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In Reply to: Re: I'm just not sure about one thing posted by Pat D on November 8, 2006 at 17:55:17:
First of all, it is not the alleged roller coaster impedance curve that causes the audible frequency response variations, but it is in great part the of the interaction of the output impedance of the amp with the impedance curve of the speaker.Same thing. Speakers with linear curves don't exhibit the +/- 1 db variations.
First of all, that the FR variations of amps with a high output impedance into many speakers loads is likely to be audible, sometimes While you might prefer the response of the S2 with a tube amp, then again you might not. quite audible, whereas the FR of low output impedance amps varies very little into most speaker loads as compared to driving a resistor.
Indeed. 1 db variations are audible. 7 db variations are grossly audible.
JA, who took the measurements of the Paradigm Signature S2 for Stereophile, commented that "the balance overall is impressively flat," and it is.
We must be reading different reviews.
"The graph is impressively flat from 80Hz to 20kHz, though with slight excesses of upper-bass and mid-treble energy apparent. The former goes some way toward compensating for the S2's lack of mid- and low-bass output, while the latter is not unexpected, given my feelings about the speaker's slightly forward treble balance."
In JA's measurements, there is no such thing as a "+8 / -13 db response" in his curves above the bass.
My mistake. I was looking at the crossover plot. The summed response is only +7 / -5.
While you might prefer the response of the S2 with a tube amp, then again you might not.
Well the errors remain complementary given the extreme impedance curve. I'm not much of a box speaker fan anyway.
rw
Follow Ups:
Where is the summed response +7 -5??? There ain't no +7 anywhere near the audible range. I can see why you could misread the divisions above 10K, but I assure that high frequency tweeter resonance is way up about 27K or so, and not even you can hear it. JA didn't mention it, possibly presuming that by now readers would know how to read his graphs, but to go by your example, evidently a dangerous assumption. Anyway, here's an earlier review where JA did describe it. See his remarks above Fig. 2:http://stereophile.com/standloudspeakers/272/index6.html
So much for the +7 dB!!
Now, the -5 dB. This is a very narrow interference dip on axis around 12.8 kHz. Being very narrow and quite high, it's not very audible. As well, the dip does not occur in the off axis curves, again reducing its audibility. If you read the review, you will see that JA commented on that as well, but apparently it slid past you. Now, the research of Dr. Floyd Toole has shown that off axis dispersion affects the sound of speakers a great deal in the real world, a conclusion accepted by JA, BTW, among others. But you totally ignore that.
You also have utterly failed to see one of my points, which is that the broad modifications introduced by using using the tube amp specified would probably be quite audible--in fact, certainly more audible than that ultrasonic ringing which even you can't hear, and also more audible the very narrow interference dip around 12.8 kHz on axis. So much for the significance of the -5 dB dip, whose audibility you exaggerate.
If the impedance curves are flat, then a good tube amp and a good SS state amp should have virtually identically FR's into the speaker load. So I see no argument for preferring tubes.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
Throughout the range of 100 hz to 10khz there is more than twice the variation in the speaker response than the +/- 1 db variation introduced by the tube amp. We'll totally ignore the fact that the errors are complementary.
Where do I start? Lessee here.
+3 db at 150 hz
-2 db at 300 hz
-4 db at 800 hz
-2.5 db at 1.5 khz (entire octave from 1khz to 2khz depressed)
-2 db at 6 khz
+3 db at 10khzrw
Well, we've talked you down to an extremely narrow -5 dB dip at 800 Hz (which you have thus far ignored for some reason) and a +3 dB peak at 10 kHz . I should point out that JA's measurements of the upper bass tend to introduce a hump anyway, and that the NRC anechoic measurements give a somewhat different picture.Point one, we all know that amplifiers have smoother frequency responses than speakers. You seem to be attempting to make some point or other by repeating this, but you are far from clear as to what it is.
Oh, and by your standards, the response of the amp you showed is about +1, -1.5 dB into the simulated speaker load--I personally would ignore that narrow little dip, but since you don't, I won't. I point out that this will be audible.
Second, if you look at the NRC measurements, it is not at all clear that the variations in the FR of the tube amp into the simulated speaker load is complementary to the the on axis response for the Paradigm S2. In any case, if you prefer tubes, that's fine with me. I don't and for some reason that seems to bother you.
In any case, you have not made a very useful or significant comparions between the FR of the tube amp and that of the S2 speaker. An amplifier's frequency response is expressible with a single amplitude vs. frequency plot whereas a speaker radiates sound in all directions, and the FR in various directions is different. If the microphone moves even slightly in relation to the speaker, the FR will be different--something which is very clear in the NRC measurements and is also ascertainable from the dispersion plots in Stereophile.
____________________________________________________________
"Nature loves to hide."
---Heraclitus of Ephesus (trans. Wheelwright)
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