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Onkyo TX-NR646 and TX-NR747 Atmos / DTS:X AV Receivers Preview



  • Product Name: TX-NR646 and TX-NR747
  • Manufacturer: Onkyo
  • Review Date: June 22, 2015 12:00
  • MSRP: $699 - TX-NR646 and $999 - TX-NR747
  • First Impression: Pretty Cool
  • Buy Now


  • # Channels:      7.2
  • Power Watts/Ch (6 Ohms 1kHz, 1 Channel Driven, FTC):    170, 0.9% THD
  • Power Watts/Ch (8 Ohms 20-20kHz, 2 Channels Driven, FTC):       100, 0.08% THD
  • Dolby Decoder:      Atmos, True HD, DD Plus
  • DTS Decoder:    DTS:X, DTS-HD Master Audio
  • Audio I/O:     7 / 0
  • Digital Audio IN (OPT/COAX):  2 / 1
  • Composite I/O: 3 / 0
  • Component Video I/O:   2 / 0
  • HDMI I/O:     8 / 2
  • HDCP 2.2 Copy-Protection Compatibility:    3 in / 2 out
  • Dimensions (W x H x D):     17 1/8" x 6 13/16" x 12 15/16" (435 x 173.5 x 329 mm)
  • Weight:  20.7 lbs (9.4 kg)


  • # Channels      7.2
  • Power Watts/Ch (6 Ohms 1kHz, 1 Channel Driven, FTC):  175, 0.9% THD
  • Power Watts/Ch (8 Ohms 20-20kHz, 2 Channels Driven, FTC):   110, 0.08% THD
  • THX Certified  Select2 Plus
  • DTS Decoder:  DTS:X, DTS-HD Master Audio
  • Dolby Decoder:     Atmos, True HD, DD Plus, PLIIz
  • HDCP 2.2 Copy-Protection Compatibility:  (3 in / 2 out)
  • HDMI I/O:   8 / 3
  • Component Video I/O: 2 / 0
  • Digital Audio IN (OPT/COAX):   2 / 1
  • Composite I/O: 3 / 0
  • Dimensions (W x H x D):  17 1/8" x 6 7/8" x 14 15/16" (435 x 175 x 379 mm)
  • Weight:  24.3 lbs (11.0 kg)


Since the merge between Onkyo and Pioneer we’ve seen some great receivers come out of the Pioneer side like their VSX-90, but what about Onkyo?  Onkyo just announced the release of two new receivers that will be DTS:X compatible. These are some of the FIRST DTS:X AV receivers we've seen officially announced on a manufacturers website.  These two new Onkyo receivers are Dolby Atmos and DTS:X ready. Pioneer and Onkyo have the most affordable entry level receivers with Atmos and now DTS:X support.  Here’s a breakdown of what these two new Onkyo receivers have to offer.

NR646front.jpg          747front.jpg

Onkyo TX-NR646 (left) and TX-NR747 (right)


The most news worthy feature of these receivers is the new DTS:X sound feature.  DTS:X is the next-generation object-based surround sound technology that includes height to deliver an even more immersive listening experience. DTS:X provides you with even more control over  which sounds can be heard.  Unlike channel-based audio, you will be able to personalize your audio experience. For example, you can turn up JUST the dialog within a mix (on supported DTS:X encoded software). DTS:X allows you to customize to your room layout as well as control dialog and dynamic range.

For more information, see:  DTS:X Surround Sound Overview and First Listen

Dolby Atmos

Along with DTS:X, both the NR646 and NR747 come with Dolby Atmos. The format combines a channel-based audio bed with object-oriented sound to place and move specific effects around the room up to 5.1.2 channels. Sound designers and artists are free to mix in a 3D space, steering effects through surround channels and adding an overhead dimension with discrete height channels. Additionally, a new Dolby surround up-mixer allows for your current channel-based content (that has not been mixed for Dolby Atmos) to be expanded to fill the flexible speaker layouts of a Dolby Atmos system.

For more infomation, see: Dolby Atmos for Home Theater Explained

4K Ultra HD

Both receivers come with the latest HDMI specification and HDCP 2.2 compatibility support (for 3 of the inputs only) the latest formats and technologies planned for Hollywood content. This latest HDMI spec offers a significant increase in bandwidth (up to 18Gbps) to support new features such as 4K@50/60 (2160p), which is 4 times the clarity of 1080p/60 video resolution, and 4:4:4 color space. These Onkyo AVR's enable transmission of High Dynamic Range (HDR) formats, and provides enhanced picture quality by simultaneously enabling greater detail for both the dark and bright parts of an image.

