I recently acquired an HD540 REFII. Since I have a MiniDSP HEARS I figured I’ll try to measure the differences between pads and the effect of different tweaks. (I’m pretty new to all of this and more of speaker listener so any comments are welcome).
The HEARS is not very accurate above 3kHz but can be “corrected” for measuring a specific type of headphone. The HD600 is built similar to the 540. I was able find measurements of the 600 on a HEARS so yesterday evening I made a correction for the HEARS using Crinacle’s measurements of the HD 600 on a GRAS 43AG as reference. The resulting correction was very similar to the general correction for over-ear type headphones proposed by Oratory (except for the bass range where Oratory uses the Harman Boost and I don’t):
Oratory over ear correction (black) and my L and R corrections
Seems to be pretty well within the error margin:
So today I made some measurements. The 540 like the 600 is not very critical of position. The measurements are very repeatable. Only the seal and clamp pressure change the bass extension somewhat. So the below measurements are single measurements not averages of many measurements as the change in doing multiple measurements is minimal.
Stock with new foam disks from “Wang” in front of the drivers and new 0,5cm foam behind the driver against measurement of “Oratory”. These are raw measurement so the ear gain peak is not removed:
Green: Oratory GRAS 45CA. Blue: Stock with “Wang” front foam and new back foam. Not a bad match. I'm looking trends and relative changes between tweaks. Not super accuracy.
As a “sanity check” Here’s Crinacle’s measurement of the HD 600 L and R channel. Differences of up to 5dB seem normal.
So now onto some comparisons of tweaks and pads. Target is Harman 2018 above 1kHz and flat below like the Crinacle target for all the following charts.
Here’s the stock version with ‘Wang" foam disks compared to adding some acoustic fabric disk in front of the wang foam. The extra fabric attenuates the highest frequencies a tiny bit:
Only wang foam in blue. Added fabric disk in green.
Notice how stable the measurements are. I removed the pads inserted the fabric and replaced the phones on the fixture between measurements
Here’s the stock pads with wang foam compared to Wang Pleather pads and foam disk (fabric still covering the foam disk):
Stock blue. Wang Pleather and foam plus acoustic fabric green.
The response is much flatter up to 5kHz. The peaks at 5 and 8 kHz are reduced a bit. Not bad.
So I was thinking how to reduce the highest frequencies. Looking at the response of the HD600 it is very smooth on top. The shape of the ear cups is different but I figured the diver would be similar. Googling for some pictures I noticed the driver is indeed similar but the baffle has smaller centre opening partially covering the driver. So I cut some Scottex disks to make the centre opening smaller.
HD600 driver:
HD600 Baffle:
Scottex baffle kept in place with tiny bits of scotch for the moment:
And the result:
Wang Pleather and foam plus acoustic fabric: green. Added paper baffle and removed acoustic fabric: red.
Bingo!
The dip at 10kHz is not there in reality. I checked with a sine sweep and I hear no dip at all. It’s just a resonance in the HEARS “ear canal”. The peak at 13 and dip 14K dip also don’t seem to be there but it’s at the limit of my middle aged hearing so I’m not sure.
Here’s both the L and R channel:
Disregarding the dip at 10k I’m roughly within ±2.5 dB up to 13k.
I’m done… It sounds fabulous!
The disks seem to enhance the staging also.
The Wang pads were installed without the clip ring since they are in my original pads. They stay in place without the rings but not really well. The rings are almost impossible to remove without damaging the pads but I figured I wouldn’t use the pads anyway so pulled the rings out and put them in the Wang Pads.
With the pads secure in place I thought I'd be a happy camper but…
Big mistake:
The rings completely change the tuning!
Come to think of it they seal the gap between the baffle and the cup. So effectively they seal the baffle edge.
So out go the rings and I need to think of a way to make the pads stick better. Maybe some double sided tape on the side of the cup or some spring metal rings in the pads. Any ideas are welcome.
Happy tuning!
You might want to check the state of the outer foams too, if they look brittle and/or patchy they too can be replaced with 5mm foam discs, something like the thicker ones that come with the wang_yifei pleather pads mentioned countless times here. They work perfectly for me. I've had a friend of a friend with a 3D printer make up some spare pad rings for me, they are a perfect fit, just a creamy white in colour instead of black. If you're prepared to have some shipped over to you from Australia, then I could arrange for you to have some made and I will put you in contact with the printer. I have no idea of price, but they certainly won't be expensive, from vague memory maybe $25 shipped within Australia. It's great to have spare rings at last! 
