The answer won't be the same, from one tube amp to the next. There's no gurantee that your sub will mate well with a tube amp, either. I just got a tube amp, and so far it seems to only lack the bottom octave, and some of the top octave. It's not broken in, so I can't say definitively yet.
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Dear Guy:Check the specs. on your speakers.i.e.how low they go.And not the+or-6db figure.That means you would have to turn it twice as loud,and your mids and highs are twice as loud now,so the bass is still lagging.Do the test disc thing.You got test [email protected] 20 30 40 50 cycles.You will hear when the loudness dops off.That is where your sub should be cut off.Most people aren't aware there is no "music"down below,say 35.You are actually looking for good low mid bass.Subs are quite a can of worms;save home theater use.To get one to work properly it needs the same tone/colors as your main speakers. That's where you get mud.Remember that down [email protected] [email protected] even tho it is down the whatever it still muds things up in overtones.(Both drivers producing overtones of the same note)By the time you have eliminated that you got bass suck-out.Good simi expensive tube amps do bass well.But good bass starts right at the source.CD players, DAC's, cables,power cords,pre amps,and speaker cables,all matter.Don't think for a minute they don't.Oh ya,and speakers have to be good enough to pass all this to your ears.Then there is room and placement,and room nodes.Another time for that.
Generally speaking, tubes aren't any good at putting out the current needed for good bass. It looks to me like you're crossing your sub over way too low(35Hz??). Unless your speakers are at or quite close to full range, go higher. Otherwise, you could be lacking base due to such a low setting your mains can't make up for. I must disagree completely with avguygeorge above. Don't bother looking at +/- freq. response of your speakers. That doesn't mean anything much unless you're system is in an anechoic chamber. Real world in-room response will vary much more, ESPECIALLY in the base. Timbre matching is also irrelevant here, since that takes place in much higher frequencies, and is more important in the midrange. Avguygeorge couldn't tell the timbral difference in a 40Hz tone, and neither can you or I. Also, that, "mud" he is talking about can happen at any frequency, so ignore that. Base is the hardest to get right usually because of room response. The reason that base is considered "omnidirectional" below about 80Hz or so is because the wavelengths are longer then the typical room, which means that the room becomes pressurized with the tone and can't be located("room lock"). The bottom line-a tube amp is probably just fine. Set the crossover just slightly above the freq. that your speakers start to roll off, then use test tones to adjust the volume. That way you'll get the best of both worlds; the tube amp can do it's job without having to work for all that base it can't do, and it'll sound better as well. Do the final adjustments by ear, but remember, if you get within +/-5dB, that would be considered quite good base results, unless you have a particularly large room.(over 40 feet long) I hope this makes sense to you; I'm writing quickly from work. Let me know if you would like more clarification. Good luck!