Cross-over basics ...

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Intro - why the need for crossovers ?The frequency range of human hearing spans from about 20 Hz to 20,000 Hz (20 kHz); likewise, the music we produce and enjoy contains audio information over approximately the same range. Now, in order to accurately reproduce this musical information it is necessary for the loudspeaker system (and the other components in the signal path) to reproduce the full spectrum.Unfortunately, most loudspeaker drivers are incapable of accurately reproducing the entire 20 Hz to 20 kHz spectrum. This is because the characteristics that make a driver good for reproducing one frequency extreme make it unsuitable at the other extreme. For example, good low-frequency drivers need to be rather large in order to move a lot of air; but high-frequency drivers need to be small to maintain a wide radiationpattern at the highest frequencies. This means that good low-frequency reproducers tend to perform poorly on highs and good high-frequency reproducers tend to perform poorly on lows. For high quality audio reproduction we are left with hardly any choice other than to use separate drivers to reproduce the frequency extremes.In combining several loudspeaker drivers into a system, our goal is to obtain an accurate (that is, "flat") response across the complete audio spectrum hence the need for CROSSOVERS.What does it do ?Crossover functions - The primary objective is to protect the speakers from frequencies it cannot handle. PERIOD. Secondary objective may be used to gain advanced "control" over the sound that it is "allowed" to produce.Car Audio Crossover - how does it work ?The crossover's purpose is to divide the music signal by frequency and send these frequencies to components "downstream" of the crossover. For example, in a system with a two-way component set and a subwoofer the crossover would send the low frequencies to the subwoofer's amplifier and the high frequencies to the component speaker amplifier(s). The crossover consists of a pair of electrical filters which modify the frequency response of the signals applied to the drivers. The full-spectrum signal passes through a "high-pass filter" on the way to the tweeter while the signal to the woofer passes through a complementary "low-pass filter." The high-pass filter passes information above a selected frequency, referred to as the "crossover frequency," and attenuates the components of the signal which fall below the crossover frequency. Similarly, the low-pass filter passes information below the crossover frequency and attenuates frequency components above the crossover frequency.An easy way to understand the crossover is to imagine an ideal pair of filters which direct all the musical information above the crossover frequency, say 1 kHz, to the tweeter, and directs all the information below 1 kHz to the woofer. When full-spectrum music is applied to the system, the woofer would reproduce everything below 1 kHz and the tweeter would reproduce everything above 1 kHz. Because the overlap in the response of the drivers has been eliminated, the system will exhibit a smooth transition from the woofer to the tweeter. The difference between real crossovers and this ideal crossover is that a real high-pass filter passes some of the information below the crossover frequency to the tweeter. Likewise, a real low-pass filter will pass some of the information above the crossover frequency to the woofer. The further a frequency is from the crossover point the less information is passed to the "wrong" driver.Slope of the CrossoverWhen any crossover splits the frequencies it is not a hard split. At the crossover frequency in a 2-way crossover both outputs will have this frequency in the output albeit at a lower level. How fast the crossover transitions from one output with rising frequency to another is called the slope of the crossover. There are many interchangable terms for crossovers. A 1st order crossovers transitions at 6dB/octave or 10dB/decade. A 2nd order one will transition twice as quickly. For tweeters a minimum of a 2nd order crossover should be use in order to prevent the tweeter from seeing any bass frequencies. 4th order crossovers are common and digital crossovers of any order are possible but expensive. Use at least a 2nd order crossover to be safe. For an example of tweeter safety, say we want to use a high pass crossover frequency of 2kHz. With a 1st order crossover (or filter) at 1kHz the level is only down by 6dB and only down by 12dB at 500Hz. 500Hz is way too low for a tweeter to play so this will probably cause the tweeter to distort or blow up. Using a 2nd order filter would have the output down by 24dB which would be a signficant improvement. 3rd and 4th order filters are even better but expensive. Also analog crossovers change the phase response so try wiring your tweeter out of phase to see if it makes the sound better or worse and leave it the way it sounds better to you. *** Credits : IASCA MALAYSIA/caraudiohelp.com/trueaudio.com ***