JBL GTiAutomotive Application And Installation Manual
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ure Designlow the simple steps below to design anported box for your GTi driver.ine the maximum enclosure sizeble for your installation by measuringultiplying the height x width x depth (in) and then dividing by 1728. This will tellactly how many cubic feet your enclosure.ermine the volume of an irregularlyd box, divide the box into sections, calcu-e volume of each section individually, thene separate volumes to determine the totallume. Here are some useful formulas toou calculate volumes:FORMULASoot = 1728 cubic inchesoot = 28.32 liters0.353 cubic feet = 61 cubiches = 1000cm31/2 diameterme = height x width x depthof triangular box section = 1/2 base xght x lengthof tubular duct = area of circle x length.1416ircle = pi (π) x radius 2r of circle = 2 x area / pi (π)quare = height x width3. Now that you have calculated the internal boxvolume, you should subtract the DRIVER DIS-PLACEMENT (listed on the specification sheet)while also subtracting approximately 0.1 cubicfeet for the port tube (if one is being used). Ifyou’d like, you may calculate the exact dis-placement of the port tube by utilizing the for-mula listed above (Volume of tubular duct).4. Using the GTi Enclosure chart (shown on yourGTi driver specification sheet), choose a desiredbox volume on the vertical chart axis, which fitswithin the size limit you have established. Drawa line across from this point until it intersects therecommended tuning frequency. Draw a linedown to the horizontal axis and read the corre-sponding tuning frequency. We have drawn anexample on the chart.5. Use the Port Nomograph on the Driver Specifica-tion sheet to determine the port diameter andlength based on the enclosure volume and tuningfrequency determined in step 4. Follow thesesteps to determine the port.Port Dimension Calculation1. Draw a line from the chosen enclosure volume tothe desired tuning frequency. Continue this lineuntil it intersects with the Lv/Sv construction line(Lv = port length, Sv = port opening surfacearea). This is called the construction point.2. Draw a horizontal line starting from the con-struction point straight through the chart. Notethat the Lv/Sv axis also appears at the right ofthe chart to help keep your line parallel all theway across the chart.3. Select the curved line with the port diameteryou would like to use. Locate the point wherethis curved line intersects with your horizontalconstruction line and draw a vertical line fromthis point down to the bottom of the chart.NOTE: Try to use a port tube no smaller than 1/3 thediameter of your speaker. Using a smaller diameterport can result in “whistling” or “breathing” noises.4. The required port length is found at the pointwhere the vertical line you’ve drawn intersectswith the scale at the bottom of the chart.NOTE: The recommended port tube dimensionsshould be considered a starting point. Since it isimpossible to predict “in-car” response exactly, youmay find that a port length slightly longer or shorterthan that recommended may produce slightly betterresults. Experiment!Lay out plans for your box using the informationdetermined in the above steps and the box con-struction tips listed on page 6.5 |
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