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Impedance question

I have a Jolida 202 integrated tube amp, it has terminals for both 8ohm and 4ohm speakers and puts out 40watts max to for both 4 and 8. My question is, if I were to use 4ohm speakers does the amp have to work harder to drive them than it would with 8ohm speakers? Also would the volume be the same if I were to compare two sets of speakers both with a sensitivity of 87db, difference being one is 8ohm nominal the other 4ohm?? The reason I ask is I'm planning to upgrade my speakers and have steered clear of 4ohm speakers because I'm unsure how it affects the sound and performance of both amp and speakers. You're input would be very much appreciated. Thanks
rdylan
eldartford
4,262 posts
 
The purpose of the audio output transformer, which has taps for 4, 8, and sometimes 16 ohms, is to make all these loads look the same to the output tubes.
elevick
2,439 posts
 
Generally speaking, most 4 ohm speakers are less sensitive than most 8 ohm speakers. Since tube amps don't double wattage when halving impedance, you will be hard pressed to find 4 ohm speakers with decent efficiency. As stated by Newbee, look for at least 90db.
Final note, 4 ohm speakers can be run off of 8 ohm taps usually without any adverse effects to the amp. Use which ever taps sound best.
viridian's avatar
viridian
4,184 posts
 
Newbee makes a good point, due to the high output impedance of most tube amps, speakers with wildly fluctuating impedance curves will cause modifications to the frequency response due to the voltage divider effect, and are to be avoided, unless you like the sound of the modified response. I would also point out that the four ohm tap has approximately twice the damping factor, or half the output impedance, of the eight ohm tap on any tube amp and so will control the bass response differently.
gs5556
769 posts
 
There's no definitive answer other than experimentation. Usually, one tap will sound better than the other regardless of speaker. But for another amp, the tap can be speaker-dependent. If the amp is stable over reactive loads, then one tap should stand out over the other.
slikric3000
638 posts
 
A measurement (in Ohms) of how much an electrical circuit pushes back when it's pushed.
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