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MultiWay Conventional loudspeakers with crossovers 

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4th June 2011, 12:25 AM  #1 
diyAudio Member
Join Date: Apr 2011

what effect does a 4 driver have on an 8 ohm crossover?
in general terms, when using a 4 ohm driver in a system that has an 8 ohm x over, what does that do to x over points/volume/anything else?
in general terms ? 
4th June 2011, 12:37 AM  #2 
diyAudio Moderator R.I.P.

in general ?
depends on whether its a tweeter or woofer, or mid in other words, high pass or low pass series inductor reacts as if twice as big, thus cuts lower series caps on a tweeter reacts the opposite, and like it was smaller and so on simpler low impedance results in smaller series inductor(low pass) high impedance results in smaller series cap(high pass) 
4th June 2011, 12:44 AM  #3  
diyAudio Member
Join Date: Apr 2011

lol, i *almost* understood that
im using one of these in a recent build, DIAMOND 2 WAY STEREO PASSIVE SUBWOOFER CROSSOVER S @NEW  eBay when i connected my (4) subwoofers, each pair was about 3.9 ohms. i think they should have been 8 ohms / pair? sounds good, just wondering whats actually xed over where ?? Quote:


4th June 2011, 01:45 AM  #4 
frugalphile(tm)
diyAudio Moderator

In general terms it just doesn't work... have you got an off the shelf generic XO? Usually they just don't work.
dave
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4th June 2011, 03:17 AM  #5 
diyAudio Member
Join Date: Jul 2008
Location: Malaysia

Say you have a 4ohm driver and use a 2 way 4ohm crossover which rolls off at 12db/oct @ 2000Hz. If you use the same crossover for an 8ohm speaker, both the tweeter and woofer will start rolling off earlier (eg 4000Hz and 1000Hz) respectively so you will be left with a "hole" in the midrange.

4th June 2011, 04:06 AM  #6  
diyAudio Member
Join Date: Apr 2011

Quote:
im guessing theres plenty of variables (impedance rise etc) in there, but thats a good simple general explanation, thank you. so looking at the crossover im using (posted above) it looks like the subwoofer xover is 150 @ 12db with an 8 ohm driver, im using (4) 6 (approx) ohm drivers, each pair wired for 3.9, so the sub is now crossed at 75 hz not 150, and i have a gap from 75150 approximately + variables. im going to wire the subs for 12 ohms tomorrow and see what that sounds like, its easier for me to listen then think Last edited by 60ndown; 4th June 2011 at 04:14 AM. 

4th June 2011, 05:02 AM  #7  
diyAudio Member
Join Date: Feb 2003
Location: Jakarta

Quote:
Volume will be higher (thus better subjective quality). This is because the power is approximately doubled. Formula are V=IR, P=VI. V is the signal from your amp. With the same V, if you half the R, I will be doubled, hence also P. System minimum impedance will be lower, probably around 1 ohm. Lets say if with 8ohm subwoofer minimum impedance is 4 ohm, with 4ohm subwoofer it could reach 3 ohm. Your amplifier will work harder. Probability to fail (at high volume) is higher. 

4th June 2011, 02:27 PM  #8  
diyAudio Member
Join Date: Apr 2011

very nice, thank you.
Quote:


4th June 2011, 02:44 PM  #9 
diyAudio Moderator R.I.P.

that is correct
not saying it will function 100% correctly tho it will start rolling off a bit earlier but maybe also more 'shallow' due to paralel caps now smaller, in relative terms but for a sub filter, it might be even better this way anyway, very low cut passive xo tend to roll off later than 'expected' woofer/box low ressonance make it almost impossible to achieve very low xo point with passive xo meaning, trafo inductors would need to be massive and looking at actual inductors used here, the 150hz claimed is very unlikely to happen but the chance is definately better now, with low impedance woofers 
4th June 2011, 03:11 PM  #10 
diyAudio Member
Join Date: Apr 2011

sometimes i just get lucky

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