6 Ohm Woofer & 8 Ohm Tweeter

[stoodood]

Hi,

Has anyone had any experience (or possess the knowledge for an educated opinion) regarding matching different impedance drivers, via a crossover circuit - e.g. 6 Ohm woofer & 8 Ohm tweeter (or vice-versa)

I know impedances alter with frequency so could I get an unlucky mismatch or a lucky match or ……… “is 6 Ohm and 8 Ohm close enough for jazz”?

Thanks in advance, grateful for any help & advice.

 

[tinitus]

all drivers have different impedance
that really of no concern at all

big problem is the varying impedance you mention
the variation changes the crossover component values, basicly
and end effect is a crossover malfunction
but fortunately there are ways to handle that

 

[sreten]

Hi,

What do you want to build and what sort of budget ? Will advise.

The issues are far more complex than the very simplistic question.

rgds, sreten.

 

[stoodood]

So if I stabilise both the 6 Ohm and the 8 Ohm using a Zobel circuit, would they be close enough and the impedance values "static" enough to tune by ear with L pads, or is there a better mathmatical way?

 

[davidsrsb]

Why, it is sensitivity that matters. I see many commercial speakers with different impedance drivers

 

[DUG]

Put 24R in parallel with the 8R and you have 6R.

Get/design a 6R crossover and you are done.

Except for the sensitivity issue davidsrsb mentioned.

That is another story.

 

[system7]

As mentioned, without driver and cabinet details it is hard to rough something up. But matching a 4 ohm (nominal) bass to an 8 ohm (nominal) tweeter is almost standard practise at the budget end. Usually all that is required for level matching is a wirewound resistor attenuator on the tweeter. A wirewound input resistor and a Zobel is also good on a tweeter, but the shunt coil gets smaller.

You will notice that the root of the product (LC) of the filter values stays the same for a given crossover frequency. The ratio of root L/C is proportional to the impedance. DC voicecoil resistance of a nominal 8 ohm driver is usually 6 ohms. For a nominal 4 ohm driver it is usually around 3 ohms.
Crossovers

You can simulate the speaker with similar Visaton drivers here. The complete answer.
Downloads

 

[stoodood]

Everyone's comments are uncovering, for me, an even greater degree of potential complexity than I had considered. I had thought, naively, that if TS values were followed forensically, together with a perfectly calculated crossover - accounting for driver response & sensitivity, in a rigid cabinet, then one would have built the "perfect" speaker - yes I know nothing's perfect. So all I would have to do is "amend" the 8 Ohm to 6 Ohm using the parallel resistor as Dug suggested. I also thought that using a Zobel circuit would stabilise the impedances enough (bass at least........can Zobel be used for tweeters or would it be audible at high Hz?) that the drivers fluctuating impedances with frequency wouldn't have much effect on crossover component values. I can design crossovers from impedance, capacitance & inductance tables and "match" speakers with the same impedance and choose a sensible crossover frequency BUT I don't have analysis equip to see the effects, only ears. So........ is Dug's suggestion (my preferred route) as good as it gets without an oscilloscope.

 

[stoodood]

Apologies Steve, your post came in whilst I was typing so I hadn't seen it. Will digest it now.

 

[tinitus]

So........ is Dug's suggestion (my preferred route) as good as it gets without an oscilloscope.

no, it is not, sorry
not even half way there

ofcourse you can do it that way
it will play, and you may even enjoy it
just dont think it will be very good

 

[stoodood]

Thanks Tinitus, could you give me some more detail and a bit more of a direction to head off in?

 

[tinitus]

you haven't said what your goal is
is it a project ?
or just general interest ?

 

[stoodood]

Thanks Tinitus, both project and a genuine learning point (teach a man to fish etc.) The project is marrying a ribbon tweeter (to be used as a super tweeter - this causes lengthy debate and passionate opinions in itself) to another speaker cabinet but where the tweeter is 8 Ohm and the cab is 6 Ohm pre crossover. This is partly an experiment because I've never heard a ST before and I won't hang myself if I don't like the result BUT the knowledge is more important because it makes it makes experimentation less daunting. I'd also like to try the ribbon tweeters with other units which could be of a different impedance if I don't buy brand new, so the facility to accurately and "scientifically" match speakers would help me immensely.

 

[tinitus]

well, basicly you need two different speakers

one you can use for listening(a proven DIY design)
and one for 'learning' and having fun(your own experiment design)

the first one, for listening, build a good 'simple' passive speaker

the other 'experimental' one, I would suggest active
its more like a building brick you can change again and again

 

[stoodood]

Ok thanks Tinitus, can you give any help on the direction(s) to go in with mismatched driver impedances and matching them via the crossover & associated components – any associated maths you can offer would be great too, relating it to your reply on Dug’s suggestion regarding using a resistor to adjust the tweeters’ impedance. You say it may not be very good, could you explain this? Thanks again.