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The StratoKOSSter – A closed DIY headphone based on the Koss KSC-75 driver and Grado cup design

post #1 of 177
Thread Starter 

How the StratoKOSSters came to be built
 

Before I go into detail with the modding process I would like to mention where I am coming from. About a year ago I bought my first Grado headphones (SR80i). By that time I had mainly listened to IPod buds or my main speakers. 

Very soon I started to take interest in modding the Grados, punching holes into the backs of the drivers, putting the drivers into wood shells I had made myself with a drill press, recabling them and trying pad rolling. 

The next step was using the Symphones Magnum drivers in wood, aluminum and hybrid encasings, thus lifting the setups onto a new level. 

While doing the mods I always wondered if/how I could achieve a closed design. Nothing worked though. Both Grado and Symphones drivers sounded canny and thin when put into a closed shell. 

It was then that I came across the Koss KSC-75 headphones. Cheap as they are, I bought a set for outdoor use. From the start I liked their natural sound. The bass is full and the mids sound quite Grado-like, forward but lacking the typical Gradoesque shout around 2kHz.

I also had some unused wood shells lying around, so one day I tried the Koss in a set of wood shells. All I can say is that I liked what I heard. Purrin measured the KSC-75 and called the Koss a poor man’s HF-2, and I guess this says much about these very capable yet incredibly cheap drivers.

Then something happened that led me into the direction I am taking with this project.I put my hands on the cup backs and expected the same to happen as with all my Grado/Magnum setups. I was expecting the tinny and thin sound, but quite to the contrary somehow they sounded  better than before. In the open design the bass could sometimes sound a little loose and murky. Closed it seemed a lot tighter and punchier. The mids and highs also matched nicely. Then and there I decided to turn these into a closed set of headphones.


How the StratoKOSSters sound

 

With the right pads the StratoKOSSters simply sound fantastic, provide rather good isolation, leaking little sound in or out.  They are neutral, balanced, have very good bass extension, the mids are forward and very engaging, the higher frequencies in nice balance with the rest.

At the moment there is only one other person who has heard the StratoKOSSters and who can give his comment on their sound. Purrin, who listened to and measured them. I am sure he will be more than willing to comment on them in this thread.


How the StratoKOSSters measure
 

Now, when you have somebody mod a headphone and tell people that his mods are making this headphone sound fantastic, normally – and I figure this is natural and quite reasonable – people will react interested but skeptical. Every too often their expectations (including mine) have not been met when trying to copy a mod.

Knowing and respecting this I decided to send in the Stratos to purrin, in order to find out myself if objective measurements correlated to my listening impressions. I simply loved the way the Stratos sounded, but I wanted to see how they measure, making sure my brain was not playing tricks on me telling me how great they sounded just because I wanted them to sound good. Below you will find the measurements.

 

Measurement 1: Stock KSC-75 clip-ons
stock_ksc_75.jpg


Measurement 2: StratoKOSSters V1
stratokosster_v1.jpg

 

 

You easily see a dramatic change in the frequency response, with better bass extension, nice midrange  and fewer treble spikes. There is this dip from 100 to 300Hz though. Purrin applied some changes in the damping scheme and tThis is how the StratoKOSSters V1.5 measured afterwards:

 

Measurement 3. StratoKOSSter V1.5
stratokosster_v1_5.jpg

 

Now, draw your own conclusions, because that seems like a pretty nice frequency response ;-)

 

 

 

How the StratoKOSSters are made – The Mod

Below I will give you some information about the modding process, so that you can build your own StratoKOSSters  and find out if you like them as much as I do.

 

What you need:

  • Koss KSC-75 drivers
  • Grado/Alessandro or custom plastic/wood /aluminum shells
  • Grado headband or some other cheap headband like from a computer headset
  • Some stiff plastic/cardboard (like from a plastic placemat)
  • Dampening materials: acoustic foam (like Paxmate Plus), medium density packing foam 

 

Modding process

Step 1 -The cups
You can use any shell you like, aluminum, wood or plastic. Most modders might have some spare plastic parts lying around, so I will go through the process using plastic shells.

 

700

 

 

Step 2 – Closing the cups

As you can see in the pics of my StratoKOSSters below, I closed the wood shells with a wood disc, making it a full woody. As I know you will not have such wood shells and  wood discs available, let me tell you how you can come up with something that will work as well.

  • Make a disc of hard plastic that you can use to close the cup with. When I first tried it, I used a plastic place mat, cutting out a circle that would rest in the cup behind the stock Grado mesh, thus closing the cup. You can use the cup as a template to get the diameter right. Then apply a layer of acoustic foam on the back of that plastic disc.  
  • Now I take for granted that you already know how to open Grados and how you remove the Grado drivers. If you do not know, there are videos online that show this process. You just have to google for them.
    So, you have an outer shell, which you have to close and an inner shell, which you will have to load with the KOSS driver.
  • Take the outer shell and glue the plastic disc on the mesh of the shell to close the cup opening. Seal everything tightly, there should be no air leakage.
  • Put the driver into the inner shell. Leave the Koss earpad over the driver, it will hold the driver in place and provide dust protection.
  • Before putting the inner shell into the outer shell, load the cup with damping material by lining the walls with acoustic foam and filling the cup with medium-density packing foam.

 

700

 

 

 

Step 4 – The pads

As pads you can use any Grado foam pad. This however will not give you the proper isolation and the sound quality you might be looking for.

