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<blockquote data-quote="highfigh" data-source="post: 8895311" data-attributes="member: 691685">That was for amps which were designed for it and usually, it was called &#039;tri-mode&#039;, IIRC. It used a coil to cross the sub over and a cap for each High Pass speaker/component. That prevents a direct connection across the whole bandwidth and prevents the impedance dropping because the frequency bands don&#039;t/shouldn&#039;t overlap. Speakers, especially woofers, have a complex impedance curve and on top of that is what&#039;s called &#039;phase angle&#039;. The latter is where some ams run into trouble because as a speaker&#039;s impedance decreases with frequency going up, it&#039;s in the capacitive phase and as the impedance increases as the frequency goes up, it&#039;s in the inductive phase. If the slope of the curve is too steep, amplifiers can oscillate, some won&#039;t provide full output power and some will just puke. When I was still doing car audio in the late-&#039;90s, Rockford-Fosgate training included the explanation of this, as well as the test results using the &#039;Power Cube&#039; system- this showed power output with straight resistance, as well as the capacitive and inductive phases- their amps were very consistent across the range, many amps were almost useless when the inductance was high- if I still have the info, I&#039;ll post photos of the results. IIRC, one of the reasons the Rockford-Fosgate amps did well is because their power supplies weren&#039;t highly regulated, so they can also provide a lot more dynamic power output.</blockquote>

[QUOTE="highfigh, post: 8895311, member: 691685"] That was for amps which were designed for it and usually, it was called 'tri-mode', IIRC. It used a coil to cross the sub over and a cap for each High Pass speaker/component. That prevents a direct connection across the whole bandwidth and prevents the impedance dropping because the frequency bands don't/shouldn't overlap. Speakers, especially woofers, have a complex impedance curve and on top of that is what's called 'phase angle'. The latter is where some ams run into trouble because as a speaker's impedance decreases with frequency going up, it's in the capacitive phase and as the impedance increases as the frequency goes up, it's in the inductive phase. If the slope of the curve is too steep, amplifiers can oscillate, some won't provide full output power and some will just puke. When I was still doing car audio in the late-'90s, Rockford-Fosgate training included the explanation of this, as well as the test results using the 'Power Cube' system- this showed power output with straight resistance, as well as the capacitive and inductive phases- their amps were very consistent across the range, many amps were almost useless when the inductance was high- if I still have the info, I'll post photos of the results. IIRC, one of the reasons the Rockford-Fosgate amps did well is because their power supplies weren't highly regulated, so they can also provide a lot more dynamic power output. [/QUOTE]

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