Measurement guys, what is your take on this?

Lately I have been working on my closed vintage Senny, HD540MkII drivers in HD250 cups, Brainwavz pads. I think I have nearly arrived at my final tuning and they do sound very good. Measurements look good, BUT ... have a look and let me know what you think.

BTW, sine sweeps do not tell the dip, there is absolutely no veil, highs are very smooth.

 

If there are no resonance issues at the dip frequency in the CSDs (there aren't, but there seems to be a resonance at 8-9kHz) and you can't hear the dip when listening to sine sweeps, then I wouldn't worry too much about it. Still, a 25db dip in the measurements is very weird.
Did you try measurements without a coupler, just holding the microphone into the earcup?

 

Could be special interaction with the coupler that doesn't exist with the ear. Not that uncommon, just not usually -25db and spanning more than half an octave.

 

Yup, noticed the same thing with my measurements.

 

Well, it is a pad and pad mounting thing. This compromise seems unavoidable if you want an otherwise flat FR. The driver exhibits quite noticable a dip in other configurations as well, but this setup kind of further deepens that dip. Anyway, thanks for your input.

 

@stratocaster
Can you hold the mic close to the driver and measure the response there? Does it also exhibit the dip with no coupling at all? Also, can you post the response again on a 5db/div scale? Things always look too good to be true on a 10db/division scale. I'm betting these would have quite a bit of bass rolloff.

EDIT: What mods did you do? I remember the HD540mk2 driver being peaky around 9kHz.

 

It's not the coupler, I tried several different ones, the dip - more or less prominent - is always there. Once I change from (p)leather to velours, it's better, but the whole FR gets kind of fucked up. I can get it flat again, but then I have to give up the closed design and go for a semi-closed, which I do not want.

Bass rolloff is there, actually similar to HD650s, for example.

As for the mods, these are hugely modded. The HD540II are open, these are fully closed. the pads rest on a system of thin layers of different felts, modulating the baffle and trying to achieve the flat FR. Without this 'felt bed' underneath the pad, the FR is everything else but flat.

I think I am done with these. They sound very nice for a closed can, at least to my ears. They are clean and fast. Plus, they isolate very nicely. You can't have everything. When listening, I will simply not look at the graph and the dip ;-)