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Old 08-24-2006   #1
 
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Default mixing 4 ohm & 8 ohm speakers

what is the effect of using 1 driver in a passive setup with say, 4 ohm impedance, and another with 8 on the same amp channel? would the amp struggle to play some freqs thru the 8 ohm driver, and some thru 4 ohm, and have variable output? variable sound volume?

thanks!
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Old 08-24-2006   #2
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Default Re: mixing 4 ohm & 8 ohm speakers

The amp won't have a problem. Just don't put both drivers behind the same passive crossover network. Different impedances require different component values.
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Old 08-25-2006   #3
 
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Default Re: mixing 4 ohm & 8 ohm speakers

it'll be connected to the same passive network but i can use component values, 4 ohm values for the 4 ohm side, and 8 ohm values for the 8 ohm side. so that should not be a problem yes?

i'm worried that the sensitivity / amplitude gets affected and i end up with difference in loudness between the 2 speakers. is that likely as well?

thanks for the quick reply!
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Old 08-25-2006   #4
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Default Re: mixing 4 ohm & 8 ohm speakers

Quote:
Originally Posted by hyun
it'll be connected to the same passive network but i can use component values, 4 ohm values for the 4 ohm side, and 8 ohm values for the 8 ohm side. so that should not be a problem yes?

i'm worried that the sensitivity / amplitude gets affected and i end up with difference in loudness between the 2 speakers. is that likely as well?

thanks for the quick reply!
Amplitude will be effected by virtue of the fact that they're different speakers. But this would be true even if they were driven off different amplifiers. Look at the sensitivity of the drivers rather than the impedance to determine how you need to get the two speakers to mesh.
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Old 08-25-2006   #5
 
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Default Re: mixing 4 ohm & 8 ohm speakers

Great hyun!! I was just about to do a post on it! When you Wire 4 ohms parallel you get 2 and in series you get 8. And when you Wire one 4 ohms and one 8 ohm what do you get?? Thanks..
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Default Re: mixing 4 ohm & 8 ohm speakers

Quote:
Originally Posted by torog
Great hyun!! I was just about to do a post on it! When you Wire 4 ohms parallel you get 2 and in series you get 8. And when you Wire one 4 ohms and one 8 ohm what do you get?? Thanks..
1/(1/4+1/8) = 2.67

But when passive crossovers are involved, it's a different story. For instance, a 4 ohm tweeter in parallel with a 4 ohm woofer would give you roughly 4 ohms.
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Old 08-26-2006   #7
 
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Default Re: mixing 4 ohm & 8 ohm speakers

Quote:
Originally Posted by torog
Great hyun!! I was just about to do a post on it! When you Wire 4 ohms parallel you get 2 and in series you get 8. And when you Wire one 4 ohms and one 8 ohm what do you get?? Thanks..
from what i understand, in a 2-way crossover, where the 2 (4 ohm) speakers are wired in parallel, this is what happens:

1. At the crossover point, the impedance has risen to double (8 ohms) due to the added impedance of the crossover components. (some crossovers increase impedance even more, and drop output by -6db at that point.) so u still get 4 ohm load at this point.

2. Above, and below this point, the impedance for the Speaker that has its frequency cut off keeps rising, because the crossover components gain impedance the deeper into cutting territory it gets. the other Speaker regains its base impedance (4 ohms) pretty soon outside this point. so the summation = 1/4 ohms + 1/high ohms (in parallel) = 1/net_impedance = about 1/4 ohms. therefore, 4 ohms is still preserved.

that's how u theoretically get a flat response ("constant" 4 ohms) with some types of crossovers.
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Old 08-26-2006   #8
 
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Default Re: mixing 4 ohm & 8 ohm speakers

FYI:

The Focal utopias and K2P's,

The TN52/51 Tweeter is 6 ohms, while the midbass driver is 4 ohms, and it's tied on a passive crossover.

So i guess it's not that uncommon.

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Old 08-26-2006   #9
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Default Re: mixing 4 ohm & 8 ohm speakers

I think it's simpler if you look at it this way. For a 2-way crossover, the passive components act as a filter between the two drivers, such that each driver is playing only the frequency range you intend. The impedance of the drivers themselves will determine the value of the components you use. The driver's impedance never changes, and any differences in output can be dealt with by attenuating the louder driver with another filter.

A speaker is only as good as the room you put it in.
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Default Re: mixing 4 ohm & 8 ohm speakers

therefore when designing a passive 2-way cross of mismatched ohm drivers, the filter on EACH side has to match its respective driver's impedance. it doesn't matter what's on the OTHER side, as long as the pass filter for that side concerned has been calculated correctly, it'll be fine.

i don't know the specs for sure of my tweeter. one way to guess what's the nominal impedance rating is to measure its DC Resistance, right? If I already see about 3.2-3.4 ohms DCResistance, it should be a 4 ohm tweeter. If I already measure a 5 ohm DCR it probably is a 6 ohm tweeter. Logical?
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Old 08-26-2006   #11
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Default Re: mixing 4 ohm & 8 ohm speakers

It's probably more accurate to look at the driver's impedance near the crossover region.

A speaker is only as good as the room you put it in.
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