Click title to read one, or click date to read all below it.
03-09-08
A very likely reason two amps can sound different, yet measu ... Germanboxers
03-09-08
Assuming only the amp changed in the signal chain, is being ... Bob_reynolds
03-09-08
Tia - i am most certainly not any kind of expert, but i did ... Mr_hosehead
03-09-08
I would bet that they don't really measure the same on the t ... Pbb
03-09-08
I am far from an expert, but from what i have read, measurem ... Cyclonicman
03-09-08
We need to bring back julian hirsch from the grave to recite ... Tiger
03-09-08
Generally if there is an audible difference then a differenc ... Shadorne
03-09-08
Cost. every amplifier is designed to a price point. since th ... Gs5556
03-09-08
I'm thoroughy convinced that we don't know how to measure so ... Danlib1
03-09-08
Amps are like ice cream flavors. i agree with most threads h ... Philefreak
03-09-08
nah, leave him there. it's threads like this one that demon ... Nickword
03-09-08
You don't listen to an amp. you listen to a system. Curtis
03-09-08
Danlib hit the nail on the head. two amplifiers can measure ... Davemitchell
03-10-08
Consider tube amplifiers. replacing the tube with a differen ... Mrtennis
03-10-08
Amps all measure differently, except our measurements are ac ... Ktstrain
03-10-08
Kurt, thanks for your input. a highly reputable swiss manufa ... Dazzdax
03-10-08
they measure the same? what did you measure? Pauly
03-10-08
Kurt, i like your wine example. in amplifiers, it is tim, i ... Shadorne
03-10-08
Dazzdax, that is still just one group of people's opinions. ... Ktstrain
03-10-08
Shadorne, the levels of distortion that can ruin an amp can ... Ktstrain
03-11-08
Although alluded to before, it seems that the amount of nega ... Atmasphere
03-12-08
Another interesting thread with great contributions by every ... Amfibius
03-13-08
Amfibius, take a look: http://www.atma-sphere.com/papers/pa ... Atmasphere
03-13-08
I never look to specs other than output power to make an amp ... Phd
03-13-08
Phd, one of the distinctions of the power paradigm vs the vo ... Atmasphere
03-13-08
Atmasphere, you are correct, that distinction has been clear ... Phd
03-14-08
Ktstrain, great posts. very interesting. Joeylawn36111
03-14-08
While i enjoy and value atmasphere's posts on the subject, i ... Kirkus
03-15-08
Kirkus, how did the loudspeaker designers gain enough levera ... Cyclonicman
03-15-08
Well, cyclonicman, legend has it that james lansing, immedia ... Kirkus
03-17-08
Hi kirkus, i'm not the one who has created these paradigms; ... Atmasphere
03-18-08: Kirkus
Hi Atmasphere . . . my main point is that hi-fi speaker designers simply do not consider an amplifier to be anything other than a voltage source, and that they never have. Further, it seems obvious to me that amplifiers have historically been intended to operate as voltage sources. And please believe that I'm not categorically critizing amplifiers that deviate from this practice, but I believe that a high output impedance, as an intentional, acceptable goal, is a completely modern phenomonon that is unrelated to what all but a very few speaker designs are anticipating.
The impedance at which an amplifier produces maximum power output, again, is completely non-sequitur. When I completed the restoration on the Marantz Model 2s currently in my system, I measured the output impedance at about 0.18 ohms from the 4-ohm taps - for all intents and purposes, a voltage source. This was the only tap I measured, but let's say that the 8-ohm taps have about 0.4 ohm output impedance. I would guess that my "4-ohm" Mezzo Utopias (typical reflex cabinet) would range from about 4-15 ohms. The modification of the speaker impedance on the voltage response of the amplifier would thus be about 0.3dB from the 4 ohm taps, and about 0.6dB from the 8-ohm taps . . . very little difference between the two. My point is that even if the load is mismatched and grossly affects the maximum power output, these 1950s-era amplifiers behave overwhelmingly as a voltage source, NOT a power source or a current source - if they're operating below clipping.
If I was to look for evidence that loudspeaker designers viewed an amplifier as a current source, here's what I would expect to find: Filter values and woofer conjugates in crossover networks that are calculated with the expectation of a high source impedance. Parallel resonant networks inside crossovers to dampen the impedance peak(s) from the cabinet/port. Standard models for calculating woofer responses from Thiele/Small parameters, that include a high source impedance. A specification from a speaker manufacturer that reads something like "recommended amp output impedance: 2-6 ohms". If I've been living under a rock, please tell me, but I've NEVER seen any of the above.
I chose the Apogee as an example of voltage-source thinking because I remember it being a very capacitive load, not simply low-impedance; maybe my memory fails me. But it doesn't surprise me that a capacitive speaker could sound nice from a high output impedance SET amp, for a couple of reasons. First, there's nothing like a high output impedance to keep an amplifier within its optimum current range . . . in the same way as a series resistor! Ditto for avoiding stability issues that many amps exhibit into capacitive loads. And third, I could easily see a capacitive load causing a resonant peak in the output transformer that might kinda offset the Ohm's-law HF rolloff. But again, I don't think the Apogee designers were anticipating these conditions.
Anyway, I find this interesting because there are so many "high-end" speakers out there that leave me scratching my head as to why they don't sound good to me at all, and I wonder if this is the way they're "supposed" to sound.
Kirkus (System | Threads | Answers | This Thread)
03-18-08
Kirkus, the acoustic research ar-1 is a good example of a sp ... Atmasphere
03-19-08
Atmasphere, i owned ar-3s (identical to ar-1 except for mid ... Kirkus
03-19-08
Hi kirkus, i have a set of ar-3s myself- i use them for moni ... Atmasphere
03-20-08
Okay, so i am a little jealous of your ar-3s. mine went awa ... Kirkus
03-20-08
Kirkus, your technique for the d130s should do the job. i'm ... Atmasphere
03-20-08
Atma, why do you say tubes obey the rules of human hearing m ... Wireless200
03-21-08
Hi atmasphere . . . i'll mock up the speakers this afternoon ... Kirkus
03-21-08
Kirkus, sounds like he did! since a feedback signal is one ... Atmasphere
03-21-08
Would an increase in sibilance at higher volume be a charact ... Tvad
03-21-08
Tvad, it can be (usually not clipping though), but there are ... Atmasphere
03-21-08
It's never easy. Tvad
|
|
