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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want a sealed, over-ear studio monitor you can wear for long sessions in a noisy room, choose Superlux HD661; if you need a lightweight, easy-to-drive in-ear with a planar driver and a detachable cable, choose erjigo KZ PR3. That's the short version. The longer version is about what each one is actually built to do — and they're built for genuinely different jobs.
• Superlux HD661's biggest strength: a closed-back, over-ear design with a 40mm neodymium dynamic driver, 68Ω impedance and a wide 10Hz–20kHz range — a classic monitor formula for studio, broadcast and live use.
• Superlux HD661's biggest trade-off: it's the heavier, bulkier option at 6.72 ounces, and it leans on passive sealing plus active noise cancellation rather than being a pocketable everyday carry.
• erjigo KZ PR3's biggest strength: a 13.2mm planar magnetic driver with a nano-level silver-plated diaphragm and low 32Ω impedance, so ordinary playback devices can drive it — plus memory foam tips and a detachable silver-plated cable.
• erjigo KZ PR3's biggest trade-off: it's an in-ear, so isolation depends on tip fit, and the sound signature leans bright and bass-forward rather than flat-neutral.
• Pick the HD661 if you want over-ear monitoring with cables in two lengths and a carrying pouch.
• Pick the KZ PR3 if you want a comfortable, low-impedance in-ear you can run straight off a phone or laptop.
The HD661 is, first and foremost, a sealed monitor. Superlux describes it as an enclosed headphone built for live monitoring, studio work and broadcast, and the spec sheet backs that framing up: a 40mm dynamic driver with a neodymium magnet, 102dB sensitivity at 1mW/1kHz, a 68Ω impedance rating, and a frequency band that stretches from 10Hz to 20,000Hz. That's a deliberately wide window. A 10Hz low end is more about headroom and rumble than about boom, and a 20kHz ceiling covers the full audible top end — the kind of range an engineer wants when checking whether a mix translates.
The design choices tell the same story. It's a closed-back, over-ear headphone with neoprene enclosure material, and Superlux explicitly says the airtight design lets you use it comfortably in areas with high external noise. There's also active noise cancellation and a volume control on the headphone itself. For someone tracking vocals in a room with a humming HVAC, or monitoring a broadcast feed in an open office, that combination of a sealed cup and ANC is the practical point of the product.
The accessories are aimed at working setups, not casual listening. You get two cables — a 3.3 ft (1 m) one and a 9.8 ft (3 m) one — plus a gold-plated 3.5mm-to-6.3mm adapter, a cable clip and a carrying pouch. The short cable suits a phone or a laptop at a desk; the long one reaches across a studio desk to an interface or a console. That two-cable setup is a genuinely useful detail if you move between a workstation and a live position.
Who should buy it? Anyone who wants an over-ear, closed-back monitor for recording, broadcast, or mixing in a room that isn't quiet. Who should skip it? If you want something that disappears into a pocket, or if you prefer in-ear fit and a cable you can swap out, this isn't that product. At 6.72 ounces it's a sit-down headphone, not a commuter one, and the 68Ω impedance means it wants a bit more drive than a bare phone jack typically offers.
The KZ PR3 is the opposite philosophy in a much smaller package. Its headline feature is a 13.2mm self-developed planar magnetic driver — a very different technology from the dynamic driver in the HD661. Planar drivers use a thin diaphragm moved by a magnetic field across its whole surface rather than a voice coil pushing a cone, and erjigo leans into that in the marketing copy: detail and dynamics across bass, mids and treble, a deep and clear low end without blurring, and vocals and instruments that stay clearly present.
The second spec that matters is impedance. The KZ PR3 is rated at 32Ω, and erjigo makes a point of saying the nano-level silver-plated diaphragm lowers impedance so ordinary playback devices can drive it. That's the practical difference between these two products in one number: 68Ω versus 32Ω. The KZ PR3 is the one you can plug into a phone, a laptop or a cheap dongle and expect to get usable volume without hunting for an amp.
The physical design is built around comfort and isolation. It's an in-ear with a metal-and-plastic enclosure, ergonomically shaped and described as lightweight enough to wear for long stretches without fatigue. It ships with memory foam eartips, which is the isolation mechanism here — foam expands to fill the ear canal, blocking outside noise so you can focus on the music. Note that this is passive isolation, not active noise cancellation like the HD661 has, so how much noise it kills depends entirely on how well the tips seal in your ears.
Who should buy it? Anyone who wants an in-ear for long listening sessions, wants to run it straight off everyday gear, and values a replaceable cable. Who should skip it? If you need over-ear monitoring with active noise cancellation, or if you specifically need a mic for calls, look elsewhere — and if you know you dislike bright, bass-forward tunings, the described sound signature may not suit you.
Side-by-Side: Which Should You Choose?
• Best for studio, broadcast and live monitoring → Superlux HD661. The closed-back over-ear design, 40mm dynamic driver and dual cable lengths are built for that job.
• Best for phone-and-laptop listening → erjigo KZ PR3. At 32Ω it's the easier of the two to drive from ordinary devices.
• Best for blocking outside noise actively → Superlux HD661. It has active noise cancellation on top of its sealed, airtight cup design.
• Best for passive isolation on the move → erjigo KZ PR3. The memory foam tips seal the ear canal and cut outside noise without electronics.
• Best for long-wear comfort in a small form factor → erjigo KZ PR3. It's an in-ear built to be worn for long periods without fatigue.
• Best for cable flexibility and repairability → erjigo KZ PR3. The detachable silver-plated cable can be swapped; the HD661's cables are fixed, but you do get two lengths and a clip.
• Best for a complete desktop kit out of the box → Superlux HD661. Two cables, a 3.5mm-to-6.3mm adapter, a cable clip and a pouch are all included.
• Best for call use → neither, strictly speaking. The KZ PR3 here is the no-mic version, and the HD661 is a monitor headphone.
In my opinion, these two aren't really rivals — they're answers to different questions, and the right one depends on where you'll use it. If your work happens at a desk, in a booth, or in a noisy room, I'd buy the Superlux HD661: the sealed over-ear design, the dual cables and the adapter make it a genuine monitoring tool rather than a listening accessory. If you want something light, comfortable and easy to drive from whatever you already own, I'd buy the erjigo KZ PR3 instead — the planar driver and 32Ω impedance are the reasons. The deciding factor is your setup, not the spec sheet.
FAQ
The erjigo KZ PR3. It's rated at 32Ω, and erjigo states the silver-plated diaphragm lowers impedance so ordinary playback devices can drive it. The Superlux HD661 is rated at 68Ω, so it benefits from more output than a basic phone jack provides.
The version described here is the "without mic" model, so no. It offers media control on the cable but no inline microphone for calls. If you need a mic, you'd want a different variant. The Superlux HD661 doesn't include a mic either.
They isolate differently. The Superlux HD661 combines a sealed, airtight over-ear cup with active noise cancellation, which is the more consistent option in high external noise. The erjigo KZ PR3 relies on memory foam eartips for passive isolation, so results depend on how well they seal in your ears.
The KZ PR3's cable is detachable and silver-plated, so it can be replaced if it fails. The HD661's cables aren't detachable, but you get two — a 3.3 ft and a 9.8 ft — plus a gold-plated 3.5mm-to-6.3mm adapter, a cable clip and a carrying pouch.
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