A couple weeks back, I measured the Dekoni Blue headphone which as I noted, is itself a "modded" Fostex T50RP Mk 3 planar-magnetic (aka "Regular Phase", aka "isodynamic") headphone. It would be completely remiss of me if in a review/discussion of the Dekoni/Fostex I were not to spend some time talking about modding!
Modding has an very long tradition in the 'head-fi' world and I think it's been generally recognized that the Fostex headphones are the classic headphones to perform surgeries on. Much of what I'll be talking about here will be nothing new to those deep into this stuff already. For more on modding, check out this Headphonesty article for a background.
To start, as always, we need a plan and a "vision". As I mentioned in the last article, the Dekoni Blue sounds pretty good for the most part, so my job isn't to change the performance completely, but to rather refine what is there. If a headphone sound highly objectionable, one should really just move on and buy something else! Let's review the measurements I published last time for the Dekoni Blue with the supplied earpads and see what we can try...
I showed the measurements using the Elite Velour earpads first because those are what I preferred so any mods will be targeted to improve performance with the Velour. Looking at the measurements above, there are a few things we could try to do that could meaningfully impact the performance in a positive way.
1. I'm not a "bass head" so I think the bass is too strong. I also don't like that 100Hz bass hump; let's see if we can reduce the bass response by a few dBs and push the 100Hz mid-bass hump to a lower frequency.
2. Notice the 10ms waterfall plot and all those lingering resonances below 1kHz. Let's see if we can improve the time domain performance a bit and reduce what looks like resonances inside that hollow ear cup.
3. The headphone is rather "hot" in the upper treble above 7kHz, especially with the Velour pads. Let's tone that down a few dBs if we can.
While I would love to show you all the measurements I went through and materials I tried, let me get to the point and talk about the simple "Arch Mod5" changes I finally settled on. It works well and sounds great to me. In the process, it taught me a few things about personal preferences when it comes to frequency response.
DISCLAIMER: Modifying your headphone will break your warranty. And doing this may damage your headphone as well. Use your discretion. I'm obviously not responsible for what you do. While I very much like the final results with mine, you are the final arbiter of sound quality and each headphone will be different! While everything can be easily reversed, proceed with appropriate caution.
For this simple mod, all you need are a couple of items as "materials".
1. I used inexpensive 1.5mm thick felt fabric sheets I found at the local dollar store (light blue of course for these headphones, MultiCraft Imports brand used). Make sure this is the soft, low-density fabric and not stiff felt.
2. I looked around for "meta-materials" but came up short ;-). So the other material I used was some SilverStone EPDM absorption foam which is usually applied to computer cases to keep the machine quiet. For headphone modding, we need only a little bit of the stuff.
I. Opening the Dekoni Blue / Fostex T50RP Mk 3.
First thing you do is remove the ear pads - it should be obvious how to do this. Stick your fingers into the ear cup, push on the edge from the inside, and release the ear pad "lip" from the headphone carefully. Make sure not to rip the pads (it's stretchy so should not be an issue).
Afterwards, you'll see the driver and baffle as below. There's a loose foam baffle pad around the driver that will just fall off (not shown), and you'll see the 4 small Phillips cross-head screws you need to remove:
This is why the Fostex headphones are popular with modders - these are the only screws you need to remove to access everything inside.
From here, we can easily remove the driver and baffle unit to reveal the rear and see inside the earcup:
II. Dampen the cup, slow down the bass decay.
As you can perhaps imagine, there's quite a bit of space inside the ear cup and this lack of damping is contributing to some excess vibrations seen in the waterfall plot. So, let's use that SilverStone foam material to reduce the magnitude and persistence of vibrations against that rear "cabinet":
You can see that I haven't bothered with any special shapes other than just rectangular cut-outs of the SilverStone foam material with the dimensions noted for the left and right. You can look at this Mayflower video and see that they have traced out some shapes if you want to get fancy. The difference between the left and right ear cup is the presence of the headphone cord jack in the left cup, so one of the long pieces has been reduced from 2.5" to 2" to fit.
Now, let's use the 1.5mm low-density felt fabric to dampen the space; reducing the air compliance within the cup. Cut out two 3" x 3" felt fabric squares, one for each ear cup. Take one of these 3" x 3" sheets and lay it across the inner cup like so:
The quick measurement above shows me that the bass level is slightly attenuated by the mod (red) and the treble was mildly accentuated. I like that the mid-bass hump is no longer centered at 100Hz, but has a smoother, more extended profile down into the sub-bass with a peak at around 75Hz now. We can imagine that the headphone is now even less "semi-open" than before.
Yup, damping has an effect particularly in that stretch from 200Hz to 2kHz. No, it's not like the smooth and clean decay we see with the open-back Sennheiser HD650/HD800, or the AKG Q701. An improvement nonetheless.
III. Time to tame that treble!
1. Peak bass is toned down 2-3dB. Rate of sub-bass roll-off less steep.
2. Bass bump now in the low-bass, around 70-80Hz instead of mid-bass 100Hz.
3. Treble tamed a bit to be consistent with the lowering of bass. There's a slight "harshness-dip" into 2-4kHz, and then the reconstitution of the "presence" and "brilliance" frequency ranges to give us "sparkle", "air" for higher order harmonics are reproduced but without too much energy into 10kHz and above.
|My preferred earpad.|
"The gentle rise from 400Hz to 2kHz of the Mk3 is highly desirable, in my opinion, and is quite similar to the Harman Target Response. My guess is achieving this rise is a tricky combination of a number of things, and may suffer during modifications. If you're a DIYer with a measurement rig, take care to note exactly what this area looks like on your measurements (they may look quite different than mine on a non-IEC-spec measurement system), and try to retain the profile between 400Hz and 2kHz during your mods."
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