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Old 30th December 2013, 09:59 PM   #1
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Default 4Ohm Rated Speakers with 8Ohm Drivers Understanding Crossover & Tweaking?

Hello,

I'm thinking a crossover upgrade is a good place to start learning to solder, a new copy of the existing crossover with hopefully better quality parts should not get me in trouble, as the original crossover will not be touched in case it is required again.

However,
The speakers are rated at 4Ohm.
In taking the drivers out, each driver is rated at 8Ohm. Tweeter 8Ohm and two 6" drivers per speaker, 8Ohm each.
As far as I understand it the two 6" drivers (in each speaker) are in parallel off of the crossover, so make a 4 Ohm load.

The tweeter has a cap and resistor in series and an inductor in parallel, I'm guessing the inductor is rated to make the 8Ohm tweeter look like it is only 4Ohms?

So, thinking of the future, it may be nice to power each driver with it's own amp... is this going to be mind blowing on the re-rating of crossover components?

Many thanks for any thoughts!

By the way, Happy New Year to All !

Cheers
DC

Last edited by Deaf Cat; 30th December 2013 at 10:05 PM.
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Old 30th December 2013, 10:45 PM   #2
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Because the tweeter uses so little power, its impedance isn't really a part of the equation.

The cap in series and the choke in parallel is known as a 2nd order filter, the resistor is to bring the level down as tweeters are often more sensitive than woofers.

As far as using 2 amps, you simply go back to where the signal splits in the first place or you do it with an active XO. Not difficult.
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Old 30th December 2013, 11:47 PM   #3
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The inductor is there to shape the filter response, not to match the impedance of the two LF drivers. Time for study; prepare for questions.Cal I must disagree; crossover theory is difficult, at least for some of us

Last edited by phivates; 30th December 2013 at 11:50 PM.
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Old 31st December 2013, 12:50 AM   #4
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Perhaps I misunderstand what he is attempting?
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Old 31st December 2013, 06:34 PM   #5
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Cheers good to know the tweeter is not really affected 8Ohms or 4, and the cap and inductor are just for frequency response.

Sorry for not being clear I shall try again. I have two floor standing speakers, each with an 8Ohm tweeter and each with a pair of 6" drivers 8Ohms each driver. The pair of 6" drivers are wired in parallel (from the crossover) so rated at 4Ohms.

At the moment I have a stereo power amp wired to the tweeters, one half for the left channel and one half for the right channel. I have one mono block for the right pair of 6" drivers and one mono block for the left pair of 6" drivers.

Thinking of the future, would the crossovers need to change in some way if I were to separate out the 6" drivers and have one mono block per driver. Two mono's and 1/2 a stereo amp per speaker?

Would it be as simple as duplicating the low freq existing crossover for the 6" drivers?

Or would things be thrown out as the 6" drivers would now be 8Ohm to the amps rather than 4Ohm and the tweeter would remain as is and may be out of balance/loud?

Hope this is clearer, as you may tell I'm pretty new to the crossover idea.

Many thanks for your thoughts!
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Old 31st December 2013, 07:19 PM   #6
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You would have to adjust the components. Basically, as you have doubled the impedance ie: 8 ohms each circuit, you need 2 coils twice the mH of the existing and 2 caps that are 1/2 the size for each speaker.

If you are going to do that you might as well buy a Behringer 3400 and turn them into a 2.5 way (flexible) or the 2310 and do the same thing with the sub outs. (less flexible but still better than passive).
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Old 1st January 2014, 12:34 AM   #7
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Agree...if you're already multi-amping then make good use of it. Passive components get expensive as you go down in frequency and up in impedance
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Old 3rd January 2014, 07:39 PM   #8
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Active is looking rather interesting.

I was very lucky a while back to get a pre/dac, broken, got it fixed and tweaked for 260 all in, and improves upon my previous pre/pro which stood its ground with a few 2-3k dacs.

I'm a little worried that something like the Behringer may not be transparent enough..?
As possibly a miniDSP I may hear too... and understand the set up could take some time if one is not familiar with crossovers etc

Something like Linn active cards tweeked to my speakers... yet to investigate.
A Bryston B10 would be nice but way way over budget! It looks easy to set up as there are only a few knobs to turn to adjust crossover volumes etc.

I came across
XM44 Electronic Crossover Network 2-way, 3-way or 4-way, 24 dB/oct or 48 dB/oct
The xm44emb looks quite good as one can build it one's self at a reduced cost...
Any thoughts?

Going passive is still tempting as fun soldering but I'm thinking from what has been said it may well be worth investigating active a bit more.

Any one have thoughts on pros / cons on DSP set up or analogue active cards..

Many thanks for comments so far!
Cheers
DC
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Old 3rd January 2014, 08:15 PM   #9
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Just taken some measurements from the components on my crossover board, some are way out and just wondered if you would know the result on the sound of being not to spec.

Tweeter:
Specification:
series cap 6uF, parallel inductor 25uH (no spec-measured), series resistor 3.9Ohm
Measured:
series cap 5.7uF, parallel inductor 25uH, series resistor 2.3Ohm

Woofers:
Specification:
series inductor 900uH, parallel cap 5.6uF
Measured:
series inductor 881uH, parallel cap <0.5pF


I'm guessing from the little I have learnt the lower series resistor value on the tweeter will make the tweeter louder than designed.
Guessing the crossover point will have changed as the parallel cap has pretty much vanished on the woofer, but unsure which way.

From a listening point of view, I'm pretty happy with bass and treble, but mid range seems a smidge lacking.

Very much appreciate any comments!
Cheers
DC

Last edited by Deaf Cat; 3rd January 2014 at 08:18 PM.
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Old 3rd January 2014, 08:27 PM   #10
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Quote:
Originally Posted by Deaf Cat View Post
I'm a little worried that something like the Behringer may not be transparent enough..?
I don't notice it in the circuit.
Quote:
I came across...
Any thoughts?
If the Marchand is cheaper then go for it. I couldn't be bothered as the 2310 is only $80 CAD or about 45 pounds.

EDIT: Ouch
http://www.ebay.co.uk/itm/BEHRINGER-...-/150868997766
Not sure why the link doesn't work but your ebay - uk shows it as anywhere from 60 to 95 pounds.
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