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In Reply to: RE: been there posted by waj4all on May 20, 2011 at 10:17:47
Well, how many dB down was the response in the lower mids than at 1 kHz? If you can hear frequency response differences, you can measure them. Some things that are audible are hard / not yet possible to measure, but frequency response is not one of these. There is no magic, no juju here. If the signal coming out of one setup has lower levels in some part of the spectrum than the signal coming out of another setup, you can measure this. You can use actual music, generated tones or noise to make the measurement, whichever you like. Measurements to fractions of a dB are easily carried out, which far exceeds the ear's ability to discriminate in terms of loudness differences.
My guess is that if this is not some impedance related issue, or a preamp that is not flat across the audio spectrum, then it is placebo effect and would vanish in blind testing. The speakers don't know that the sound is coming through an active preamp - but the listener DOES.
Follow Ups:
Triamp,
I beg to differ.
I've had amps which measure identically, in frequency-response - virtually ruler-flat from 20hz to 20khz - yet one displays more (and more realistic) lower-midrange prowess than the other - differences are apparent in other regions too. The same occurs with pre-amps, speakers, and other components. This is why we're always best advised to listen before buying, if possible - there are differences (including frequency-related) regardless of measurements.
It's been proven, time and again, that measurements do not tell the whole story. If so, then we could have bought our components whole-scale, based on just the measured specifications. We don't. Do we? Low-fi components would also be neck and neck with those at the high-end - some would even be superior, based on all measurements, or even just frequency-response measurements.
However, I do respect your views. Thanks for sharing them!
WAJ
We were discussing passive vs. active PREAMPS, and you are talking about amplifiers, so you're off topic- apples to oranges.
When you say "amps which measure identically, in frequency-response - virtually ruler-flat from 20hz to 20khz" did you measure what these amps were actually delivering into the speakers you were using? I'll bet if you did that, you'd find that they were more than 1 ~2 dB away from "ruler flat." In some cases, an amplifier that measures near perfect into a pure resistive load can vary by more than 6 dB from "ruler flat" - and you will CERTAINLY hear this.
I'm guessing that you actually made no measurements yourself, and that when you say " amps which measure identically, in frequency-response - virtually ruler-flat from 20hz to 20khz" you are relying on the published specification from the manufacturer, or a review test. Such measurements are made using a purely resistive load, not a speaker. All amps behave substantially differently into the complex impedance of a speaker; this is especially true of tube amps, transistor amps show this effect to a lesser degree but it is still present, especially with speakers that present "difficult" loads.
These effects occur because current can lead or lag voltage as a function of frequency when driving a speaker with it's crossover. No such effects are seen when a source (DAC, phono stage, tuner, tape deck) drives a power amp through a passive attenuator or drives the input of an active preamp. The input impedance of a power amp or a preamp is a very simple and "mild" load when compared to a speaker that must be driven by an amplifier.
O.K., I hear you.
No further comment, though.
Thanks again!
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