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Geometric Crossover Points
Many are the different and conflicting views on crossover slopes and design. Several programs exist that crunch out the values for the capacitors and coils and resistors of a certain type of crossover. This program does not even attempt to get entangled in that jungle of complex crossover design and debate. Instead, what we have here is a program that helps you decide where the crossover points should be, not what the crossover topology should look like. It does this by calculating where a geometric division of the frequency range can be made. Basically, a geometric mean crossover point is one that equally divides the octave ranges between the drivers. In other words, it is a crossover point that divides the music spectrum into equal portions of octaves so that each driver does the same amount of range coverage (work). To divide the 20 Hz to 20 kHz range at 10,010 Hz, the result of adding 20 to 20k and dividing by two, is not fair, as the tweeter will only have to handle one octave while the woofer will have to handle nine octaves. Whereas, 640 Hz would give the woofer five octaves (20 to 40, 40 to 80, 80 to 160, 160 to 320, 320 to 640) and the tweeter five octaves (640 to 1280, 1280 to 2560, 2560 to 5120, 5120 to 10240, 10240 to 20480). Three-way crossovers can also follow a geometric ratio. The range of 20 Hz to 20 kHz can be divided into three even octave spans by crossing over at 200 Hz and 2,000 Hz, as 200/20 equals 2,000/200 equals 20,000/2,000.
Notch Filters
Often, a small adjustment to the frequency response of a loudspeaker needs to be made. A bump at kHz let's say. Here is where a contour network, also known as a notch filter, is handy. Audio Gadgets helps you design such a network by displaying the Q and attenuation of the network. It also works backwards: you specify the attenuation and it displays the network values.
The contour network is composed of a resistor and capacitor and inductor in parallel. This configuration defines a resonate tank circuit that will present the driver a higher impedance at the resonate frequency, which will decrease the driver's output at this frequency. The steepness of the impedance rise as it climbs toward the resonate frequency and the steepness of the falling of impedance as the frequency move up away from the resonate frequency is referred to as the "Q", which is a measure of the magnification of the resonance factor of the circuit. A high Q means that the circuit will sharply resonate at its resonant frequency. Whereas, the low Q circuit will have a much broader, rounder range of resonance. Ideally, we want a contour network's Q and degree of attenuation to be an inverse match of the peak in the loudspeaker's frequency response.
To design of a contour network with Audio Gadgets requires the impedance of the driver, the amount of attenuation needed, the frequency at which it should resonate, and some idea of how wide a spectrum of effect is needed.
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