The name Bose is synonymous to the noise-cancelling (from here on will be referred to as NC) headphone market, producing what many, even Tyll of Inner Fidelity, consider one of the best NC headphones. But there’s a caveat to that. They’re only known for their NC technology. In regards to sound, the Bose headphones aren’t exactly wonderful. They have a pleasing sound, at least in my opinion, but it’s not exactly “Audiophile Approved™,” whatever that actually means. Way back in 2007, Sennheiser released their challenger to Bose’s then monopoly, the PXC450. Since then, it has received shockingly little attention. A while ago I mentioned in another Sennheiser product review, I was quite interested in hearing what Sennheiser was capable of on the mid-tier of their products. I had my hearts set on the HD600, but, in a fit of sheer impulsiveness, I bought a pair of PXC450 because I remember really, really wanting a pair back when my journey started in 2007.

(Again, for clarification, I bought this with my own money, so there may be a tinge of purchase justification, but not really)

The PXC450 comes with a very nice ballistic case, 6.3mm adapter, and airplane adapter. I bought these used and they didn’t come with the original packaging, but I’m sure it looks nice for something that will only be a dust-gatherer after the headphones are taken out of it.


Sennheiser construction is known to be rather suspect in their full-sized headphone line, with a number of users reporting cracked, or even snapped headbands on their headphones ranging from the HD280s, all the way up to the HD650. The top of the PXC450’s headband is plastic, but of the extremely resilient nature. Bending it doesn’t seem to cause any type of harm to the plastic, as it’s quite thick. However, to create a classy vibe, Sennheiser covered the headband with pleather with an embossed “SENNHEISER” across it. Strangely enough, instead of using foam as headband padding, Sennheiser filled the headband pad with air. It’s an idea I haven’t seen implemented in any other recently-released headphone (but my vintage Kosses have air-filled pads that, even after four decades, has not disintegrated, so probably a smart choice on Sennheiser’s part).

The earpads are extremely comfortable; unlike the similar-looking HD380 with paper-thin pleather on its pads, the pleather used for the PXC450’s pads is of much better quality, with softness almost comparable to the lambskin on Sennheiser’s more recently-released Momentum. The pads’ suppleness is actually a bit more comfortable than the leather pads of the Sony SA5000. If I haven’t made it blatantly obvious, I’m quite infatuated with the PXC450’s pads, which Sennheiser better have gotten right if Senn’s intent was to create a luxury headphone in the PXC450. I’ve been able to wear them for at least six hours at a time. Thankfully, the rest of the headphone feels the part as well. The replaceable cable is rather respectable. It’s a little thicker than AKG’s mini-XLR cables used with the K2XX and K/Q70X series. However, it’s rather short at around 4.5 feet, so these are definitely meant to be used with a portable player of some sort, at least designed as such.

Selfish on Sennheiser for making the cable impossible to replace with an aftermarket cable.

The drivers themselves are not angled, but there is a thing of some sort (I really can’t explain it so I’ll post a picture of it) that…quite honestly, I really don’t know what it does. I’m utterly baffled by this, but if I had to take a guess, I’d assume it helps with the sound stage because the, uhh…protrusion is angled in such a way that sound could conceivably be directed…you know what, no. I really don’t know what Sennheiser tried to achieve here so I’ll wait for someone to correct me and add that explanation here. One more odd thing about the construction: the driver is not centered. Another picture will go along because a picture will describe it better than words can.

Now, to the NC system; it’s actually, in theory, a more user-friendly system than Bose’s. One of the main issues people have with Bose’s QC series is that they need batteries to function. Strange concept right—headphones that actually require batteries to output sound! Now, I’m sure there’s a reason for that regarding the topology of Bose’s NC circuit, but Sennheiser has done something fantastic with the PXC450: they have a passive mode. What does that mean? Well, if one does not particularly want to deal with NC and its inherent problems, that’s perfectly fine! The PXC450 does not require batteries to function if one does not want all that gizmo hooey for listening to music at home, which people may want to do when they hear how respectable the PXC450 sounds. This is not to say that Sennheiser’s NC system stinks. It doesn’t. On the contrary, it works pretty well. It doesn’t work as well as Bose’s system, or from memory, Sony’s digital NC, but for a headphone released in 2007, it’s actually kind of impressive. I’m not an NC guru, but…it works. I haven’t been on a plane in the time I’ve had the PXC450, but road noise is non-existent with the PXC450’s NC on. But the NC isn’t even the coolest part of the PXC450’s technology. On the side, there is a prominent circular button on the side with the Sennheiser logo. That, right there, is a magical button that says “Talk.” What does that mean? Well, if NC is on, the music is cut off and the microphones employed to pick up droning noise are used to pick up voices. The vocal range (not even going to try to attempt to BS the hertz, but it works) is amplified by the internal circuit, and the user will be fully able to carry out a conversation without ever taking the headphones off. It’s not perfect though; only the upper range is accentuated, so voices sound off, but in a pinch, it works quite nicely.

Now for the sound. I’ll split this into two parts because of the PXC450’s unique ability to work without its NC on. The system I’m using for this review is an iFi iCan or iBasso D12 paired with an iFi iDAC. The iCan is on the bright side and more analytical while the D12 is a bit warmer and fuzzier.

