Gramo One

MSRP $249 (USD, EUR)

Proprietary 16 mm Celsus Sound transducer • Reference-grade open-back in-ear headphone
(Gramo One has been discontinued. Several new earphones are under development.)

The Celsus Gramo One is a reference-grade open-back* in-ear headphone that sits comfortably on the outer ear.

One’s first – and enduring – impression is of an overwhelming, three-dimensional audio experience that can fairly be described as a virtual live event. The proprietary 16 mm Celsus Sound transducer produces a sense of space, depth, detail and dynamic as impressive as that of an audiophile’s dream sound system. A mesmerizing midrange and dynamic bass are among the more impressive of the Celsus Gramo One’s signature qualities. And no IEM we’ve ever heard can match the Gramo One’s production of seductive vocal textures.

The term reference-grade typically connects with a few widely celebrated over-ear and on-ear headphones. Their drawback – and it’s a serious one – is weight and size as principal contributors to listener fatigue. In recent years, a few in-ear headphones (IEM) have achieved reference-class status. Again, as a drawback, IEM devices suffer from an ultimately fatiguing “music-in-the-middle-of-one’s-head” phenomenon along with the excessive ear pressure that inevitably accompanies prolonged listening. With the portability of an IEM, the Celsus Gramo One’s exceptional sound quality equals or betters the most highly regarded over-ear headphones.

The following features of the Gramo One contribute to its superior sound: As with high-end speakers, the driver is mounted with damping materials to effectively absorb vibrations. With the same purpose in mind, damping materials also line the unit's interior. Sophisticated acoustic design and the Gramo One’s horn-type design together create especially vivid vocal reproduction and a wide sound stage.

*Open-back earbud is specifically designed for use in quiet environment



  • A proprietary 16 mm Celsus Sound transducer produces a sense of space, depth, detail and dynamic as impressive as that of an audiophile’s dream sound system
  • A mesmerizing midrange and dynamic bass
  • Seductive vocal textures.

Included with Gramo One are:

  • 3 pairs of ear tips
  • Genuine Leather pouch


  • Transducer principle: Dynamic Open
  • Size of driver: 16 mm
  • Impedance: 32 Ohms
  • Frequency Response: 15 to 23000 Hz
  • Sensitivity: 100 dB
  • Sound pressure level (SPL): 125 dB
  • Ear coupling: Intra-aural (ear buds)
  • Connector: 3.5 mm
  • Cable length: 1.20 m

Gramo One Reviews


"…I'm usually not a fan of earpieces that rely on the size of your outer ear to stay in place, but these Gramo Ones turned out to be pretty comfortable in everyday use. As for sound, once you get the placement right, the 16mm drivers deliver great, accurate bass and a balanced sound…", - Gary Krakow, tech editor/

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"...Right away there was a healthy amount of bass greeting my ear, and I don't mean the flabby wubwub kind. Slightly boosted but clean, and strong down to about 60Hz before I noticed any significant rolloff. There was still decent response down to 40Hz...The open back gives the bass and good distortion performance. Covering it with your fingertips immediately drops the bass and cranks your distortion up...", - Armaegis/

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"…I always expect that in-ear headphones will be a shadow of the over-ear version but in this case I’m surprised at what I’m hearing. This is far superior to my iPod and Apple headphones. I guess that should not come as a surprise but I had never tried an in-ear headphone other than what got shipped with my iPod or my iPhone. I must say, it’s really good…The sound is smooth, absolutely full range, it's rich and oh so easy to listen to. This is not my typical Apple musical experience. This is more like being at home. It’s portable luxury!…", Rick Hopkins, founder/Sonic Unity

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"...not just the bass that's accurate, the mids are favored the most, and that's a good thing with the Gramo One. Vocals are front and center right where they belong, so if you are a fan of singer/songwriter music, you will love these...", - Bill Henderson, editor/The

"…Soundstage on the Gramo One is all about width more than depth with good headroom and decent extension. Imaging in that respect is above average with good left right separation that never sounds disjointed or unnatural. I did say I hated earbuds but the big soundstage and openness of the Gramo One combined with a controlled neutral response and coherent presentation was actually quite enjoyable…”, - MARCUSD, Editor-in-Chief/

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"...Even though Celsus Sound is new and untested, we can vouch for the sound quality of the Gramo One...", -

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