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
IF you are picking speakers that are properly matched to tube amps in the first place, those having relatively flat impedence curves with no really large sharp peaks or dips in the impedence values, the the issue of 4 or 8 ohms is not a big deal and the amp wouldn't 'work harder for either'. The output for 87db speakers would be the same with either 4 or 8 ohms. You just pick the impendence connection that sounds best to you.

However if all you are taking into consideration is the nominal impedence value, not the actual curve or the minimum impedence, stick with 8 ohm speakers. A speaker with a nominal 4 ohm impedence could have a substantial dip down into the 2's which would make it hard for many tube amps to drive, absent a 2 ohm tap.

These issues have been discussed extensively in this forums. Perhaps a bit of archive reading will help you understand them better.

Hope that helps a bit.
Its OK to use 4 ohm speakers as long as you use the 4 ohm taps on your amp. But in my opinion you should be looking at speakers with a little higher sensitivity, something like 90db 1watt@1meter or higher. Every 3db up is almost like doubling amp power.
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.