Many of us have odd, rare headphones and a guide explaining general techniques for improving issues makes sense.
The phones I'm targeting at the moment are the Sony MDR-XD400. Massive soundstage, 50mm drivers, highly capable. Surprisingly doubled in price since release.
Which of these (possibly ridiculous) ideas make sense, as they seem to be logical and in some cases common to popular headphone mods:
1. Is there benefit to removing a lightweight foam pad between the driver and the ear? Will this improve HF? Is dust and hair possibly contacting the diaphragm now a problem? Hairs would end up touching and rattling against the phragm but many high end phones have holes leading to the driver that would allow things to get trapped inside.
2. Do thin plastic cups benefit from having soft plasticine applied on the inside, apparently reducing resonances? Mashing soft foam bits in with the plasticine helps or hurts?
3. Acoustic foam between cups and the back of the driver. Fiberglass insulation, namely Corning 703 seems to be superior to actual acoustic foam. Any other material placed in specific places helps?
4. Removing restricting paper/hard foam seals from the back of the driver, or just punching holes in them. This apparently gives more bass since large volume airflow is unrestricted; however, it seems that when the driver is at longer excursions, HF performance would be impeded and dulled.
5. Earpad size. Over time, earpads flatten and the phones get closer to your ears. This at minimum changes resonant peak frequencies. What actually happened here is that the two sides have their resonant peaks in two different places and one of my ears touches one driver cage slightly! Makes it hard to EQ. A sine sweep pans from right to left quickly in one location. I plan to stick a length of emptied out power cable (a thick, sturdy but lightweight tube) deep in the inside edge of the earpads to push them back out.
On these phones specifically, there is a switch that opens or closes a port between the inside of the headphone chamber, and the back of the earlobe just under the earpads. Opening is said to give more sq for music, making it a semi-open headphone, closing it gives more bass. I found that closed, the port isn't sealed completely, and there may be differences between the two sides. Opened mode just opens a 3mm gap around the doorway which has a large 5cm^2 area. I will try to simply remove the door completely making it a rather open port. There will however be foam between the back of the driver and this port on the inside, but the goal is to allow airflow?
I hope to see a guide that more generally explains the physics of modding headphones as a starting point, and why certain mods do what they do. As seen over the years, there are some ridiculously well made drivers in dirt cheap phones and the issues come mostly from bad enclosure design.
