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Adding Up The Ohm's

pliskin

pliskin

Active Member
OK, so here is the deal. I have a pair of 4ohm speakers that consist of the following:
1- 8ohm tweeter
2- 16ohm mids
1- 8ohm woofer
Somehow this comes out to be a 4ohm speaker.
I'm about to replace one of the 16ohm mids with a 8ohm one because.....well just because.

What will my ohm's be now? I understand this is not an static number but I don't want to end up with a 2ohm or 50ohm Frankenstein that vaporizes my amp as soon as I turn it on.
1- 8ohm tweeter
1- 16ohm mid
1- 8ohm mid
1- 8ohm woofer
 
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I'm not sure, but I think there's the crossover network to also consider, as that is what presents the load to your amplifier. I don't believe that the driver impedances are the only part of the math.
 
With any multi driver speaker you have to take the X-over into consideration to determine the overall impedance of the speaker. The tweets will present a low impedance to the highs and a high impedance to the mids and lows. The mid-range drivers will present a low impedance to the mids and a high impedance to the highs and lows. The woofer will present a low impedance to the lows and a high impedance to the mids and highs. All together the combination presents an overall 4 or 8 or whatever Ω load to the amplifier.
 
I agree with what's been said. Plus, if you shift from the stock mids, to 8 and 16 Ohm mids, you're going to change how the crossover see's the load, and shift your crossover points and slopes. That, and now the midrange drivers will be out of balance with each other. The 8 Ohm mid will probably sound louder that the other. So, if you're worried about the speaker impedance, measure it at the binding posts. That'll give a better idea, than guessing how each individual driver will read, and affect your system.
 
Keep in mind that a multi-meter measures resistance. Resistance is NOT the same as impedance. Resistance is a DC measurement. Impedance is an AC measurement that varies with frequency.
 
StimpyWan said:
I agree with what's been said. Plus, if you shift from the stock mids, to 8 and 16 Ohm mids, you're going to change how the crossover see's the load, and shift your crossover points and slopes. That, and now the midrange drivers will be out of balance with each other. The 8 Ohm mid will probably sound louder that the other. So, if you're worried about the speaker impedance, measure it at the binding posts. That'll give a better idea, than guessing how each individual driver will read, and affect your system.
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That's what I figured....different sounding mids. I can live with that as these speakers will likely be played at low to moderate volume indoors. Or, at higher volume outdoors where sound quality does not matter on a rare party occasion if at all.

I'm just going to do it and see what happens. These are a pair of big 400w Cerwin Vega 380's earthquake makers I'm bringing back from the grave anyway ( somebody already litteraly blew them apart...see my other thread). There is little to no info about rebuilding these that i could find. They play now but tweets are blown as well as two bad mids and some seperated plywood, inside and out. Still, they look really good on the outside and are worth saving IMO.

I'll post my progress in the other thread. I just needed to ask for the ohm question here because the other thread is circling the drain until I get some parts.

Out of curiosity what determines the ohm on a speaker? Is it the coil, magnet, or both.
 
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By convention, the impedance of a loudspeaker use to be the lowest point of the impedance curve just above the resonant point of the woofer. So tweeters could be and are often higher impedance than mids as the tweeters use to be attenuated to balance and for excessive power protection. Now days its a totally different can of worms. Though the convention is pretty much the same depending on crossover loading, Zobel impedance correction circuits and a desire to get all the efficiency they can from speaker systems. Just because a driver has an 8 ohm free air impedance label on it doesn't mean it is as types of enclosures and ports and tuning can do strange things to speaker parameters. You really need some pretty advance test equipment or apps to make sure replacement speakers match the original specs to allow the crossover to work properly and maintain the original tonal balance. You can't expect to walk into a speaker shop and buy an xyz speaker that will match your originals. .
 
Of course the x-over gets before the drivers and alters the impedance, but somehow, I can't see this set of drivers giving an overall 4Ohm loudspeaker, no matter what the x-over does and how it's implemented. Unless it uses high wattage resistors in paralel to the drivers to reduce the impedance and consume a lot of power for nothing, not something to be expected in a crossover.

Could it be that these are not the original drivers in the enclosures?
 
SaSi said:
Of course the x-over gets before the drivers and alters the impedance, but somehow, I can't see this set of drivers giving an overall 4Ohm loudspeaker, no matter what the x-over does and how it's implemented. Unless it uses high wattage resistors in paralel to the drivers to reduce the impedance and consume a lot of power for nothing, not something to be expected in a crossover.

Could it be that these are not the original drivers in the enclosures?
Click to expand...
I'm pretty sure they are all original. We'll see how they sound as soon as I get the replacement mids and tweeter domes. Unfortunately I won't be able to compare it to an all-original set first.
 
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