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Old 15th August 2005, 07:30 PM   #1
regal is offline regal  United States
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Default Adding series resistor to sub

I have a sub which is only 2 ohms, I need to get it up to 3 ohms by adding a 1 ohm resistor. Is there any way to predict how would this change the T/S parameters ?
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Old 16th August 2005, 01:19 AM   #2
Tweeker is offline Tweeker  United States
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Diy article on dipole setups.

Let's say we want to build a dipole bass system using four 12" drivers with the following specifications: Vas: 164 litres., Fs=30Hz, Qts=1.10, Qes=1.30, Qms=7.0, R=8 ohms, Xmax=8mm, Sd=0.0547m^2 .

To maximize efficiency, the drivers will be wired in parallel, giving an effective Re of 2 ohms. We also want to know what SPL levels we can expect if we drive the system with 100W of power.

To increase the Qts to the target value, we can use a series resistor Rs, and calculate its value as follows:

Qes' = 1.75*7/(7-1.75)
Qes' = 12.25/5.25
Qes' = 2.33

Rs = Re*(Qes'-Qes)/Qes
Rs = 2*(2.33-1.30)/1.30
Rs = 2*1.03/1.30
Rs = 1.6 ohms

As we plan to drive the system with 100W of power, assuming 10:1 differences between average and peak levels, we can use a 10W or greater resistor for Rs.

As the total resistance, Rs+Re, will be 3.6 ohms, the amplifier will have to be capable of driving at least a 3.6 ohm load.
Edit: could be figured out from here, but this link has the direct equation.
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Old 16th August 2005, 07:19 PM   #3
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Does the sub not have two 2 ohm coils?

Adding series resistance to the woofer is pretty much the last thing you want to do. What kind of resitor are you planning to use?
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Old 16th August 2005, 10:50 PM   #4
regal is offline regal  United States
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it is a SVC 2ohm sub. It was cheap, I may just order another and run them in parrallel
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Old 16th August 2005, 11:51 PM   #5
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you will want to run those in series if you get another sub.....
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Old 17th August 2005, 12:08 AM   #6
rcw is offline rcw  Australia
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Default re series

Putting the drivers in series has the effect of one driver seeing the other drivers voice coil resistance as its source resistance and it nearly doubles Qt.
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Old 17th August 2005, 12:53 AM   #7
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With all respect, rcw, I tried that and the Qts for the drivers stayed the same.

The bass shape stayed the same in reference to the midband, which is what Qts controls.

Two woofers in series doubles the nominal impedance, but keeps Qts identical.

Two woofers in parallel halves the impedance, but keeps the Qts identical. It will also increase your SPL per 2.83 Volts by 6 dB.
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