Distortion from Ports

[69stingray]

Hello everyone, I have been doing some research on port geometry. I have read some AS papers. One paper has a port geometry that has excellent odd-order distortion but not so great even-order distortion.

In "Distortion for Dummies" language, what is the difference? For a subwoofer, which one should you be more worried about and why?

[simon5]

Odd order usually sound worse for our ears than even order distortion.

So higher even order is better than higher odd order distortion.

No distortion is even better on the other hand hehe!

Why? Test it with a tone generator.

Use a 90 dB sinewave at 250 Hz, that's your reference.

Then, use a 90 dB sinewave at 250 Hz then add a 500 Hz sinewave at 80 dB.

Then, use a 90 dB sinewave at 250 Hz then add a 750 Hz sinewave at 80 dB.

What's worse? What's closer to the reference and what's sounding better for your ears?

[sreten]

hi,

for a sub even = 2nd harmonic, odd = 3rd harmonic.

3rd harmonic is much nastier than 2nd harmonic.

Generally you would never choose low 2nd if it meant high 3rd.

/sreten.

[muhy3]

I always thought that the harmonics, 2nd, 3rd, 4th etc in a FFT are always in decreasing order of magnitude, for example you might have the reference peak at 20Hz, then 40Hz @ -3dB (2nd), 60Hz @ -6dB (3rd). That would mean that the 3rd harmonic is -6dB from the reference, and far more inaudible than the 2nd harmonic. How then can you simply say that odd or even are better or worse? The odd harmonic 7 will be inaudible, I mean unless your SPL is high and decay of each harmonic is low.

[simon5]

The harmonics aren't always in a decreasing order of magnitude.

Some tube amplifiers for example due to their design cancel most odd order distortion so you're left with 2nd, 4th, 6th...

On the other hand, solid state mostly cancel even order distortion so you're left with 3rd, 5th, 7th...

Also even if the 3rd harmonic is less loud, it will be more audible because it's 3 times higher in frequency than the natural harmonic.