Review: Fidue A91 Sirius – Pure Black Wizard

Disclaimer: The Fidue A91 Sirius was sent to us directly by the Fidue. The Fidue A91 doesn’t need to be returned to Fidue as far as I know. HFN is not related to Fidue in anyway and they expect our honest analysis, nothing else. Most of the pictures were taken from the Fidue website.


I’m a bit embarrassed to say so but this actually is the first Fidue in my collection. Fidue of course is no stranger to those who have been serious about personal audio and universal monitors in particular. Over the years the Chinese Fidue has released a series of popular universal IEMs and Fidue Acoustics’ goal is reproducing original sound accurately while maintaining clarity, dynamics and natural expression. The engineer responsible for the new A91 is Mr. Benny Tang. With 20-year development experience, producing ultimate headphones for world-famous brands,  the Chinese Top Earphone Designer and Chief Engineer of Fidue, has unique methods and insight into all aspects of headphone design – from high fidelity speakers and acoustic chambering to audio cabling and sonic tuning.

More information about Fidue and their range of products can be found on their Chinese website which partially has been translated to English.

A91 aka Sirius

The Sirius A91 unfortunately doesn’t have a translated page on the Fidue website but our English speaking readers can read all about it here. Luckily for us the well-known Penonaudio webshop has a very detailed description.

“Sirius A91 Reference-Class 4BA+Dynamic 5-way Hybrid In-ear Monitor”

 The Sirius A91 is Fidues latest Flagship IEM. It was released several months ago already so you will probably already know its name refers to a star system with the brightest star in the sky. I personally always link it to Harry potter. The Fidue engineers needed around 700 days to fully develop and test the A91 but they ended up creation a very special universal monitor.


The Fidue Sirius aka the Fidue A91 is a hybrid 5-driver universal in-ear monitor and it houses 4 hi-end Balanced Armature drivers delivering lively instruments and voices, and one customized bass dynamic driver that surpasses the conventional bass diving ability, making music full and extended, grand and magnificent.

Price & Accessories

The Fidue A91 Sirius as a flagship model isn’t the cheapest and it retails for about $899. For a 5-driver flagship – looking at the rest of the market – this price actually is very reasonable and it certainly is one of the, if not THE best, equipped universal inear monitor.

To start with, it comes in a nicely presented square box with on the inside, the monitors and a whole bunch of accessories. The A91 comes with a nice metal box to safely store your monitors and I absolutely love it. It’s small, well built, it looks nice, locks and it even has a soft fabric on the inside to protect the monitors. I been throwing it in my bag and I have no worries whatsoever that anything might happen to the monitors.

Of course you get a stock cable with the monitors, a cable disconnection set, a cleaning tool, a whole set of silicone and foam tips and no less than four adapters. There’s the basic 3.5mm to 6.3mm adapter and the airplane plug but the two other adapters are something I have never seen a monitor equipped with. As the stock cable is terminated in a balanced 2.5mm plug, Fidue as included to cable adapters going from 2.5mm balanced to 3.5mm Single ended and 3.5mm balanced (like the new Hifiman Supermini uses). I’ve been using these adapters the whole time with other gear and cables and I can’t praise Fidue enough for supplying them with the A91 as they will come in handy, you can be sure of that.


Design & build quality

The A91 Sirius has a tough all-metal shell with high precision CNC incisions. Its finish is very nice and the monitors look and feel very qualitative. You either hate or like the design of course but I do think they look great when you’re wearing them. Looking inside the short “canals” you will notice that Fidue implemented a wax filter and 3-tube sound system to deliver the sound to your eardrum.

The cable measures about 1.3m and is made out of lower internal resistance 8-core silver plated OFC. According to Fidue the signal becomes clearer and prompt as a result. The cable has a nice sleeve and based on my testing it very well limits interference and friction noise. Some people have complained about the thickness and the weight of the cable, but I can’t say it bothered me in any way. Fidue chose to terminate it with a 2.5mm plug and MMCX connectors of the 4th generation. They also added a ring locking mechanism using rings to make sure the connection stays optimal.

I do have to admit that the two very useful extra adapters are rather heavy and I kind of wished they had been shorter but that’s the only negative thing I could say about this.

Comfort & Isolation

Comfort wise the light universal Fidue A91 – 7gr/monitor on my scale – is very good. It fits my smaller ears perfectly and the shorter canal makes it feel extremely comfortable. Wearing the A91 is completely painless and I can wear it for hours without any discomfort. There do are sharper edges on the outside of the monitor but once you’ve inserted them into your ear, you won’t ever feel it. The inside of the monitor is smooth and soft and it feels very sturdy. According to Fidue they did more than hundred experiments and adjustments just to get a better fit with top level noise isolation.


Isolation wise these for universals, with foam tips, isolate pretty well. They’re not up to custom IEM levels but I’m very pleased with their isolation level and they’ve been perfectly fine to use on the train ride home or when walking around town.


  • Color: Dark Grey
  • Driving Units: 4 Balanced Armature driver & 1 dynamic driver
  • Frequency Response: 4-45000 Hz
  • Impedance: 20Ω
  • Sensitivity: 113Db
  • Input Power: 30mW
  • Total Harmonic Distortion: <1%
  • Plug: Protogenous 2.5mm balance stereo rhodium plating plug
  • Cable Length: 1.3m 8cores silver plating OFC audiophile cable
  • Converting Cable: 2.5 to 3.5mm quadruple balance converting plug; 2.5 to 3.5 mm universal stereo converting plug
  • Price: Around $899


  • Fidue Sirius A91 earphone
  • Monolayer silicone case x 4
  • Comply T500 memory sponge cover x1 pair
  • Holder belt x1
  • Disassemble kit x1
  • Clean kit x1
  • Tailor-made aluminum alloy housing case x1
  • Aviation stereo plug x1
  • 5 to 6.3 stereo converter x1

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