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Testing audiophile claims and myths - Page 198

post #2956 of 3037
Quote:
Originally Posted by TransparentHolo View Post
 

One of the problems I believe I and others have, is though the arguments are convincing, I am not an electrical engineer, and I don't understand a lot of the things being said when you say I should level match with an "AC volt meter" that alone is hard to understand, I will have to research this. For me, In order to show myself that there is no value in high end amps, or that there is value in high end amps, I can't settle for just experience, that's why I want to AB test in some way, even if it's hackneyed, to get myself started in one direction or the other.

 

Another problem is testing myself seems to be prohibitively expensive / require experience. There are testers that claim differences in amps (Tyll from InnerFidelity) and testers that claim no difference in amps.

 

So I suppose i'm looking for some way to roughly test myself, without breaking a huge amount of bank (on testing equipment), if that makes sense. Even a rough test is satisfactory to me to start me on a path.

 

The best way to match levels is to measure the voltage across the speaker terminals while playing a test tone of 1000 hz or so.  If you are using headphones, then you would measure the voltage at the cable connector.  Set the meter to AC volts and put the probes on the connector.  Very simple. 

 

The major problem in audio is the existence of hearing bias.  What happens is that people fall prey to expectation.  They expect one unit to sound better than another because it is prettier, or  more expensive or because some magazine writer said it does.  Expectation bias is a self fulfilling prophecy.  The only way to eliminate bias is to use the ABX test you are talking about.  That means the listener has no idea which unit in a comparison is playing at any give time.  Those audible differences caused by bias will disappear and those audible differences caused by the equipment will be real and confirmed.  Because some writer says something sounds better than something else, unfortunately, means nothing at all.  It may be true and it may not be but the writer's saying so is meaningless.  Remember these folks are in the business of entertaining good prose is good entertainment.  To know if one piece of gear has an audible difference from another, the only meaningful method is the blind ABX test.

 

All amplifiers have different measurements and it is easy to make measurements as long as you have the expensive equipment to do it.  the problem is that not all differences in measurements are audible.  Testing audibility is lot different than testing electrical performance because of hearing bias.

 

I got started with bias controlled testing when people began claiming that one digital cable "sounded better" than another.  Since it is impossible that a competently made cable can change the values of the data, I knew this was nonsense.  So I did some tests with my wife helping me to determine that I was right.  One thing led to another and I got an audiophile group together to do a bunch of tests of nearly everything hifi.  It is a very boring and very time consuming process and can't be done by oneself.  It always requires help, otherwise you will know which unit is which.  Personally, I would never go through it again.  I learned from it to be sure but it was a hassle.


Edited by blades - 7/14/14 at 8:21am
post #2957 of 3037

Can someone please advise me on something. I've always believed that driving an amplifier at higher levels meant that distortion would increase, even below clipping.

 

I've also been told by many audiophiles and salesman that it is far better to drive an amp that has power in reserve, so that it is not stressed than one that is running close to its limits. Hence a larger amp would be better, because it can handle the demands easier.

 

Now for the advise part. What I've recently gathered from other places is that distortion does not increase linearly with power output.  Is this true? So if I use an amp that is rated to deliver 100W, and I use 70W, the distortion between say 30W-70W won't be all that different?

 

If I'm wrong about this then it means that amp headroom doesn't really do anything useful, which goes contrary to what I've learned for years.

post #2958 of 3037
It depends solely on the amp! Go to stereophile (I think it is) or something and look up their amp measurements, you'll se distortion vs power plots.
Often, SS amps will have a little higher distortion At lower outputs, distortion falling as output increases. Then, the distortion will eventually start climbing at some point, and sky-rocket at last (clipping). Try looking up some measurements..
post #2959 of 3037
http://www.innerfidelity.com/images/130620_AmpMeasurements_PDF_Booklet.pdf

These headphone amp measurements show nicely. Until clipping something like the O2 stays under audible distortion levels.
post #2960 of 3037
Quote:
Originally Posted by Mezzo View Post
 

Can someone please advise me on something. I've always believed that driving an amplifier at higher levels meant that distortion would increase, even below clipping.

 

I've also been told by many audiophiles and salesman that it is far better to drive an amp that has power in reserve, so that it is not stressed than one that is running close to its limits. Hence a larger amp would be better, because it can handle the demands easier.

 

Now for the advise part. What I've recently gathered from other places is that distortion does not increase linearly with power output.  Is this true? So if I use an amp that is rated to deliver 100W, and I use 70W, the distortion between say 30W-70W won't be all that different?

 

If I'm wrong about this then it means that amp headroom doesn't really do anything useful, which goes contrary to what I've learned for years.

 

Yeah, I know that story about headroom. "You can hear the amp's power below the surface, just waiting to be used."

