| Re: 4pi build and questions [message #89212 is a reply to message #89201] |
Wed, 14 November 2018 16:36   |
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Wayne Parham
Messages: 18683
Registered: January 2001
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Illuminati (33rd Degree) |
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There are two things to consider when substituting a driver with different impedance:
1. Voltage sensitivity
2. Reactive load
The voltage sensitivity is the easier of the two to understand. You need to match the SPL of the woofer and the tweeter at a given drive voltage. If their load impedances are different, then each will receive a different amount of power, because power is a function of the reciprocal of resistance (V2/R). So you have to match their sensitivity at a given voltage level, rather than to consider their W/M output levels. Or to make a long store short, if you substitute a 16Ω driver for a design that called for an 8Ω driver, then you must understand the 16Ω part will dissipate half the power of the 8Ω part at any given voltage level. So the 16Ω part will be 3dB lower than the 8Ω part, and you must compensate for that in the crossover. A 2226J generates about 95dB/2.83v/M whereas the 2226H generates 98dB/2.83v/M. Both parts generate 98dB/W/M, but the drive level to dissipate one watt is different.
The load presented to the reactive parts in the crossover is different, so the components must be scaled. Generally speaking, if the load impedance is doubled, then the inductance of the coils should be doubled and the capacitance should be halved. But this is not always exactly the case, so it's best to verify with testing.
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