108 lines
7.0 KiB
Plaintext
108 lines
7.0 KiB
Plaintext
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HIGH-LEVEL 12 dB/OCTAVE CROSSOVER DESIGN CHART
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Values selected for typical loudspeakers
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and their associated impedance characteristics.
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FREQUENCY 4 OHMS 8 OHMS 16 OHMS
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in Hz CAP. COIL CAP. COIL CAP. COIL
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|---------------|-------------------|-------------------|-------------------|
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| 50 | 564 18 | 283 36 | 141 72 |
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| 60 | 472 15 | 236 30 | 118 60 |
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| 70 | 400 12.8 | 200 25.7 | 100 51.4 |
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| 80 | 354 11.3 | 177 22.6 | 88.4 45.2 |
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| 90 | 313 10 | 156 20 | 78.1 40 |
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| 100 | 283 9.0 | 141 18 | 70.7 36 |
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| 120 | 236 7.5 | 118 15 | 59 30 |
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| 150 | 188 6.0 | 94.5 12 | 42.2 24 |
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| 200 | 141 4.5 | 71 9.0 | 35.4 18 |
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| 250 | 113 3.6 | 56.4 7.2 | 28.3 14.4 |
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| 300 | 94.5 3.0 | 47.2 6.0 | 23.6 12.0 |
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| 350 | 80.5 2.57 | 40.3 5.14 | 20.1 10.3 |
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| 400 | 71 2.26 | 35.4 4.52 | 17.7 9.0 |
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| 450 | 62.5 2.0 | 31.3 4.0 | 15.6 8.0 |
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| 500 | 56.4 1.8 | 28.3 3.6 | 14.1 7.2 |
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| 550 | 51.3 1.64 | 25.6 3.28 | 12.8 6.56 |
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| 600 | 47.2 1.5 | 23.6 3.0 | 11.8 6.0 |
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| 700 | 40 1.28 | 20 2.57 | 10 5.14 |
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| 800 | 35.4 1.13 | 17.7 2.26 | 8.8 4.52 |
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| 900 | 31.3 1.0 | 15.6 2.0 | 7.81 4.0 |
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| 1000 | 28.3 0.9 | 14.1 1.8 | 7.07 3.6 |
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| 1200 | 23.6 0.75 | 11.8 1.5 | 5.9 3.0 |
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| 1500 | 18.8 0.6 | 9.45 1.2 | 4.22 2.4 |
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| 2000 | 14.1 0.45 | 7.1 0.9 | 3.55 1.8 |
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| 2500 | 11.3 0.36 | 5.64 0.72 | 2.83 1.44 |
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| 3000 | 9.45 0.3 | 4.72 0.6 | 2.36 1.2 |
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| 3500 | 8.05 0.26 | 4.0 0.5 | 2.0 1.0 |
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| 4000 | 7.1 0.22 | 3.55 0.45 | 1.77 0.9 |
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| 4500 | 6.25 0.2 | 3.13 0.4 | 1.56 0.8 |
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| 5000 | 5.64 0.18 | 2.83 0.36 | 1.41 0.72 |
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| 5500 | 5.13 0.16 | 2.56 0.33 | 1.28 0.66 |
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| 6000 | 4.72 0.15 | 2.36 0.3 | 1.18 0.6 |
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| 7000 | 4.0 0.13 | 2.0 0.26 | 1.0 0.5 |
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| 8000 | 3.55 0.11 | 1.8 0.23 | 0.88 0.45 |
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| 9000 | 3.13 0.1 | 1.56 0.2 | 0.78 0.4 |
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| 10000 | 2.83 0.09 | 1.41 0.18 | 0.71 0.36 |
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-----------------------------------------------------------------------------
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All capacitor values are in microfarads ( uF ).
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All coil values are in millihenrys ( mH ).
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NOTE: as the chart shows, values scale up and down directly, in
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octaves, for changes in impedance of half or double, and by factors of
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ten for frequency factors of ten. To determine crossover points higher
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or lower than those shown on the chart, select the proper impedance (4,
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8, or 16 ohms) then look up the frequency in the left column that is
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ten times or one tenth of your desired frequency and simply move the
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decimal points to the right or to the left to determine the correct
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values. Higher frequencies require moving the decimal points to the
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left, and lower frequencies require moving the decimal points to the
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right.
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EXAMPLE: 8-ohm crossover for 80 Hz subwoofer will require a 177 uF
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capacitor and a 22.6 mH coil.
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CROSSOVER INDUCTORS
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Wire gauges used for winding air-core inductors should be chosen
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so that crossover-associated power losses are minimized. Look at the
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wire table to get an idea of the approximate added resistance you will
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have when using a particular wire gauge to wind inductors. This added
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resistance not only spoils amplifier damping factors, but can also de-
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tune vented low frequency loudspeaker systems. Use the heaviest gauge
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double formvar insulated wire possible for winding inductors. If you
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are buying ready-made inductors, don't be misled; the coil in the 80 Hz
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subwoofer example above would be 100-200 mm (4"-8") in diameter and
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weigh from 2 to 8 kg (4-16 lb) depending on wire gauge. An RF coil
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designed for use in radios may have the same inductance (at high
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frequencies) and be wound on a pencil-sized bobbin with fine wire.
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This type of inductor will definitely not work in a crossover with
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loudspeaker loads connected.
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Make sure your coils are wound tightly with neatly stacked layers
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which produce a winding cross section that is approximately square.
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The bobbin used to wind coils for crossovers should have an inside coil
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diameter which is twice the coil width or thickness, and the outside
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coil diameter should be wound out to four times the coil's width, or
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twice the inside diameter. After winding, saturate the coil in laquer
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or resin. After drying, wrap it with stretchable cloth tape and give
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it another coat of laquer. Keeping the layers stacked neatly and the
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coil cross section square, helps minimize the wire resistance for a
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given inductor value.
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Use a mounting board made of non-magnetic material such as
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masonite or plywood. Place coils on your crossover mounting board so
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that all coils are facing each other at right angles to minimize
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magnetic inductive coupling. Some distance between coils helps reduce
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coupling also. Keep any coils away from large metal surfaces. Place
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insulating tubing over coil leadout wires to prevent shorts in case of
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speaker system vibration. On long leadout wires, clamps or blobs of
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hot glue should be used to dress wires securely to the mounting board.
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CROSSOVER CAPACITORS
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Capacitors used in crossovers MUST BE NON-POLARIZED and for best
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sound must have low self-inductance. High-quality 100-200 volt rated,
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foil wound Mylar capacitors should be used and should be individually
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parallelled by 0.01 microfarad polypropylene or polystyrene capacitors
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to short out the high-frequency self-inductance of coil formed by the
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many layers of foil winding inside. Capacitors should be placed on the
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crossover mounting board away from heat-producing power resistors.
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Capacitor placement is not critical in terms of electrical operation of
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the crossover, however, capacitors should be attached so that speaker
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system vibration will not break their leads by bending and metal
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fatigue.
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