Distortion on low frequency

I'm trying to figure out what exactly causes the problem. Lets say on EQ, when I set the 50hz frquency to +6 (max), the speakers start to distort at no matter what volume. Setting the level to -3 (or something like that) will make the distortion go away. Now, this is also depends on the song played. Some distort at +6 (or whatever value), others don't. Weak speakers or weak amp? What do you think?

Neither.  Probably distortion introduced by your EQ.Support the12volt.com

EQ is built-in in the hu. It doesn't seem to me that it is the EQ itself that would mess up things.

Sure it is.  An EQ is usually the noisiest part of any system, even if it is built into the head.  Often it is the head unit itself (or more accurately the preamps in teh HU) that causes most of the distortion and noise heard in systems.  But anytime you turn any control to the max, no matter what it is, you operate at its limit and are much more likely to introduce noise, distortion and unacceptable sound.Support the12volt.com

So how can this be fixed?

It can't.  If I'm right, it is simply a limitation of your equipment.  Don't turn it up to +6!Support the12volt.com

DYohn is right on. This will usually happen one of 2 places: either the EQ runs out of headroom internally (the DSP runs out of digits to calcualte the math of the +6 boost) or the EQ's output is clipped when it hits the power amp in the head unit. Either way, short of buying new gear, the only way around it is to turn it down. -daveThis is not a sig. This is a duck. Quack.

Why would it run out of space to calculate the math? Doesn't it make the whole eq boost useless then? And what will cause it to clip? This EQ is actually of the Pioneer 8600 head unit. Retails for around $500. So I don't know why it would perform poorly. But that is also because I set loudness to on and bbe to +4. This adds to the distortion. Turning it down works, but that means I sacrifice the features of the unit for normal, undistorted sound. This sucks :(

If you have the loudness on and bass boost up, then I am not at all surprised the EQ is overdriving the head unit pre-amp.  Just because a control goes to 10 (so to speak) does not mean the equipment will operate well there.  Adding all that signal processing takes you far, far away from "normal undistorted sound," especially with Pioneer equipment.  If you need or want more bass, you will need to do something other than try and squeeze it out of your head unit, such as add a subwoofer or use a larger amplifier.Support the12volt.com

vbel wrote: But that is also because I set loudness to on and bbe to +4. This adds to the distortion.

That's probably your problem. You're adding 2 things that crank the hell out of the low end. Loudness is usually between +6 and +10dB at 50Hz and the BBE bumps it another 4dB or so. When you crank 50Hz to +6dB, you all of a sudden have somewhere between +16 and +20dB of 50Hz boost dialed in. +20 is 10x the voltage, so if you started with 1Vrms sinewave, now you need 10Vrms, or about 14Vp-p, which is easily within the realm of clipping for signals inside (or even outside) the head unit. BBE also does some dynamic expansion, so that +4 number will vary by as much as 3dB depending on the signal, the BBE recovery, and the precise BBE algorithm that Pioneer licensed. I bet if you kick off BBE or turn down your loudness a notch or two, you'll find you can get a little more boom before the splat. It's not that you're being restricted from the "full potential" of your head unit, it's that you're asking it to do too much. Look at it this way: Inside the head unit, there is a fixed amount of gain that can be had before things clip. If you have the volume up a fair amount, it'll take off a fair portion of that. Add some BBE, a little more. Loudness, a big 'ol chunk. +6@50? Sorry, you're out of room. If you need more bass, move the EQ to an outboard unit, ditch the BBE...soemthing. You're asking it to do too much. I figure Pioneer designed that head to have enough headroom to handle about 80% of what "everything on 11" would need. Frankly, that's pretty generous. -daveThis is not a sig. This is a duck. Quack.