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# How to read the different graphs?

So I believe we all know about the HeadRoom graphs. I would like to know how to read them. Mostly the distortion and the two sq. wave graphs. The "how" section contains few infomation in this regard. Thanks.

Quote:
 Originally Posted by 3602 So I believe we all know about the HeadRoom graphs. I would like to know how to read them. Mostly the distortion and the two sq. wave graphs. The "how" section contains few infomation in this regard. Thanks.
Understanding the graphs are a bit complicated, but they are more than they seem. I will do my best to explain the to my person understanding.

The distortion graph shows the difference between the input and the output. You can see big spikes at the harmonics. A harmonic is where the physical size of the driver creates a frequency at which vibrations is effectively "easier" to reproduce. This is like the same as when you put a sub woofer in a small enclosed space and certain frequencies are very loud and boomy.

The square wave graphs show the response to square waves. The input to the headphones is a square wave. This is a wave that stays up for a certain amount of time, then goes to zero for a certain amount of time. It has 2 states. The headphone however, will not be able to reach the state as fast as the signal itself, so it oscillates until it reaches the state. I would assume that the faster it reaches a flat state, the better. This means that the headphone would not introduce more frequencies than it needs to.

The other square wave graph is merely a faster square wave. This wave will be harder to reach its steady state than the slow one, because it is a much faster wave.
I've taken flack for bringing up FR graphs, but I think the graphs have something to say.
Square waves are actually made up of an infinite series of sine waves (sum of odd multiples of the harmonic), that gradually drop off in amplitude as they get smaller. Since materials with mass and elasticity oscillate and do not just assume some spatial position in proportion to an applied magnetic force, I believe that the graphs show the degree that all of those frequencies don't happen exactly when they should because the material has all of those pesky features like mass, inertia and resistance. So the distortions show something like the lack of perfect speed and responsiveness of the speaker material across many frequencies.

Quote:
 Originally Posted by DayoftheGreek The distortion graph shows the difference between the input and the output. You can see big spikes at the harmonics. A harmonic is where the physical size of the driver creates a frequency at which vibrations is effectively "easier" to reproduce. This is like the same as when you put a sub woofer in a small enclosed space and certain frequencies are very loud and boomy.
No, that's resonance and hasn't anything to do with harmonics.

Harmonics are an integer multiple of some other frequency. And harmonic distortion (which is what the distortion graphs show). What the graph shows is the non-linearity of the headphone being measured. If you apply a non-linear transform to a pure tone, it produces new frequencies at multiples of the original tone. This is what's called harmonic distortion.

If the headphone were perfectly linear, then all you would see in the FFT plots would be the stimulus tone. But no headphone is perfectly linear so it will produce harmonic distortion which is shown as the other spikes in the graphs.

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