hi everyone ! plz tell me how to choose a speaker for an audio amplifier. 4 ohm or 8 ohm?? and what is meant by the resistance that speaker has on its label. e.g 4 ohm speaker, 8 ohm spkr....either its the resistance of the coil or anything else?
I have designed an MOSFET based audio amplifier. its no load gain is 56. but when i connect 8 ohm load (in proteus simulation) the output becomes zero. why?? plz help me

 

What does your load look like? A resistor? Is the output of your amplifier AC coupled to the speaker?

A speaker is basically a moving coil of wire. It has a DC resistance, but it also has inductance. Any device that has both resistance and inductance has impedance. Impedance is represented by a complex number. The resistance is the real part and the inductive reactance is the imaginary part. The impedance depends on the frequency. The magnitude of the complex impedance is averaged over a portion of the audio frequency range and this number is used to match speakers to amplifiers.

 

hi everyone ! plz tell me how to choose a speaker for an audio amplifier. 4 ohm or 8 ohm?? and what is meant by the resistance that speaker has on its label. e.g 4 ohm speaker, 8 ohm spkr....either its the resistance of the coil or anything else?
I have designed an MOSFET based audio amplifier. its no load gain is 56. but when i connect 8 ohm load (in proteus simulation) the output becomes zero. why?? plz help me

You can get more power from a 4 ohm speaker using the same power supply voltage.
Most of the speakers 4 ohms is resistance, but a small portion 10 - 15% is reactance.
Can't see what might be wrong with your amplifier. Maybe a schematic would help.

 

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A speaker is basically a moving coil of wire. It has a DC resistance, but it also has inductance. Any device that has both resistance and inductance has impedance. Impedance is represented by a complex number. The resistance is the real part and the inductive reactance is the imaginary part. The impedance depends on the frequency. The magnitude of the complex impedance is averaged over a portion of the audio frequency range and this number is used to match speakers to amplifiers.

You neglected to list the part of the impedance that actually moves the cone and makes the sound.
That appears as an added resistance to an AC signal, since it is doing work.

 

You neglected to list the part of the impedance that actually moves the cone and makes the sound.
That appears as an added resistance to an AC signal, since it is doing work.

You're right, but I think the TS might need to swallow all of this in small chunks since this is apparently terra incognita.

 

hi everyone ! plz tell me how to choose a speaker for an audio amplifier. 4 ohm or 8 ohm?? and what is meant by the resistance that speaker has on its label. e.g 4 ohm speaker, 8 ohm spkr....either its the resistance of the coil or anything else?
I have designed an MOSFET based audio amplifier. its no load gain is 56. but when i connect 8 ohm load (in proteus simulation) the output becomes zero. why?? plz help me

This is probably happening because you need to connect a resistor in series with the speaker for proper impedance matching. Try to put a 500 ohm resistor in series with the 8 ohm and tell us the results.

 

This is probably happening because you need to connect a resistor in series with the speaker for proper impedance matching. Try to put a 500 ohm resistor in series with the 8 ohm and tell us the results.

That's okay for the test, but it will limit the speaker output to a very low level.

What do you mean "proper impedance matching"?
Modern solid-state amps have a very low output impedance which is not matched to the load.