[margam]

Hi guys , my 2 year old  32 ohm/106 db philips closed headphone is dying ,now am looking for open headphones. but im confused whether i need a dac because my source is a dell laptop (15r turbo) using conexant  audio codec.
 
When i asked dell support about on board sound card they replied me that it gives output at 31 mW per channel into 32 ohms. The output voltage is 1 Vrms. with an integrated headphone limiter.( the link is given below ).. note that when i use my 32 ohm headphone there is no volume left to increase in my laptop & at full volume its not louder & its crap.So can i use 50 ohm headphones with 32 ohm source.
 
I am looking at Sennheiser HD 518 & HD 558 with 108 db and 112 db sensitivity.Among these which is best for my source. i dont know whether i should i stick with 32 ohm headphones like HD 449 .which i am considering in to...I am interested in  HD 558 since it has more sensitivity, What would you guys recommend ? Can i go for it or should i stick with 32 ohm headphones ?
 
Link to the specs of my source http://www.conexant.com/Product/Audio/pchdaudio/CX20672/Pages/default.aspx
(Hope its not a bad source.........................)
 
Thanks.

 

[NA Blur]

It is not the impedance that is what is going to control the loudness, rather, the sensitivity.  The Sennheiser headphones you are looking at are slightly more efficient so you will gain a very small amount of volume, but if you want more you are going to have to use an external headphone amp.
 
Take a look here:
 
http://www.head-fi.org/t/620775/the-sub-200-portable-amps-shootout-11-10-amps-compared/120
 
Think of resistance ( Ohms ) more of how well a device can control the driver and think of the sensitivity as how easy it is to get to a specified loudness.  Of course resistance does come into play, but as long as the sensitivity is over 95dB you should be able to achieve loud listening levels.