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Old 16th August 2004, 08:59 PM   #1
ancorp is offline ancorp  Canada
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Unhappy Boost the impedence? Who wants to help the newbie?

im looking to replace a pair of woofers in a pair of old speakers. Current woofer drivers are 15", 5 ohms and are 50w nominal (im going to replace them with 350w-500w so im going to drive the crossovers at more than 50w) the drivers that i will use will be 4 ohms. anyway to boost them to 5? a resistor or two? ive posted something similar before, but i need help to do this within toronto (no online orders). any help, plz? im not an audiophile, but i understand some stuff about speakers, and surround sound, etc.
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Old 16th August 2004, 09:02 PM   #2
SY is offline SY  United States
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Resistors are a poor idea- heat, wasted power, lowered damping factor. What's your motivation for raising the nominal impedance?
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Old 16th August 2004, 09:07 PM   #3
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thanks for the quick reply, . the originals were 5ohms, and the relacement will be 4, so if its lower, than the total speaker crossover impedence (8ohms) will be less too (i think), and my reciever wont pull it, it supports 8-16.
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Old 16th August 2004, 09:24 PM   #4
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Well, here's the dirty secret: impedances are NOT a single number. They actually vary all over the place. For a typical woofer-in-a-box, you might see the impedance swing from 3 to 30 ohms, depending on frequency. The "nominal impedance" spec is a piece of fiction. Same with power handling figures.

And changing the woofers to something else opens up a whole can of worms. The Thiele-Small parameters, which determine how the woofer will perform in the bass with a given box, are HIGHLY unlikely to be the same from one type of woofer to another. The impedance at crossover is the least of your problems here.

Is there no chance of getting a replacement set of woofers from the manufacturer? Or repairing the woofers? You'd really be much better off.
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Old 16th August 2004, 09:28 PM   #5
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ive already been told all those things. i doubt i can repair the speakers properly. the surround on them is ripped, and its not a foam type speaker. the original replacement woofers will probably cost like 300$ each, these are quite old speakers. Sansui sp-5500x...

Im gonna replace them with cheap woofers, only 19.99 canadian each (clearance sale)!. Its either that, or probably the trash bin....
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Old 16th August 2004, 09:56 PM   #6
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Cann't you get cheap 8R ones?.
I know of someone who replaced woofers without any consideration other than frame size, and they were happy with the result. They sounded better than the ripped cones.
You can learn about crossovers etc. later.
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Old 16th August 2004, 10:28 PM   #7
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8R? u mean 8 ohms? naah, unfourtinately i cant.
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Old 16th August 2004, 11:07 PM   #8
ancorp is offline ancorp  Canada
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so no way to boost to 5 ohms?

btw. thanks alot for the tips so far.
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Old 16th August 2004, 11:26 PM   #9
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I think that the message is that you shouldn't worry about mice when you've got elephants running around. Drop your 19.95 drivers in, then play around with crossover and box stuffing.
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Old 16th August 2004, 11:35 PM   #10
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Just add a 1 ohm resistor. It will waste a little power and may impact the woofers' sound slightly, but we're talking about $20 canadian woofers anyway. Add some bracing inside the box while you have it open and that benefit may help offset the negatives. Give those $20 drivers a listen before purchasing to make sure they aren't just total crap to begin with. If you end up with some sonic characteristics that you don't like, post the results and maybe someone here can help. In the worst case, you could turn the box into an aperiodic box which can be adjusted to any driver using the same box with only a little work. Maybe you'll get lucky and the new driver with the resistor has very similar characteristics of the original.

Another alternative is to repair the originals. What exactly is the nature and extent of the damage?
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