Hi Nirmalalow.
Specs, IEMs and Dynamic Range (with a dash of hiss)
Short answer:
Attenuators do NOT attenuate the line, but the headamp signal to the headphone, so hiss is attenuated equally along with the signal, but NOT the line.
As the nano iCAN has more than enough power/gain for some of the IEMs (too much power in some cases), adding an attenuator between the headamp and the headphone, it will reduce the overall hiss and improve overall sound/enjoyment.
Long answer:
At the outset, it is worth outlining that that the iPhone has a 15mW amplifier. The nano iCAN puts out 150mW so 10x the power output (and most other aftermarket headphone amplifiers have even more power).
Set against this is the headphone market which is as broad as it is wide. At one end you have super high-sensitivity IEMs and at the other end, very demanding headphones like the very impressive HE-6.
Therefore, using an IEM designed for the iPhone and inserting into a medium-power headphone amplifier like the nano iCAN will not be a “match made in headphone heaven.”
This particular JVC IEM, normalizes to 124dB/1V (this is exact same as the official spec of 106dB/1mW, just normalised to one common format - which we use internally).
What does a sensitivity of 124dB/1V mean? This means the iPhone (output is ~0.9V) can produce near 124dB of sound pressure, this kind of sound pressure is just below "threshold of pain". By comparison a chainsaw at 1 meter is "only" 110dB.
If using the iCAN nano, maximum available SPL will be around 134dB! (Painful, hearing damage unavoidable). And if playing at 115dB peak the dynamic range is only 73dB, so noise will be 73dB below 115dB or at 42dB absolute (to arrive at those figures, one needs to use the below mentioned excel file for proper calculations and conversion). This will be quite audible.
Now before anyone says “hang on, the iFi iCan nano has lots of hiss,” if we compare the numbers for a competitor’s DAC/Amp rated at 116dB Dynamic Range @4.25V, once we NORMALISE with the same headphones the noise floor in absolute terms will be 41dB, only 1dB difference. So for both this competitor’s product and the iCAN nano the headphone is way, way too sensitive and it needs to be attenuated to become useful.
If we use a 24dB Attenuator with these IEM's, the maximum SPL with iCAN nano is reduced to 110dB (chainsaw @1m) and the competitor’s product can deliver 113dB, crucially in both cases noise will also be attenuated by 24dB, so we will get 18dB/17dB absolute noise, which is way below a "quiet bedroom at night" and the actual dynamic range is equally increased, due to SPL Limitations to 92dB for the iCAN nano and 95dB for the competing product.
And of course the volume control needs to be turned up 24dB (say 2 o'clock instead of 10 o'clock) for the same playback level.
If anyone is curious, we have an excel where customers can "plug" their headphones specs in and allows the pertinent specs of 3rd party products to be entered. It will give an indication of the pairing with all of the iFi headphone-based products.
Just pm/email (tech@ifi-audio.com) and we shall email it through.
Background reading on Sound pressure levels:
http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm
. But thanks so much. Unfortunately I am in US so i guess no direct sending for me. However, I would appreciate it so much if you can add me to the wait list for the ifi attenuators and the ifi iRack. Is this the correct site? http://www.avataracoustics.com/home.html and do i just need to call them? Or do they have a preorder page somewhere? Thanks!
