The cups have a large, black, oval grating over their exterior and removable cloth pads on their interior. Removing a pad lets you peek at the sound element through a thin piece of cloth and a plastic ribcage. This is the closest you'll get to the sound element.
The cups tilt forward and back in a 30-degree arc, and can rotate a few degrees perpendicular to the band.
The band itself is predominantly black plastic and extendible. The top of the band has a pad on its underside that's removable, but uses an adhesive to stick on, so we wouldn't recommend prying it off unless you're looking to replace it.
The cord extends from the left ear cup, and is quite long. It ends in a 1/4-inch jack.
The Sennheiser HD 555 headphones come with a single extra in the box: a 3.5mm adapter. This adapter is almost a necessity since, while 1/4-inch ports are common outputs in home theater equipment, it's rare to see them elsewhere; most portable media players and an increasing number of audio systems now come with 3.5mm sockets. The inclusion of this adapter increases the HD 555s' usability significantly.
The HD 555 headphones seem to be fairly durable, but do have some issues. For the most part, everything is made out of some pretty solid plastic. The band isn't collapsible, and is made out of softer plastic so it'll buckle if bent back. This is obviously preferable to simply snapping in two, but this bending could still have an adverse effect on the wires inside. Additionally, bending the band will pop out the panel the padding is attached to, revealing wires.
The tilt and rotation of the cups also feels a bit flimsy. When they're fully tilted/rotated, it feels like just a bit more force could easily snap them off.
The cord is arguably the most durable aspect of these headphones. The cord itself is nice and thick, and feels incredibly strong. Also, the cord guards are exceptionally good. The guard near the headphones provides both good flexibility and protection, and the guard toward the jack is simply one of the best ones we've seen; this cord should last for a good long time.
In general, we like the look of the Sennheiser HD 555 headphones. They aren't particularly eye-catching, but they do look clean and well-designed. The cloth pads certainly denote that these headphones aren't a throw-away pair. The width of the band and the size of the cups makes the set look respectably robust. The grating on the outside and the tiltable cups save them from looking plain. In general, the HD 555s manage to look good without looking garish; they are more about function than form.The HD 555 headphones hail from Sennheiser's lineup of over-ear home theater solutions. They have open backs, which will provide a more natural, airy aural experience. This quality also means people in the same room will also get an earfull, however. The cord is long enough to comfortably tether you to a jack across the room, whether it's 1/4-inch or 3.5mm. Their cloth-covered padding and swiveling ear cups provide a comfortable fit. Our testing system analyzes the frequency response of headphones by sending a frequency sweep to the headphones that goes from the very low to the very high. How well the headphones reproduce these frequencies is shown on the graph below: low frequencies are on the left, high are on the right. The green line is the left channel, the red is the right channel, and the dotted lines are the limits the red and green should fall between. The dotted lines indicate the limits we look for; if anything is to veer too widely above or below these limits, it could indicate an issue that might affect sound quality. The Sennhesier HD 555 has a fairly smooth frequency response, which is what we look for in a pair of headphones; big peaks or troughs in the frequency response would mean certain frequencies are being overly exaggerated or suppressed. The HD 555 has a few peaks and troughs in the mid to high range, though, which is a little less than perfect. But these quirks are nothing major, so the sound they produce should be accurate and clear. Overall, the HD 555 performed well in this test.
Distortion is the bane of the music lover's life; music sounds bad when the sound gets distorted because the headphones aren't up to the task. It doesn't seem to be with the HD 555's, though; we saw low levels of distortion across the board in our tests.
Our system examines the distortion headphones introduce by playing back a series of very tightly controlled sounds at the typical listening level of around 78 dBSPL and examining the results for any differences from the original waveform. The graph below shows what's called the Total Harmonic Distortion (THD), which is the amount of distortion (as a percentage) of a frequency and the higher frequency harmonics that give a sound its texture. The graph starts with low, bassy frequencies at the left and goes up to higher-pitched frequencies at the right.
Across this wide range, the HD 555 has low distortion, only peaking lightly at the very low end, where we typically see some distortion with even the best headphones. What this means is your music will be cleanly reproduced at all frequencies; there are no big peaks in this graph that would indicate it has problems with particular frequencies. And the distortion at the low end isn't a big problem; if you're a fan of drum and bass, the HD 555 will reproduce the big bass sound you love cleanly.
Because most people have two ears, headphones have two channels; the left and right channel. In this test, we see if there are any major differences between the sound that comes over the two channels; if there is, the music would sound unbalanced. Again, the HD 555s do well here: we only saw very, very minor differences between the two sides. The maximum difference between the two is just 1.27 percent, which is pretty much inaudible.
Our test system also produces the graph below, which shows the tracking across the frequency range of 80 to 10,000Hz. If the line is at 0 percent, that indicates the sound at that frequency from the two channels is identical. If it goes above that line, the left channel is stronger, and if it goes below, the right channel is stronger.
The HD 555 did well in this test as well; although the tracking goes off slightly at higher frequencies, the great majority of the graph is close to the 0 percent line, which means the HD 555s produces well balanced sound for all but the most finicky of audiophiles if properly placed on the head.
The distortion test we do above is run at a pretty normal listening level of 78 dBSPL, but some people like it loud, so we also test how high we can crank up the volume. We test this by how high we can take the volume until the distortion in the sound reaches an audible (and annoying) level of 3 percent.
