A subwoofers surround is part of the sub’s suspension system. The surround protects the cone and prevents it from being displaced as it flexes out from the basket. It is usually made of a durable material like treated foam or rubber in order to withstand the strenuous job of producing bass frequencies.  If the cone rocks and is not perfectly linear, it will put a lot of stress on the voice coil. The two main surround types are foam and rubber, which are combined with other substances to enhance their flex and strength properties. With so many subwoofers, and so many different surround types, it can be difficult to find out which one is the best for you. Here is some information on the two main types of surrounds.

Foam Surround – MTX T4512-44

Foam: Back in the 70’s foam surrounds tended to deteriorate very quickly, but due to recent advancements, the average life span of standard foam surrounds is about 8-16 years. New foam formulas last much longer and are a superior product for speaker drivers that need a large excursion. Foam keeps the cone centered and yields a high excursion. Foam is self damping and reduces its own standing waves. It is also very light and has a minimal effect on the motion of the cone. Foam can be mixed with other substances to produce different flex and strength properties.

Rubber Surround – Alpine SPR-13C

Rubber: Back in the day rubber surrounds suffered from what is called “suck-back,” where a vacuum inside the box acts on the surround and causes it to invert at higher excursion levels. Scientists have since learned from this and it is now an uncommon occurrence. Modern rubber generally lasts longer, but is less compliant then foam. Rubber can be made more rigid and durable than foam. Most rubber formulas become stiff at higher frequencies and will dampen cone resonances.

There are various forms of rubber surrounds mixed with other materials to change the property of the rubber. Here are brief explanations of the most popular rubber derivatives.

Urethane: A plastic compound that is weather resistant and more flexible than standard rubber.

Santoprene Surround – Kicker CVR124

Santoprene: A thermoplastic compound that is unique in that it possesses the same flexibility and durability as most rubbers. It has a longer life span than rubber in both hot and cold environments.

Butyl: Also known as polyisobutylene, butyl is a synthetic rubber that structurally resembles polypropylene and has excellent impermeability and good flex properties. Butyl is also found in chewing gum and tire inner tubes.

Some people say foam surrounds are ideal for sound quality and high excursion while rubber surrounds are slightly stiffer but they last longer. The cost difference between rubber and foam is pretty insignificant. No one material type has the market pinned down, so the best thing to do is to let your ears decide. There are so many other factors involved with choosing a car subwoofer than just its surround type, for example magnet size and cone material, that the surround alone is not going to seal the deal. Both material types serve their purposes well, so do not fret if the subwoofer you like does not have your ideal surround preference type, just take a listen.

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