Today's market is inundated with woofers that offer respectable performance and great cosmetics at affordable prices. The variety is terrific for consumers in terms of the buying options they have; but the sheer quantity makes it difficult to pick a speaker. Things are then further complicated by the issue of enclosure style. This is one of the more controversial topics in car audio. Everyone has an opinion as to which kind of enclosure is best, but some people like to think that there is only one truly superior box design. In fact, there are several styles to choose from and each one has its upside. In the end, the issue comes down to what you want to do or the kind of music you listen to. The focus of the following tutorial is to elucidate the popular enclosure designs, discussing it in laymen's terms, so that even passing enthusiasts will find it easy to read. I'll also explore the various pros and cons, and explain the trade-offs involved in a given enclosure design, in addition to providing a brief history of "making boxes for speakers" (a simple way to describe something that has become somewhat complex).
Everyone wants a clear-cut response to the following question: "What speaker enclosure produces the best sub-bass performance?" I'm asked that a lot; and to this day I have not arrived at any kind of absolute answer. While I have developed my own opinions on the various styles of enclosures, I would have to say that for the most part the good and bad aspects of the different styles tend to cancel each other out in the end.
Like I said, this is perhaps the most controversial area of car audio. Of course, that's because you have competing methods or technologies at work and no single enclosure design that provides users with all of the benefits the various boxes offer with none of the shortcomings. Many enthusiasts swear up and down that sealed enclosures produce the best performance, while others are equally adamant about the benefits of ported and bandpass designs. Most of these people are well-intentioned in recommending enclosures that they have had success with, but anyone who says that a given enclosure type is superior in every way is always wrong.
Infinite BaffleInfinite baffles (IB), often termed "Free Air", are possibly the simplest enclosures to build, and a great way to conserve space. This design is defined as an enclosure that contains a greater volume of air than the Vas of the speaker. Applying an infinite baffle system in an automobile is relatively easy. The concept of an infinite baffle is to isolate the sound wave produced by the front of a speaker from the back wave. This normally involves mounting the speaker(s) on a board that seals off just behind the rear seat while using the trunk of the vehicle as the enclosure. When all is said and done, an IB enclosure is truly quite large.
Trade-offs come in many forms when working with IB enclosures. Sure, using IB enclosures conserves a lot of space, especially in the trunks of smaller cars. However, there are some losses to be noted. The most prominent is efficiency. Without a solid structure built around the woofer, it is difficult to reinforce the sound. Trunk interiors are filled with flimsy panels, thin sheet metal, and usually a measly spare tire - none too pleasing for sound reproduction. This same issue holds value with the speaker's power handling. As much as 50% of the nominal power handling of a woofer can be lost when placed in an infinite baffle. Another anomaly that plagues IB enclosures is the tendency to lose control of cone movement when played below the Fs (resonance frequency of the driver), much like ported systems when played below the tuning frequency. For this reason, it may be desirable to utilize a subsonic filter below the Fs of the speaker.