[DS21]

I recently picked up a pair of AKG K550's for my office, to give me better isolation than my previous office cans (Denon D2000) and also because I've grown tired of the D2000's unipivot working its way loose. I use them with a HeadRoom Micro Amp with "home" electronics module, because it's a good-looking piece of equipment and I find crossfeed a big sonic advantage.
 
Overall, they're pretty decent. Obviously, their balanced-dome drivers aren't going to move as much air as the Denons' edge-suspended cone down low. But they also have some sonically deleterious midrange and treble resonances. I've found that often such resonances come not from the driver, but from cabinet resonances, even in tweeters. Often, damping the cabinet can reduce or even resolve such things. It works in midrange/wideband cabinets, and even in tweeters.* 
 
I opened my K550's (the earpad just pulls off, and the cabinet comes apart with five small Philips-head screws), and found two relevant things:
 
1) The inner cabinet is bifurcated, with a rubber subchamber for the driver's vented pole piece to feed into, and then an outer cabinet for the diaphragm.
2) There is no damping material in either subchamber .
 
I didn't take a picture of the opened cabinet, but here's Tyll Hertsen's pic of the right earcup (the left has more wires, and a PCB to distribute the man cable to the lead wires for each earcup:
 
 

Source: http://www.innerfidelity.com/content/wonderfully-competent-akg-k550-sealed-headphone
 
My favorite material for damping cabinets is Bonded Logic Ultratouch, which is recycled denim insulation, and available online from Home Depot.** It is more-or-less an acoustic clone of fiberglass, but doesn't irritate the skin or lungs. (It is quite a bit more expensive than fiberglass insulation, true, but while that might be an issue when insulating an attic, it's a minimal difference when filling a speaker cabinet.) So, I popped open the cabinet and put a tuft of the BLU in the polepiece subchamber, and a loose fill in the outer chamber. My postal scale doesn't have adequate resolution at these fill levels, but here's what the right cup looks like:
 

 
Anyone else tried anything similar? Thoughts?
 
*See, e.g., the Larry Van Wormer mods for the Vifa [now ScanSpeak Discovery] D27-series tweeters,  http://www.raylectronics.nl/pdfs/Modifying_Vifa_tweeter.pdf
**http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=202709974&storeId=10051&langId=-1&catalogId=10053&ci_sku=202709974&ci_kw=%7bkeyword%7d&kwd=%7bkeyword%7d&cm_mmc=shopping%2d%5f%2dgoogleads%2d%5f%2dpla%2d%5f%2d202709974&ci_gpa=pla#.USkGDqWNRmI

 

[tzjin]

Could you post a few impressions on the effects of the damping? I'm considering doing the same to mine.

 

[DS21]

Not sure stuffing the main enclosure did anything.
 
Stuffing behind the pole vent did seem to make the treble less splatty-sounding.

 

[tzjin]

There was some others who reported damping the back, although I believe they used felt. Either way, if I get the time, I may try this.
 

 

[DS21]

So far, I have to say that the biggest improvement I've found in the K550s was...installing the Audyssey amp app on my iPhone. It doesn't do much for my Senn 580s or ADDIEMs, but their target curve fixes most of the things that ail the K550 up top.

 

[tzjin]

I typically do not use EQ, but thank you for the tip!

 

[api9]

Quote:

I recently picked up a pair of AKG K550's for my office, to give me better isolation than my previous office cans (Denon D2000) and also because I've grown tired of the D2000's unipivot working its way loose. I use them with a HeadRoom Micro Amp with "home" electronics module, because it's a good-looking piece of equipment and I find crossfeed a big sonic advantage.
 
Overall, they're pretty decent. Obviously, their balanced-dome drivers aren't going to move as much air as the Denons' edge-suspended cone down low. But they also have some sonically deleterious midrange and treble resonances. I've found that often such resonances come not from the driver, but from cabinet resonances, even in tweeters. Often, damping the cabinet can reduce or even resolve such things. It works in midrange/wideband cabinets, and even in tweeters.* 
 
I opened my K550's (the earpad just pulls off, and the cabinet comes apart with five small Philips-head screws), and found two relevant things:
 
1) The inner cabinet is bifurcated, with a rubber subchamber for the driver's vented pole piece to feed into, and then an outer cabinet for the diaphragm.
2) There is no damping material in either subchamber .
 
I didn't take a picture of the opened cabinet, but here's Tyll Hertsen's pic of the right earcup (the left has more wires, and a PCB to distribute the man cable to the lead wires for each earcup:
 
 

Source: http://www.innerfidelity.com/content/wonderfully-competent-akg-k550-sealed-headphone
 
My favorite material for damping cabinets is Bonded Logic Ultratouch, which is recycled denim insulation, and available online from Home Depot.** It is more-or-less an acoustic clone of fiberglass, but doesn't irritate the skin or lungs. (It is quite a bit more expensive than fiberglass insulation, true, but while that might be an issue when insulating an attic, it's a minimal difference when filling a speaker cabinet.) So, I popped open the cabinet and put a tuft of the BLU in the polepiece subchamber, and a loose fill in the outer chamber. My postal scale doesn't have adequate resolution at these fill levels, but here's what the right cup looks like:
 

 
Anyone else tried anything similar? Thoughts?
 
*See, e.g., the Larry Van Wormer mods for the Vifa [now ScanSpeak Discovery] D27-series tweeters,  http://www.raylectronics.nl/pdfs/Modifying_Vifa_tweeter.pdf
**http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?productId=202709974&storeId=10051&langId=-1&catalogId=10053&ci_sku=202709974&ci_kw=%7bkeyword%7d&kwd=%7bkeyword%7d&cm_mmc=shopping%2d%5f%2dgoogleads%2d%5f%2dpla%2d%5f%2d202709974&ci_gpa=pla#.USkGDqWNRmI

I bought a pair of K550 to replace my Senn HD280 of 6 years which recently broke.  But the K550 just don't isolate noise (for me) as well as the 280. This in a loud office setting (chatter, loud server fans). Adjusting/pressing the cans closer to my ears didn't lower the noise, and that gave me the impression that maybe noise is coming through the casing more than through the pads.
Did you have similar issues about isolation?
 
PS - this thread seems closer to my problem but I can try others (the K550 appreciation thread discusses many things)... suggestions welcome.

 

[davek]

Did something similar today, and I'm very happy with the outcome. I used sponge, and both the outer and the inner damping have audible effect. The outer part helps preventing resonances in the back of the housing which are present because unfortunately AKG didn't take care of the problem. The inner part has even more effect: depending on the thickness/airiness of the used material, it can soften the trebles. First I used some 3-4 mm thick sponge, it made the trebles really soft and the headphone overall much less brighter, it was a bit too soft for my taste so I changed it to an approximately 2 mm sponge and it is working for me: trebles are not that spikey any more, they are more natural, yet detailed and can bite when they need to, but can do silky laid back treble also which was not the case before. I always liked the K550, it sits comfy on my head, have a good seal at 4 and 5 positions, I just felt that the treble has some unnatural plastic sound and it can be too sharp simetimes. It can be solved with the above method pretty easily, and with it the overall sound becomes more coherent, balanced. I am not a fan of mods, but this one is working and should have done by AKG.