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MultiWay Conventional loudspeakers with crossovers 

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23rd May 2005, 05:27 PM  #1 
diyAudio Member
Join Date: Feb 2005
Location: Kaleefornia

Ohms wiring question: How does the tweeter fit in?
I'm getting ready to order some speakers for my first diy project and am wondering how the tweeters fit into the whole ohms equation, (I know, really basic question). I need between 68 ohms total and was planning on some MTM's using two 4 ohm Dayton or Vifa woofers, wired series to get 8 ohm. Ok, what about the tweeter, how does that affect things? Do I need two 8 ohm woofers wired series (16 ohm) and then a 4 ohm tweet wired parallel to add up to 8 ohm? Again I know, a really basic question but I haven't been able to find an answer anywhere.

23rd May 2005, 05:37 PM  #2 
diyAudio Member

There will be a capacitor in series with the tweeter, so its resistance will read as an open circuit; putting the capacitor and tweeter in parallel with the woofer (and its inductor) will make for a net 8ohm load.
Read about crossoversread a LOT about crossovers. That should answer your questions. 
23rd May 2005, 05:52 PM  #3 
diyAudio Member
Join Date: Feb 2005
Location: Kaleefornia

Thanks! I'm planning on using someone else's design for the first time out and have been reading a ton about crossovers but haven't found a whole lot of info as to how it actually translates into loads. So I'd be fine with two 4ohm woofers and an 8ohm tweeter then?

23rd May 2005, 06:05 PM  #4  
Warp Engineer
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Yes.
__________________
 Dan 

23rd May 2005, 06:07 PM  #5 
diyAudio Member

Yes. 2 4ohm woofers in series, and an 8ohm tweeter, would be just fine.
What you have to understand is that the resistance you measure with your multimeter is DC resistance; but your amplifier sends out AC signals. So you have to keep track of what the impedance of the speaker is at and frequency you expect the amplifier to reproduce. In a very simple example, you put an inductor in series with the woofer, and a capacitor in series with the tweeter, then hook those two circuits up in parallel. The inductor's impedance goes up with frequency, and the capacitor's impedance goes down. So, as far as the amplifier is concerned, the tweeter is 8 ohms, but only above the crossover frequency, and the woofer is only 8 ohms below the crossover frequency, and the combined load is about 8 ohms over the whole frequency spectrum. 8 + 8 = 8. (And it works, too!) 
23rd May 2005, 06:09 PM  #6 
diyAudio Member
Join Date: Oct 2004

Also, keep in mind that the impedance of the tweeter will only be a factor above the crossover frequency.
When doing MTM systems, I have always preferred to use two 8 Ohm drivers wired in parallel for 4 Ohms and increased efficiency. Larry 
23rd May 2005, 06:22 PM  #7 
diyAudio Member
Join Date: Jun 2001
Location: Eugene, OR

If you are building some existing design you will need to follow it exactly: same woofers, tweeter, crossover and hookup. So, what do you mean Dayton or Vifa? You don't have a choice but to use what they used.
Your question on crossover, then, becomes meaningless. Your only concern is whether the impedance of the systems falls into the 68 ohm range that you have somehow determined is acceptable. 
23rd May 2005, 06:49 PM  #8 
diyAudio Member
Join Date: Feb 2005
Location: Kaleefornia

I've seen a few different plans, some using Daytons and some using Vifas. I'll probably do the Daytons based purely on cost for the first time out. And as far as the load, it's what my receiver requires. I really don't have an interest in putting a few 4ohm speakers on an amp that likes only 68ohm loads. Thanks for the input guys!

23rd May 2005, 07:20 PM  #9  
Speakerholic
diyAudio Moderator

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