[papamogl]

A common complaint about the AKG K701 which I share is a lack of bass, or rather of bass impact/punch. Listening to a Beyerdynamic Dt 880 I can hear and FEEL just the right amount of deep bass, with the K701 I just hear it.
 
On a german speaking forum somebody posted a completely reversible, easy to do mod which alledgedly increases the bass. It is as simple as removing a small piece of felt or something glued on the middle bassreflex.
 

 
Wrap this piece in polysthene foil so you can later easily undo the mod if you wish to. Here's another picture showing the small piece that has to be removed:
 

 
 
Has anybody yet tried this? I sadly can't for myself, as I don't own a pair But it would be interesting to know if this actually works.
 
Even if the mod is said to be reversible: try at your own risk only. Not of my invention, so kudos and all credits to the "inventor". Original thread: http://www.hifi-forum.de/viewthread-211-474.html

 

[Dafo]

After reading your post and the german thread I tried this mod on my k701. 
I have very good experience with adding bassports to Shure srh940 and also with adding an extra variable bassport to the Beyerdynamic dt770pro250ohm.
 
The bass in k701 goes very deep standard and is very clear, dry and articulated, but it lacks body and punch. This mod (removing the circular piece of tape on the back of the driver) adds some body and punch to the bass. Only the bass is affected so you will not loose any of those nice mids and clear highs, you just gain an overall more balanced sound signature.
 
I think the bass in k701 standard is overdamped.
With this mod the driver is able to move more freely without any unnecessary restraints but still sounding very good and detailed.
 
Some might think you loose something with this mod and yes, you do loose something, you loose some of that dry unrealistically light bass, that appears very detailled, but on the other hand you will gain the body in the bass, and body is essential for bassnotes to sound proper. The standard bass only appears detailled, but really it is not, it lacks the weight and body which in fact also is a part of the detail in the bass. The detail in the bass is not only on the sharp "edge" of the bass notes like a whisper, it's also "inside" the notes, in the body of the bass, the ressonance, that powerfull massive sound you can feel in your body at a concert or with speakers. This does not mean the modded bass sounds loose, slow or any less detailed or anything like that. The bass is still very fast, precise and detailed but now it also has the body and weight to back it up, just like it is supposed to have. 
 
Akg must know how the k701 sounds with this bassport opened up. To start with they prepared the driver with this bassport, but they chose to shut it off. I simply disagree with akg in their choices regarding this, I think they went too far in dampening the driver. The bass just sounds better and more realistic when it is not overdamped, in my opinion.
Objectively it is not a matter af "better" or "worse" with this mod. Sure I believe I can make compelling arguments to doing this mod for gaining a better bass response in the k701, but really it all comes down to taste; do you want a bass with more body to it, or do you not want this kind of bass response?
 
So the answer to your question wether this mod actually works is: Yes.

 

[papamogl]

Thank you for that detailed account. I bought a K701 myself some time ago and I have to say the mod works like a charm from my point of view. I really like the analytical fingerprint of these headphones, but, as you stated, the bass is missing some impact. It goes real low and all the frequencies are there, but it just has no body, you can hear it but you cannot feel it.
 
The mod didn't change anything else than adding a little of this missing impact from what I can hear. It's still far from being a bassmonster, mind you. But now the still very precise bass has some body too. From what I can hear this mod does really well (as well as being reversible, so it can't hurt to try it yourself) and makes these headphones even better!
I would love to see some measurements of this mod! I already asked Tyll from Innerfidelity and he might do it when he finds the time.

 

[Khalaris]

I just tried this and it works very well. I find it adds just enough to make listening to Metal (for instance) more comfortable, but thankfully doesn't change the overall sound in any other way (as far as I can tell). Not that not having this mod stopped me from from listening to Metal the last 3 years

Comfortable or not, I like my details.
 
It's not actually necessary to take them apart like on the pictures, though. I opened the grille on the outside and got the covering off with some pliers and a lot of patience. It's a bit fiddly, but as long as it works...

 

[papamogl]

Glad you like it. It definitely improved my K701s. Now if somebody could measure some modded phones - or even better a before/after-comparison  that'd be awesome.

 

[Sir Tmotts III]

Has anyone tried this with the 6XXs or the 712s?

 

[scottzg]

I'm not sure this is widely known, but it looks like this is the change between the k701 and the q701.  My Qs did not have anything there.

 

[papamogl]

Don't know if that's the only difference. But it's possible that it's the one that accounts for the better bass response of the q701. Anyway, I definitely recommend the mod for owners of the k701.

 

[kooncm]

Nice! I tried this on my K701 and very happy about the result.

 

[moriez]

Thanks for starting this informative thread papamogl. I'm about to receive a K702 which I intend to use for gaming but this mod makes it a tad more interesting for listening to music. I guess K702 has the exact same inner lay-out. Can anyone confirm this?

 

[Dafo]

I'm not sure this is widely known, but it looks like this is the change between the k701 and the q701.  My Qs did not have anything there.

This is a very important piece of information!
All k7-owners should be informed about this.

 

[papamogl]

@moriez I think the K702's layout is slightly different, but only in the shape of the plastic surroundings. It may look slightly different than on the pictures above, other than that it should be the same. You should be able to remove the felt/silk/whatever piece with the same results as on a K701.

 

[Dafo]

Now I have compared my modded k701 to the Hifiman he-500 using my Audio gd compass2. I listened at quite high levels of output to be sure the he-500 didn't fall behind the always clear and fast k701. Orthos do in general need a bit higher listening levels to shine through. Btw the k701 and the he-500 requires almost exactly the same amount of power. 
 
Bass level is the same as the he-500 with velour pads. I couldn't hear any difference in level or extension between the two, the k701 went just as deep as the he-500 and was just as powerful. The k701 was even a bit faster(more speed) and a tad more punchy due to the overall more clear presentation and this includes the bass. The texture or "surface" on the bass-notes was every bit as good on the k701 as it was on the he-500.
So if you think the bass level, detail, texture and extension is on a high level and is good in the he-500, then you will like the bass performance in the modded k701.
To my big surprise the bass performance in the modded k701 is just as good and is right up there with the high rated he-500. I thought the he-500 would beat my k701, but this is not the case. I was a bit shocked when I started comparing the two. The k701 is indeed a wild bargain. 

 

[papamogl]

Thanks for that comparison. Interesting that it holds up so well, but I'm not surprised: the mod does really improve the bass performance quite a bit. I just don't understand why AKG put that felt piece there in the first place.
 
Agreed, the K701 offers incredible value for the price. Even more so with the mod.

 

[tdockweiler]

I did this mod tonight and will post impressions later. Right now I'm really impressed. The bass is even better on my Q701 now than the Annie ever was.
So far I haven't really heard anything else different in the sound signature..how is that even possible?
 
My ears are really bombarded now due to spending about 5 hours today on modding things and listening to music.
 
Strangely with the extra bass impact the sound is even clearer?!
 
NOTE: This mod is very dangerous if you don't know how to solder if you pull apart a wire. You have the mini-XLR plug just hanging there.
It was a pain to remove this piece without tweezers and without removing that inside bracket. Luckily this just peels off.
 
It was actually more of a pain than recabling my HD-598

 
I wonder if the K712 and Annie have the bass port open? On my Q701 it was closed (Well, duh). Some have said it's open, but it definitely isn't.
 
It'd be hilarious if the K712 bass port was open.