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Active vs. Passive: An attempt by me to explain
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<blockquote data-quote="thch" data-source="post: 1555340" data-attributes="member: 562032"><p>actually, i've never heard that term used.</p><p></p><p>bessel filters are filters that have coefficients based upon bessel polynomials. the result is a filter where the phase response is fairly linear -- giving a simple delay that is constant for all frequencies. (actually not true, but the bessel filter is the best for constant delay).</p><p></p><p>the speaker has an impedance that can affect the passive crossover. there exists a few solutions to the common problems.</p><p></p><p>the easy solution is to place a resistance in parallel with the speaker. if you place a 4ohm resistor in parallel with a 4ohm speaker, the impedance will be between 2 and 4ohms. but this uses a lot of power (the resistor gets equal or more power then the speaker).</p><p></p><p>the other solution is to use a resonantor to effectively place a resistor in parallel with the speaker, but only at one frequency. the idea is to place the resistor in parallel with the speaker only when the speaker has a high impedance and thus to remove the speaker's high impedance, at least as far as the amp/crossover is concerned.</p><p></p><p>speakers also have an inductance. so a "zobel" network is sometimes added in parallel with the speaker to basically place a lower and lower value resistor in parallel such that the parallel combination of the inductive speaker and capactive zobel ends up with a constant impedance.</p></blockquote><p></p>
[QUOTE="thch, post: 1555340, member: 562032"] actually, i've never heard that term used. bessel filters are filters that have coefficients based upon bessel polynomials. the result is a filter where the phase response is fairly linear -- giving a simple delay that is constant for all frequencies. (actually not true, but the bessel filter is the best for constant delay). the speaker has an impedance that can affect the passive crossover. there exists a few solutions to the common problems. the easy solution is to place a resistance in parallel with the speaker. if you place a 4ohm resistor in parallel with a 4ohm speaker, the impedance will be between 2 and 4ohms. but this uses a lot of power (the resistor gets equal or more power then the speaker). the other solution is to use a resonantor to effectively place a resistor in parallel with the speaker, but only at one frequency. the idea is to place the resistor in parallel with the speaker only when the speaker has a high impedance and thus to remove the speaker's high impedance, at least as far as the amp/crossover is concerned. speakers also have an inductance. so a "zobel" network is sometimes added in parallel with the speaker to basically place a lower and lower value resistor in parallel such that the parallel combination of the inductive speaker and capactive zobel ends up with a constant impedance. [/QUOTE]
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