User manual ALPINE SWR-1221D

[. . . ] Before doing any electrical wiring, disconnect the cable from the negative (-) terminal of the battery. Arrange wiring and cables in compliance with the installation manual to prevent obstructions when driving. Cables or wiring that obstructs or hangs up on places such as the steering wheel, gear lever, brake pedals can be extremely hazardous. Do not install in locations which might create hazards for the vehicle occupants or hinder vehicle operation (such as the steering wheel or gear shift) by obstructing forward vision or hampering movement etc. [. . . ] Now as a part of that tradition, we welcome you to the great number of discerning audiophiles who own Alpine products. This manual has been prepared to help you maximize your enjoyment of the outstanding performance and features of your new Alpine SWR-304D/SWR-304E, SWR-1221D/SWR-254E subwoofer. This low frequency subwoofer incorporates many advanced technical and performance features. To realize the exceptional performance for which this product is capable, it is necessary that all signal sources, power amplifiers, and interconnects are of the highest sonic quality. we recommend Alpine head units , crossovers , amplifiers , satellite speakers , cables , and accessories. Due to the complexity of properly enclosing and installing subwoofers, we strongly recommend you have the SWR-304D/SWR-304E, SWR-1221D/SWR-254E installed by your authorized Alpine dealer. Please study this manual carefully to become acquainted with all the special features and capabilities of your new Alpine subwoofer. Should you have any questions, please contact your authorized Alpine dealer. dEFINITION OFTERMS: Resonance: Most objects vibrate naturally at certain frequencies. If you hang a weight on a spring, then pull it and let go, the weight will bob up and down at a certain frequency determined by the amount of mass and by the stiffness of the spring. Generally, Q denotes how well controlled the movement of the speaker cone is near resonance. " As you can see from the graph and table on page five, low frequency output decreases, because the amplifier has to push the speaker against a stiffer air spring. Simply decide whether you want a tight sound (low Q) or a boomy sound (high Q), then size the box accordingly (see table). Disadvantages : Compared to free air, a sealed box takes up more room in the trunk. For Qtc = 1 (a Chebyshev alignment), cone motion shows moderate ringing ; bass is slightly boomy. 707 (the Butterworth alignment), there is no ringing, giving a neutral bass quality. Many consider this the optimum sealed box, a good compromise between size and bass output, with good sound quality. Bass has a very tight, controlled sound, but some people may think it sounds "thin. Tips : To make the box act about 20% bigger than it is, use filling (stuffing). Stuff the box with one pound of polyester per cubic foot, or fill the box with fiberglass mats (loose fiberglass can get into the voice coil). Box volumes between those listed yield results in between what the graph and table show. VENTED (PORTED) BOXES : Adding a port to the box increases system complexity to 4th order (24dB per octave low and rolloff). [. . . ] Also, ported systems are much easier to get bad results from than a sealed box. Alignments : Ported boxes also have alignments, many more than the scope of this Guide. Very motivated individuals should look at the References for more information. Tips : Fb should be kept below the lowest bass note you want to reproduce. [. . . ]