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Wire 4 ohm and 8 ohm speaker in series?

post #1 of 11
Thread Starter 
In my bathroom, I have a pair of 4 ohm (in the shower) and a pair of 8 ohm in ceiling speakers (above my sinks). The shower has a glass door to the ceiling, so I wanted to be able to listen stereo sound while at the sinks and while in the shower.

The 2 channel amp I plan on using has a minimum impedance of 4 ohms/channel (Sonos Connect:Amp).

It doesn't appear I can wire them in parallel, because the 8 ohm and 4 ohm load would lead to an impedance of 2.67 ohms/channel, and the minimum is 4.

Would I be able to wire it in series? I wasn't sure if there would be a problem combining speakers with different impedance? Any help would be appreciated.

In order to clarify, I would run a wire from the (+) terminal of my left channel to the (+) of the 4 ohm speaker, then from the (-) of the "left" 4 ohm to the (+) of the "left" 8 ohm speaker, then from the (-) of that speaker to the (-) terminal on the amp.

It is my understanding that this will create a 12 ohm impedance load. Would it make a difference if the speaker above the sink was a single stereo speaker instead of 2 mono speakers? Thanks!
post #2 of 11
Connect them in series. The only problem I see here is that 8 Ohm ones will sound louder than others. But since they are different speakers anyway, it may not be an issue.
post #3 of 11
Quote:
Originally Posted by ap1 View Post

Connect them in series. The only problem I see here is that 8 Ohm ones will sound louder than others. But since they are different speakers anyway, it may not be an issue.

Although the 8 ohm speaker will have twice the power, the efficiency of the speakers may alter the perceived loudness from one set compared to the other.
post #4 of 11
If for some reason there is a bothersome difference in loudness that can be attributed to the impedances, you could wire an 8ohm power resistor in parallel with the 8 ohm speaker, and then wire the 4 and 8 ohm speakers in series for a total 8 ohm load. You would lose efficiency as power is dissipated in the resistor (which would need to be appropriately sized and positioned), but your amplifier will have additional output at 8 ohm as compared to 12 ohm so end result may not be much lost.

A transformer (volume control) would be the better, more expensive, option. Chances are that for your application wiring them in series as is will work adequately.
post #5 of 11
Quote:
A transformer (volume control)

Are you talking about a a variac type 'volume control' or a variable resistor?
post #6 of 11
I was thinking of transformer based wall mounted volume controls. Maybe I misspoke. I know there are many kinds, some transformerless, and maybe they just act as variable resistors.
post #7 of 11
Quote:
Originally Posted by Bigus View Post

I was thinking of transformer based wall mounted volume controls. Maybe I misspoke. I know there are many kinds, some transformerless, and maybe they just act as variable resistors.

LPADS are the classic speaker level controls. I have seen them up to 100 watt ratings. But just like the series resistor, they waste power.
post #8 of 11
My bad then.
post #9 of 11
Quote:
Originally Posted by ap1 View Post

Connect them in series. The only problem I see here is that 8 Ohm ones will sound louder than others. But since they are different speakers anyway, it may not be an issue.

No.

Impedance magnitude varies significantly with frequency. An "8 Ohm" speaker might have a low of 6 Ohms and a high of 60.

Voltage will divide across the two speakers in proportion to their impedance at a given frequency; so where one speaker hits a peak you'll get less output in the other speaker.

The 8 Ohm speakers may (if sensitivity was greater than 6dB below the 4 Ohm speakers) or may not (otherwise; an 86dB/2.83V/1 meter 8 Ohm speaker in series with a 92dB/2.83V/1 meter 4 Ohm speaker will play just as loud).

I'd do something other than wiring them in series (extra amplifier, transformer based volume controls, L-pad volume controls with the two loads wired in parallel, replace the 8 Ohm pair with ones matching the shower speakers and run them in series, replace the 4 Ohm speakers with ones matching the sink speakers and run them in parallel) most likely something that gave them each their own volume control accessible in the bathroom.
post #10 of 11
Quote:
Originally Posted by Bigus View Post

My bad then.

No, they make transformer types too. There are also TPADS but they don't maintain constant impedance.
post #11 of 11
I wouldn't sweat overhead bathroom speakers unless there was a major problem. How much critical listening can you do in the shower?
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