Why don't most headphones have adjustable volume control?

[whatisheadphone]

Let me start by saying I'm not much of an audiophile, so this is probably a really dumb question. I had a cheap pair I picked up at Walmart that I used pretty much all day every day and never even questioned the sound quality (looking them up they seem to be Koss KHP21v).  Now I'm in the market for a replacement and figured it would be a decent time to educate myself a little more.

The problem is, after doing a bunch of research I noticed none of the recommended headphones in the $50 price range have adjustable volume controls.  This is something I've grown accustomed to, so I'm hesitant to go with any of them.

My question is, why?  To me this seems like a very convenient feature. If a cheap pair has it, why don't the more respected brands such as Sennheiser?  Is it because headphone volume control is an unnecessary function I've been tricked into thinking is more useful than it really is?  Or is it something they leave out to convince you to buy the more expensive pairs?

Again, sorry for the pleb level question (though somehow it turned into a bunch of questions...) and thanks to anyone who can shed some light on my ignorant self.

 

[Enigma29]

They dont have it because most headphones need an amp, thus having 2 dials would be kind of silly (at least this is how i think it is).

 

[Marximus]

In my opinion, the less electronic gimmicky stuff a headphone has, the better.  It's just one more thing that can break/malfunction.  And it's probably cheaper to exclude a volume control.  I think all the volume control should come from the source/amp.

 

[whatisheadphone]

Eh, is an amp really necessary for headphones?  Won't that end up ruining your ears?   Or do high-end headphones have weak/lower sound output?

 

[Enigma29]

Quote:

Eh, is an amp really necessary for headphones?  Won't that end up ruining your ears?   Or do high-end headphones have weak/lower sound output?

An amp is required to power some headphones, some have a ridiculously high impendance so unless you put an amp to them they wont be fully powered and can sound sluggish/muddy/bad.
As for ruining your ears; isnt the dial on the headphones capable of doing that the same way an amp can?

 

[whatisheadphone]

Quote:

As for ruining your ears; isnt the dial on the headphones capable of doing that the same way an amp can?

I see your point.  I guess I just have the false impression that an amp makes everything boom like crazy.

 

[Gnomeplay]

Amplifiers aren't really purchased in most cases for additional volume, it's to provide the headphone with sufficient power to be able to perform at the top of it's ability. It's more of a matter of sound quality not quantity.