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Old 14th December 2007, 07:35 PM   #1
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Default Parallel/Series crossover wiring question

I was planning on buying a midrange speaker along with a tweeter. I was told that if I hook a 2uF capactior from positive of the tweeter to the positive of the speaker, the tweeter will be rolled off at 10 khz, at 6db/octave.

Does this mean that the tweeter/speaker combination would be wired in parallel? Both are 4ohms and my amplifier has 2 channels that needs no less than 4ohm per channel. By wiring the tweeter and speaker with the 2uF capacitor, would they end up being 2ohms? If so, is there a way to avoid this?

Thank you for any information
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Old 14th December 2007, 09:22 PM   #2
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Yes it is a parallel XO.

2 uF into 4 ohms gives a 6dB/octave XO at 20 kHz (you need to use 4 uF for a 4 ohm T)

The impedance of the cap at low frequencies, and that of the voice coil in the midbass mean that you end up with a nominal 4 ohm speaker (ie 4 ohms in parallel with lots & lots of ohms is still 4 ohms.

dave
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Old 14th December 2007, 09:26 PM   #3
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Ok, so if I understand correctly, with a 4ohm tweeter and a 4ohm speaker, the end result using a 4uF capacitor in between will still be 4ohms?

I'm new to this, so I was confused with this part since I thought parallel would half the ohms.

Thanks for the response! =)
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Old 14th December 2007, 09:30 PM   #4
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Quote:
Originally posted by cerupcat
Ok, so if I understand correctly, with a 4ohm tweeter and a 4ohm speaker, the end result using a 4uF capacitor in between will still be 4ohms?
yes

Quote:
I'm new to this, so I was confused with this part since I thought parallel would half the ohms
a common misconception, people thinking that a nominal impedance means a flat line.

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Old 14th December 2007, 10:30 PM   #5
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It would be half the ohms if the two speakers were carrying the same frequencies, but since the capacitor eliminates the lower frequencies, there is no real parallel as only one of the drivers is carrying the low end. Basically you are paralleling a 4 ohm with a gazillion ohms which effectively results as 4 ohms.
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Old 14th December 2007, 10:39 PM   #6
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Thanks Carl and Dave. That makes a lot of sense. I didn't realize that different frequencies would change that. I appreciate the quick responses! =)
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Old 21st November 2011, 06:04 AM   #7
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Hi. Bringing this topic back because I have some questions regarding this topic too.

What if the the impedance of the twitter and woofer is not the same? for example, tweeter is 8 ohms and the woofer is 4 ohms. what will happen to the total impedance of the finished speaker?
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Old 21st November 2011, 06:25 AM   #8
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You have to ask the question to the amplifier

'Xcuse me , Mr Amp , what happens when there is a mixed load at your output '?
A : ' Well, errrrr , I don't know ,sometimes I stumble but I always try to keep
the right track ; you should ask those stupid engineers that make a mess
inside those boxes '

Q: 'So you would be happier in driving a loudspeaker directly ? '
A :' I preferred to seat on the table in my lab , when I was only asked to deliver my power to a set of resistors ; outside , it's hell !!'
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