Speaker Resistance ?

• posted
Hello,
Not an E.E., so please bear with me a bit.
Have a 2" dia speaker in kid's toy.
Seem like it doesn't work, but hard to get to, to verify.
It says 8 ohms.
I imagine that this is the Z, and not the dc resistance; correct ?
a. What might be a "typical" dc resistance for a
really small (2") speaker like this ?
b. Can't get a really good look at it, as it is really embedded.
It might be more of an electrostatic type of speaker, than the typical
moving coil type.
How would your answers for (a) change, if this is so ?
Thanks,
Bob
• posted
8 ohms is 8 ohms. If you were to completely disconnect the speaker and connect an ohmmeter across it's leads, the ohmmeter would read 8 ohms.
• posted
A little investigation would show that typically a speakers resistance is 2/3 to 3/4 of the speakers impedance. So your 8 ohm speaker will probably read around 6 ohms or so with a multimeter.
dave y.
• posted
USE GRAMMATICAL SENTENCES so that we can understand you.
• posted
Even though I could not understand the OP, I do understand that you are WRONG! Ideally, the speaker voice coil would have a resistance of ZERO. Unfortunately, it is impossible to manufacture such voice coils short of having superconductivity. The impedance of the voice coil is ideally found by applying am ac signal voltage V, measuring the resulting current flow I and finding the impedance Z = V/I using complex numbers. The applied V is countered by a back emf so that Z is not equal to the measured resistance of the voice coil.
• posted
Really? Did you even try measuring the resistance of an 8 ohm speaker before say that it won't measure 8 ohms?
• posted
Yes. There is an advantage to having resistance in the voice coil. If the speaker is driven from a low impedance source,
• posted
I've measured speakers before and yes, an 8 ohm speaker I measured was an ohm or two. In this case I doubt they'd invest much copper in a speaker for a cheap child's toy so I'd guess that one would probably read higher.
(Piezoelectric tweeters ohm out as infinite, however)
• posted
With an ohmmeter--yes. But suppose you use an ac bridge. A typical bridge can usually be driven by an external generator as well as an internal generator usually at 1 kHz. An HP 200A or one of its descendants is typical.
At low frequencies, the equivalent circuit of the crystal or film will look like a capacitor in parallel with a resistor. As frequency increases, the resistance drops from infinity. The capacitive reactance also drops. As the mechanical resonant frequency is approached, the reactance drops until it (ideally) reaches zero at resonance.
• posted
Oh I know all that. I have a degree in electrical engineering. I just mentioned that for the poster who seems to think 8 ohms is 8 ohms, DC to daylight.
• posted
Probably about 3/4 - 7/8th of the impedance. For a higher power speaker, the resistance will be significantly lower.
A passive electrostatic speaker is capacitive, but they are normally used for higher frequences only, together with a coil speaker for the lower frequencies.
• posted
Hi Bob, If it says 8 ohms on it,it is most likely just a cheap speaker you could get at rat shack in several diameters. Not sure what you mean by "Seem like it doesn't work " Does sound come out of it or not? The speaker is not the only thing responsible for the sound. It's also down on the list of failures on such products.
Tom
• posted
If the reason for this discussion is to see if it works, just put a 1.5 v battery across it intermittently and see if it crackles.

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