Nexum AQUA+ Review

Nexum AQUA+  The 32 bit Wireless Headphone DAC & Amplifier




1. About NEXUM:

NEXUM comes from Taiwan and is established in 2013 with focusing on wireless audio technology design. Over the years, NEXUM launched several products into the market like the MEMO, AQUA, TuneBox2 and LINKA. They are care about design to bring more value to our lives.


2. Disclaimer:

First of all, a big thanks to NEXUM for providing me a free sample of the AQUA+ for review purposes. I am not affiliated with NEXUM beyond this review and these words reflect my true, unaltered opinions about the product.


NEXUM Official Web Page:

Price: $139.00

3. What is the AQUA+:

The AQUA+ is Wireless operating DAC with a built in amplifier that supports Hi-Res music files with sampling rates up to 32bit 384K and is compatible with multiple operating systems like Windows, Mac, Android or IOS etc.


4. Package and Accessories:

The device comes in small card-box and contains the following items;

  • 1 x AQUA+
  • 1 x Charging Pad
  • 1 x Leather Clip
  • 1 x microUSB cable
  • 1 x User Manual




5. Design and Build Quality:

The NEXUM AQUA + is a small (4.5*4.5*1.2cm), lightweight (25g) and well made device that has a square shape with rounded corners. The AQUA+ has a frame that is made of aluminum, while the top and back covers/caps are made of plastic for a better wireless transmission.


On the sides you can find the power button with a 32 bit marking, the volume wheel that has multiple functions, a led light and the 3.5mm headphone jack.

The NEXUM AQUA+ has three different options for the cover caps; these are midnight black, Sublime Gold and Radiant white. My device is Sublime Gold model.

Aqua+ ,Colors

6. Technical Specifications:

  • Audio Codec              : aptX/aptX LL/AAC/SBC
  • Support Impedance   : 8ohm-300ohm
  • Output Power             : 7.5mW@300ohm per channel (1.5Vrms output)
  • Bluetooth Range        : 10M
  • Noise Level                : -93dB
  • Dynamic Range         : 92.7dB
  • THD+N @1KHz         : 0.0067%
  • Stereo Crosstalk        : -92.5dB
  • Microphone                : MEMS type with high sensitivity
  • Charging time             : 2hours
  • Certifications              : BQB/FCC/CE/NCC
  • Size                            : 4.5*4.5*1.2cm
  • Weight                        : 25g


7. Hardware and Operation:

The NEXUM AQUA + has some nice hardware specs like a high quality DAC, Wireless charging etc. that I will now explain for you.

a) DAC Section:

The DAC (Digital to Analog Converter) used in the NEXUM AQUA+ is the CS43130 of the Company Cirrus Logic Inc. that supports sampling rates up to 32bit – 384kHz. According to Cirrus Logic, the CS43130 features a high impedance of 600 Ω and inter channel isolation of >110 dB to minimize pre-echos and ringing artifacts.

The CS43130 is designed with proprietary digital-interpolation filters that support five selectable digital filter responses. Filtering options include low group delay with pseudo-linear phase and a fast or slow roll-off. Volume matching of the analog output levels and channel mixing enable a seamless transition between the DSD and PCM playback paths.


The onboard low noise, ground-centered headphone amplifier provides proprietary AC impedance detection to support headphone fingerprinting to provide a consistent and transparent audio experience for the end user regardless of transducer impedances or frequency responses.


b) AMP Section and Drivability:

The NEXUM AQUA + has an onboard amplifier that is integrated in to the CS43130 SOC (System on a Chip). The amplifier supports earphones & headphones with impedance between 8ohm-300ohm and has an output power rating of 7.5mW@300ohm per channel (1.5Vrms output).

The AQUA+ was able to drive my Audio-Technica ATH M50 to pretty loud volume levels.

According to Cirrus Logic, the onboard headphone amplifier provides proprietary AC impedance detection to support headphone fingerprinting to provide a consistent and transparent audio experience for the end user regardless of transducer impedances or frequency responses.


c) Bluetooth and supported Audio Codecs:

The AQUA+ supports the Bluetooth 4.2 protocol and different types of codecs. This means whenever you pair the AQUA+ with a Bluetooth device it selects the best possible codec that your audio source (DAP, Tablet, Smartphone) supports.

Supported codecs are aptX / aptXLL / AAC and SBC. That means that you no longer hear an FLAC, WAV, MP3, DSD, etc. music file. All audio formats will be decoded by the output device to PCM and then transcoded to aptX, AAC or SBC via Bluetooth audio (in 16bit) to AQUA+. Then AQUA+ leverages its 2 embedded chipsets, high-quality SRC & Hi-Res DAC, to convert it to 32bit.



What do these codes actually mean?


In digital audio data reduction technology, aptX (formerly apt-X) is a family of proprietary audio codec compression algorithms currently owned by Qualcomm.

