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Reversible AKG K701 bass mod - Page 13

post #181 of 206
Quote:
Originally Posted by dabtpa View Post
 

This video is GREAT ! I have hands the size of Bigfoot's and I was able to complete it without a hitch. Just be careful with the little screws. They are very small and there are open areas on these where they could slip through to the inner part of the driver if you don't have a good grip on them. I would use needle nose pliers or tweezers, yet I got them right back in with my thumbs.

 

+1 re: those tiny screws.  I lost one inside once and ended up having to resolder the red and white cables.  Fortunately, none the worse for wear.

post #182 of 206

The Reversible Bass Mod elevates the bass and slightly attenuates the upper mids and treble frequencies as described by many others in this thread. The sound quality changes are audible and an improvement, IMO.

 

I'm going to try felt and other materials to partially open/block the bass ports and some ear side of baffle mods, too.

 

My simple DIY measurement kit is shown and my methods described HERE.

 

Here are my graphs. Take them FWIW. 

 

~BMF

 

 

 

 

 

 

 

 

 

 

   

 

 

 

EDIT: VARIABLE Bass Port Mods and Measurements

 

IMO:

1. Stock = Sealed Bass Ports ---> Not enough bass

2. Bass Port Mod = Fully Open Bass Ports after removing the Stock Tape Disk from each driver makes a 2.5 mm bass port ---> Too much bass

3. Partially Open Bass Port Mod = 1.8 mm hole using Double-Sided Tape ---> Just right amount of bass

4. Partially Open Bass Port Mod = 1.3 mm hole using Double-Sided Tape ---> A little more bass than Stock

5. Remove ear side foam disks = Too much bass

 

Compare to the graphs, above, and draw your own conclusions:

 

 

 

 

 

 

 

 

 

 

  

 

 

EDIT: Here is a photo of double-sided tape with a 1.3 mm hole. 

 

 

To my ears, a 1.8 mm Variable Modified Bass Port falls in The Goldilocks Zone and sounds better than Fully Open (Stock Tape Disks Removed), Fully Closed (Stock Disks in Place), and 1.3 mm Variable Modified Bass Ports.

 

I used a hole punch with 6 different sizes. The smallest size punch = 1.8 mm and makes a uniform hole in each double-sided tape disk. I usde a thumbtack and toothpick to make the 1.3 mm holes in disks shown in this picture and the holes are not uniformly round. A hole punch is recommended.

 

 

turbobb's youtube video shows how to get to the bass ports...Well Done!


Edited by bluemonkeyflyer - 8/8/14 at 6:23am
post #183 of 206
Spectacular view and very comprehensive, nice work.
post #184 of 206
Quote:
Originally Posted by Dafo View Post

Spectacular view and very comprehensive, nice work.

 

 

Quote:
Originally Posted by papamogl View Post
 

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

Props to 'oldidi' on the German site and to you for sharing this information.

 

Quote:
Originally Posted by Dafo View Post
 

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.

 

After my Trials and Measurements, I agree with you.

 

The Bass Port Mod is also Variable. The effect is "tunable" by varying the size of the bass port. 

 

The Stock Bass Ports covered by the adhesive disks is ~ 2.5 mm in diameter (at the "tube," not at the flare at the top. Punching a 1.8 mm hole in the Stock Adhesive Disk and re-applying it over the Bass Port brings the bass to a level that sounds better to me than Fully Open.

 

Cheers,

 

~BMF

post #185 of 206

Yes, that wimpy, slamless bass is an important drawback of the k701/702. 

 

I have not tried any version of the mod yet, but the concept is intriguing. WRT the stock unit, I wonder why incorporate a reflex port when it's to be covered up at the factory? Maybe the designers found an easy way to present two different sonic signatures during the prototype phase ... the no-port version got voted in 51/49 (out of 100) im Wien, Österreich HQ auf Akustische und Kino-Geräte Gesellschaft m.b.H., aka AKG aka HARMAN holdin' an AK47 ....but rather change the costly thermoplastic cast/die, just cover it with an adhesive tape "bodge" ;)

Me, I would've opted for a postage stamp or kids sticker ...

 

...or better ...

 

LOL!!!!!!!!!!!!!!!!!!!!!!!

 

The tunable aspect is also appealing. BTW... Is that stock adhesive disk porous?

 

FYI: I've owned a pair of k701s since 2006 and long-term use has been an interesting evolution. These cans take quite a while to break/burn in ... but the resulting increase in SQ is worth the wait. 

