nominal impedance missmatch of drivers

[SamClassA]

Just a quickie,
My tweeter is 4 ohms, my Midrange & Bass are 8 ohms. Do I need to add a resistor in series with the tweeter in the Filter circuit to balance the impedances?

[rabbitz]

Quick answer.....no.

[SamClassA]

lolol.....I love quick answers

Thanx

[Will]

Originally posted by SamClassA
Just a quickie,
My tweeter is 4 ohms, my Midrange & Bass are 8 ohms. Do I need to add a resistor in series with the tweeter in the Filter circuit to balance the impedances?

Long answer YES !
In your situation I can see 2 advantages in adding that resistor :
1) Tweets are usually more efficient, hence it serves as padding down the sensitivity
2) With higher impedance on the tweet, you'll find that you don't need that big of a cap to cross over (if compared to 4 ohms) - hence some cost savings here.

cheers.

[SamClassA]

Thanx Will...I thought I read that somewhere? and it sort of makes sense..... I asume a 4 ohm resistor in series with the 4 ohm Tweeter will do???

[Will]

It's more complex than just adding a 4 ohms resistor. I'd do this; add the resistor on the tweet till the sensitivity of the tweet matches your woofer. Bbest is to measure at around 3khz of the tweet and woofer. I assume that is your target x-over point; only then measure the final impedance of your tweeter (with the resistor in place) and then use that value to calculate your cross over values.

cheers.

[noodle_snacks]

as far as i am aware simply putting a resistor in series with a tweeter is a bad idea, my memory is a tad fuzzy at the moment but i believe it can have a negative effect on electrical dampening for the tweeter, leading to a peak before the low end roll off, unless you are doing so in order to try and match a target slope, l-pads are a better idea.

[SamClassA]

lol....let me see,.....so far we have, yes,....no.....maybe.....
try l-pads....not an exact science??? I wish life was easy....lol
As for l-pads...I dont see many loudspeakers useing them??
but thanks for your ideas...keep them coming.

[rabbitz]

The L-Pad that noodle_snacks is referring to is not one of those turn the knob things you see on some speakers. It's a dividing network of 2 resistors.... 1 in series and 1 in parallel to the tweeter.

Here's some basic info I have on my site and will give you some insight.
http://www.rzaudio.com/rz52/Crossover.htm

Each builder has their own preference and I've a preference for the single series resistor but other like the L-Pad.... they both have advantages and disadvantages. The disadvantage of the series resistor is that with each change it alters the impedance of the filter and so it has to be recalculated but makes tweaking quicker but an L-pad generally keeps the impedance constant but is a bit more fiddly when tweaking.

They both however do the same thing by reducing the SPL of the tweeter so it matches the woofer's SPL.

[SamClassA]

rabbitz.... very interesting and informative....thanx