This is from a commentary by John Janowitz:
So that all said, what does Xmax really mean? It's a good way to tell how much range of the driver is really useful while keeping distortion inaudible. In speakers, the low end limit for being able to notice distortion is considered to be about 10%. In reality most people can't hear distortion and notice the audibility up until way over 25% even. That seems high, but while at Michigan Tech, the regional AES vice president, Tom Nousaine, came and did a discussion on distortion. Not just subwoofer distortion, but distortion full range. He played a track of Tom's Diner by Suzanne Vega. This was a blind listening test where the track was played over and over again with progressive amounts of distortion added. The trick was to say when you could hear audible distortion, but we didn't know the amounts until later. In a room of about 20 people, all audio geek AES members, we all sat and listened and would say "ok, the 4th time i could hear it". It turned out that only a couple in the room claimed to hear distortion at the point where 10% was added. Most claimed at 25-50% distortion.
Of course, he's talking about THD, not just 2HD, but 2HD is usually the highest.
I've been intrigued by SpectrumLab because it lets you see the playback at the LP and off the disc for direct comparison.
I'll post Irene because I have it handy, but I've been working on others as well. This idea may be something worth discussing that could become a very good test for non linearities using selected high quality source material instead of sine waves/sine bursts.
Worthy of noting is that fact that all of the odd harmonics of the fundamental, through 19HD, are part of the effect. Once I began to focus on the graph, looking at every tiny detail, I have since noticed that many other LFEffects designers use this trick.
With an effect like this, it's impossible to tell what the actual THD is because the odd order distortions would be masked by the effect itself.
I agree with Max. 30% 2HD at 30Hz is absurd. I couldn't force my system to give that, and I'm shocked it's a standard of any kind. Are you SURE those numbers are correct? My math says that list represents 73% THD through 6HD!!
OTOH, John's AES/Nousaine blind listening test story sure makes you wonder when it comes to THD and music vs sine waves.
I know Ilkka didn't retest all of the subs on his list so I assume there's a math formula to translate sine sweep data into CEA 2010, which is obviously way the holy heck more forgiving than the 10% limit I grew up on (TV, Nousaine, Mullen, Ilk, JJ, AVTalk, Wiggins, etc).
Nousaine still uses 10%, no? Does anyone actually use the CEA 2010 standard? I know Ilk did the math and posted the results, but time will render that list useless as the subs on it disappear and news one show up, and I've never seen it anywhere else.