Headfonics made a review for Sendy Audio Aiva
"The Aiva is a beautiful looking planar headphone. You can tell that there was (and is) some serious love and pride put into such an attractive design with those premium wood cups and excellent form factor.
I am not sure there is a better looking planar headphone under $600 and it puts some $1K plus headphone builds to shame. Despite its 420g weight, it is perhaps one of the comfiest planar headphones under $1k. The headband and pads pressure displacement is hugely satisfying.
In terms of performance, the Aiva is not the hardest to drive but I do strongly suggest you demo widely because the tuning requires a level of control on its treble to stay in balance that I found best achieved with around 1W into 32Ω and a natural to slightly warm amp stage. DAP’s such as the HiBy R6 Pro and amps such as the Xi Audio Broadway were my preferred matchups. Tube Amps also will give you a nice sweet tone to the Aiva’s timbre.
Overall, the Aiva plays for modern pop, R’n’B, synth wave and some genres of EDM such as traditional trance. It has a punchy fun-sounding low-end, clean and clear vocals, and an upper-treble that is very airy and articulate. Though not a choice for the midrange purist with that upper mids/lower treble dip, the Aiva remains an exciting ‘contrasty’ modern music planar headphone with a unique and competitive performance for this price point. "