2 way speaker ohm's question

[nukaidee]

I'm trying to build 2 drivers into a single box, does it matter if the woofer is a 8 ohm while the midrange is a 4ohm?

thanks

[Jonathan Bright]

Hi. The short answer is NO. No problems

There are other things to consider. The amp must be able to drive a 4ohm load. The cross-over tables you consult will need to give the appropriate value for the different impedences (i.e. 4 and 8).

Otherwise shouldn't be an issue.

[Richard Ellis]

No not really...
Remember speakers are designated as "8 Ohm"...but that really is an approximation as speakers are a dynamic thing. Speakers really have whats called an Impedence (Z).
The "rating" at eight ohms is kinda an average as the 'Impedence changes with frequency.
Provided your crossover is arranged OK the only other thing to consider is output level (SPL@1w,1M) at four Ohms , does it match the output of the woofer at eight ohms??
Recall the characteristics(Math) of a coil and a capacitor at differing frequencies....your coil will start to climb in ohms as frequencies go up, conversely you capacitor will climb in ohms as the frequency goes down....somewhere at your crossover frequency these two slopes will intersect.

1
Xc= --------------
6.28x frequency x Capacitance(microfarads)




Xl = 6.28 x frequency x Henries ( millihenries)


Take some graph paper & graph out some Impedences for your project.
_______________________________________Rick.......

[Cal Weldon]

Hi nukaidee, looks like you have your hands full again. On top of what Jonathan and Richard have said, remember that the midrange, if it has an open back, shouldn't go in the same box as a woofer. Why don't you post some driver info and what you are trying to do and maybe we can help. Is there a tweeter involved?

[nukaidee]

yeah I was worried about the open back hence all my posts all over the place. I was looking at the tang bang drivers..

5" sub http://www.parts-express.com/pdf/264-826s.pdf
and
3" bamboo mid/high http://www.parts-express.com/pdf/264-844.pdf

initially i wasn't even going to put in a cross over... but maybe i'll throw in a cheap one that cuts at 800hz.

My crude calculations are showing approximately a 4L box would be suitable for both the drivers, but I guess I'm also wondering do I need to build a "barrier" semi dividing the 2 drivers and I would really like to keep it small, so I don't want to double it up to 8L. Ported would work too I guess, but from what I see, ported boxes are bigger than sealed enclosures.

btw. I'll be driving these things with a single ended tube amp.