I’ve run a 30.5 through an AR pre to 8 ohm 86db sensitivity speakers in a fairly small room. No problem at all with volume to pretty loud levels. I don’t believe it ever got out of class A but have no way of verifying that. Pass will also tell you that there is no sudden change in sound when it goes to A/B. If mine ever changed to A/B I didn’t know it. This 30 watt amp was tested long ago by Stereophile to output about 150 watts I believe, which is slightly higher than the .8 model.
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" The Aerial 5t is a 4 ohm speaker. BTW, why do you feel that you need a 4 ohm speaker? The impedance changes with most speakers!"
Ok, well, I don't know anything about impedance changing. Not that I needed another variable in the mix, but if it's there, it's there! One thing I did not clarify earlier on because I was still learning, was that I want to stay with in the amps Class A rating, and at 8 ohms, that is only 30w/ch. By going with a 4 ohm speaker (as in, only 4 ohm), the amp is now making (advertised) 60w/ch, fully class A.
So I guess in short, my answer is volume and headroom. How much of that I'll need depends on the speaker and likely the source, too. Though my listening levels will tend to be low, sometimes moderate, I can appreciate knowing that I have some flexibility there. 60w/ch still isn't a lot, most amps today make 100/ch.
One thing thats hard to pin, is what is the minimum wattage any speaker needs to sound full or at it's potential. That varies with speakers, and I don't know how to validate what power they need minimum. Maybe most book shelfs only need 10 watts to sound good? Others, more? And thats where sensitivity comes into play. Most book shelf speakers, or stand mounts, seem to be rated 85-86. Not helpful with low output amps. 95 would be a different story, etc. But I seem to be finding more and more 4 ohm speakers,not so much highly sensitive ones. I do know Klipsch makes some, though. So, that said, I'm also open to highly sensitive speakers, I just don't know at what sensitivity level they are on par with twice the volume, which would only be needed as a reference point so I could calculate other sensitivity figures, too.
... is a speaker with sensitivity of 100 at 8 ohms as loud per watt as a speaker of sensitivity 85 at 4 ohms?
If the specs are accurate (and speaker sensitivity and efficiency specs are often optimistic by a few db), and if the specs are defined on a per watt basis, an 85 db 8 ohm speaker will be equally as loud as an 85 db 4 ohm speaker, for a given input power. A 100 db 8 ohm speaker would be **vastly** louder than both of them, for a given input power.
However, such specs are most often defined on the basis of an input of 2.83 volts, rather than 1 watt.
2.83 volts into 8 ohms corresponds to 1 watt; 2.83 volts into 4 ohms corresponds to 2 watts. 2 watts is 3 db greater than 1 watt. Therefore an 85 db/2.83 volt/1 meter 4 ohm speaker corresponds to only 82 db/1 watt/1 meter, while an 85 db/2.83 volt/1 meter 8 ohm speaker corresponds to 85 db/1 watt/1 meter.
In that situation, **if** the amplifier is capable of providing twice as much power into 4 ohms as into 8 ohms the maximum volume it will be able to produce with the 4 ohm 85 db/2.83 volt speakers will be exactly the same as the maximum volume it can produce with the 8 ohm 85 db/2.83 volt speakers. Again, assuming the specs are accurate.
Second, you may find it informative to plug some numbers into this calculator:
You’ll find that under conservative assumptions about placement 30 watts into a pair of 85 db/1 watt/1 meter speakers will result in a sound pressure level of 93 db at a distance of 10 feet. Less conservative assumptions will increase that volume by an additional few db. And doubling that power to 60 watts will only result in a 3 db increase.
Given your preference for "lower listening volumes up to moderate," and the fact that you are in an apartment, I would expect that you would exceed 93 db at the listening position very rarely, and then only on very brief and very occasional dynamic peaks on certain recordings. Consequently, when and if that were to happen a correspondingly brief excursion into class AB seems to me to be almost certain to be unnoticeable.
Given all of that I would strongly recommend that you put aside your stated preference for a 4 ohm speaker. And as you realize doing so would greatly expand the range of available choices.
Also, you may find this paper by Nelson Pass to be of interest, if you haven’t already seen it:
Good luck. Regards,
" I’ve run a 30.5 through an AR pre to 8 ohm 86db sensitivity speakers in a fairly small room. No problem at all with volume to pretty loud levels. I don’t believe it ever got out of class A but have no way of verifying that. Pass will also tell you that there is no sudden change in sound when it goes to A/B. If mine ever changed to A/B I didn’t know it. This 30 watt amp was tested long ago by Stereophile to output about 150 watts I believe, which is slightly higher than the .8 model."
Thats helpful to know, and even surprising! Great to hear from some one that owns the xa30. 8 ohms and 86. Well, sounds like I am being a little to careful here. Just curious, what make/model of speakers?
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