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In Reply to: RE: Second guessing my used tube amp purchase... posted by V01 on March 22, 2017 at 08:48:55
The speaker **sensitivity** is 89 db. The impedance is 4 ohms.
The amp OTOH makes 20 watts whether its 4 or 8 ohms.
Now here's the tricky bit:
The sensitivity spec is 2.83 volts at 1 meter. 2.83 volts into 4 ohms works out to 2 watts.
So your efficiency of the speaker is only 86 db 1 watt/1 meter.
In my room which is 17' by 21' I would need about 800 watts to really make that fly. I used to have speakers that were 89 db and I found that 200watts was not really enough power if I was pushing it. 400 watts might have been enough in my situation; now imagine that the speaker needs 3 db more power and now you see why I would need 800 watts(!) with a speaker like that.
That is very very inefficient, bordering on criminal as the amplifier power requirements become profound; there really aren't any amplifiers made that sound like music and make that kind of power.
This is not to say that the amp won't play- it will and might sound pretty nice, but you won't be able to turn it up much in an average room.
The fact of the matter is that tube power is expensive; back in the old days when tubes were the only game in town that is why there were so many high efficiency loudspeakers. If you are really sold on tubes, do yourself a major favor and get a speaker that is higher efficiency **and** higher impedance!
Tubes in general will perform better on higher impedance speakers- going from 8 ohms to 4 can cost you an octave worth of bandwidth on the bottom end due to the output transformer. Plus the transformer will be less efficient so it will run warmer. OTOH with an 8 or 16 ohm speaker the tube amp will not only have more bandwidth, but its distortion will be lower and you might have a slight amount of more power.
Fantastic post, Ralph. Thanks for taking the time.
Yes, thanks for the info.
I think you are better off with a good tube amp and easier to drive speakers than you are with speakers that are harder to drive and solid state amp that can do the job.
All amps (tube, solid state, class D) make distortion. Not only that but in all cases distortion is higher when driving lower impedance loads. You would think that distortion is inaudible but that is not the case at all!!
The distortion is audible and measurable too.
The human ear converts distortion into tonality! This is why tube amps generally sound richer and smoother (more lower ordered harmonics, less higher ordered harmonics) and transistors tend to sound leaner, brighter and harder (less lower ordered harmonics but more higher orders than tubes usually make).
In fact that's the tubes/transistor debate in a nutshell.
So when you are increasing the distortion by driving a lower impedance, in just about all cases the amp is making more of the higher ordered harmonics. This means it will be less detailed (more distortion masks low level detail due to the ear's masking rule) and harsher (due to the fact of higher ordered harmonics being added).
So any loudspeaker company and make their speaker sound smoother and more detailed at the same time simply by designing it to be higher impedance. Of course if the amp is solid state it will not make as much power, but if sound quality is your goal this is less of a concern.
So its something to think about:
If sound quality is your goal go with a speaker that is easier to drive and especially higher impedance.
If sound pressure is your goal there is a 3db argument for 4 ohms over 8 ohms if your solid state amp can double its power into half the load impedance. IMO/IME 3 db is not much of an argument.
But if you have a tube amp and sound pressure is your goal a higher impedance will serve you better.
So before getting an amp or speaker, first figure out where your preference lies- if you prefer tube amps, try to find a speaker that works with it rather than the other way around. Don't try to make it work hard to drive a difficult speaker, because even a powerful transistor amp driving a hard to drive speaker will never sound like real music, it will at best sound like a hifi. Instead, have the amp drive something easy, so it won't have to make distortion and then you will find the music there as well.
Back to the drawing board I guess. Maybe I should stick with SS amps for now. I previously had my eye on a Peachtree Nova 150.
If you've got the Nighthawk coming, give it a try. If your room is on the small side, you don't listen at higher volumes and your speakers don't dip below 4ohms you might like it. I do believe you're on the right track in regards to the Peachtree Audio Nova 150 but I would actually go for the Nova 300. Ultimate volume is one thing but actually driving the speakers correctly is the bigger issue IMHO.
John Darko @DAR has good write-ups on both the PT 150 and 300. It will give you some insight on what the 300 will give you over the 150.
Computer Audiophile also has good write-ups of the PT 150 and 300. Good luck with your search.
You also might want to check out the Wyred 4 Sound STI500 MKll
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