What is the reason for tweeters wired out of phase?
Scooter49
Posts: 1
When I researched replacing the SL2000 tweeters in my Monitor 5JR+ speakers I came across the Polk crossover diagrams. It shows the tweeters wired with the speaker's ground wire connected to the tweeters + and the speaker's positive connected to the -. Reverse polarity from the woofer. Sure enough, that's just what I found inside. So I connected the new RD0194 tweeters just that way. Sounds great. Okay, I know, if it ain't broke don't fix it, but why the polarity change? What does this do? Also, if I plug in the crossover values for a 1st order filter (just the one inductor in series) using 8 ohms for the MW6503 woofer and 0.65 mH for the inductor I come up with around 2,280 Hz which seems reasonable. But the tweeter's 2nd order filter with 8 ohms for the RD2000, a 12 µF capacitor in series and 0.19 mH inductor in parallel just doesn't seem to work with the usual online X-over calculators. A Polk revision of the crossover for the SL2500 tweeter uses a 13.5 µF capacitor, and the same 0.19 mH. What's going here, any ideas?
Answers
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Ive opened up a few sets of the 5Jr and 5Jr+. They should have mw6502 from factory. They are 4 ohmDon't take experimental gene therapies from known eugenicists.
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It is due to phase response of the crossover. Some crossover designs cause the low frequency section to lag by 90 degrees while advancing the high frequency section by 90 degrees, for an overall 180 degree shift between LF and HF sections. Reversing the polarity of the tweeter section realigns the HF phase to the LF phase.Proud and loyal citizen of the Digital Domain and Solid State Country!
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Learn something new everyday.
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So, besides the Xover freq. point shift when using an 8 Ohm woofer in place of 4 Ohm, will there also be a phase shift?Don't take experimental gene therapies from known eugenicists.
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Its not related to the Ohm, its the 2nd order crossover. They usually have a 180 degree phase shift. https://en.wikipedia.org/wiki/Audio_crossover#Second_order.
On a side note the difference in the capacitor values for the SL2000 and SL2500, RD-0194 / RD-0198 are for crossover / attenuation between the two tweeters. What I find really strange is when you factor in the differences in crossovers between each 5 and 7 series for each tweeter vs. the 5jr+ for each tweeter. They all use the same MW and tweeter combos as I recall.
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Im familiar about the 2nd order rule, but wasnt sure on the ohm difference.
I learn something new myself.
I think the Xover diffs were the amalgamation of experimenting and supplies at the time. It wouldnt suprise me if an 8 ohm MW was thrown in to a batch lol.Don't take experimental gene therapies from known eugenicists. -
Hang on, are you saying that when I wire up a tweeter, I'm supposed to be connecting them with the ground wire to + and the signal wire to the unmarked post on the tweeter?Good music, a good source, and good power can make SDA's sing. Tubes make them dance.
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No. Tweeters only need to be connected out of phase if a particular speaker's crossover causes a 180 degree phase shift.Proud and loyal citizen of the Digital Domain and Solid State Country!
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http://www.livesoundint.com/archives/2003/july/align/align.php
This explains it quite well, maybe more than most want to know!
But partway down, it describes how you can measure the null and tell if it is truly wired correctly. -
WhewGood music, a good source, and good power can make SDA's sing. Tubes make them dance.