Another "easy" mod is to replace the cable (with one of better quality and shorter). It does not have to be $$ Cardas. I'm using JSC industrial Multi-Conductor Foil Shield 75°C, 300 V, SR PVC Insulation.


Edited by alphaman - 8/15/14 at 2:06am
post #186 of 206
"FYI: I've owned a pair of k701s since 2006 and long-term use has been an interesting evolution. These cans take quite a while to break/burn in ... but the resulting increase in SQ is worth the wait. "

The little round piece of tape on the back of the driver is soft and strechy.
What if this little piece of tape just gets softer and more responsive to the movement of the driver when used over time ("burn in")?
That increase in sound quality over time may very well be close to just removing the tape as suggested in this mod, and you are right, that sound is indeed an increase in SQ wink.gif
Edited by Dafo - 8/15/14 at 12:06am
post #187 of 206
Quote:
Originally Posted by Dafo View Post
The little round piece of tape on the back of the driver is soft and strechy.

Hmm...and only a smaller diameter of it covers the actual port hole.

 

In dynamic loudspeakers, a type of similar implementation is called a passive radiator (sort of a dummy driver) :

 

Anyone with a zest to experiment care to use some other material?? .... say rubber-balloon latex.

 

Or create a tuned/damped system, again borrowing from speaker design....

... using, maybe, the filter from a cigarette?

 

A transmission-line system is used in some "tuned" loudspeaker designs, like classic TDL...

 

... so, for the k701s ... maybe use drinking straw ...the kind with accordion flex part ....

 

.... but, no plastic straws for me, boyz  ....now where did I put my crack-pipe???


Edited by alphaman - 8/15/14 at 2:38am
post #188 of 206
Quote:
Originally Posted by Dafo View Post
The little round piece of tape on the back of the driver is soft and strechy.
What if this little piece of tape just gets softer and more responsive to the movement of the driver when used over time ("burn in")?
That increase in sound quality over time may very well be close to just removing the tape as suggested in this mod, and you are right, that sound is indeed an increase in SQ wink.gif

While the change in elasticity (compliance) of that tape stuff may contribute minorly to burn-in improvement, it's removal (partial or full) seems to perform an entirely different acoustic function: increase bass. The burn-in for the k701, IME, qualitatively reduces glare/brightness and improves image focus. Those contributions come from changes in mechanical compliance of the main drivers as well as, perhaps, the "breaking in" of the wiring/coils/electricals.

post #189 of 206
I find all this very interesting. If I was to design a closed back headphone, there is no doubt I would experiment with bass ports, the diameter, tubes and the length of these tubes into the chamber. I also find designs like the cone-shaped tube, the b&w "nautilus design" behind the driver very intriguing.
Quote:
Originally Posted by alphaman View Post

Hmm...and only a smaller diameter of it covers the actual port hole.

In dynamic loudspeakers, a type of similar implementation is called a passive radiator (sort of a dummy driver) :



Anyone with a zest to experiment care to use some other material?? .... say rubber-balloon latex.

Or create a tuned/damped system, again borrowing from speaker design....


... using, maybe, the filter from a cigarette?

A transmission-line system is used in some "tuned" loudspeaker designs, like classic TDL...



... so, for the k701s ... maybe use drinking straw ...the kind with accordion flex part ....

.... but, no plastic straws for me, boyz  ....now where did I put my crack-pipe???

Edited by Dafo - 8/15/14 at 3:36am
post #190 of 206
Just a thought really. "Burning in" that piece of tape is probably not all.
Could be fun though, then we could change the name of the mod to "The AKG 5 minute burn-in!" ;-)
post #191 of 206

In traditional loudspeaker design, acoustic suspension (i.e. non-reflex or non-port or no passive rad. or transmission line) gives tight but wimpy bass. Whereas, reflex/ported/etc. gives more powerful (deeper/punchier) but not-as-accurate bass.

I don't know the specifics of the k701's actual driver -- but there is a topical h-f driver thread, with some good info and pics....

 

Also note that way back in June 2012, in the 701 vs. 702 thread, MDR30 noted (about the above diver image):

Quote:
You see the openings on the left, right and centre covered with filter paper/nylon fabric. These affect themovement of the diaphragm, and the bass response. If you remove the centre fabric you would get more bass, but also a less controlled membrane. It's all a give and take. I'm very curious as how the back of the Q701 driver looks.
post #192 of 206
Quote:
Originally Posted by Dafo View Post

I find all this very interesting. If I was to design a closed back headphone, there is no doubt I would experiment with bass ports, the diameter, tubes and the length of these tubes into the chamber. I also find designs like the cone-shaped tube, the b&w "nautilus design" behind the driver very intriguing.

