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Old 5th November 2013, 03:47 PM   #1
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Default crossover calculators and impedence

Hello all !

So I've been fooling around with online crossover calculators and got wondering.... For say a two-way speaker it asks for the impedance of each driver in order to do the calculations. So my question is if I am adding resistors to each driver to make each one a 16 ohm load should I be entering in the original impedance (sans resistors) of each driver into the calculator or the impedance after adding resistors ? Values change so drastically when you add resistance to the mix !
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Old 5th November 2013, 04:04 PM   #2
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A resistor dissipates energy, it doesn't convert it into acoustical energy- well, speakers are rather inefficient too !
However, the answer is a no-no.
The online calculators might be of some utility for high pass only, as woofers are rather unpredictable..
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Old 5th November 2013, 09:14 PM   #3
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I am actually looking to run a fullrange driver with a tweeter to top off the top end. So the tweeter is a 6 ohm. The impedance curve show by seas shows that it stays between 6-8 ohms in the frequency range I would be using it for. So I am looking at using it from about 10 kHz up. So I've put a 10 ohm resistor on it to make around 16 ohms. The fullrange is a 4 ohm with a 12 ohm on it.
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Old 5th November 2013, 10:09 PM   #4
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I think you need to back up a notch or three. It sounds like you're trying to use resistors to make your drivers 16 ohms to match the output of a tube amplifier- this is not a good method. Crossovers are fairly complex, and the impedance in the passband isn't the only issue.

Can you be very specific about what you're using and how?
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Old 6th November 2013, 12:16 AM   #5
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I am making both drivers 16 ohm to make an 8 ohm load when run in parallel. I am using just cap for the tweeter, It's not for my tube amp.
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Old 6th November 2013, 01:34 AM   #6
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OK, are you also to be running these in parallel physically? Ie, will they be in the same cabinet, or beside each other or something else?
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Old 6th November 2013, 05:31 AM   #7
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You don't put any resistor in line with a woofer- at least not more than 1-1.5Ω in some ( sealed enclosure ) case - and the capacitor decouples the tweeter
from the amplifier. Look at any design whatever it may be fullrange + tweeter
or woofer-mid-tw...the resistors in series alone play a different role.
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Old 6th November 2013, 09:53 AM   #8
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Quote:
I am making both drivers 16 ohm to make an 8 ohm load when run in parallel. I am using just cap for the tweeter, It's not for my tube amp.
That is plain wrong. If you use a cap then you have a crossover, and the drivers are not seen as separate entities anymore. The impedance will be a combination the of drivers impedance and the crossover.

Adding a series resistor to a woofer is basically a no-no because you are wasting energy without a real benefit. If your amp cannot drive a 4 Ohm driver then change driver or amp. Mixing a 4 Ohm woofer to a 6 Ohm tweeter doesn't pose any problem.

Another problem I see is running the fullrange without a low pass filter. You'll have lobing problems in the treble.

Ralf
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Old 6th November 2013, 12:05 PM   #9
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So what I am using is a Seas FU10RB 4 ohm fullrange with just an 12 ohm resistor run in parallel with a Seas 27TBCD DXT tweeter 6 ohm with a 10 ohm resistor and a capacitor. (I do have a pair of Seas FU10RB in 8 ohm available if needed). I am not worried about a lowpass filter as of yet as my amp will let me control it.I would just like to start with a simple first order crossover and expand along the way. I am looking to learn along the way and expand as a go. I do see many coaxial speakers with just a capacitor on the tweeter and they seem to work okay for what they are. The drivers I have are in a sealed box currently and I could modify to port them if needed. Basically what I am looking for is a 6 ohm load or higher as the amp says 6-8 ohms.
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Old 6th November 2013, 12:07 PM   #10
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Quote:
Originally Posted by giralfino View Post
That is plain wrong. If you use a cap then you have a crossover, and the drivers are not seen as separate entities anymore. The impedance will be a combination the of drivers impedance and the crossover.

Adding a series resistor to a woofer is basically a no-no because you are wasting energy without a real benefit. If your amp cannot drive a 4 Ohm driver then change driver or amp. Mixing a 4 Ohm woofer to a 6 Ohm tweeter doesn't pose any problem.

Another problem I see is running the fullrange without a low pass filter. You'll have lobing problems in the treble.

Ralf
So should I lose the resistor on the woofer and put a higher value on the tweeter ?
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