The aptX audio codec is used for wireless audio applications, notably the real-time streaming of lossy stereo audio over the Bluetooth A2DP connection/pairing between a “source” device such as a Smartphone, Tablet Laptop or a DAP. Products bearing the CSR aptX logo are certified for interoperability with each other. (Ref: Wikipedia)

aptX LL:

aptX LL = Low Latency is intended for video and gaming applications requiring comfortable audio-video synchronization whenever the stereo audio is transmitted over short-range radio to the listener(s) using the Bluetooth A2DP audio profile standard. The technology offers an end-to-end latency of 32 ms over Bluetooth. By comparison, the latency of standard Bluetooth stereo varies greatly depending on the system implementation and buffering. Solutions are available that use standard SBC encoding/decoding that achieve end-to-end latency of less than 40 ms. (Ref: Wikipedia)


Advanced Audio Coding (AAC) is a proprietary audio coding standard for lossy digital audio compression(Ref: Wikipedia)


SBC, or low-complexity sub-band codec, is an audio sub-band codec specified by the Bluetooth Special Interest Group (SIG) for the Advanced Audio Distribution Profile (A2DP). SBC is a digital audio encoder and decoder used to transfer data to Bluetooth audio output devices like headphones or loudspeakers. It can also be used on the Internet.

It was designed to obtain a reasonably good audio quality at medium bit rates while keeping low computational complexity, having Bluetooth bandwidth limitations and processing power in mind. (Ref: Wikipedia)


How the Bluetooth pairing works:

 The Bluetooth pairing of NEXUM AQUA + is quite simple and has an operating range of about 10 meters. You need to press to the 32 bit key until the led flashes in red and blue colors. This operation is needed only for the first time. For the next time you need only to power on the device and enable Bluetooth connection of your source (Smartphone, Tablet, etc.) and a female voice of the NEXUM AQUA + will say “device is connected”.

Please note, that the AQUA+ is designed for headphones with 3.5mm jacks and is unable to support wireless headphones.


d) Wireless Charging:

The Nexum AQUA+ supports the Qi Wireless charging that is an open interface standard that defines wireless power transfer using an inductive charging over distances of up to 4 cm (1.6 inches). Thanks to this feature, the only thing you should do is to but the AQUA+ on the charging pad that is included in the package AQUA+. The charging time takes about 2 hours and has even charge my Samsung Galaxy S8+ that also supports this feature.



e) Battery life:

According to NEXUM, the AQUA+ should be able to play for 8 hours @ 16bits and 5.5 hours @ 32bits on a full charge.

My test have show that the AQUA+ is able top ley for 7.5 – 8 Hours in 16 Bit mode and approx. 5 hours in 32 Bit mode. These values are pretty good for such a small and constantly wireless working device.

f) Background Noise / Hissing:

The NEXUM AQUA + is a very silent working device. There was small to non hissing with some of my sensitive IEM’s like the HiFi BOY OS V3 and Dunu Falcon-C. This is a great capability for a wireless working device.

g) Operation:

The Nexum AQUA+ is easy to handle and has two physical keys/buttons. The first key is the digital volume control wheel of the AQUA+ that supports 64 different volume points and that has also some multiple functions. These functions are Play/Pause (Short Press) /Next Song (Double Short) /Prev. Song (Triple Short).

The second is the 32 Bit key. The 32 Bit key operates as power on/off button and it also activates or deactivates the 32bit/384kHz up-sampling function of the device. The led light changes to a turquoise color when you activate this feature.

h) Microphone:

The headphone mic and wire control will not work while connected, but AQUA+ has a built-in mic and can perform wire control functions with the keys on the device.


8) Equipments used for this review:

  • DAC’s                          : Nexum AQUA +, Astell&Kern XB10
  • Digital Sources        : Ipad Air 2, Samsung Galaxy S8+
    IEM’s                           : Audeze iSine20, Dunu Flacon-C, TFZ TEQUILA1,
    Earbuds                     : Penon BS1 Official Version, NiceHCK EBX, HiFi BOY Dream
  • Headphones             : Audio-Technica ATH50M



9) Albums & tracks used for this review:

  • Sebastian Ingrosso, Thommy Trash &John M. – Reload (Apple Music)
  • Michael Jackson – Billie Jean (DSD)
  • Casey Abrams – Robot Lovers (Tidal Hi-Fi)
  • Emmanuel Pahud (Claude Debussy) – Syrinx (Flac 16bit/44kHz)
  • Melody Gardot – Who Will Comfort Me (Flac 16bit/44kHz)
  • Aretha Franklin – I Say a Little Prayer (DSF)
  • Diana Krall – So Wonderful (DSF)
  • Otto Liebert & Luna Negra – Up Close “Album” (DSD) – Binaural Recording
  • Alboran Trio’s – Cinque Lunghissimi Minuti (Flac 16bit/44kHz)
  • Megadeth – Sweating Bullets (Flac 16bit/44kHz)
  • Opeth – Damnation (Tidal Hi-Fi)
  • Metallica – The Black Album (Flac 24bit/96Hz)
  • Lorde – Royals (Flac 24bit/48kHz)



10. Sound:

 I believe in burn-in and have done that for approx. 100 hours before I wrote this review.

