Thanks for posting the pics.
CAL!2 just looks like an overall improved version of the CAL!1 to me. Just look at the felt around the driver - it looks nicer finished and more even compared to CAL!1. There often were rests of glue on the felt of the CAL!1. I think production has been optimized. The few measurements that have been posted look very good - especially the left-right channel match in frequency response. CAL!1s often had some sort of imbalances.
I owned and modded about 5 CAL!s alltogether. I will try to sum up my findings here:
-- Stuffing the cups does reduce sub bass and slightly decreases precision and speed in sound to my ears. I never really liked it. Also adding stuff to the cups decreases their air volume and leads to more "closed in" or congested sound. CAL!2 seems to have a tiny port on the backside so this should not me as much of a problem there.
- Adding dampening to the inside of the cups did never change the sound much. In my last mod a just added one layer of Micropore to the inside of the cup right opposite the driver. It decrease hollowness a little bit.
-- Sticking dampening materials to the magnet of the driver does significantly change the sound. I have tried different kinds of tapes and felts but if you do this you always need to leave the center hole open. Punching a hole with an office hole puncher will create a hole the right size.
The thicker the material you add the more significant the changes to the sound. Adding layers of Micropore, Dynamat or furniture felt pads will: decrease treble and make the hole sound smoother and the mids more colored, in other words "lusher". I believe it increases harmonic distortions, which can sound natural but if you overdo it it might sound too colored or unnatural. In my first mods I believed it dampens the driver and I thought, the more dampening the better. This is not exactly true here. The layer should not be much thicker than 1 or 2 mm ! My experience with standard furniture felt pads with a punched out hole in the middle is: they are usually too thick - sound becomes very colored and hollow with them.
-- The stock felt on the backside of the magnet is a very important part of the CAL!' sounding. Do not remove it unless you know what you are doing. Once removed it cannot be put in place again and you will not easily find a felt that will restore the original CAL! sound. It my opinion removing it will change the sound far for the worse. It will extremely improve speed and midbass but CAL! will lose it's balance, natural timbre and the highs will be lost. Better leave it as it is.
-- The wire used in CAL!1 was very thin. I replaced it with a Cardas microphone cable with a higher conductor diameter. I believe it increased bass precision and brought forward the mids a bid. The cable mod is more or less irreversible and will void the warranty so that's probably the least one to consider.
Also soldering skills are needed and one needs to work fast. The driver housing starts to melt almost immediately when I start to solder at the connector. Even though I am experienced in soldering and I use high quality solder I often had troubles with cold solder joints after a few months causing channel imbalances. Resoldering was needed.
-- I installed ports, about 4mm in diameter into the cups. It clearly improved the sound. Bass became more precise and less boomy. It improved overall clarity and it significantly improved soundstage ! As it seems, the CAL2s already have small ports - there are openings on the backside of the baffle which end on the sides behind the earpads.
I think the CAL!2 is already optimized in most regards and it does not necessarily have to be modded. Modding does not necessarily improve the sound in technical terms but it might change the sound to your liking !
If you want to tweak the sound signature and get a smoother sound try Micropore or Dynamat on the backside of the driver (but leave the hole in the center open!). This mod is reversible so it won't void your warranty.
I have tested a CAL!2 already but I do not own one yet. When I get one I will post my mod experiences with it here.
Edited by zachgraz - 12/12/13 at 2:46am