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We compare products from their published specs and features; the verdicts below are our independent editorial opinions.
If you want an open-back planar magnetic headphone that pushes flat, neutral reproduction across an unusually wide band, choose DROP + HIFIMAN HE5XX; if you need a monitoring tool that stays balanced and isolated in a loud room, choose PHONON SMB-01.
• DROP + HIFIMAN HE5XX – biggest strength: A dual-sided planar magnetic design with 2-micron Nano Diaphragm membranes and double-sided magnets, tuned brighter and more neutral than the classic HE500, with a 15 Hz–50 kHz range.
• DROP + HIFIMAN HE5XX – biggest trade-off: It's open-back with no noise control, so it leaks sound both ways and won't isolate you from a noisy room.
• PHONON SMB-01 – biggest strength: A 40mm Free Edge dynamic driver tuned for natural lows and spatial accuracy, with sound-isolating pads and switchable closed/semi-open plates (sold separately).
• PHONON SMB-01 – biggest trade-off: It's a closed dynamic design with a 20 Hz–40 kHz range, so it gives up the extreme upper treble and the open, speaker-like presentation the HE5XX is built around.
• Who each pick is for: The HE5XX is for listeners who want an open, flat-leaning planar sound at home; the SMB-01 is for engineers and detail-chasers who need isolation and tuning consistency on the job.
The HE5XX is a deliberate attempt to bring back a classic sound without the penalty that used to come with it. HIFIMAN's older dual-sided planar designs used magnets on both sides of the membrane, which gave them remarkable sensitivity but also made them heavy. Drop and HIFIMAN kept the dual-sided layout, thinned the magnets, and switched to 2-micron Nano Diaphragm membranes — the result is a headphone that's 30 percent lighter than the Legacy HE500 at 354 g, with a newly designed conductor layer that raises efficiency.
Sonically, the pitch here is "flat, but not sterile." The tuning is described as a brighter, more neutral take on the HE500 Series signature, and the numbers back up the ambition: 15 Hz to 50 kHz from a planar magnetic driver. That's a genuinely wide window, and planar drivers are known for even, low-distortion behavior across the band when they're done right. The 18-ohm impedance means it doesn't demand a monster amplifier to get loud, though a decent source still matters for headroom.
PHONON SMB-01: Who It's For
The SMB-01 comes at flatness from a completely different direction. This is a Japanese-made studio monitoring headphone, and the design brief reads like one: faithfully reproduce what's actually in the recording rather than flatter it. PHONON's tuning was handled by a seasoned mastering engineer, and the stated goal is acoustic balance that holds up across genres — which is exactly what you want from a reference tool, because a monitor that only sounds good on one kind of music is a monitor you can't trust.
The driver is a 40mm dynamic unit with a Free Edge structure, where the diaphragm's surround is effectively freed so it loses less energy as it moves. That's the mechanism PHONON credits for its ultra-natural low frequencies and its spatial reproduction, and it's why the frequency range reaches 20 Hz to 40 kHz — full-range for practical purposes, and high-resolution capable at the top. The dynamic driver approach also tends to give you a more conventional, punchy low end than a planar, which some engineers prefer for judging kick drums and bass guitar.
The genuinely interesting feature is the interchangeable ear plates. The SMB-01 ships as a closed headphone, but you can swap plates (sold separately) to turn it into a semi-open design — one unit covering two very different working situations. The ear pads are built for comfort and sound isolation, the cable is a detachable 4-core design with independent ground connection, and there's remote control support. At 324 g with leather, metal and plastic in the enclosure, it's in the same weight class as the HE5XX.
Buy it if you're mixing, mastering, tracking, or just want a closed-back reference that won't bleed into a microphone and won't let the room bleed into your ears. Skip it if you already know you want an open-back planar sound, if you want the option of switching to a semi-open design without buying extra parts, or if you don't need isolation at all.
• Best for a flat, neutral, open-back presentation → DROP + HIFIMAN HE5XX. The brighter, more neutral tuning and the wide 15 Hz–50 kHz planar range are aimed squarely at that.
• Best for isolation and studio work → PHONON SMB-01. Sound-isolating pads and a closed design mean it works where the HE5XX can't.
• Best for low-end naturalness and spatial accuracy → PHONON SMB-01. The Free Edge 40mm dynamic driver is explicitly tuned for natural lows and spatial reproduction.
• Best for driving from modest gear → DROP + HIFIMAN HE5XX. At 18 ohms it's easy to get loud; the SMB-01's impedance isn't specified, so there's less certainty there.
• Best for flexibility over time → PHONON SMB-01. The optional switchable ear plates let one headphone cover closed and semi-open duty.
• Best for cable upgrades and balanced use → DROP + HIFIMAN HE5XX. It's wired to accept a balanced cable, and the SMB-01's detachable 4-core cable uses an independent ground connection rather than a balanced termination.
• Best for a lighter, more comfortable long session → PHONON SMB-01, narrowly. 324 g versus 354 g, though both are over-ear and the HE5XX's ultralight redesign closed most of the old gap.
• Best for a clean, simple wired setup → either. Both use a 3.5 mm jack and both are wired; neither is a wireless headphone in practice.
If "flat frequency response" is the actual goal — a neutral, uncolored baseline you can trust and EQ from — I'd buy the DROP + HIFIMAN HE5XX. In my opinion, the planar magnetic driver, the 2-micron diaphragm, the 15 Hz–50 kHz range and the explicitly neutral retuning of the HE500 lineage add up to the more convincing flat-response story for home listening, and the 18-ohm load makes it easy to live with. I'd only steer you to the PHONON SMB-01 if isolation is non-negotiable or you're working in a studio, where its mastering-engineer tuning, natural lows and switchable plates make it the more practical tool. Before deciding, check the current price on Amazon — that gap is the one thing that could flip this call.
does frequency response matter in headphones
Yes, and it's the single spec most worth reading. It tells you the range a headphone can reproduce — the HE5XX covers 15 Hz–50 kHz, the SMB-01 covers 20 Hz–40 kHz. A wider range doesn't guarantee better sound, but it does mean the driver isn't rolling off early at either end.
The HE5XX uses a planar magnetic driver, where a thin diaphragm is driven by magnets on both sides. The SMB-01 uses a conventional 40mm dynamic driver with a Free Edge surround. Planars are typically praised for even, low-distortion behavior; dynamics are typically praised for punch and efficiency. Both can be tuned flat — it's the tuning, not the type, that decides it.
For tracking with a microphone in the room, yes — the HE5XX is open-back with no noise control, so it leaks. The PHONON SMB-01 is closed with sound-isolating pads, which is why it's positioned as a monitoring headphone. For mixing alone in a quiet room, open-back is usually the more natural choice.
The DROP + HIFIMAN HE5XX, at 18 ohms, is explicitly designed to be efficient and easy to drive. PHONON doesn't publish an impedance figure for the SMB-01, so there's no way to compare them on that basis — plan on a decent source either way.
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