I want to use an external speaker with a Uniden BCD996T. The speaker I have is rated 4 ohms - well, according to my multimeter using the resistance setting (3.8 Ohm to be exact). There's no Ohm rating or manufacturer name on this small speaker, but feels well built and probably weighs a good pound (454 grams) or so. My question is can I use this speaker? I'm not sure if an external speaker needs to be 8 Ohm or not. I've read the audio will just be louder on a 4 Ohm speaker (makes sense), but I worry about a possible fire. This scanner will be going into my car.
Thanks.
First, note that the impedance of a speaker is an impedance measurement at the lowest frequency. (The impedance is like resistance for AC and the impedance depends on the frequency.) It is not simply a resistance measurement as you measured. HOWEVER, most of the impedance is resistance, so a multimeter resistance measurement will be quite close, depending on the lowest rated frequency, it might measure 15% lower than the true impedance. So your 3.8 ohm calculate out to be perhaps and impedance of 3.8 (your measurement)/(1-0.15)=4.5 ohms but, as I noted, to be exact, this actually depends on the rated lowest frequency and another calculation, but you do not know the lowest rated frequency so I will not go into that. Generally, a lower impedance, will mean more bass, but the difference between 4 and 8 ohms on a given system may not be detectable by most people. And volume is more driven by the setting on the receiver. You are not going to hurt the receiver unless you really over drive it and that is true if you use 4 or 8 ohms and that is very unlikely as it will likely distort if you set the volume too high and you would not leave it set that high. (The weight of the speaker is totally irrelevant as the heat goes into a small coil and not that weight.) I have never heard of a speaker catching fire and if it were a thing, we would all have heard of it.