 

But that is not how amps work. Headroom is basically just power that's not used. There is no point in headroom in and of itself; it doesn't guarantee less distortion or better sound. All you need is sufficient power at the level you listen to at its loudest.

 

It seems like you think that if the amp has a certain amount of power that it can deliver, then its distortion will fall into a certain range, making it more or less audible. But that's complicating the issue way too much, and approaching the idea of headroom in a very convoluted and unpractical manner (and I don't mean that with any offense at all).


Edited by SunshineReggae - 8/6/14 at 7:00am
post #2961 of 3037
Quote:
Originally Posted by Mezzo View Post
 

Can someone please advise me on something. I've always believed that driving an amplifier at higher levels meant that distortion would increase, even below clipping.

 

I've also been told by many audiophiles and salesman that it is far better to drive an amp that has power in reserve, so that it is not stressed than one that is running close to its limits. Hence a larger amp would be better, because it can handle the demands easier.

 

Now for the advise part. What I've recently gathered from other places is that distortion does not increase linearly with power output.  Is this true? So if I use an amp that is rated to deliver 100W, and I use 70W, the distortion between say 30W-70W won't be all that different?

 

If I'm wrong about this then it means that amp headroom doesn't really do anything useful, which goes contrary to what I've learned for years.

 

Yes it is generally true that distortion increases with amplifier output.  In fact power ratings are based on distortion.  Virtually every amp will perform past its full rated output but the distortion then becomes audible.

 

There is nothing wrong with having reserve power.  Virtually every amplifier has plenty of it.  But 20 watts from a 50 watt amplifier isn't any different from 20 watts from a 200 watt amplifier.  It doesn't cause more stress or heat.  it doesn't sound any different.

 

The question is not something that cannot be answered without more information.  Let's say that at 70 watts (something you aren't actually likely ever to encounter) your amp might measure a THD figure of 1/10 percent.  At 30 watts it may have 1/100 of a percent distortion.  Neither figure is audible so it isn't an issue.  At 150 watts the amp might be at 2% distortion and you could likely hear that if you concentrated on it.

 

Headroom is nothing more than unused power.  Let's say that your amplifier dissipates 1/2 watt on average driving speakers of average sensitivity.  That is a pretty typical number.  In order to have the ability to handle a peak SPL that is twice as loud as average, you would need 5 watts of power.  All the power above 1/2 watt is overhead and you would need at leats 5 watts of overhead to avoid distortion on peaks.  So your amplifier may get its average from SPL's ranging from the 5 watt dissipation down to milliwatts.  So headroom is important.  What it is not is complicated.


Edited by blades - 8/6/14 at 10:51am
post #2962 of 3037

well you can dumb it down and see what you need.

-obviously having not enough "headroom" is a bad idea. we get an amp so it can drive our gears.

-just enough is a little tricky because as mentioned it's important that the amp has enough for the peaks outputs.(well it's not really tricky, you just need to be careful with the specs they are using for marketing).

-too much headroom, depending on the amp might lead to noise. troubles fine tuning your volume knob and channel imbalance, if you have too much gain and depending on the volume control, analog, "digital", with steps(pairs of resistors). and a few amps have actually more distortion when being forced to output really low voltage.

 

so some headroom yes. a shiiiiitload of it, why?

post #2963 of 3037

Headroom is only important if a peak comes along that requires it. More headroom isn't better. All you need is enough.

post #2964 of 3037
I understand that theoretically one doesn't need tons of power. But I've always subscribed to that saying; "better to have it and not need it, than to need it and not have it"wink.gif
post #2965 of 3037
Quote:
Originally Posted by Hijodelbrx View Post

I understand that theoretically one doesn't need tons of power. But I've always subscribed to that saying; "better to have it and not need it, than to need it and not have it"wink.gif

 

One could say the same thing about low noise electronics. In this case it reverses whether or not you want 95% unused power for headroom.

 

 

Cheers

post #2966 of 3037

you would rather have noise and not need it?

post #2967 of 3037
I have a 100W Music Reference RM9 tube amp, an Audio Research LS15 tube preamp, and Spendor SP100's. The music sounds glorious! The 'noise' you guys are harping about is inaudible. If you're ever in Palm Beach Florida you're welcome to come over and hear for yourself!wink.gif
post #2968 of 3037

Not all tube amps have audible noise or distortion. Some tube amps sound as good as solid state amps.

post #2969 of 3037
Quote:
Originally Posted by bigshot View Post
 

Not all tube amps have audible noise or distortion. Some tube amps sound as good as solid state amps.

 

Yes, there are a few.  I used to have an Audio Research tube amp that scored no audible difference when compared to a solid state amp.  But there aren't many.

post #2970 of 3037
Quote:
Originally Posted by jcx View Post
 

you would rather have noise and not need it?

 

That's basically what we are debating with 90% headroom amps, no? 

:tongue:

 

Cheers

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