speaker 8ohm/100ohm

[RAILCAT]

If I use an 8ohm speaker with a loksound 3.5 which is designed for 100ohm is it acceptable to use an equivalent series resistor when using the 8ohm speaker. Dont want to destroy the decoder by trying it out without some guidance.

[lyled1117]

While adding a resistor to get an approximate 100 ohm impedance will protect the decoder from overload, you may not hear much if any sound from the speaker. I'm going to use round numbers to explain. Pretend the speaker is 10 ohms, the resistor would then be 90 ohms to get a total 100 ohm load. The voltage put out by the decoder will split across the two devices proportionally. The 10 ohm device gets 10% of the voltage, the 90 ohm device gets 90%. At full volume nearly all of the voltage (and thus power) is going to the resistor. Only 10% of the voltage is going to the speaker. This would result in low volume, maybe not heard at all. To get any appreciable volume, you want the speaker to get most (all) of the output voltage. You really want something close to 100 ohm for a speaker.

Lyle

[babbo_enzo]

Just a "gold" cent here:
Never connect any other speaker with lower impedance then 100 Ohm to your decoder!

PS: Remember that AC "impedance" is not exactly corresponding to DC "resistance"....

[Iain]

There is a but here .... you can use a matching transformer, but good luck finding one small enough to fit.  Just buy a 100 ohm speaker, otherwise your results will be less than satisfactory.

Putting a resister in series with the speaker will not work.

[RAILCAT]

Just a "gold" cent here:
Never connect any other speaker with lower impedance then 100 Ohm to your decoder!

PS: Remember that AC "impedance" is not exactly corresponding to DC "resistance"....

That is why I asked.