On the speaker side, I'm with Lonewolf, slightly higher sensitivity, minimalist design.
Like Chris I've heard lots of speakers. Many that claim to be tube friendly really aren't. Sure they have a Zobel in it to show a flatter impedance to the tube amp but
every Zobel I've heard sucks the life right out of the sound.
If I had a research budget and loads of time to experiment I would construct a speaker like this;
First and foremost, use a 1st order XO. A simple cap and coil, no more, no less (unless you want to do the Zu and Infinity trick letting the woofer run wide open then cap a tweeter into the -6db point). If the designer does a good job of picking a driver that rolls off
evenly and
doesn't exhibit nasties at cone breakup on the upper frequency extremes, there is no reason you can't use a simple 1st order XO on the woofer (assuming it sounds good above 2.5k or so). The tweeter is less of a concern. Just push the XO frequency up a bit to handle the -6db slope and you'll have a decently flat XO point. Next, I'd position the drivers or construct the cabinet so that you have a minimal issue with baffle step compensation. Again, taking a notch filter out of the signal chain will keep from sucking up precious tube (and SS) power.
Sensitivity isn't crucial but I think its important. Something around 92 would be a good baseline for starters. You could always go with an MTM or an MMT design to increase the output assuming the tweeter is up to it (lobing issues aside). Reason I say this is that the majority of tube amps out there are 20+ watts. With 92+db and assuming you have decent output iron on the amp, you will drive them to very comfortable listening levels in a moderately sized room.
When it comes to cabinet design, I've recently listened to some very good sealed cabinet designs. They go deep enough that many people wouldn't require a sub. The plus side of this issue is that it should help in reducing the impedance peaks and phasing issues in a ported cabinet. As part of the overall design, the speaker needs to maintain less than (about) a 50ohm impedance peak. This will present a much easier load for the tube amp thus making it completely unnecessary to install the
life sucking Zobel. The sealed cabinet isn't absolutely necessary, if you can extend the bass an octave or two without causing too many negative issues with the tube amp, all is well. A transmission line is an option too.
Think absolutely old school here. Designs and manufacturers like Dynaco, Advent, KLH and others didn't over design their speakers. They used common sense to produce speakers that worked well with tube amps. Sure, some of them used 2nd order XO's which aren't horrible but it does add a tremendous expense to the speaker (if you use quality parts) plus it does suck just a bit more life out of your speaker (more parts=less life). Granted, the speakers and passives of the day didn't sound all that terrific but any amp of the day would drive them without a problem.
Even though speaker technology has advanced, not many 'designers' have figured out all they have to do is look to the past to come up with a good sounding speaker. They all want to come up with some new fangled approach to crossover design that they can tout as 'inventive' or 'novel' and use as ad copy to sell their product. I know, I know, I just made a wide sweeping statement that doesn't hold true in every instance.
The
KISS principal is all you need to succeed, honest. It will take work. Nowadays, it seems that speaker designers and manufacturers are far less concerned about a speakers interaction with a tube amp because they know if they put enough bandaids in the filter circuit, they can get it to measure flat.
Oh, when you test your tube friendly speaker designs, don't use some monster 150wpc tube amp. Try a simple push pull EL84 design with reasonable output iron and very little NFB. If it works with this amp, it will work with nearly anything.
....sorry for the (sort of) mini-rant against conventional speaker designers. sure, if you are using solid state, you have no issues because it can handle the extra load seen by the speaker but so few actually design speakers
specifically for tube amps. if they
really understood the interactions, there would be a wider selection of truly tube friendly transducers out there.....but then again, I just ranted some more........sorry
..just my $.02 from a grumpy minimalist