With NC off:

The sound in both modes is generally pretty light—some would say neutral, but I struggle with that description. If anything it leans more towards brightness, but not harshness. Starting from the low end, the bass really isn’t the most fantastic. It’s a bit light, a little more than my AKG K271’s, and reaches to about 40hz before completely dropping out, and the path there is slightly muddy unless it’s amped (even a CMoy would be enough). The details are a bit blurred unamped, sadly. However, in my opinion, Sennheiser’s implementation is better than attempting to do too much and end up with a muddy mess. Through my iBasso D12, the bass is better defined with much better timbre, but like I said earlier, even a CMoy would help to improve the sound.

The midrange is iffy. Since the bass is rather laidback, the midrange is able to come forward to shine. Vocals have nice timbre and are rather airy (for a closed headphone), but male voices can sound thin at times because of the lack of midrange body. Instruments have some timbre issues however. I could never really listen to an acoustic guitar on these because PXC450 always managed to make them sound a bit on the bright side. Same with brass instruments; the PXC450 emphasized the brassiness in the sounds of the horns, which is great if you want brass to be awkwardly accentuated, but for most of my listening, the PXC450 needed a slice of felt in front of the drivers to tame the highs. Female vocals, however, sound much nicer than males because of a large peak in the upper mids. Do take note, though, that the iCan is on the bright side. Through the warmest opamps put in my D12, the upper mids are tamed and I warmed up to the midrange. It’s not on the same level of my modded Fostex T50RP, but better than something like the Bose QC15. Though, I did notice that there’s a severe dip in the midrange with strings that not even a warm, midrange-heavy amp could solve. The end result is a glassy tone that can get uncomfortable.

Treble isn’t spectacular. It doesn’t extend very far and has a fair amount of grain (Think Audio Technica AD700 levels of grain and tone them down about 20%). But thankfully, it’s rarely sibilant. Other than that, there’s not much to speak of. It’s not impressive, but not grating, so that in itself is at least somewhat impressive.

Soundstage, even though the drivers are slightly angled, isn’t that wide or deep. Imaging is tight, but slightly blurred. Overall, the basic sound signature of the PXC450 sans-NC is bright, bass-light, and midrange-heavy, while at the same time having a rather brittle midrange. It’s definitely strange, but at the same time, quite interesting. It sounds similar to a closed version of the Sony SA5000, but with less detail and a blurrier sound.

With NC On:

NC on changes the sound rather significantly, like most NC systems do, but Sennheiser’s implementation comes with a twist.

Usually, NC circuits add bass. Therefore, it completely mystifies me as to why Sennheiser’s NC circuit decreases bass. Like, seriously; the PXC450 was a bit south of neutral in bass before NC, but with NC, it’s basically dropped off the earth. There’s very little definition, to the point where even I’m not satisfied, and I’m more than fine with the rather anemic bass levels of the SA5000.

With the lowered amounts of bass, the midrange becomes more upfront, but for some reason, it sounds a little smokier. They sound much more intimate, less glassy. It’s most likely due to the decreased treble that accompanies the NC EQ. So basically imagine the mids from the top section and remove most of the negative parts and add a little haziness. It ends up being pretty soothing.

Treble with the NC is a bit subdued; like the treble, it’s less glassy, so the end result, while still grainy (even more so actually), is less grating. That’s basically it.

The rest is mostly the same. With NC, the sound is a bit paradoxical. It sounds even more bass light, but at the same time, it sounds warmer, more natural. Or maybe not. I’ve never been as mystified by a headphone’s sound until now.

So…that all looks like a horrible lambasting against the PXC450. And it should, because its sound really isn’t good…unless you EQ it. Thankfully, the PXC450 is quite receptive to EQ, and even better with something like a ZO. With EQ, and to my ears, it surpasses other popular NC headphones like the Bose QC15, Ultimate Ears UE6000, and Klipsch M40. So all in all, it’s a rather mediocre first try at a flagship NC headphone without any adjustments, but with some very simple adjustments, it makes for a very capable headphone…at half MSRP. Would I recommend it? If you can get it for under $200, then it’s a great deal for a headphone with a great NC system, especially due to its Talk Through feature. But keep in mind that half of the price you’re paying is for the NC. If you can EQ, then it’s an even better deal. As for me, I sold it to someone whom I hope is very happy with it. With all its quirks, I’ll miss it. With its faults, it should have been easy for me to get rid of it, but there was something about its oddness that made me like it; it was like Sennheiser tried so hard to rush out a flagship NC headphone that they hastily threw an HD555 driver in a closed frame and hoped it sounded good. In many ways, it was so close to being something other than bad that I feel that if Sennheiser actually spent more time tuning the driver, this wouldn’t be one of the only comprehensive reviews of the PXC450. To Sennheiser, this is the second product I’ve had that was close to sounding good—even great, but fell just short. Why? I completely understand that you don’t want to cannibalize the sales of the HD600-HD800, but with something as miserable as the PXC450, would a little more effort be the worst thing in the world? There is definitely a market for NC headphones that also sound good. The NC market definitely wouldn’t intrude in the open headphone’s business, so what gives?

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