Are amplifiers worth it - Page 15

Different authors make different choices. In this case there can be an isomorphic transformation between watts and dB so the choice of one over the other is in some sense arbitrary.

There are several diode effects related to wire. In the end, if they were significant they could at least be measured.

Commercial speaker and interconnect wire is usually carefully made so that diode effects are pretty much avoided.

Copper and other materials used in fabricating wires and connectors are themselves highly linear stuff.

Over a period of time corrosion by oxygen, sulfur and other contaminants can lead to the creation of chemical compounds on the surface that are nonlinear. In my experiments highly corroded copper wire remains highly linear, even if finely stranded and heavily corroded, provided you make a good electrical connection to the actual copper core.


In some of my experiments I took heavily corroded (literally green-blue) stranded copper wire, cleaned up the ends with fine sandpaper, soldered the wire to electrical contacts, and tested it for linearity. The wire remained linear to well below the -110 dB level. That is something like my local measurement limit.

I've seen tests that claim to have found non linearity in copper wire somewhat below the -140 dB level but those experiments were questionable simply because audio measurements at that level are inherently flaky. At that level the thermal air currents in your living room are magnified so that they are more like a hurricane.

The threshold of human hearing for nonlinear distortion under very ideal conditions is more like -66 dB. Under typical conditions it may be has poor as -20 dB or even poorer.

So whether tests show nonlinearity 100 dB down, 110 dB down or 140 dB down its all sonically moot.

OTOH make a inadequate connection with corroded cables and you can have large amounts of measured distortion: 30% or more. Corrosion can simply mute the signal.
Edited by arnyk - 12/19/12 at 7:41am

1% distortion is -40 dBV or -20 dBW and I bet most can't hear that if it happens to musical peaks whilst listening to a CD (record, tape, whatever). Most speakers set the distortion floor of the system, not the electronics let alone the wires.

Arny has done an excellent job of discussing skin effect, along with good insights from others. It is often very misunderstood by audiophiles, in part due to misapplication of the concepts by some cable manufacturers. I can't recall specifics off-hand (and don't care enough to look any up) but there have been some very "interesting" white papers posted. It can be a huge issue for me in my work (which has ranged from 10 to 100+ GHz); it is something I don't worry about in my stereo.

It is presented in dB because dB is a ratio and as such makes the chart universal. If the y-axis was based on watts you've need to have a different chart, or at least different y axis scale, for every wattage discussed. With dB, the ratio is the same regardless of the watts so you just use the dB (ratio) to calculate based on the watts in the specific application.

Just for an example, the -0.1dB @ 100kHz would be about -0.023W relative to 1W and about -8.6W relative to 375W.
Edited by whoaru99 - 12/19/12 at 10:55am

Yo KB; did you read Quantum Studio's earlier post? He ANSWERED your Q about post #375 before I got to it & and he answered WAAAY better than I could have. Thank you QS! I'm w/ya, QS buddy on many other points in that post, my fav, the one on our Creator.

T

Don't forget that DIY you get more for less. As mention, the main benefit is you can fine tune the amp gain to match your pre-amp or receiver. I think this is a part where it will influence the SQ plus knowing your speaker power requirement. Also need to mention I listen at close to reference level around -2db to -5db. In my situation, I don't think Denon 4311 alone can drive all 7 channels at reference level. If you don't listen at such level + high efficiency speaker, I agree you might not need an external amp.

This was a nice read, yet disturbing at the same time, because now I see that the FTC is freaking aware of this, yet like many government bodies simply does nothing about it. A very similar issue takes place with computer PSUs and everyone savvy knows about it, it seems unbelievable that it has been allowed to go on for over 3 decades now. It seems to me that by now they should have come up with a pretty simple universal power rating because it only serves to confuse the consumer even more. Just like in HT, in computers people are often duped into buying new PSUs that are way more powerful than they need because the companies that make say video cards have learned that most PSUs are so over rated they in turn must way over rate what the requirements of their video card are to play it safe.