Saw a review some days ago on the hf5, which i have also bought. Especially following quote seems to be interesting
Adding Impedance and Amping
So I heard that by adding impedance to these such as the ER4P to ER4S adaptor or an attenuator bundled with earphones that you can make these pretty much as good as the ER4’s. So I got my UE airplane attenuator out which add 100 ohms of impedance and then went iMac to Objective 2 to HF5. OH GOD! The improvement was unreal, more details, more body, better presentation and transparency and a smoother sound overall. It was great.
So the after some more experimenting I made the best iPhone rig that I have done today using the attenuator, my Phone 4 and my cMoy BB amp. Same effect and also super portable.
If you have these I recommend playing around with this stuff.
I thought about building my own amp. Anyway adding the attenuator before the iem's what does it do? To me, it makes sense that it would make the static noise from the audio source less audible, but you have to turn up the volume louder. At this point i am a bit confused, because many people around talks about output impedance and the impedance of the earphones, and so to speak does the attenuator just add to the earphone impedance?
Also, what would happen if i just use the attenuator directly with my iphone, would it be able to drive my hf5's then? If it eliminates background/static noise, that alone would help, because the impedance of the hf5 is very low, and it seems that it picks up a lot of static noise..
My overall question is, does the attenuator just reduce static noise or are there more to it?
I guess the reviewer must think, that the audio quality benefits from doing so, and it seems that it helps a lot, but is it rather the amplifier that does the job, and why use the attenuator anyway then?