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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: About SS output impedance?? posted by Frihed89 on August 9, 2017 at 00:04:33:
This expands a bit on what Davey says below. However, this is also just a basic generalization and simplification, and therefore doesn't address all the intricacies of amplifier and speaker interaction.
Generally speaking, a solid state amplifier is like a voltage source. For example, if you play a 1000-Hz test tone using a solid state amplifier, it will apply the same voltage to different speakers regardless of their impedance. In other words, if the test tone causes the amplifier to produce 1-volt at its output, it will apply that same 1-volt to an 8-ohm speaker as well as to a 4-ohm speaker or even to a 2-ohm speaker. This is because of its very low output impedance. A tube amplifier will not do that. A tube amplifier is more like a power source.
This means that if the test tone causes a tube amplifier to produce 1-watt of power into an 8-ohm speaker, it will also produce 1-watt of power into a 4-ohm speaker. This results in different voltages. The tube amplifier will be applying 2.83-volts to the 8-ohm speaker but only 2-volts to the 4-ohm speaker. Therefore, if the two different speakers have equal sensitivity, the 8-ohm speaker will play louder than the 4-ohm speaker because the tube amplifier is applying higher voltage to the 8-ohm speaker.
Speakers are designed to produce a flat frequency response with constant voltage. Therefore, if a speaker's impedance curve fluctuates across the audio frequency bandwidth, it's loudness output will also fluctuate when using a tube amplifier but not so much with a solid state amplifier. In other words, regardless of its impedance curve, a speaker will have a relatively flat frequency response with a solid state amplifier but not necessarily with a tube amplifier. To achieve a flat frequency response with a tube amplifier the speaker must have a relatively flat impedance curve.
Speaker sensitivity is a different matter. A more sensitive speaker requires less power to play at the same loudness as a less sensitive speaker. Speakers with high sensitivity can be used effectively with low power amplifiers, but speakers with low sensitivity require higher-power amplifiers to achieve the same loudness.
Suppose one speaker's sensitivity is 85-dB and another speaker's sensitivity is 100-dB. If you were using a 10-watt amplifier with the 100-dB speaker, you would need a 316-watt amplifier to make the 85-dB speaker play just as loudly as the 100-dB speaker.
Hopefully, this will give you a better appreciation of the difference between tube amplifiers and solid state amplifiers relative to speaker impedance and speaker efficiency.
Good luck,
John Elison
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Follow Ups
- RE: About SS output impedance?? - John Elison 08/9/1710:54:49 08/9/17 (1)
- RE: About SS output impedance?? - Davey 17:43:05 08/9/17 (0)
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