Axiom Home Page Forums General Discussion Stereo INSANELY BRIGHT?

Curtis, I don't, because if they're flat, they aren't.

so something can't be explained, because the on axis graphs of the 170 and M22 are very close...yet the brightness of the M22 can not be denied as being there on M22...of missing from the 170.

curtis

Curtis, if there's in fact a difference it has to be measureable. Instruments are far more sensitive than human ears, even "golden ears"(i.e. those who can hear the inaudible).

This is by far my favorite online audio group that I visit, but where some groups are overly interested in cables, amps, etc...this group seems to be just as overly dismissive of these things.

One thing I will add to this conversation is that though you suggest there should be no audible difference in amps, you go on to compare receivers. There's a difference. The amp is only one small part of a receiver. There's a hell of a lot more going on in that little box than sending power to the speakers. So even if all amps are sonically the same, all receivers won't be.

John,

All of us that have heard the CBM-170 and M22 hear a difference....especially in the highs. Are we imagining it? There is something that is not explained in the graphs.

curtis

Again, those NRC graphs are plotted on logarithmic scale and are rather small to look at.
Those graphs are ANYTHING but flat and they certainly are NOT identical.

Talking about the frequency response of 2 receivers that ARE identical on these graphs would mean they both look EXACTLY the same and just as flat as this:
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until they trail off at the lower or upper end of the spectrum.

The brightness perceived in the Axiom speaker could be due to any number of varying peaks shown in those NRC measurements.

OK OK...next topic. I also like this board, and do not want to reduce its value.

I hope the upcoming Ascend board is this good, and I hope that you kind Axiom folks participate where you see fit.

curtis

Curtis,

Don't worry about it; you're not going to win this argument with these guys. Believe me, I've tried.

First of all, anyone claiming that there are no differences, audible or measurable, between amps is seriously misguided, as any audiophile knows. Technically, I believe sonic differences may have a lot to do with dynamics and transients.

Anyone can design a solid state amp that measures with a flat frequency response curve. But if you read the fine print, even in Stereophile, you will see that tests are typically performed at 1W into a constant 8 ohm load, 2W into 4 ohms, and 4W into 2 ohms.

Sure, those curves are flat because they go into a non-reactive test load. And speakers measure awfully flat when tested at a fixed volume (1W ?). However, impedance curves are far from flat, on any speaker. So what would happen if I took a fixed voltage and fed actual music to a speaker who's impedance varies from 4 ohms to 20 ohms (rated with a nominal impedance of 8 ohms)? Well the high impedances are pretty easy to deal with linearly, but as the impedance drops, the speakers demand much more power. To perform linearly, the amp must provide exactly double the power from 8 ohms to 4 ohms given a constant voltage. And quickly.

But wait a minute. Notice that the curves for the different resistive loads, while individually flat, are not at the same absolute level. 2 watts at 4 ohms will virtually always produce less than double the power than 1 watt at 8 ohms; the magnitude of the difference depends on how well-equipped the amp is to handle high-current / low-impedance. Okay so there's maybe a few-decibel difference at 1W. How about comparing 10 watts @ 8ohm to 20 watts @ 4ohm? What happens if a peak in the music demands instantaneous power of 300 watts for a tiny fraction of a second? Will it produce exactly double that power into 4 ohms? Will the relationship between resistive loads, non-linear or not, be the same for all frequencies? Of course not.

Additionally, Stereophile also tests amps into a "dummy loudspeaker load," which has a typical loudspeaker impedance curve. Amps always produce the same general freq. response curve, dipping where impedance drops, with the degree of interaction being dependent partly on the amount of amp output impedance. The slope of the loudspeaker impedance curve also has an effect on its load to the amp.

Back to transients. This is partly why a square wave is often used in testing amps. When there's a rapid change in the voltage signal, the amp has to quickly supply the current as well. Does the amp just go straight to that voltage/current, especially at high wattages? Depends on the amp. It may overshoot the increase to the top of the wave, then undershoot the drop to the bottom. Tube amps round off these square waves substantially, leading to a softer, warmer sound that many people appreciate or prefer.

