The Speaker is a DIY design with a Purifi 6.5" woofer and a Blesma T34B tweeter. The crossover is 2nd order. The tweeter circuit has a 12ohm resistor to bring it down to the woofer. I haven't done an impedance measurement yet on it so I will do that and report back. I wouldn't think that this crossover and driver combination would be a difficult load to drive.
First off, nice build, I was thinking of going DIY and those drivers were very high on my list. Eventually ended up with LS60s but I'd still love to hear a Purifi + Bliesma build.
Oh yeah. Everything was exactly the same. The measurements were taken within the same minute.
Then would you say that it is just a poor performing amplifier? It's 4 ohms above 3Khz and the phase angle is rising smoothly so I wouldn't think there is a problem. But the measurements also different around 100Hz which is the other spot that it dips to 4 ohms. Tube amps suck.
I think it only means your tube amp has an output impedance of .5 ohm or more which isn't bad or good it is just so. With a different speaker you don't get this. With some speakers it might even be a plus. This issue is high frequencies into that speaker have low impedance and at low frequencies the speaker has a high impedance meaning the output impedance is a lesser factor on the low side. If speaker were 4 ohms all the way from top to bottom the FR would be even. It is not however, it has more impedance below 3 khz. If you like the sound don't worry about it.
But what speaker has a flat impedance? I like the sound of the speaker. It measures incredibly well on and off-axis. It sounds great with the Parasound or Buckeye Class D that I use to design them but the tube amp sounds so dark. It's clear that this tube amp struggles with loads below 5 or 6 ohms. Thanks for your insight on this. I would need a speaker that doesn't dip below 6 ohms on this amp. It's fine, I'm selling it and buying a Benchmark amplifier or another Buckeye.
I forgot about the magnepans. Not a fan of those due to their frequency response being far from flat. My tube amp has always been fine with my 8 ohm (nominal) speakers. I know that they are a distortion factory but it sounds great. For these speakers (which measure spectacularly and are designed with the lowest distortion drivers) I will be moving either to a Class D or Benchmark amp. Cheers and thanks again for the help.
Only if the amplifier's output impedance is also resistive, or very-low relative to speaker impedance across the frequency range like a solid state amp.
Speakers are a reactive load, and the Equivalent Peak Dissipation Resistance (EPDR) may actually be lower than the measured impedance. This may or may not be contributing to the cause the 2dB drop.
The EPDR is a bit lower than the measured Impedance since I can see that also in REW. I'm definitely ditching the tube amp. I realize that it has been changing the frequency response of every speaker I've put it on. When the impedance is low then it doesn't drive it well. When the impedance is high then it it increases that spectrum of the frequency response. These are not difficult speaker loads to drive at all. I knew that this was possible with a tube amp but I didn't know it could be this drastic. It's changing as much as 3db over a wide spectrum, which is not only easy to hear, but is destructive. No thanks. Hey @Buckeye Amps: Another order coming your way soon.
