Thursday, 29 September 2011

Sennheiser HD438 Modifications (work in progress)

The Sennheiser HD 4X8 series are very similar in design. The internals of the HD418, 428, 438 and 448 are roughly 90% similar. The only differences are the drivers, the detachable cable (HD438). Wiring and everything should be the same on all the HD4X8 models.

All you need for the following mods are commonly found household materials. Disclaimer: Don't blame me if you screw something up while modding your 'phones. Also, your mileage may vary with these mods. Everyone has got different tastes but the good thing is that none of these mods are irreversible.

Quality vs Quantity

Bass quantity and bass quality are two different things. An increase in bass quantity will make your headphones sound a little boomy in the bass department. Bass quality depends on the headphones. Some headphones can reproduce bass that extends deep down in the frequency (20-50hz) without any problem. Some struggle to reproduce bass that low.

Examples: Denon D2000 vs Grado SR80, Ultrasone HFI-580 vs Sennheiser HD448

Most of the modifications that I will be sharing involves tweaking the bass on the Sennheiser HD438 by using different materials to mask the holes behind the drivers. This will affect the whole sound signature and the tone of the headphone. However, you cannot change the frequency response curve of the headphones without changing the drivers or adding filters.

You can experiment and come up with suitable configurations or "settings" that suit you best. 

Must-try mods will be marked with a 

HD438 internals

This is more or less what the HD438 will look like when you remove the ear pads. The yellow circles indicate where the screws are. You have to remove the screws to access the back of the driver chamber. 

The tricky part is that the screws are under the grey foam so you have to locate it with your finger, fit a screwdriver on that spot and start unscrewing. The grey foam will come off along with the screw. You will need a small philips screwdriver for this.

Removing the ear pads

Pinch at the yellow circle and pull it across the face of the driver in the direction of the red arrow. It takes quite a bit of force. Be firm. Don't go Kong on your headphones, you don't wanna have to end up paying 15 bucks for replacement pads.

1. Tape mod

If you feel the thin fabric on your ear pads vibrating against your ear and you want to remove that sensation, add some double sided tape as shown on the first image. Be careful not to cover too much of the grills.

2. Inverse ear pads mod 

As illustrated in the following picture.

Just reverse the ear pad and stick it together to the cup with double sided tape. This makes the HD438 supra-aural. I prefer using this mod when the weather is really warm. You can experiment with other ear pads from other headphones. Different ear pad shape and material results in a pretty large difference in sound.

3. No earpads 

Without the earpads and with the cups not touching the ear as illustrated above, you get the clearest sound. If you like the HD4X8s this way, I suggest getting some cheap ear pads that resemble quarter modded Grado comfies and stick them onto the cups. This setting is perfect for piano (imo) but doesn't really work well with club music and rock songs.

Edit: second thoughts --> I don't like them like this.

4. Dampen the inner cup surfaces

There isn't much space between the inner surface of the cups and the driver when you put everything back together. If you put too much blutack or plasticine on the surface, you might not be able to fit the driver back in properly.

If you like opening up your Senns to mess around with the internals and do some further tweaking, the bluetac might make it really difficult to pry the cup from the driver. I used a coin for this.

The blutack dampens the resonances in the cups to make the sound less muddy.

5. Dubstep mod 
Step 1: Remove the tape covering the 3 holes.
Step 2: Apply a thin layer of blutack on the inner surface of the cup to dampen resonances.
Step 3: Put everything back together. 

The back of the driver enclosure. The black tape is covering 3 holes. The black tape used here is semi-permeable and allows air through it. Uncover all three holes for maximum bass quantity.

This is the surface of the cup. 

Cover this area with a layer of blue tack. Make sure it is not too thick but don't spread it out too thin either. 

What I did was remove the small circuit board first so that I could apply some blue tack underneath it. This makes the thin wires less prone to breakage.

6. Bring out the highs 

with an equaliser.

Tune up the equaliser to +5db at 10kHz and the change should be gradual starting from 2kHz, so step the equaliser down by 1db as you go along. You should end up with a gradual slope as indicated on the right hand side of the image. If you want to be a little more adventurous, equalise the mids a little. What I did was +1db at 220Hz, +1 db at 311Hz, +2db at 440Hz and +2 db at 77Hz.
The increase in highs gives the impression of a clearer sound signature, at the cost of sibilance. Vocalists such as M. Shadows of Avenged Sevenfold sound a little sibilant after equalising but it's not too bad. I think this is a must-do for the HD438. Even if you're against equalising, try it out. You don't need a sophisticated equaliser program, the Foobar eq will do.

7. Neutralised HD438 (sorta) 

Things you need: 
1. Gauze or bandage (doesn't need to be new/clean).
2. Some blutack, putty or plasticine. 
3. Philips screwdriver and maybe a small coin to open up the cups.



As you can see from the image aboves, I applied some blutack around the 3 holes and then stuck some gauze on the blutack to act as the filter. Without any material/filter covering the holes, the bass will be overwhelming. I actually used the gauze I "tore off" my SR60. I suppose speaker cloth could work just as well. Extra porous bandages are good substitutes if you don't have any thin gauze.

I'm currently using this with the ear pads on and with the equaliser settings I posted above. After modding and applying the EQ, the same warm sound signature is retained but since the bass is leaner, highs are a little more prominent giving the impression of clarity. I think it sounds a lot cleaner. 

Currently listening to The Killers, Radiohead and other random songs on my Sansa Clip+ and E7. Love this set-up. 

By the way, the ear pads used is a huge determining factor of the overall sound signature. Some pads make these headphones sound very shrill and thin, some give the headphones warmth or a more full bodied sound.

Experiment with the holes. Use different materials. Instead of blue tack, use cloth, etc. Some configurations are really bad but the only way to find the type of sound that suits you best by trial and error.

My Current EQ settings for HD438

It's the one on the right. As you can see, the Equaliser settings are pretty huge. It goes up as far as +5db on some frequencies. I did this to make the headphones more detailed at low volume. The Equaliser I'm using is actually the ElectriQ Fosihfopit (free). It works great on Foobar.