Regarding distortion. Decades ago, amp manufacturers engaged in a THD war. Solid state was in, and so was negative feedback. Problem is that extreme use of negative feedback can have a very detrimental impact on sound quality. Sure, the 1W frequency response looks great though! Some amps run with little or no feedback, though the middle road today is to simply use it in moderation. It's also worth noting that when distortion levels, while maybe high in absolute terms (especially with tubes), decrease with each fundamental (2nd, 3rd, 4th, etc.), the result is subjectively pleasing according to research done some time ago. That's maybe one important reason why some people still prefer the sound of tube amps; solid state distortion does not have this characteristic.

If amps are imperfect dealing with varying frequencies and dynamics, then what about loudspeakers? What does a square wave look like from a speaker? How much does a speaker overshoot a voltage during rapid changes, when the tweeter is vibrating at 10,000Hz with 100W of instantaneous power? And is it not reasonable to expect these characteristics change after many hours of initial use?

Now what I will concede is that the net audible differences are not as catastrophic as I'm making them out to be. But audiophiles are in this game for the subtleties. Subtleties become painfully obvious when your job is to compare high-end equipment, or when you make a serious hobby out of audiophilia. Hey, I'm not going to go spend five grand for a nice amp at this point, but I won't fault anyone for doing so.

-Cooper

I havent read that much since college....is there a quiz i have to take now? =)

I almost missed this post.
Reading the forums too quickly this morning.

In reply to:

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First of all, anyone claiming that there are no differences, audible or measurable, between amps is seriously misguided, as any audiophile knows.

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Now Cooper, there is no reason to insult people with a different opinion. There are those in the industry far more experienced than you or I that question myths and principles of audio every day. I highly doubt they are all 'misguided'. I'm sure many are highly educated both through experience and academic training.

The term audiophile is one that no educational institution bestows upon any profession, so if someone wishes to call themselves an audio expert, there is really no one to argue against that.
Audiophile by definition is "a person who is enthusiastic about high-fidelity sound reproduction" (Merriam-Webster dictionary), not one who has to believe a set group of myths or half truths in order to merit the title.

In reply to:

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Technically, I believe sonic differences may have a lot to do with dynamics and transients.
Anyone can design a solid state amp that measures with a flat frequency response curve. But if you read the fine print, even in Stereophile, you will see that tests are typically performed at 1W into a constant 8 ohm load, 2W into 4 ohms, and 4W into 2 ohms.

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First off i would very much scrutinize the tests performed by a magazine review. Some are better than others, some are very much useless.
But this topic leads into exactly what sushi had iterated to long ago, expand the breadth of the tests to included MORE than just simple measurements or limited parameters (a full 1W-110W as opposed to just 1W as you say), more than one load, etc. etc. and then show the graphs/numbers that demonstrate how the changes affect the sound frequency curve (or other parameter) that makes the difference audible.
Out of the decades of research on audio, these tests MUST have been done somewhere, by someone already.
So where is the proof? Where are the graphs? The white papers?
That is all i want to see. A well designed examination of the principles.
Many theories have been put forth and yet left unmeasured, untested.

As for this statement, correct me if i'm wrong but are you referring to speaker break-in again?

In reply to:

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How much does a speaker overshoot a voltage during rapid changes, when the tweeter is vibrating at 10,000Hz with 100W of instantaneous power? And is it not reasonable to expect these characteristics change after many hours of initial use?

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If you are referring to speaker break-in, i have to ask, how can an item break-in and yet not continue to break-down?
Theoretically by this reasoning, the materials should continue to degrade over time with each use and hence have a constantly changing sound until the day they die. Metal molecules do not just settle into a comfortable bed after having vibrated for awhile. They can either take the stress or they cannot.

One thing we can certainly agree upon.
The difference that may exist at this level of signal reproduction is very SUBTLE, if any. This is why so often i would like to see the blind listening tests take place of the always used 'sighted, uncontrolled' listening sessions. Everyone would like to consider themselves to be superior in the area of determining signficant sound changes at the 'subtle, golden eared' level, but a more objective approach is required to remove any bias from human behavioural responses from the equation. We cannot do that consciously no matter how hard people may try.