Please note that this is a low budget Bluetooth DAC and all my comments about the sound quality are in consideration of this price range.

Tonality / Bass / Mid / Treble / Soundstage & Imagine:

 The AQUA+ is a balanced sounding source with a relative flat frequency response and quite neutral tonality.

The AQUA+ is an energetic sounding device with a well extended and tight bass response. The bass is textured and it sounds pretty transparent. The most impressive part about the bass is the speed; it is pretty fast and accurate for a DAC (especially a Bluetooth one) in this price range.

As mentioned before the AQUA+ is a relative neutral sounding device around the whole sound spectrum. The midrange of this device sounds clear and transparent and has also a good amount of detail retrieval.

After some intensive vocal comparisons I have come to the conclusion that Female vocals like Lorde, Diana Krall or Melody Gardot sounded more natural and emotional then most of the male vocals I have listened during this review.

The instrument presentation sounded pretty natural with some of my IEMs like the HiFi BOY OS V3 and the TFZ TEQUILA1, but the especially the synergy with the AUDEZE iSine20 was very satisfying. The separation and definition of instruments is also pretty good.

The upper midrange of the AQUA+ sounds soft and quite controlled. There is no over sharpness that would be uncomfortable after long listening periods.

The treble range of the NEXUM AQUA + sounds fast, clear and vivid. It is not too bright or too smooth. The detail level is above average and presents a nice amount of shimmer/glimmer.

The soundstage of the AQUA+ is well extended and has a nice sense of space. The soundstage depth is above average but it is pretty wide in staging.



11. Comparison:

 Nexum AQUA+ vs Astell&Kern XB10:

Astell&Kern XB10 vs Nexum Aqua+

The Astell&Kern AK XB10 and the Nexum AQUA+ are one of the best choices if you are looking for a wireless DAC/AMP solution. They are sharing also the same retrial price.

a) Design & Build Quality:

Both devices are well made and very lightweight. The AK XB10 weights only 23g and the AQUA+ 25g.

The Astell&Kern XB10 has an all plastic shell while the AQUA+ has an aluminum frame with plastic caps. Both devices are very small and share the same form factor. The size of the XB10 is 5*5*12.3cm  vs  4.5*4.5*1.2cm for the AQUA+.

b) Technical Specifications:

The AK XB10 has to headphone outputs, one for 2.5mm balanced wit a power output of 1.8Vrms and one 3.5mm single ended headphone out with a output power of 0.9Vrms. The AQUA+ has only one 3.5mm single ended output but with a higher output power of 1.5Vrms.

The AQUA+ supports the aptX/aptX LL/AAC/SBC Bluetooth Audio Codec’s, while the SBC, AAC, aptX and aptX HD. The main difference is that the AQUA+ supports aptX LL vs aptX HD for the XB10.

Both devices have a built in microphone that is needed for phone calls.

The AK XB10 has a battery life is around 5 hours while the AQUA+ is able to play up to 7.5 Hours. The AQUA+ has also the Qi Wireless charging option that is a nice extra.

Hi-Fi DAC of both devices is capable of reproducing high-quality sound. The AK XB10 supports sampling rates up to 24-bit/192 kHz, while the AQUA+ is capable to support sampling rates up to 32bit – 384kHz.

c) Sound Comparison:

The AQUA+ has a quite neutral tonality and a relative flat frequency response, while the Astell&Kern XB10 sounds warmer and has a V shaped frequency allocation.

The bass of the AQUA+ sounds faster, tighter and is more natural in presentation, while the AK XB10 has more quantity and depth.

The bass of the AQUA+ sounds cleaner, clearer and has more detail rendering compared to the XB10. The bass of the XB10 is not as tight as the AQUA+ and sounds a little bit loose.

The midrange presentation of the Astell&Kern XB10’s sounds a bit muffled compared the clearer midrange of the AQUA+. The Astell&Kern XB10 sounds better with Male vocals, while the AQUA+ performs better with female vocals.

I think that the AQUA+ has the upper hand in terms of instrument clarity, separation and naturalness.

The upper midrange of XB10 sounds a bit too stiff compared to the softer and more controlled sounding AQUA+.

The treble range of the Astell&Kern XB10 sounds pretty good, but it can not commentate with the performance of the Aqua+, which has the sharper, more extended and faster treble response.  Because of these characteristics, the AQUA+ sounds like the better choice if you listen to tracks that need additional speed and control.

Both devices have a good soundstage performance, but the Astell&Kern XB10 has the better depth while the AQUA+ has the better send for soundstage wideness.


12. Conclusion:

The NEXUM AQUA+ is a good performer with its great features, nice build quality and quite detailed sound performance. People who are looking for a wireless DAC/Amp solution should definitely give the AQUA + a try.

13. Pros and Cons:

  • + Small form factor
  • + Nice Accessory Package  
  • + Great sound Quality
  • + Good Battery Life
  • + Low to none hissing


  • – No independent volume control
  • – No battery means additional battery drain for the source

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