System assembled; only a final decision about speakers remains

you also need to demand EVIDENCE of this perfect phase coherence in the crossover region. 

I wouldn't plug a power conditioner into a power strip.

I wouldn't plug a power conditioner into a power strip.

Steve, that is not what he will be doing.  This particular conditioner/surge suppressor mounts directly on the wall outlet.  It in turn provides only two outlets.  He will plug a power strip into one of those two outlets to provide up to ten outlets he can use for the components in the system.  The power strip will contain nothing other than wires and outlets.

Regards,
-- Al

IF: you have a 60w tube amp with a damping factor of 20,
THEN: make sure you get a speaker that is, at least:
___ sensitivity
___ ohms nominal
___ ohms curve that looks like [insert description]
___ other metric(s)?

Having a rough and ready chart like this could help me rule out of bounds any number of speakers.

A lot depends on the room- a bigger room will mean that you need greater efficiency. A chart would be nice but you don't really need one.


A flat impedance curve is nice but not mandatory. What's important for a tube amp in the bass is that the impedance is benign. As a general rule of thumb I avoid speakers with dual woofers as they tend to be nominally 4 ohms, and that's going to be a lot harder to drive. You need to make the most of the watts you have; a 4 ohm woofer array for a tube amp is like using a poor lubricant in an engine- it won't make as much power and the tubes will wear out faster.


The more feedback the amp has the more peaks it can tolerate in the impedance curve. If the amp has no feedback then the speaker has to be designed to accommodate that. Since the ear tends to favor tonality induced by distortion (brightness of solid state, 2nd harmonic warmth of tubes) over actual frequency response, this can be important. There is more information about that at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

IME 50 watts is a bit lean in the power department if the speaker is only 90dB. My speakers are nearly 98dB and I find 50 watts is pretty nice on that; that would be like running a 300 watt or so amp on a speaker that is only 90dB. Now you can see how important speaker efficiency actually is!

One further note- since the industry has gone over to voltage measurements rather than power, you can run into important issues when trying to suss out speaker efficiency! In the old days a speaker was measured at 1 watt/1 meter to get a certain output (Efficiency). Nowadays a voltage measurement is used (Sensitivity) which is 2.83 volts/1 meter. 2.83 volts into 8 ohms is 1 watt but 2.83 volts into 4 ohms is 2 watts. The difference there is 3dB, a doubling of amplifier power. Now tube amps don't double power as impedance is halved; this is why Efficiency is a more important and useful spec when sussing out speakers. But since Sensitivity is used you always have to do that math. For example, if a 4 ohm speaker is 90dB, subtract 3 dB off the Sensitivity to get the Efficiency value; its actually 87 dB 1 watt 1 meter. Conversely if a 90dB Sensitivity speaker is 16 ohms, add 3 db to get the Efficiency.


So beware of that! IMO, in most average American rooms, 93dB and 8 ohms is a good place to start if your amplifier power is 50-60 watts. One other thing to watch for is some speaker manufacturers are more conservative about these ratings than others, depending on what part of the efficiency curve (bottom or top) the speaker's rating is derived.

@kenjit I could ask Jim what makes his speakers better, but my guess is he'd do what anyone who makes good equipment would do — shrug and tell me to try them and return them if I don't like them. And I suppose if I ask for evidence of perfect phase coherence, I should use all caps — just to let him know I'm "on to his little scheme"? [I mean, dude — didn't I already say, right at the beginning — that this is simple? Buy, try, keep, or return? I can explain that to you, but I can't understand it for you.]