Perforated Tubes: Suppressing Sound and Increasing Performance
Perforation is a common practice for metal across industries. The same could be said about the use of metal tubes. Almost anywhere you look you are able to see a metal tube of some kind. However, can you name a place where a perforated tube is present in an object or stands alone as a tool? When initially thinking about perforated tubes it may be hard to pinpoint exactly when and where they would be used, but after further thought we use something everyday that has perforated tubes in its construction. That “something” is our automobiles, motorcycles and cars alike. Not only our automobiles, but machinery in the workplace has exhausts systems as well that use these tubes. The perforated tube is located inside of the muffler.
These metal tubes have some responsibility for how loud or quiet your car sounds. In addition to the sound suppression there is a correlation with vehicle performance. If the vehicle is very quiet the perforated tube likely has more back pressure in the resonating chamber to making the vehicle quieter. If the car or motorcycle is louder there is less back pressure making it perform at higher levels. Have you noticed a difference between the correlations between noise and performance in your own vehicles?
Not all mufflers use perforated tubes because there are pros and cons to using them. Mufflers that do not use the tubes tend to be quieter, but have more back pressure which hinders the performance of the engine. These mufflers are predominately equipped on stock cars from the factory. Many people and cities prefer the quietness over a little extra horse power. On the other hand, performance exhaust and motorcycles tend to use perforated tubes in their exhaust systems. In mufflers that use perforated tubes, the sound absorption is created differently than the traditional resonating chamber. However, this insulation is used to find a happy medium between performance and sound. Have you ever replaced a stock muffler for a higher performance muffler?
Some mufflers with resonating chambers have perforated tubes as well. The mufflers without a resonating chamber are sometimes called glass packs or cherry bombs. Here the inner tube (that is perforated) is surrounded by sound insulation, which is then surrounded by housing, usually made from steel. The hole patterns in the tube varies across brands. The variation also adds to the exhaust flow either reducing back pressure and increasing performance or contributing to the quietness of the system. Without mufflers all of our vehicles would sound like NASCAR cars, where they do not use mufflers.
Mufflers are one of many ways to utilize perforated tubes. Some other uses include irrigation, EMI shielding and filtration. Some industries that benefit outside of the automotive industry are construction and plumbing. Now that we are on the topic of perforated tubes have you thought of any other applications?