materials such as wood boards, mineral rock or fiberglass batts, and acoustic foam inside to absorb reflections and reverb. If the sound booth’s room already has insulated windows, the overall STC can be over 60, which is excellent for recording audio products.
Here there is a list of the STC obtained with different combinations of glass panes:
| Glass Thickness | STC |
| Single pane | 26 |
| Double pane | 28 |
| Single pane PLUS soundproof pane | 50 |
| Double pane PLUS soundproof pane | 50 Using double pane is not worth it |
Types of Soundproof Glass
Soundproof glass comes in two types: double glazing and laminated. Double glazing consists of two thick panes (one at least 9 mm or more, the other 5 – 7 mm thick) and a gas-filled gap in between.
Laminated glass is made by applying heat and pressure on two or three panes, which will create a thick “mega pane” sound barrier.
What to Avoid When Using Glass as a Soundproof Material
If you want to DIY your windows or create a sound booth using glass panes, the main issue to avoid when using glass as a soundproof material is coincidence frequency, which means that instead of reducing the unwanted sound, the glass panes will amplify it.
The following video shows each type of soundproof glass:
With double glazing, soundproof glass manufacturers fix this problem by making sure that the thickness of the glass panes is different. One 9 mm layer or more and the other 5 – 7 mm thick, plus an argon-filled gap between them can create an efficient sound barrier. Now you know! Better safe than sorry!
How to Reduce Noise Coming From a Window
If you want to keep the value of your property, removing the window from a room is not a convenient choice. Instead of changing the current window for a double glazing or laminated replacement, you can look at alternative materials that will help reduce unwanted sounds.
The following three options can help you reduce noise without sacrificing natural light:
- ¼” Soundproof Window Insert (by indowwindows.com): It’s made of an acrylic transparent sheet and window seal rubber. They have two models, starting from standard to acoustic noise reduction, $30 to $45 sq/ft.
- DIY window insert: If you have the time and persistence, buy a ¼” acrylic (also called plexiglass) sheet, window seal rubber, and metal (not plastic) window screen clips.
Make sure to take accurate measurements of the window you want to soundproof and make sure you don’t leave any holes or gaps, to avoid sound leakage.
- Sound attenuation blankets and acoustic curtains: They can achieve up to STC 25. Using window inserts and then an acoustic blanket can reach on average a total STC 55. When recording audio products, you can use velcro around the window frame, so that the space between the curtain and the window can be as little as possible.
How Much Noise Does A Window Insert and Acoustic Blanket Reduce
| Type of pane | STC | STC PLUS acoustic blanket |
| A single pane window PLUS a ⅛” acrylic window insert | 10 – 12 | 25 |
| A single pane window PLUS a ¼” acoustic acrylic window insert | 18 | 30 |
| A double-pane window PLUS ¼” acoustic acrylic window insert | 42 – 45 | 50 |
The following options can help you reduce noise but will block natural sound light from the window:
- ¼” Window insert PLUS MLV layer: STC 30
- Acoustic panels of the same size as the window, made of wood board, fiberglass batts, and acoustic fabric. Acoustic tape on the edges to help reduce sound leakage. STC 35
- Acoustic panels of the same size as the window, made of wood board, but mineral wool batts instead of fiberglass, plus acoustic fabric. Acoustic tape on the edges to help reduce sound leakage. STC 35
How Much Noise Can a Carpet Reduce
Carpets are excellent sound absorbers on floors, like acoustic foam is for walls. A ⅛” pile carpet is STC 0.10 – 0.15. Using a 40 on/sy cushion and 0.56 pile height carpet can reach up to 0.70 NRC.
Carpets reduce airborne (noise, speech) and impact sound (objects that hit the floor, footsteps) as their tiny irregular shape fibers have different resonance frequencies that reduce most of the noise in the human audible range.
Using carpet underlay with thick carpets can boost the noise reduction coefficient. Let’s take a look at some ratings, according to www.carpets-rug.org
| Carpet on Concrete, with no Cushion | |||
| Pile weight Oz/Sy(Fiber weight only, backing not included) | Pile height in(Fiber height, backing not included) | Type of surface | NRC |
| 44 | 0.25 | loop | 0.30 |
| 88 | 0.50 | loop | 0.40 |
| 35 | 0.175 | cut | 0.35 |
| 36 | 0.43 | cut-acrylic | 0.50 |
| 43 | 0.50 | cut-wool | 0.55 |
| Carpet on 40 oz/sy Hair Cushion | |||
| Pile weight Oz/Sy | Pile height in | Type of surface | NRC |
| 44 | 0.25 | loop | 0.40 |
| 32 | 0.56 | cut | 0.70 |
| Carpet on 40 oz/sy Various Cushion TypesThe more permeable the cushion type the higher the NRC | ||
| Cushion Weight | Cushion Material | NRC |
| 86 | Hair | 0.60 |
| 86 | Hair-jute | 0.65 |
| 41 | ⅜” foam rubber | 0.60 |
Before you make a sound booth to record voice-over audio products you need to know how much noise the room gets and the sources where it comes from. You can use free mobile phone apps to determine:
- For the amount of noise you need to reduce (in dB): Use a sound meter app
- To choose if you need fiberglass or mineral wool (the highest STC possible): Use a Spectrum frequency analyzer app. It will show you what are the dominating frequencies in the unwanted noise.
- Fiberglass does a good job from 300 Hz and above.
- 300 Hz and below, mineral wool is the best choice as well as for the rest of the frequency range
