If you’re looking into CLD sound deadening, we’re going to assume that you’re into car audio or come from a technical background. The CLD stands for constrained layer damping, and it’s a technology that’s been around for a long, long time. The tech really started blossoming about 100 years ago, and was mostly used by the military (think ships and planes). By about 50 years ago, a bunch of smart scientist folks had worked out the formulas which described a theoretical process, then proved it with real-world experiments.
This deeper understanding allowed for the mass commercialization of these materials and the sound deadening mat (as well as the liquid sound deadener) made the jump to a much wider market. Constrained layer damping developed into a critical material for the automotive and building industries. CLD also found a home in the modern tech industry, primarily damping vibrating computer hardware.
What is constrained layer damping?
Constrained layer damping (or CLD) is a method of stopping vibrations, and thus structural energy/noise, in a system. The basic idea is to put a viscoelastic interlayer between two rigid, constraining layers. When that viscoelastic inner layer is subjected to shear motion, the constraint layer (often metal) resists that motion and the vibrational energy is converted into low level heat energy. Part of the reason constrained layer damping was such a game changer, is that now we could substantially reduce the structural energy in a system while adding significant less mass (weight) to that system.
What makes a good constrained layer
The formulas that describe how effective a CLD will be predict several factors that matter for performance. Understanding how these variables work together is necessary to formulate an successful damping product, and is why our Damplifier Pro, Damplifier, and Spectrum products are so much better than most other damping materials out there.
- Thickness of the viscoelastic material – thicker materials perform better than thinner materials, with eventual diminishing returns. Spectrum can be applied in layers up to 5mm thick. Damplifier Pro is twice as thick as Damplifier, but both are still great due to key factor #2.
- Composition of the viscoelastic material – it does not matter how thick your material is if the composition is garbage (asphalt or butyl with cheap fillers). Without a viscoelastic interlayer of precisely formulated butyl, you will only get modest reductions in vibrational energy due to the added mass.
- Rigidity of the foil – thin, crumply foil cannot act as an effective constraint layer. A cheap sound deadener always skimps on the foil, and is typically sold in a roll or folded up.
- Quality of the adhesion – a CLD tile much be firmly bonded to the surface in order to perform at its best. Use a hand roller to ensure a strong bond and no air bubbles! If the adhesion is bad enough, you won’t just have bad performance – the material will fall right off (most common with asphalt based deadeners).
Are there other automotive soundproofing strategies besides CLD?
Yes! A constraint layer damper only reduces the structural noise by stopping the vibrations. There are two other common types of noise in vehicles.
- Structural noise due to hard surfaces rattling and smacking into each other. The key to stopping this type of noise is to decouple the two surfaces. We use a specially designed closed cell foam (OverKill Pro or OverKill) to isolate the two hard surfaces from each other.
- Airborne noise from the engine, exhaust, and tires. A lot of what people think of as road noise is airborne as well. To stop airborne noise, you have to block it with 100% coverage from a barrier. Luxury Liner Pro is our best performing automotive noise barrier. It’s a dense, mass loaded vinyl barrier layer that comes with a fused decoupling closed cell foam already bonded to it.
Unfortunately, it’s impossible to look at a picture of a sound deadening mat, a bucket of liquid deadener, or a piece of foam and know if it’s going to be awesome or mediocre. That’s where testing data comes in! Standardized testing is really the only way to know for sure that a material does a good job of what it claims. That’s why we publish testing data on all Second Skin materials, so you can evaluate the properties and know that they are great at what they do.
As always, if you have questions on your specific project – whether it’s about our CLD sound deadening, our liquid deadener or other car soundproofing materials – just reach out to us and we’ll be happy to help with your project.