6 Ohm Woofer & 8 Ohm Tweeter - diyAudio
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Old 27th November 2012, 07:26 PM   #1
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Default 6 Ohm Woofer & 8 Ohm Tweeter

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.
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Old 27th November 2012, 07:32 PM   #2
tinitus is offline tinitus  Europe
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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
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Old 27th November 2012, 07:43 PM   #3
sreten is offline sreten  United Kingdom
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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.
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Old 27th November 2012, 07:48 PM   #4
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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?
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Old 28th November 2012, 01:42 AM   #5
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Why, it is sensitivity that matters. I see many commercial speakers with different impedance drivers
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Old 28th November 2012, 02:41 AM   #6
DUG is offline DUG  Canada
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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.
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Old 28th November 2012, 07:23 AM   #7
system7 is offline system7  United Kingdom
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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.
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File Type: jpg Visaton_8Ohm_Crossover.JPG (34.8 KB, 88 views)
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Old 28th November 2012, 07:39 AM   #8
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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.
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Old 28th November 2012, 07:46 AM   #9
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Apologies Steve, your post came in whilst I was typing so I hadn't seen it. Will digest it now.
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Old 28th November 2012, 07:46 AM   #10
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by stoodood View Post
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
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