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Our goal in developing a subwoofer system was to produce a product that achieved very high sonic quality and that did not exhibit the sonic problems typical of subwoofers. In particular, subwoofer systems usually do not integrate well sonically with the other speakers in the system and this product was originally inspired by the conception of an electronic means of generating subwoofer low-pass crossover characteristics that could be made to perfectly match any main speaker.
Further impetus was added to the project by the realization that the placement problems of altered and unbalanced response caused by nearby walls could also be solved. We believe that the major problems of subwoofers have been effectively eliminated in the SmartSub subwoofers and the following details the highlights of their performance features.
The problems
Subwoofer performance problems can be categorized into three types:
- Output/distortion/uniformity problems.
- Problems of sonic integration with the main speakers.
- Room interaction problems.
Examples of the first type are thumpy, dirty and strained low frequencies; of the second disjointed sound character, misbalanced levels and seemingly disconnected low frequencies; of the third are subjectively overly dominant or "missing" tones and sonic balance and character that change with different subwoofer placement.
Low-frequency performance
It is difficult and expensive to reproduce deep bass at high loudness levels with the low distortion that can be achieved by high quality speakers at higher frequencies and/ or lower loudness levels. Therefore, many subwoofers do not attempt to reproduce truly deep bass but rather are designed to accept very high input levels of bass energy without obvious distress. Often this characteristic is achieved by restricting reproduction of deep bass and by incorporating severe compression of the signal so that demanding inputs do not overtax woofers and amplifiers of modest ability.
These limitations of most subwoofers can be overcome with normal engineering. However, such performance requires very high output drivers and a large amount of power, neither of which can be obtained at low cost. And even when a product is engineered to provide a truly high level of low frequency performance, this does not solve the two other categories of problems subwoofers exhibit.
Integration
The second category of problem is the result of the fact that the crossovers typically employed are generic types and that they do not take into account the low frequency characteristics of the main speakers. This is true whether the crossover used is the bass management capability of the processor or the built-in crossover included with most subwoofers.
Usually these crossovers will provide the desired blending only for the theoretical case of the main speakers and the subwoofer both having low frequency response flat down to DC. Since this is never true, the results obtained are off a little or a lot, depending on other variables.
Most subwoofer crossovers attempt (or merely profess) to deal with the unknown variables of the main speaker's response by providing additional controls, including phase, polarity, and separately adjustable low- and high-pass frequency. While it is possible that in some cases good results can be obtained by use of these controls, in most cases it is still not possible to achieve the desired blending and integration of the subwoofer and the main speakers.
And even in cases where good results can be obtained, there is no way to know how the controls should be set to achieve optimum performance since the required settings are not usually those that would seem logical. We needed a completely different approach to subwoofer crossovers that was able to take into account the response of the main speakers in order to provide crossover performance that achieves desired results with simple and logical control settings.
Room effects
The effects of the third category of problem are well known. Almost every subwoofer installation is plagued by response irregularities that are habitually attributed to "room resonances".
A study of the situation reveals that the majority of serious problems are not, in fact, and strictly speaking, room resonance problems, but rather, boundary problems of cancellation and reinforcement. Even though the effects on performance are similar, the distinction is important because it indicates a quite different type of solution.
Room resonance problems cannot really be solved by any method other than physically changing the proportions and size of the room. Further, even mitigating the effects with equalizers can only be accomplished for one listener location, with the usual result of worsening the problems for other locations.
In contrast, boundary problems are fundamentally and importantly different. Boundary effects are substantially consistent throughout the room and therefore corrections are improvements for all locations. Also, the effects of nearby boundaries are predictable and therefore can be corrected without measurements.
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