The Q701 Bass Port is actually flared similar to the B&W Nautilus Bass Port. The flare diameter is ~ 2.5 mm and the "tube" is ~ 2 mm.

 

The stock self-adhesive disk covering the Q701 Bass Ports looks impermeable to me and the glue is very strong.

 

I tried to modify the tube effect with thin craft felt, 3mm open cell foam, and punching various hole sizes in double-sided tape vs silicone furniture bumpers. The felt and open cell foam had no effect, functioning pretty much like the stock self-adhesive disk. Changing the hole size in silicone furniture bumpers seems to allow for a tunable bass port: smaller = less bass, larger = more bass.

 

Angle Hair over the ear side of the driver sucks out the lower mids around 500 to 700 Hz by ~ 5 dB.

 

Removing the stock foam ring on the ear side of the baffle causes even greater suckout by ~ 8 dB.

 

The best sounding bass port mod to my ears (so far!) results from:

 

1. Fully open bass port after removing the stock tape disk + add an equal size Arctic Cotton disk overlaying the stock foam disk + Paxmate on the underside of the plastic grille receptacle, only at the bottom, leaving all 4 "vents" fully open (2 small at the top, 2 large at the bottom).

 

2. Partially open bass port after removing the stock tape disk + silicone disk with 1.5 mm hole placed over the open bass port + self-adhesive craft felt instead of Paxmate, as above.

 

I have measurements and photos of each mod combination. I will post everything in a new thread this weekend and post a link in this thread for anyone interested.

post #193 of 206
Quote:
Originally Posted by alphaman View Post
 

Anyone with a zest to experiment care to use some other material?? .... say rubber-balloon latex.

 

 

I've experimented with a few different materials and configurations on my Q701s.  Currently, and probably permanently, I'm using squares of porous spongy foam ~2-3mm thick over the port.  They are significantly wider than the original stickers I removed, but do not overhang the plastic piece in which the port is set.  For me, it's a nice compromise between closed and totally open, but the type of foam does make a difference.  I also tried some painter's tape over the ports with pin holes poked in them.  That was OK, but I went back to foam.

post #194 of 206
Quote:
Originally Posted by ThurstonX View Post
 

 

I've experimented with a few different materials and configurations on my Q701s.  Currently, and probably permanently, I'm using squares of porous spongy foam ~2-3mm thick over the port.  They are significantly wider than the original stickers I removed, but do not overhang the plastic piece in which the port is set.  For me, it's a nice compromise between closed and totally open, but the type of foam does make a difference.  I also tried some painter's tape over the ports with pin holes poked in them.  That was OK, but I went back to foam.

 

I tried a 10x10x3 mm square of camera repair open cell foam over the ports. Pivoting the the cups in the vertical plane caused the edge of the foam near the bottom of the driver to "flap" upwards. This essentially opened the port, negating the desired effect of a partially open, "tuned" bass port. I placed double sided tape under the bottom edge of the foam and it stayed put with cup pivoting.

post #195 of 206
Quote:
Originally Posted by bluemonkeyflyer View Post

I have measurements and photos of each mod combination. I will post everything in a new thread this weekend and post a link in this thread for anyone interested.

It's important to note that while metrics (objective data/graphs) may, indeed, improve as a result of various mod(s), the actual subjective sound may not correlate to those changed metrics. E.g., flattening of the freq. response may not appeal to all ears (as the ever-controversial diffuse field vs. free field results indicate). 

One particular subjective (controversial) quality is PRAT. I find that even 'phones that display a clean/impressive impulse response may not, in fact, sound as snappy/punchy one that graphically looks (measures) worse. Another unquantifiable is long-term listening -- this may yield subjective results (e.g. listening fatigue) that immediate sonics (or metrics) just can't correlate to. In this case, it's not that objective science is wrong ... rather, it's that currently known-to-human science is missing something ... and may be discovered/quantified by some future da Vinci or Galileo. 

Unfortunately, for logical-fallacy reasons -- like sunk-cost fallacy, etc. -- various mod projects (audio forums are full of them!) gain a sort of "pop inertia" ... like some quaint pop celebrity ... and that may very well be the case with THIS thread. Indeed, as I noted a few posts back ... that AKG was probably aware of the port vs. no-port sonic issue .... and they SELECTED to cover it up after important/informed/well-founded decision metrics.

Hence, with  proposed mod projects , I almost always (now) either ignore or treat them with extreme skepticism ... a lesson that was learned the hard way

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