The HD 555s manages to reach an impressively loud 115.4 dBSPL before our testing system cries foul, which should be loud enough for even the most hardcore loud music fans; that's about the equivalent of a jet airplane taking off, and is getting close to the level that will cause permanent hearing damage. We don't recommend you do this test yourself (we use a testing system with replaceable ears; yours are not), but it's good to know you can crank up the volume if you want to without the sound becoming distorted.
The flip side of the volume you listen to music at is isolation; how well do the headphones block outside sound? The HD 555s do a poor job of this; their open design and lack of any active noise canceling circuitry means it only blocks an average of 3.2 dB of outside sound. In other words, they don't block much. Contrast that with the typical in-ear ear canal headphones (such as the Etymotic ER6i and the Shure SE210), which block an average of 30 dB of sound.
The graph below shows the same frequency range of 80 to 10,000Hz, with the line indicating how much sound is blocked at that frequency; higher is better.
As you can see, for most frequencies, it doesn't block much at all; pretty much nothing at the low and mid frequencies (such as airplane noise), but a little at the high frequencies (such as music and speech). If you're looking for a pair of headphones to help you hide from the world, the HD 555s are not the right ones for you; look at a pair of in-ear headphones like the ER 6i or a pair with active noise canceling, such as the Bose QuietComfort 2 or 3.
Give that the HD 555s don't block much outside sound, it's perhaps not surprising that they let a lot of their own sound leak out. We found in our tests that a significant amount of sound leaked out from the headphones; you could easily hear and identify what was being played over them from a few feet away even at moderate volume. The HD 555 are not a good pick if you would rather the person on the bus next to you not know about your unfortunate fondness for New Kids On The Block.
Here we simply customize the headphones to conform to our heads, then wear them for an hour.
In general, we really think these headphones are comfortable. Although we never forgot we were wearing the headphones because of their moderate weight (9.5 ounces) and the pressure on our ears, we never felt uncomfortable, either. They sit well, and the open design means your ears don't get sweaty. The HD 555 headphones make for a comfortable listening experience.
After about six hours of use, we did notice the weight a bit more, and the cloth had begun to feel slightly itchy. These sensations were very subtle, however, and didn't really detract from our listening experience. The main annoyance - which is very minor - is that our head movement was restricted a bit, since craning our neck too far forward or back would eventually cause them to slide off. So, these headphones aren't going to work with exercise or other vigorous activity.
The HD 555s have a cable that is three meters long. This is about 9.84 feet, which make these headphones a viable jump rope surrogate. The cable ends in a 1/4-inch plug, but fortunately there's a 3.5mm adapter.
Other than the headphones themselves, there is only one other object in the box: a 1/4-inch adapter. A user is only privy to the basics of normal wear: extending the band and pivoting ear cups to better fit his or her head. The Sennheiser HD 555 headphones do not offer many options for customization.
The Sennheiser HD 555s are not portable at all. As over-ear headphones, these things take up a lot of space. They also have about 10 feet of cord, but no case to keep everything organized. Granted, these headphones are made for in-home use, but it would've been nice if Sennheiser had included something to help ferry the HD 555s from place to place.
The HD 555s' cup padding can be removed, but that's the extent you'll be able to disassemble these without a screw driver. Under the padding is a cloth screen over the sound element that can't be taken off easily.
While this feature will allow you to replace the pads easily, it won't let you get at the sound element without ripping its cloth covering. Also, the band padding cannot be removed.
The HD 555 headphones do not require a battery. This ability nets them some easy points. Bose's QuietComfort series should take notice.
The Sennheiser HD 555 headphones run about $179.95. While that's not cheap, it's not a bad deal considering the quality of sound they produce and their overall build quality. But you should just be aware of what you're buying. These headphones are meant for a home theater setup, one where their leakage and lack of noise cancellation won't be much of an issue. The headphones don't come with many extras, but that's mainly because in-box extras are meant to enhance portability. They are quite comfortable (if a bit itchy at times), and the cord is a very good length. Overall, the HD 555 headphones are definitely worth consideration.
The Sennheiser HD 555 headphones are clearly meant for a home theater environment. While they fit this role well, they are unfortunately limited to it. These headphones aren't a good choice if you're looking for something you can also commute with. First of all, their cloth padding doesn't do much to isolate you from the outside world. Secondly, they do have open backs. While this helps portray a more open, airy sound, it will also let everyone on the bus know you're rocking out to La Bouche. Further, while you could just ball the extra six or so feet of cord up into your pocket, it's cumbersome to do so.
In their native environment -- a home theater setup -- these headphones should fare a lot better. Sound quality should be good, and distortion should be minimal, even at high volumes. The long cord allows you to easily hook up to your stereo system across the room without having to rely on a sometimes-spotty wireless connection. Their cloth pads also make for a comfortable wear experience, though over time the cloth can get a bit itchy. The only possible downside is the lack of noise cancellation and the leakage factor. If you're looking to minimize the noise from watching action movies at 3 AM, the HD 555s will help you out, but don't expect to get away with it if you're in the same room as someone snoozing. Likewise, if you're looking for some peace and quiet from your roommate who blasts music, don't expect the HD 555s to block out much of it.
Overall, the Sennheiser 555 headphones aren't a bad set. They aren't built as well as some other on- or over-ear headphones, and are sorely lacking on extras, but at $180 they're cheap enough to be considered.
Meet the tester
Mark Brezinski is a senior writer with seven years of experience reviewing consumer tech and home appliances.
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