Dual speaker set up

[norwid]

Hello,

I am quite new to all this, so please excuse my probably quite trivial question. I have two sets of speakers, one 4ohms and one 8ohms. They are both connected to an amp that can take speakers between 4 and 8 ohms. At the back of the amp, it says that if I want to use both sets of speakers simultaneously I need to use 8ohms speakers. What will happen if turn on both pairs at the same time?

Thank you!

 

[spark1]

It depends upon the amp. What is make/model?

If it has some sort of overload protection, it will shut down. If not, it may overheat and damage its output transistors and related components.

Be aware that speaker impedance ratings are nominal and are quite likely to be quite a bit lower at some frequencies. But even if they don't drop below their stated value (very unlikely), the combined impedance of 8 ohm and 4 ohm speakers is 2.7ohms. This is well below the amp's implicit limit of 4 ohms (two 8 ohm speakers = a 4 ohm load on the amplifier).

There are ways around this problem, but they are not ideal from the standpoint of sound quality. They include wiring the speakers in series or using a speaker selector box designed with impedance protection.

Another alternative is to feed the signal from this amp to a second amp, to which the second pair of speakers are attached.

 

[Dan13105]

You can damage the amplifier by running too low of an impedance load. 8 ohm and 4 ohm speakers working together only provides a nominal load of 2.67 Ohms. That also doesn't take into account that speakers do not present a steady impedance load to an ampli, across all frequency ranges. The actual load can be much lower. This will cause the amp to work harder and overheat, or possibly fry components. Not advisable

 

[norwid]

Hi, thank you for your quick and thorough reply. It's all vintage stuff, nothing very fancy. So there is probably no built in protection. I was not really planning on using both sets together, I was mostly curious.

Amp: Jbn CR-8080SE
Speakers 1: Sonab-Carlsson OA-5
Speakers 2: Phillips DX 144/61

 

[rothwellaudio]

What will happen if turn on both pairs at the same time?

...there is probably no built in protection.

Smoke may pour out of the amp.

 

[ProudArmyBra]

Learn about parrelle and series speaker wiring. Learn about nominal impedance and dynamic impedance! Probably look at car audio for this since it is a more common and every day problem you deal with since some amps are certified down to 1/4 ohm in car audio none of this idiotic 8 ohm standard in home audio.

 

[twiiii]

One 4 ohm running with an 8 ohm speakers is around 2.66 ohms. We know speakers impedance changes with frequency, but back in the good old days the impedance published was usually the minimum impedance just above the woofer cones peak resonance which could be many times higher. We when the power wars and loudness wars started manufacturers changed from 16 ohms down to 8 ohms and then to 4 ohms to make their speakers sound louder with direct coupled SS amplifiers. Now days you will speakers that say they are rated at 4 ohms, with an addendum that might say 2.56 ohms at a given frequency. Or you might find speakers where the impedance dips very low above 10 KHZ or so.

But if all you do is most casual listening where you are using a watt or two for each speaker I wouldn't worry. But when you get to the 1/3 power level of the amp is where the trouble starts as that is where SS amps seem to be the most thermally inefficient. Thats where you need to be careful. If you can't touch your unit or if there is a smell being emitted that isn't normally there it is time to back off or turn the unit off and let it cool. If this happens more than once or twice its time to go shopping for a newer unit. Because the amplifier could not only shoot itself in the foot, but damage your speakers beyond economical repair.