When comparing Sennheiser IE 800 vs JBuds J4, the Slant community recommends JBuds J4 for most people. In the question“What are the best rugged and durable earbuds & IEMs that last?” JBuds J4 is ranked 4th while Sennheiser IE 800 is ranked 6th. The most important reason people chose JBuds J4 is:
J4 cables are reinforced with kevlar to resist breakage. The flat design helps prevent kinks, as the cable coils rather than twisting or bunching. Also, tough and flexible reinforced exoskeletons protect the cable connections and joints.
Specs
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Pros

Pro Good noise isolation
The IE 800s allow some ambient sound to pass, but not enough to be bothersome.

Pro No bass distortion at any volume
Precisely engineered pressure vents behind a single dynamic driver leave no opportunity for distortion to occur.

Pro Ear tips provide a good seal
The ear tips are a step up from the common silicone ear tips on the market today. The part that comes into contact with your ear is made out of soft, flexible, high quality silicone. The inside canal of the ear tips however is made out of a firmer plastic material, with a metal mesh in the middle.
This combination allows the ear tips to create a very good seal when worn, reducing sound leakage/bleed while also ensuring optimal sound delivery.

Pro Fantastic listening experience
Sennheiser is known for audiophile gear, and these earphones qualify. Their frequency response, dynamic range, and clarity of definition do justice to their price tag.
Pro Good durability with scratch resistance
Instead of using metal or plastic in the construction of the earpieces, Sennheiser has used a special ceramic material on the IE 800 which is scratch resistant. This helps to keep the weight of the in-ears down, yet can still withstand use and abuse pretty well.
The cable on the other hand is very high quality and covered with Kevlar reinforcement for added durability.

Pro Oxygen-free, kevlar-reinforced copper cable
Wrapped and sealed in an oxygen-free environment, these cables are immune to corrosion so long as their tough kevlar shielding remains intact.

Pro Durable Kevlar-reinforced flat cables with strain relief
J4 cables are reinforced with kevlar to resist breakage. The flat design helps prevent kinks, as the cable coils rather than twisting or bunching. Also, tough and flexible reinforced exoskeletons protect the cable connections and joints.

Pro Heavy-duty aluminum housing
JBuds J4 components are protected by rigid aluminum cylinders, capped with aluminum grills.
Pro Detailed sounding highs with punchy bass
Overall sound is quite bassy, with low end that is very punchy and fast, so it does not muddy up the music. The mids are slightly recessed, though the vocals can still be quite clearly heard as the bass does not overpower it. Highs on the other hand sound pretty good as they are clear and detailed without getting harsh.
Pro A good number of accessories are bundled
With the J4, you get an EVA foam carrying case for even more protection and convenience when bringing these on the go. Also, there are two sets of silicone ear tips: 3 pairs of single flange tips as well as 3 pairs of double flange tips. A shirt clip is also included.
Cons
Con Cable noise
Touching the cable or rubbing it against clothing makes a rustling sound that transmits into the earpiece.
Con Y-split connection can pull down the earpieces
The detachable cable after the Y-Split cable adds a bit of weight to the earpieces. This can pull them down and cause them to dislodge at times.
Con Does not come with an in-line microphone/remote
While not really a CON, this omission can make or break your purchase decision for these headphones. Sennheiser offers an add-on cable which features the mic and remote, but is quite expensive.

Con Headphone cable is not completely removable
While the headphone cable can be attached/detached via a 2.5mm connection from the Y-split down, the cable cannot be removed from the earpieces themselves. This can make replacing the fixed cables very difficult and potentially expensive.

Con Heavy wires generate noise
The J4's thick cables carry sound like a stethoscope, including the sound of the cables themselves moving and rubbing against things. This can be particularly bad while walking or running.

Con Significant defect rate
Although the J4s are built to be durable, many users report them breaking down after 1-3 months of light use.

Con No volume control
The J4s come with a mic and control switch, but no built-in volume control.
