User manual ALPINE SWR-304D

[. . . ] Avoid installing the unit in locations with high incidence of moisture or dust. Moisture or dust that penetrates into this unit may cause smoke or fire. Failure to make the correct connections can cause fire or accident to occur. Route the cables and wiring so as not be crimped by moving parts like seat rail or make contact with sharp or pointed spots which might damage the wiring. [. . . ] Alpine tests speakers at full power for 96 hours to confirm the mechanical toughness of each woofer. ENCLOSURES (BOXES) : Designing and building the best speaker enclosures takes time, tools, and know-how. If you don't have a lot of experience, consult a professional who has designed and built successful enclosures. : Subwoofers ideally work like a piston, moving air back and forth. If the woofer isn't enclosed, the sound just moves from the front to the back of the speaker, and you won't hear much bass. Tips : For best results, try to make the box rectangular instead of square, and mount the driver(s) off-center. Port ends should be spaced at least one diameter from any obstructions to breathe properly. If the speakers are not connected to the same amplifier channel, they should be in separate cavities. fREE AIR : Free air mounting uses the trunk as a "box. " Please note that rear hatch covers do not isolate very well and are not usually strong enough to support the weight of a subwoofer. advantages : Free air is easier , quicker , and cheaper. disadvantages : In most cars , the trunk leaks to the passenger compartment. Therefore, free air mounting will lose bass output compared to a boxed woofer. Since the woofer is not loaded by box air pressure, it handles less power. Tips : Reinforce the factory rear deck and seat back, and caulk any remaining openings to the passenger compartment. Of course, this can be more work than making a proper enclosure!SEALED BOXES : A sealed enclosure is just what it sounds like : a closed box around the woofer to isolate the front and rear sound waves from each other. It rolls off 2nd order (12 dB per octave) at low frequencies. How they work : The trapped air in the box adds stiffness to the speakers' own stiffness. This raises the resonance frequency and Q from free air values. The smaller the box, the stiffer the trapped air acts, and the more Qtc and Fc increase. Cone motion tends to "ring" (keep moving after the amplifier signal stops) more because the box is "springier. [. . . ] The graph above shows some ported designs, as a starting point to experiment from if you wish. SPEAKER OUTPUT: Sound pressure level (SPL) is determined by how much air the woofer moves. This is set by the woofer's surface area Sd and by its excursion (motion back and forth). Maximum output at low frequencies is set only by the woofer's excursion (movement)capacity, since most amplifiers have enough power to drive most woofers to full excursion at low frequencies. [. . . ]