Bluetooth / Wi-Fi with Pandora, Spotify, and AirPlay

The TX-NR646 and NR747 have AirPlay, Wi-Fi and Bluetooth technologies built in. The free Onkyo Remote app puts a range of streaming options at your fingertips, from universal hi-res audio via network-attached devices to internet streaming services to music on your smartphone and tablet. Or pair up and enjoy whatever's playing on your Bluetooth-compatible device.  This receiver comes loaded with Spotify, Pandora, SiriusXM Internet Radio, Slacker and TuneIn. You can select a station and search for music available on these services via the Onkyo Remote app on your phone.

Hi-Current Amp Design for Authentic Sound Reproduction

Onkyo's exclusive amplification technology enhances the audio dynamics of your movies, music and games. This Wide Range Amplifier Technology (WRAT) is at the core of Onkyo's signature sound.

Onkyo amplifier design is comprised of three key elements:

  • a low negative feedback design which is said to provide punchy, true-to-life sound, and cleaner audio across the frequency ranges;
  • closed groundloop circuits to reduce individual circuit noise and keep the ground potential free of distortion; and
  • a high instantaneous current to handle big dynamic gains.  Though be careful with the HCC Current Spec/Claims of Receiver manufacturers.

For the NR646 this means  170 W/Ch (6 Ohms, 1 kHz, 0.9% THD, 1 Channel Driven, FTC) or the proper way to spec power of 100 W/Ch (8 Ohms, 20 Hz–20 kHz, 0.08% THD, 2 Channels Driven, FTC)

For the NR747 it allows 175 W/Ch (6 Ohms, 1 kHz, 0.9% THD, 1 Channel Driven, FTC) or the proper way to spec power of 110 W/Ch (8 Ohms, 20 Hz–20 kHz, 0.08% THD, 2 Channels Driven, FTC).

 Editorial Note on Amplifier Power in AV Receivers:

We don't like the new trend ALL of the major AV receiver manufacturers seem to be doing these days by rating amplifier power with 1 channel driven, at 6 ohms and usually into clipping.  Ignore those power figures. They are lame.  Instead, always look for full bandwidth (20Hz to 20kHz, 8 ohms and at least 2 channels driven and at distortion levels below clipping or 0.1% THD+N) to get a better representation of actual real rated power.

646back_large.jpg          747back_large.jpg

Onkyo TX-NR646 (left) and TX-NR747 (right)

Streaming, Multi-Zone and High Res Audio

384 kHz/32-bit Hi-Grade DAC

A premium-quality AK4458 digital-to-analog converter from Asahi Kasei implements low-distortion filtering technologies for clear sound. Which means clearer sound from audio formats such as compressed, lossless, and hi-res audio (MP3, WMA, WMA Lossless, FLAC, WAV, OggVorbis, AAC, Apple Lossless, DSD 5.6 MHz, LPCM, and Dolby TrueHD). In addition, these receivers are engineered for hi-res analog and digital audio. With a dedicated Phono input line you can spin your classic vinyl and hear it in all its analog glory and stream your networked hi-res digital files. The TX-NR646 and NR747 support hi-res audio playback, gapless playback, and the ability to play DSD, Double DSD, FLAC and ALAC along with other Hi-Res formats.

Powered Zone 2 and Zone 2 Line-Outs

The TX-NR646 and NR747 also feature Powered Zone 2 and Zone 2 line-outs. This lets you assign two channels to power audio in a room equipped with speakers. An existing hi-fi system in a third room can also be connected via the line-out, enabling the use of the A/V receiver as a pre-amp and audio server. Control content in the two zones via remote app; play the same song in all zones using Whole House Mode; or enjoy a different song in each room.

What’s are the differences between the models?

Retail price for the NR646 is $699 and retail for the NR747 is $999.  For the $300 you not only go from 170 to 175 Watts per channel at 6 ohms and from 100 to 110 Watts per channel at 8 ohms, but with the NR747 you get a THX Select2 certified receiver.  THX certification guarantees the same high volume, low distortion sound you experience in a commercial theater in your listening room (up to 2000 ft^3). The TX-NR747 meets the most demanding & rigorous performance certification: it has to pass 75 test categories, 2,000 tests, covering 14,000 data points. It also weighs about 4lbs heavier than the NR646 implying it has a bigger power supply to achieve higher sustained power levels.


If you’re looking to the future for the next generation of sound it’s going to be hard to beat either of these AV receivers.  Obviously both receivers will need a firmware update to support the DTS:X format.  Like the Pioneer VSX-90, they only have 7 internal amps.  So they can only support up to two height channels for a 5.1.2 configuration.  Four height channels are preferred in a 5.1.4 configuration but given the price points, it’s understandable. With a price under $700 for the NR646 and features such as DTS:X, Dolby Atmos, 4k Ultra HD, Bluetooth, Wi-Fi, and Apple Connect, these two receivers should keep you ahead of the game for the near future (or until the next best sound and video imaging format comes out).

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.

About the author:
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Tony is our resident expert for lifestyle and wireless products including soundbars. He does most of the reviews for wireless and streaming loudspeakers and often compares soundbars in round ups and helps us cover the trade shows.

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