Fixing a DT250-250

Thanks to our forum member @Psalmanazar I recently got my hands on an unbalanced DT250-250 for free and attempted to find a simple fix to its problems, here's the stock measurements (solid plate coupler, no compensation):



It sounded bad.
Here's what I came up with:

Fix the channel imbalance

Materials:

• Electrical tape
• Flat head jeweler screwdriver
  
• 1-2mm thick foamie / craft foam
• Scissors

1. Disassemble the cable connector on the left cup.
2. Cut a small piece of foamie (~1" side square) and stick it through the connector pins, then trim the excess material around the connector like this:
   
3. Cut a small piece of electrical tape and place it over the connector screw opening on the cup like this (no need to poke the hole, you can do that with the screw while reassembling):
   
4. Reassemble the cable connector:
   

Here's the resulting FR:


Much better, channels are balanced but kinda lean sounding, I wasn't entirely happy with the result.

Fix the frequency response

Materials:

• ~1mm thick rubberized microfiber cloth for cleaning glass (I used this).
  Note: ~1mm felts or foams should work as well, no guarantees on the resulting bass elevation, though.
  
• Compass
• Ruler
  
• Scissors
• Tape

1. Remove the earpad assembly from both cups by pulling along the edge firmly, it should look like this:
   
   (Notice the depressed ridge where the stock foam sits, you will use this a template to make a sealing gasket out of a cloth/felt ring)
2. Measure the inner and outer diameter of said ridge and trace a template using your compass tool on the piece of cloth / felt / whatever. Cut said template, it should look somewhat close to this:
   
   
3. Mount the ring over the backside of the assembly like this:
   
4. Place the foam over the gasket:
   
5. Do the same for the other cup and carefully reassemble, making sure that neither the gasket or foam gets displaced during the installation.

Here's the resulting FR:


Balanced and full sounding

 

Going by the FR alone it would seem that the pair should sound sorta bassy and midrangy like the M50x does, but that's not the case, the seal around the head is not as tight as this rig and this driver is very sensitive to coupling / pressurization, here's a take with my ear-mounted rig that better reflects what I'm hearing:



Pay no mind to the dip at 6 KHz, it's a measurement artifact.

There are several ways to achieve a lower/greater bass boost, you can use more permeable materials instead of the microfiber cloth to lower the boost, or make an incomplete (not a whole ring) gasket to let some of the pressure escape in a controlled fashion, or use a better sealing material like closed-cell foam or rubber to have a greater boost.

Happy modding.

 

Here's mine I got for 50 bucks.

Before
L https://i.imgsafe.org/f78007b256.png
R https://i.imgsafe.org/f784ead995.png

After (Vileda ring + 2 layers of toilet paper)
L https://i.imgsafe.org/f78993fc91.png
R https://i.imgsafe.org/f780296051.png

 

I'm glad it's working out.

 

@spoony this is a fascinating discovery. can you help explain WHY the foam+electape mod fixes a channel balance issue? From what I can tell, it makes the cable sit a little further away in the pin holes and removes a tiny amount of play between the cable connector and the frame.

 

The connector play allows more airflow between the pins into the cup chamber, it acts as a port reinforcing the lower frequencies. The foam is a lid or gasket to this 'port'.

 

Just want to thank you spoony for your really helpful advice. I was interested in trying a Beyerdynamic headphone, but was really hesitant about the usual candidates - 770's, 880's etc because of the thing everyone mentions - the over heightened treble. Don't get get me wrong, I like clear highs but the comments put me off. However, I read a couple of reviews elsewhere that said the 250 was a good egg and not so treble emphasised. I located a secondhand 250 ohm DT250 that needed a bit of tlc. Bought some new pads. However, I was not enamoured with the sound. To be honest I was really disappointed. There was no bass (I'm not a bass head),vocals were recessed. The treble was the only redeeming factor. The headphones weren't really any good as it was.
I was aware of potential imbalance issues from a YouTube review. This directed me to your thread. So I followed your first step of instructions and put some craft foam on the lead connection etc. There was some improvement but it wasn't still satisfactory. Then I thought I'd try the second step and put some circular material in front of the foam disc. Tried this out and WOW!. This has completely transformed the Beyer's. I am so pleased. There is nice bass, the mids and vocals have been corrected to be more appropriately in the right place, i.e. not recessed, dry and somewhat boring and the treble is nicely analytical. Amongst other things It's great to hear the different cymbal notes i.e. not one-note cymbals.
I am really pleased and I say Thank you again .