Why do I need an amp (for full-sized headphones)?
Posted 09-20-2009 at 01:40 AM by Currawong
Tags amps
Uncle Erik wrote a fantastic explanation about this, too good not to post. To explain some of the reply: In the thread that was posted, BlaineShelby had plugged his Denons into an amp his friend was building, which was probably a cmoy, whereupon he heard crackling, so since that was not an improvement, he wanted to understand better why people suggest he gets an amp.
Quote:
Originally Posted by Uncle Erik
J.S. Bach, Toccata and Fugue in D Minor. You have heard this before, by the way. It's a famous piece used in lots of media. If you like it, try the rest of Bach's organ works.
BlaineShelby, the crackling you heard might have been clipping. If an amp cannot sustain the headphones' demand for power (almost always with low notes), then it "clips" or cuts out. A fine example of why all amps are not created equal, as well.
Amps are not about power. They are about control. You might want to compare an amp to the engine of a car. True, in some ways. However, a much better analogy would be to a car's suspension.
A car handles differently depending on the road it's driven on. The same is true of music. If you're driving through a curvy road at 55MPH with terrible suspension, the car will be all over the place and might put you in the ditch. The same road at 55MPH in the same car, but with a finely tuned suspension, will be an entirely different sensation. Instead of slopping all over the road, the car feels secure and pleasurable to drive.
That is the difference between a good amp and a bad one.
There are lots and lots of technical reasons why amps sound different. Further, there are many, many different circuit designs that affect the sound.
It would take a book to go through everything, but take a look at impedance. Amps have an output impedance curve - it changes depending on how itis being driven and what is connected to the amp. Similarly, headphones have impedance, also on a curve.
Impedance tells you how efficiently power transfers from the amp to the headphones. Since that constantly varies depending on the amp and the headphones also constantly vary, you get a particular sound signature.
Yes, this is complicated, but just think about overlaying a graph on another one and looking at the differences by frequency.
This is part of the reason why two (for example) 500mW amps can sound entirely different with the same music and headphones. Each amp will have a unique output impedance curve which will interact differently with the headphones' impedance curve. That gets you a different sound from each amp.
There are a number of other factors that influence the sound of an amp, too, but I hope this example makes sense.
Also, you might run across opinions of those who say an amp makes no difference whatsoever.
That's nonsense, and demonstrably nonsense. As with the clipping you hear (probably it's clipping) you have amps with differing levels of output. Most importantly, however, is that you can measure an amp's output impedance and other relevant stats. It's not one of those "just trust us and give us money" audio deals, you can put an amp on an oscilloscope and measure it. You can directly compare two amps scientifically and demonstrate differences in repeatable tests using standard equipment.
Further, the deniers usually cite several studies where people were not able to hear a difference. Fine. Funny thing is, if you look at the rules of those tests, you will notice that they exclude certain types of amps.
Hmmmm... so to prove that all amps sound the same you can't test amps that sound different because all amps sound the same.
Does that make any sense to you?
If you want to go a step farther, there are often wide variances in the build quality of amps. Poke around here and you'll find examples of manufacturers gone horribly wrong. You'll want to make sure that whatever you buy was built correctly.
BlaineShelby, the crackling you heard might have been clipping. If an amp cannot sustain the headphones' demand for power (almost always with low notes), then it "clips" or cuts out. A fine example of why all amps are not created equal, as well.
Amps are not about power. They are about control. You might want to compare an amp to the engine of a car. True, in some ways. However, a much better analogy would be to a car's suspension.
A car handles differently depending on the road it's driven on. The same is true of music. If you're driving through a curvy road at 55MPH with terrible suspension, the car will be all over the place and might put you in the ditch. The same road at 55MPH in the same car, but with a finely tuned suspension, will be an entirely different sensation. Instead of slopping all over the road, the car feels secure and pleasurable to drive.
That is the difference between a good amp and a bad one.
There are lots and lots of technical reasons why amps sound different. Further, there are many, many different circuit designs that affect the sound.
It would take a book to go through everything, but take a look at impedance. Amps have an output impedance curve - it changes depending on how itis being driven and what is connected to the amp. Similarly, headphones have impedance, also on a curve.
Impedance tells you how efficiently power transfers from the amp to the headphones. Since that constantly varies depending on the amp and the headphones also constantly vary, you get a particular sound signature.
Yes, this is complicated, but just think about overlaying a graph on another one and looking at the differences by frequency.
This is part of the reason why two (for example) 500mW amps can sound entirely different with the same music and headphones. Each amp will have a unique output impedance curve which will interact differently with the headphones' impedance curve. That gets you a different sound from each amp.
There are a number of other factors that influence the sound of an amp, too, but I hope this example makes sense.
Also, you might run across opinions of those who say an amp makes no difference whatsoever.
That's nonsense, and demonstrably nonsense. As with the clipping you hear (probably it's clipping) you have amps with differing levels of output. Most importantly, however, is that you can measure an amp's output impedance and other relevant stats. It's not one of those "just trust us and give us money" audio deals, you can put an amp on an oscilloscope and measure it. You can directly compare two amps scientifically and demonstrate differences in repeatable tests using standard equipment.
Further, the deniers usually cite several studies where people were not able to hear a difference. Fine. Funny thing is, if you look at the rules of those tests, you will notice that they exclude certain types of amps.
Hmmmm... so to prove that all amps sound the same you can't test amps that sound different because all amps sound the same.
Does that make any sense to you?
If you want to go a step farther, there are often wide variances in the build quality of amps. Poke around here and you'll find examples of manufacturers gone horribly wrong. You'll want to make sure that whatever you buy was built correctly.
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