We performed a number of tests measuring SPL (sound pressure levels) with the Radio Shack SPL meter using 2 different power cords and 3 different amps. The rest of the system remained fixed (Levinson 39 CD player, Valhalla interconnects and speaker cables, Burmester 877mk II preamplifier, and the Acapella Audio Arts Campanile High speakers. At the time of the tests, neither the Edge NL-10 amplifier, the Audio Aero Capitole Amplifier, the Nordost Eldorado power cord, or the Acapella speakers were broken in. We used the Stereophile Test Disk #2 Low Frequency Warble Tones as the signal generator for our tests.

Our original goal was to determine the in-room response of the system with respect to bass performance. However, what we found was that as we changed out amplifiers and their power cords, we measured radically different frequency responses of the system. This was contrary, to our expectation at least, that solid state amplifiers all have more or less flat response curves and would measure the same, that solid-state and tubes amplifiers would share a more or less flat response curve for most of the lower frequencies, and that different power cords only differ in the amount of detail transmitted and grunge removal they are capable of.

Please note, that the flatness of the frequency response curve for any component, including power cords, has little to do with the overall quality of the component (which involves maintenance of timbral accuracy, transmission of all of the information (detail), quickness, etc.). In fact, the overall magnitude and shape of the frequency response has mostly to do with the room itself (primarily) and with the speakers (to a much lesser degree).

These test results are only a rough approximation and will hopefully prompt further study - especially in the area of trying to correlate the (objective) measurements with the observed (subjective) quality of musical reproduction - because otherwise all measurements are worthless. Also, it would be interesting to see the measurements as to how the frequency response changes for a component before and after break-in.

One, that the 2 different power cords have identifiable frequency response characteristics.

Two, the Nordost has a pronounced dip at or around 125 Hz.

One, the Nordost dip at 125 Hz is still present.

Two, that there is a measurable difference in frequency response between a cold amplifier and the amplifier after it has warmed up (and these amps actually get quite hot when warmed up)

Three, that each amplifier also has its own frequency response, and that this frequency response is not flat.

Four, that for some reason, the apparent bump in the 63 Hz frequency response (presumably do to in-room re-enforcement of this frequency) is not present with these monoblocks after they are warmed up.

One, that there is a bump in the frequency response around 63 Hz.

Two, that there is a suck-out in the frequency response of the Nordost power cord around 125 Hz.

Three, that this amplifier also has its own, unique frequency response.