HD600 vs HD650

[isostasy]

It did have the metal grille and a carbon-fibre look paint job and the black silk front-damping.
Also the driver material seems different (from milk-white to clear plastic) which will have some influence as well.
Later on Sennheiser replaced the black silk with the white/silver metal mesh.

I did not replace the rear foam b.t.w. which would have probably made the bass response a bit lower and closer to the HD600.
The foam looses some of its properties so the lower frequency response and around 2kHz will be slightly different from 30 years ago.
Still the descriptions from those (HD580 vs HD600) days seem to match what I found.
Probably the nice box the HD600 also came in probably also came into existence with this Jubilee version (1995).

It looks like the HD600 was a bit 'leaner' sounding than HD580 (tighter bass) and due to the many comments about the 'lean' nature of the HD600 Sennheiser launched the HD650 which had a bit more body/warmth/bass extension than HD600. It was 'warmer' than the HD580.

You're correct the rear foam brings up some middle frequencies too. See here from my post on another thread comparing HD545 (same baffle + driver construction):

Not only is the bass lowered by there is an increase of a few dB centered around 3kHz.

So I imagine, looking at your measurement, with foam the HD580 would be more like the HD600 below 1kHz and probably a bit too "forward" for most people around 3kHz.

 

[Svperstar]

I wonder if these grilles make any difference in measurements? I got some for my 580 a year ago or so, they claim with how dense the 580s grilles are it really helps:

Custom Sennheiser Replacement Grilles

Fits HD 580, HD 600, HD 650, HD 660s, HD 58x, and HD 6xx. For improved soundstage, punch/slam, mid-range evenness, and reduced treble congestion. Recommended especially for HD 580 due to the very restrictive stock grille design. Quantity 1 = 1 pair POLICY This item is a custom order, and will...

store.malvix.com

 

[solderdude]

The differences between no grille (basically what the custom grille is) and pretty 'dense' plastic grille is measurable.
1dB, narrow band differences are bordering on audibility.
That said, a few mm closer or moved around on the head will lead to bigger differences.
The HD6** grille seems to be the best 'option'.
It was not very easy to swap the grilles without moving the headphone as one doe have to apply some pressure and force to remove the grille while in position.
Note the unusual 1dB/div scale.
Differences between those grilles are narrow band and < 0.5dB. When you play around with similar EQ and switch that on and off one might have a hard time AB-ing that difference successfully, that's how small the actual differences are.

 

[Svperstar]

The differences between no grille (basically what the custom grille is) and pretty 'dense' plastic grille is measurable.
1dB, narrow band differences are bordering on audibility.
That said, a few mm closer or moved around on the head will lead to bigger differences.
The HD6** grille seems to be the best 'option'.
It was not very easy to swap the grilles without moving the headphone as one doe have to apply some pressure and force to remove the grille while in position.
Note the unusual 1dB/div scale.
Differences between those grilles are narrow band and < 0.5dB. When you play around with similar EQ and switch that on and off one might have a hard time AB-ing that difference successfully, that's how small the actual differences are.

Personally I didn't hear much difference between grilles and no grilles

 

[solderdude]

I did not either.

 

[RoA]

Surprised the 58X 'Jubilee' hasn't got a mention yet ...