DVV, would you care to comment on Butler Audio`s Hybrid tube amps that utilize solid state for a power output of 150w/8 ohms? Would this allow for a wider variety of speaker choices with a greater dynamic headroom while still maintaining it`s tube-like characteristics? Kickass softness would be nice,,,, any thoughts? Regards, Robin
Sure, Robin. First, let me make this VERY clear - my comments are related to drive capability and amp/speaker interface, not how it will actually sound, and not related to any particular product or company.
How an amp amplifies the incoming signal, whether with tubes or transistors or op amps, is its own business and in any good design, has nothing to do with its actual speaker drive capability. What has everything to do with drive capability is how is its current gain stage designed, implemented and what kind of power supply backs it up.
In short, 150W/8 ohms is 150W/8 ohms, period. This is 21.4 dBW, meaning that it will let you have 21.4 dB of loudness at 1 meter above 1W levels. So, if you have two speakers, one producing say 89 dB/1W/1m and the other producing say 95 dB/1W/1m, the 6 dB difference between them means the second one is four times as efficient as the first one.
Thus, for the same power, the second will produce four times the loudness, or it will produce the same loudness with one quarter of the power the first will need.
Let's assume for the sake of the argument that you are 3 meters, or about 10 feet, away from your speakers. Let's also assume that the theoretically doubled loudness of twin speakers in a stereo system is lost on room furnishing, carpets, drapes, etc. Loudness levels drop by 3 dB, or they halve, every additional meter away from the speaker, again in theory. Thus, at 3 meters, the first speaker will produce (89-6) 83 dB/1W and the second will produce 89 dB/1W.
You have 21.4 dB extra power in your amp. In real life, this could well be more, as no designer is very likely to allow his amp to clip very soon above its nominal power rating, though this could well happen in amps with fully regulated power supplies (which tend to have little headroom above the nominal, but respond to lowered impedances better - a well known trade-off).
With the first speaker, maximum loudness is (83+21.4) 104.4 dB at 3 meters. With the second speaker, maximum loudness is (89+21.4) 110.4 dB at 3 meters. Loudest orchestral music tends to peak at around 109 dB, while the loudest rock concert was placed at 111 dB.
Obviously, with the first speaker, you will have a good dynamic range, but still short of the maximum. With the second, you are almost there.
Now, this is theory, real life is different. For a start, anything over 100 dB is hellishly loud at 3 meters, and you would have the cops, and probably the air force, navy and army at your door long before you started hitting such peaks. Also, women tend to complain at anything over 90 dB, because they feel they cannot be properly heard by you/me/us by then.
The point is, having a lot of power available does not mean you HAVE to use it all, but it does mean your amps should not run out of steam before any other component does with average speakers (whatever that means). You can expect - and receive - faithfully reproduced transients, at least in terms of power, under real life conditions with most speakers, at least those in the 90 dB/1W/1m class and better (which is say 90%+ of all speakers made today).
I reiterate, all this is rather simplified, but it does show what I wanted to say.
Since a good priest does as he preaches, I own relatively efficient speakers, rated at 92 dB/1W/1m, which are powered by amplifiers rated at 180W/8 ohms, or about 22 dBW, meaning I could attain as much as (92+22) 114 dB SPL at 1 m, or 108 dB at 3 m. Since the amp will clip at 257W/8 ohms, this is 24 dBW, so I actually have 110 dB available at 3 m. I never tried getting there, and I never will, mostly because I don't want to be arrested for disturbing of peace.
Thus, the key is the power available from the output stage, in your case 150W/8 ohms. With all but the really inefficient speakers, under normal listening conditions of music, that should be enough, unless you have an unusually large room and sit away from your speakers at over 10-12 feet. I assume you are not a headbanger.
Where that MIGHT hiccup is with DVD movies. This is because Hollywood is not in the business of high fidelity sound, but in the business of effects, and this certainly applies to audio effects as well. They tend to overblow bass sounds, as in explosions, sort of boost it in volume and frequency, and this can suck up tremendous power. Incidentally, this problem caused the appearance of powered subwoofers.
Cheers,
DVV
