Frzninvt Posted August 11, 2006 Share Posted August 11, 2006 I used to have a formula to calculate passive cutoff frequency based on the total capacitance value, ohm load, and driver diameter but do not remember how. Here is the situation I have a 4 ohm load (2-way plate speaker with a 4" woofer and 1" dome tweeter) I am using a total 44uf (40uf electrolytic bypassed with two 2uf Kimbers Kaps) what is my effective cutoff frequency I am hoping that it is in the 500-700Hz range. Help! Quote Link to comment Share on other sites More sharing options...
Guest " " Posted August 11, 2006 Share Posted August 11, 2006 easy what is the impedance of the tweeter what is the impedance of the woofer need individual values assume t=6 ohms w=4 ohms c1=44uf l1=? cutoff=? l1 is 1.06 and cutoff is 600hz http://www.carstereo.com/help/Articles.cfm?id=55 assume t=8 w=8 cutoff would be 450hz c1=44 l1=2.8 would need actual impedance for T and W to verify Quote Link to comment Share on other sites More sharing options...
Frzninvt Posted August 11, 2006 Author Share Posted August 11, 2006 The impedance of the plate as a whole (both drivers) is 4 ohm. I am reasonably sure the woofer and tweeter are both 4 ohms but they are hooked to a passive two-way network which should present a 4 ohm load at the input. Maybe it makes more sense that they are 8 ohms each and yield a 4 ohm load when connected in parallel to the network. The caps are in line preceding the connection to the two-way passive network to limit frequency prior to the crossover. Based on your calculations though it appears I am in the ballpark of where I wanted to be in 450-600Hz and up range. Thanks! Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 15, 2006 Share Posted August 15, 2006 Two 8 ohm drivers connected in parallel are only going to present a 4ohm load where there is crossover overlap (the tweeter crossing over lower than the low-pass on the woofer). So they're probably 4ohm load speakers. Here's a good reference for first and second order networks: http://colomar.com/Shavano/construction.html (It's the 3rd section down from the top). Quote Link to comment Share on other sites More sharing options...
DrWho Posted August 15, 2006 Share Posted August 15, 2006 Here's an excerpt from the website that describes it better than I just did: ======================================================= What happens to the Impedance? Am I putting speakers in Parallel? If you pick the same cross-over points for both the high-pass and the low-pass filter, then when you connect these together to the same power amp output, the impedance is the same as if it was a single speaker. Why is this? Since the speakers are now conducting on a limited frequency range, as long as those ranges do not overlap, the net effect (as far as your power amp can tell) is that its only a single speaker load. You are not putting speakers in parallel. Cross-overs always overlap as the power to the individual speakers roll off, however this roll off is generally equal to the gain as one speaker starts conducting more, the other conducts less. The speakers are now made frequency specific. Sound, being a complex waveform, can have components of highs and lows at the same time - cross-overs simply split those components out onto seperate speaksers without altering the load. If you use badly matched cross-over points, you can have overlap - in those cases, the overlapped frequency is like wiring the speakers in parallel, but only for that frequency range. For Low frequencies, this will be quite a strain on your power amp. ======================================================= http://colomar.com/Shavano/crossover12db.html Quote Link to comment Share on other sites More sharing options...
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