User manual JBL 1800GTI

[. . . ] The cone motion is controlled by a synthetic rip-stop suspension which resists tearing for safe, effortless high-power use. The cone is driven by a massive motor structure utilizing a 3" or 4" edge-wound OFC copper wire, high temperature fiberglass, voice coil. This motor structure includes JBL's patented Symmetrical Field Geometry (SFG) to create a uniform magnetic flux field through the coil and thus lower distortion. The frame and cone are contained in a high strength die-cast aluminum frame for maximum rigidity and higher magnetic energy concentration on the coil. [. . . ] This adds a significant bass reinforcement to the actual output of the subwoofer. If this rise in bass is not addressed in the design of your enclosure, bass performance may be boosted to the point where it is actually too strong for some tastes. The enclosure design recommendations which appear on the specificaNormalized Amplitude Response (dB/Hz) dB 6 0 ­6 ­12 ­18 ­24 ­30 ­36 5 Hz 10 50 100 Frequency 500 Enclosure-only response with Standard "Optimum" Tuning (42Hz) In Car Response Curve Vehicle Transfer Function tion sheet for your particular model, were chosen for optimum in-car performance. You may find them to be different than the recommendations from formulas used to design enclosures for in-home or professional sound-reinforcement applications. These "Transfer Function Compensated" tuning recommendations result in small enclosures with excellent in-car low frequency performance. Normalized Amplitude Response (dB/Hz) dB 6 0 ­6 ­12 ­18 ­24 ­30 ­36 5 Hz 10 50 100 Frequency Enclosure-only response Transfer Function Compensated Tuning (33Hz) In Car Response Curve Vehicle Transfer Function JBL SpeakerShop 1. 0 500 1000 2000 This graph shows the result of tuning the enclosure to compensate for the effects of the vehicle transfer function. Note that the in-car response is smoother and the ­3dB point moves down to approximately 22Hz. Normalized Amplitude Response (dB/Hz) JBL SpeakerShop 1. 0 JBL SpeakerShop 1. 0 dB 6 0 ­6 ­12 ­18 ­24 ­30 ­36 In Car Response with Transfer Function Compensated Tuning In Car Response with Standard Tuning 5 Hz 10 50 1000 2000 100 Frequency 500 1000 2000 This graph shows the effect of vehicle transfer function added to an enclosure using "standard" tuning. Note the peak at 50Hz, with a ­3dB point of approximately 31Hz. This is a comparison of in-car response curves with and without transfer function compensated tuning. 4 Enclosure Design Follow the simple steps below to design an optimum ported box for your GTi driver. Determine the maximum enclosure size available for your installation by measuring and multiplying the height x width x depth (in inches) and then dividing by 1728. This will tell you exactly how many cubic feet your enclosure will be. To determine the volume of an irregularly shaped box, divide the box into sections, calculate the volume of each section individually, then add the separate volumes to determine the total box volume. Here are some useful formulas to help you calculate volumes: USEFUL FORMULAS 1 cubic foot = 1728 cubic inches 1 cubic foot = 28. 32 liters 1 liter = 0. 353 cubic feet = 61 cubic inches = 1000cm3 Radius = 1/2 diameter Box volume = height x width x depth Volume of triangular box section = 1/2 base x height x length Volume of tubular duct = area of circle x length pi () = 3. 1416 Area of circle = pi () x radius2 Diameter of circle = 2 x area / pi () Area of square = height x width 3. Now that you have calculated the internal box volume, you should subtract the DRIVER DISPLACEMENT (listed on the specification sheet) while also subtracting approximately 0. 1 cubic feet for the port tube (if one is being used). If you'd like, you may calculate the exact displacement of the port tube by utilizing the formula listed above (Volume of tubular duct). Using the GTi Enclosure chart (shown on your GTi driver specification sheet), choose a desired box volume on the vertical chart axis, which fits within the size limit you have established. Draw a line across from this point until it intersects the recommended tuning frequency. Draw a line down to the horizontal axis and read the corresponding tuning frequency. Use the Port Nomograph on the Driver Specification sheet to determine the port diameter and length based on the enclosure volume and tuning frequency determined in step 4. Follow these steps to determine the port. 2. Draw a horizontal line starting from the construction point straight through the chart. Note that the Lv/Sv axis also appears at the right of the chart to help keep your line parallel all the way across the chart. Select the curved line with the port diameter you would like to use. Locate the point where this curved line intersects with your horizontal construction line and draw a vertical line from this point down to the bottom of the chart. NOTE: Try to use a port tube no smaller than 1/3 the diameter of your speaker. [. . . ] Fiberglass Application - Apply a 1" blanket of fiberglass or polyester to interior walls (except the baffle board) of all vented enclosures. For sealed enclosures (no ports) fill the entire volume with fiberglass or polyester (12-16 oz. If you do not wish to use damping material then make the box size 10% larger than recommended by the graphs. Ports - Construct port tubes from PVC pipe or cardboard tubing with a wall thickness of at least 1/16". [. . . ]