Reviewing Process

Build and Fit

Sound Quality

Overall

Much thanks to Bob at Rock Jaw for the review sample!Comfort, overall sound quality, isolationBuild quality, build design, sub-bass, congestionCircumaural full-sized headphonesMild v-shape with rolled off sub-bass. Strives for neutrality.Musicbee (Wasapi) -> Oppo HA-1~$170 USRock Jaw recommends 100 hours of burn-in for their products before they are fully settled in. I’ve ensured that at least 100 hours of listening time or off the head music playing have occurred before commenting on the sound quality of these. The Acero have been used solely at home and from my desktop set-up. My views come solely from listening to music and the views expressed are that of a hobbyist who simply enjoys music.The Acero are a mixed bag here, from the construction worker-esque design with potentially shoddy construction to great comfort and fit on my head. Perhaps my worries about the build quality are unwarranted, I’m not sure, only time will tell.As I said in the TLR, the Acero have some questionable build concerns which start with the headband. The headband is made from thin stainless steel and is connected to the adjusting band with visible screws. I find the visible screws to be somewhat of a good thing here, as it seems that these could easily be taken apart and modded with a more luxurious headband for those who care to. If I had the know how I certainly would though. The headband feels a bit flimsy and clanks when moved around. The headband also feels sharp, I’d certainly be afraid of stepping on these. Meanwhile the adjustment locks feel a tad loose and I worry that over time it will become loose, causing potential fit problems.The cups of the headphones are made of lightweight wood, held onto the headband by two screws on each side. Neither earcup features a right or left indicator, instead this is left to tiny raised lettering on the 2.5mm single ended cables. This makes it hard to discern even in good lighting conditions. The earcups themselves look rather nice though, but the pads feel rather cheap. The pads are stiff from the start and the orange stitching doesn’t line up when the two sides meet. The pads also don’t seem easily replaceable. Lastly, the cable feels a bit thin, I’m using these primarily for home use so durability isn’t too much of a concern, but I feel a computer chair running these over might put some serious damage on them.The build feels a bit flimsy and looks a bit cheap, like someone cobbled these together with parts from a hardware store. They aren’t awful, but with conversion rates as they are these should have a much more refined feel for $170.The fit of the Acero was rather poor at first, mainly due to stiff pads. Fortunately the pads become softer rather quick, allowing for a good seal to form around my ears. The cups rotate 90 degrees facing down and a few degrees left and right to allow for enough adjustment for most people. The top of the headband doesn’t look it, but is rather plush. The fit reminds me a bit of the Samson SR850, if the Samson had a bit more plush pads. The Acero is rather light on the head and combined with the comfort these would be great for long listening sessions. The clamp on the Acero is moderate, I feel pressure, but not enough to cause discomfort. The clamp isn’t so much as to make headbanging safe either. When turning my head back and forth I could cause the headphones to fall off if I were violent enough with it.Comfort is solid here, as is the fit overall. If the Samson SR850 feel fine on your head than the Acero will also.The Acero has an immediately enjoyable mildly energetic sound with rather good clarity and soundstage for a closed headphone. Once they are delved into though the weak sub-bass and tendency to sound congested during complex passages take a lot of the enjoyment away.From memory the Acero’s bass response has me reminiscing of the Ad700. Slightly punchy mid-bass but lacking any weight in the sub-bass to enjoy bass heavy music. I’ve tried a few bass heavy tracks and have been left underwhelmed due to the weak bass extension. The Acero simply don’t have the weight or extension to enjoy bass heavy music at all. During Jay-Z’sit’s as if the Acero are stretching with all of their might to reach the lows, but they’re a few inches short of their goal. The bass has a slight distant rumble, but leaves me unsatisfied and remains the biggest flaw of the sound.The mid-bass has a slight hump in favor of kick drums and bass guitar, bringing some life into dance genres as well as rock music, but ultimately it suffers from not having any serious weight behind it. The mid-bass comes off a bit thin and despite the initial energetic burst it gives out rather quickly. This causes bass guitars to feel a bit thin and underrepresented at times as well as kick drums to, ultimately, feel a bit weak. The mid bass has a bit of a one-note texture as well, coming off a bit flabby at times, lacking real definition that I expect of a headphone in this price range.Now one thing I noticed is that the bass noticeably vibrates the back of the headphone. I’m not very handy, but perhaps this is part of the issue? Maybe they are poorly damped inside of the housing? That’s just speculation from someone who’s never opened headphones though, so take it with a grain of salt.The mids exhibit a slight recession, though very mild and mostly around the vocal range for males, female vocals seem to be balanced with the rest of the midrange and the highs. The mids, overall, sound rather clear and quick, neither full or thin. Guitars in particular sound rather well done when they are alone, each string sounding clear and unencumbered. Female vocals come off a bit thin, though sibilance isn’t enhanced. Sibilance is shown, but never more so than the recording initially had and I can say that I don’t have a problem with it even on the most sibilant heavy tracks I have.The upper-mids and highs are rather clean with good extension and a sense of air about them. There’s a slight recession in the upper mids though. The recession isn’t immediately noticeable to my ears but the note that Sara Bareilles hits infalls a bit flat with the surrounding instruments. Even so, I find myself happy with the overall quality of the upper mids and highs.The Acero have a rather decent presentation for a closed headphone. The headphones have a decently wide soundstage, though definitely lacking in depth. Instrument separation is average at best and congestion can get the best of them. What impresses me about the soundstage, though, is the sense of airiness about them at times, similar in ways to the NVX XPT100. The soundstage won’t impress and open headphone listener, but it’s definitely a slight cut above the other closed headphones I’ve heard.When looking at the Acero as a total package I find myself liking them. They make for a respectable full-sized closed headphone with some qualities that I find rare in a closed headphone at $100. Unfortunately the price of these, after currency conversions, puts them around $170 in the states. I think that the Acero sound rather decent, fit rather well and isolate nicely, but when compared to something like the NVX XPT100 they lose in my books, even at the same price as I find the XPT100 to have a more refined sound. With that said, I think Rock Jaw has a lot of potential to create high value headphones and I look forward to their future offerings.I don’t think that the Acero are bad headphones by any means, but the cost of them puts them in leagues with Sennheisers portable options, the KAM HP1 and V-Moda, and I can’t find a reason to recommend these over those tried and true options.See more pictures here