Proprietary 16 mm Celsus Sound Transducer • A Reference-Grade Open-Back In-Ear Headphone

The Celsus Gramo One is a reference-grade open-back in-ear headphone that sits comfortably on the outer ear. With the portability of an in-ear headphone (IEM), the Celsus Gramo One’s exceptional sound quality equals or betters the most highly regarded over-ear headphones. It is designed for long listening without the drawback of the weight of over-ear headphones or ear pressure of in-ear earphones.

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 16mm Celsus sound transducer produces a sense of space, depth, detail and dynamic range as impressive as that of an audiophile’s dream sound system. A mesmerizing midrange and solid bass are among the more impressive of the Celsus Gramo One’s signature qualities. It has a seductive vocal textures rarely found in high-end earphones.

The term reference-grade typically connects with a few widely celebrated over-ear and on-ear headphones. Their common 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 have achieved reference-class status. Again, as a drawback, IEM devices suffer from an ultimately fatiguing music-in-the-middle-of-one’s-head effect along with the excessive ear pressure that inevitably accompanies prolonged listening. The Gramo One, a different animal entirely, avoids these pitfalls through creative engineering.


  • A proprietary 16mm transducer that 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


  • 3 pairs of ear tips. The Gramo One is tuned to sound best without the ear tips.
  • Leather pouch


"…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, user review

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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!…"

Sonic Unity, Rick Hopkins, founder

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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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  • 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

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