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.
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:
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
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.
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.
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.
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
Olive - African Ebony
Mahogany - Zebrawood
Olive - Blackheart
Rosewood - These were sent in for measurement.
Alu - Rosewood