There are some cheap computer headsets with pleather pads of the right diameter out there, which you can use. I myself am using DIY leather-covered L-cushs. These are extremely comfortable and isolating, plus provide the nicest sound. In the picture below you see the L-cush, 2 sets of leather covered L-cushs and two sets of pleather pads taken from cheap headsets. Personally I strongly prefer the leather-covered L-cushs.

 

700

 

 

Step 5 – Fine-tuning

If your StratoKOSSters do not sound right, the time has come for fine-tuning, i.e. dampening/damping the cups to fine-tune the sound signature. The damping scheme that gave the best results as in measurement 3 consists of the following:

  • Covering the bottom and walls of the shells with acoustic foam
  • Fill the cups with medium-density foam
  • Lift the drivers out of the shells until they are in perfect distance to your ear and provide the best bass response

 

 

Step 6 – Recabling

The KOSS drivers are easy to recable, if you find the cable too short or flimsy.

 

Step 6 – Headband

You can use a stock Grado headband, which I personally hate. Instead I use headbands of cheap computer headsets, which do not allow the cups to swivel. To increase comfort you can make yourself nice and soft headband pads from some spare leather you use to line your L-cushs with.

 

 

 

 

StratoKOSSter Gallery - Just a few ideas, I am sure you will come up with lots of cool designs and setups

 

mahog.jpg
Mahogany - Bloodwood
 

olive1.jpg

Olive - African Ebony

 

mahog2.jpg

Mahogany - Zebrawood

 

olive2.jpg

Olive - Blackheart

 

rosewood.jpg

Rosewood - These were sent in for measurement.

 

 

alu.jpg

Alu - Rosewood


Edited by stratocaster - 10/5/13 at 1:13pm
post #2 of 177

Wow, those look great! Great job!

 

Do you feel that these can be considered those ever elusive closed grado's, seeing as they are compared to the PS500?

 

Where can those (non grado) headbands be found? What models did you sacrifice? :)

 

Oh, and another question, do the koss phones stay loose inside the cups? Don't you glue them on or something?

 

Anyway congrats on the headphones!

post #3 of 177

Wow, very nice.  Those look awesome.

post #4 of 177

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post #5 of 177
Thread Starter 

@ kAbUZi:

I keep the drivers loose in the shells. This makes the modding process easy and quick. If you do not use force, they will not move in the shells.

The headbands are from Chinese headsets. They come for something like $12 - $ 30, depends on what style you like. I prefer the cheap ones and make myself soft pads or cover the plastic with lambskin leather or the like.

post #6 of 177
Well done, looks amazing.
post #7 of 177

Great job! Even better are those pads, dear lord they look comfortable.

post #8 of 177

A pad tutorial should be in order I would assume. For The Greater Good and all that jazz.

post #9 of 177

ever try portapro/ksc35/sportapro drivers?

post #10 of 177
Thread Starter 

I have the PortaPro drivers in the alu-rosewood set. All in all it the PP drivers are a little darker than the KSC-75 drivers with less sparkle in the upper-mids and lower highs. This corresponds well with the alu shells, which tend to slightly enhance the higher frequencies compared to wood.

post #11 of 177
Quote:
Originally Posted by stratocaster View Post

I have the PortaPro drivers in the alu-rosewood set. All in all it the PP drivers are a little darker than the KSC-75 drivers with less sparkle in the upper-mids and lower highs. This corresponds well with the alu shells, which tend to slightly enhance the higher frequencies compared to wood.

I agree, to my ears, when using clips.. the PP drivers are more balanced and natural than the ksc 75. But if i use the portapro head band.. and the ksc 75 with clips I find both unnatural, the portapro more displeasing than the ksc 75, for most music. all things considered they are both really nice drivers, just need a little work to be balanced. I'm very curious how these stratokossters sound. In what ways do closing it alter the sound? or does it all depend on the dampening?

post #12 of 177

looking forward for the guide on making leather pads =)

post #13 of 177
Thread Starter 
Quote:
Originally Posted by chrislangley4253 View Post

I agree, to my ears, when using clips.. the PP drivers are more balanced and natural than the ksc 75. But if i use the portapro head band.. and the ksc 75 with clips I find both unnatural, the portapro more displeasing than the ksc 75, for most music. all things considered they are both really nice drivers, just need a little work to be balanced. I'm very curious how these stratokossters sound. In what ways do closing it alter the sound? or does it all depend on the dampening?

 

I did not do much listening with the clips. When putting the KSC-75 into wood housings and using Grado foam pads, they have a kind of Grado sound signature, upfront but with less to no shout at around 2kHz. The highs are much less fatiguing than those of a SR80i or SR353i for example.

When I closed the cups, even by covering the opening of the cups with my hands, I noticed that the bass tightened and the whole spectrum was much more in balance. The dampening is just finetuning AND avoiding resonances and  standing waves in a closed design.

post #14 of 177
Thread Starter 

...


Edited by stratocaster - 7/21/12 at 1:11am
post #15 of 177

thanks! will try this if i get a hands of a smooth and soft leather to use for pads. does this work for grado/alessandro headphones only? or i should make a "lip" to use it for other headphones?

 

also, what type of glue did you use? i think glue melts foam, right?


Edited by Dyaems - 5/29/12 at 12:46am
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