Audio Research Vs115

Bifwynne - The speakers under test were Thiel CS2.3 driven from the 4 ohm tap. The CS2.3 are a notoriously difficult load for amplifiers, with large swings in impedance over frequency and a minimum impedance of 2 ohms. However, the Thiels and the VS115 match up extremely well, far better than with solid state amps. I currently have the Sonus Faber Cremona M and get pretty much the same results with the VS115.

@Jake, your results line up with the test results from Stereophile and Soundstage I posted above. Did you also have a chance to near-field mic the actual SPL outputs of the Theils. That would seem to be the ultimate test.

I switched over to the 4 ohm tap and am getting used to it. Very different acoustic presentation, probably because the 8 ohm taps has a higher output impedance than the 4 ohm tap, ergo permitting a touch more output variation in the high impedance parts of my speakers, mainly the 2.2K to 4K Hz region of the freq. band. Per Atkinson at Stereophile, the SPL variation is almost half.

Jake, out of curiosity I googled to find bench tests of the Thiel CS2.3. May have looked at the wrong site, but the test results I found showed impedance remarkably holding at a near 4 ohms almost across its entire FR spectrum. As expected the impedance curve had the normal two spikes in the bass region, but that was it.

I'm not saying every amp could eat a constant 4 ohm load for lunch, but I was surprised that past 100 or 150 Hz, impedance hovered at 4 ohms. I must have looked at the wrong speaker. If you have a link to the bench test results you had in mine when you made your post, I'd be very grateful if you'd either e mail me or post it here.

Thanks.

Bruce

Bifwynne - I have a Radio Shack SPL meter but it's not really accurate enough to make good near field measurements.

The 4 ohm tap does have lower output impedance than the 8 ohm tap. However, if you are driving an 8 ohm load you'll get more power out of the 8 ohm tap. My Sonus Fabers are nominally 4 ohms so I use the 4 ohm tap.

Jake,

I re-checked the net to view the bench tests for the Thiel CS2.3 speakers. What I saw in fact was bench test results for the CS2.4s, which as I said had an amazingly flat 4 ohm impedance plot from 50 or 75 Hz through the audible acoustic spectrum.

Do you know whether the CS2.3 was configured differently? I ask because you posted that the 2.3s had modulating impedance plots? Do you have any idea what the SF Cremonas impedance and phase angle plots look like? Couldn't seem to find any hard data on the net.

The reason I am so curious is because I'm trying to gather some real life anecdotal information about how our amps perform when driving speakers with goofy impedance and phase angle plots.

Btw, how do you even measure the output performance of the amp and speaker combo? I have a digital meter that I use to bias the amp's tubes. But I have no idea how to check actual output with the amp hooked up to the speakers. Or how to check output impedance (with no load) off the 4 and 8 ohm taps. Can you advise?? I kinda would like not to damage my gear just to satisfy my curiosity.

Thanks and have a great Memorial Day weekend.

Bruce