Acurus ACT 4 AV Processor Review

Looks great and sounds even better

SRP: £12,300.00

What is the Acurus ACT 4?

The Acurus ACT 4 is the latest high-end multichannel AV pre-amp and processor from the US manufacturer Indy Audio Labs. There are actually two versions – the ACT 4-16, which I'm reviewing here, and the more expensive ACT 4-20, which was released recently. The main difference is that the ACT 4-20 has 15.5 configurable channels, while the ACT 4-16 is 'limited' to 13.3.

Those extra four channels of processing aside, both appear to be identical with support for Dolby Atmos and DTS:X immersive audio formats, and Hi-Res Audio. There's also HDMI 2.0b and HDCP 2.2, so the ACT 4 can pass 4K/60p and High Dynamic Range (HDR10 and Dolby Vision). The ACT 4-16 isn't cheap though, costing a hefty £12,300 as at the time of writing (July 2018).

There are some genuinely impressive pre-amps and processors at the high-end of the market, so the ACT 4 will need to deliver an exceptional performance if it's to hold its own. Let's see how it does...


Acurus ACT 4
The Acurus ACT 4 definitely looks the part, with the kind of elegant design, solid build quality, and slick features that often differentiate products at the higher-end of the market. Thanks to a large 7" central display that is not only informative, but also a touchscreen interface, the ACT 4 has a very cool front facia that creates a pleasingly minimalist effect.

I've been arguing for manufacturers of AV receivers to take this approach for years. You don't need loads of buttons and connections on the front: an on/off button, a volume dial and a touchscreen covers everything. That's exactly what the ACT 4 does, with an illuminated power button on the left, a touchscreen in the middle, and a large volume dial on the right.
Acurus ACT 4
This design means that what is actually a very sophisticated product, doesn't look remotely intimidating. You turn it on, select the appropriate input, set the volume and the ACT 4 takes care of the rest. The graphical interface on the touch screen is also very well designed, and manages that delicate task of being both intuitive to use and informative to read.

The build quality is excellent, with a solid aluminium front plate, and an excellent level of engineering and construction. The ACT 4 uses a very fetching black brushed metal and satin anodisation finish with a laser-etched logo, and measures 432 x 178 x 381mm (WxHxD) and weighs in at 13.6kg.
The design is simple but attractive, and the touch sensitive screen is very cool


Acurus ACT 4
The connections are all at the rear, and the Acurus ACT 4 boasts a decent selection. There are eight HDMI inputs and two HDMI outputs. All the inputs and one of the outputs are full fat 18Gbps HDMI 2.0b/HDCP 2.2, which means they can handle 4K/60p at 4:4:4, High Dynamic Range (HDR10 and Dolby Vision) and Wide Colour Gamut (Rec.2020). The second HDMI output is HDMI1.4, and is intended for connecting to legacy devices.

There's no support for ARC (Audio Return Channel), but since the ACT 4 is designed for home cinema installations that will almost certainly use a projector, its absence isn't really relevant.

There are three gold-plated unbalanced RCA stereo inputs, a gold plated RCA phono input, and one balanced XLR stereo input, along with three digital coaxial RCA inputs and three digital optical inputs. There are also 7.1-channel analogue inputs using RCA connectors, and 16 gold-plated RCA outputs and 14 balanced XLR outputs.

There are also two RS232 serial ports for system control, an Ethernet port for web interface and two-way IP UDP control, one 12V trigger in and four 12V trigger outs (all using 3.5mm jacks), an IR jack, two USB 5V 2A charging ports for connecting Amazon and Roku streaming devices, and one USB A programming port.
There are plenty of connections, including 8 HDMI inputs and 14 XLR outputs


Acurus ACT 4
The remote control that comes with the Acurus ACT 4 is fairly basic, with a simple black plastic construction. However it includes all the basic controls that you need, so you can turn the ACT 4 on, change the volume, select an input, and choose the audio format.

To be honest, for a product at this price point the remote is a disappointment, but the ACT 4 is aimed squarely at the custom install market. That means it will undoubtedly be part of a dedicated system with third-party control, and as such it supports Crestron, Savant, Elan, URC, and Control4.
There's a simple remote included, but the ACT 4 is compatible with third-party control

Acurus ACT 4 Features

Acurus ACT 4
The Acurus ACT 4-16 supports both Dolby Atmos and DTS:X, and theoretically it can decode and render 13.1 channels. However it isn't quite as simple as that because the ACT 4-16 is limited to either 7.3.6 or 9.3.2, it can't decode 9.3.4 or 9.1.6. This is due to technical limitations in the chipset, but I should point out that the ACT 4-20 has no such limitations and supports a massive 9.5.6-chnanel speaker layout.

The decoding of Atmos soundtracks use the full 13.1 channels but DTS:X soundtracks max out at 11.1, although this is a limitation of the format rather than the processor. Since the ACT 4 supports both Dolby Atmos and DTS:X, that means it can also upscale 5.1 and 7.1 mixes to take full advantage of the additional immersive channels. It can cross mix as well, which means that Dolby soundtracks can be upscaled by DTS Neural Surround and DTS soundtracks can be upscaled by Dolby Surround.
There's support for Dolby Atmos and DTS:X, with up to 13.1 channels of processing


Acurus ACT 4
Thanks to some thoughtful design and clear labelling, the Acurus ACT 4 is actually fairly easy to setup. All you need to do is connect your sources to the processor and then connect it to your amplification using either RCA or XLR cables. The speaker configuration you choose will obviously depend on your system, but in my case it was 7.2.4 channels.

I actually tested the ACT 4 with the dARTS Theatre 7.2-channel speaker system, which I was reviewing at the same time, and I used my Arcam P429 4-channel power amp for the four overhead channels that were already fitted in my dedicated home cinema.

Then all I needed to do was select the correct audio bed from nine possible speaker locations, I chose the seven standard channels but you also have the option of two front widths. Then I selected the number of subwoofers, here I chose two but there are options from zero to three. Finally I set the number of overheads, which in my case was four, but there are options for two, three, four or six (unless you select nine audio bed channels, in which case you're limited to two overheads in the front, middle, or rear of the room). In terms of the overhead channels, you can choose between height or top speakers, and in my case I have downward firing top speakers.

The touchscreen user interface is excellent, clearly showing you what needs to be set and providing you with the necessary choices. Once you've chosen your speaker configuration and connected everything up, then it's time to fine tune the set-up. You can change the polarity with a choice of 0˚ or 180˚, although if you've set your speakers up correctly then you can leave this at the default setting of 0˚.

Then you can set the size of the speakers, either small or large, and I normally use small which allows the subs to handle the lower frequencies. I left the crossover at its default setting of 80Hz, which is optimal for the dARTS 7.2-channel speaker system.

Now it's time to set the levels and delays for each speaker. For the levels you'll need an SPL meter, but it's very easy to select the relevant speaker and play the test tones with a choice of sinusoidal, white and pink noise generators. You can also use an external test tone generator, which will come in handy later.

As great as the touchscreen on the front of the ACT 4 is, you don't want to be constantly going over to the processor when setting the levels. Thankfully there is a useful Web interface for configuration, that can be accessed using a laptop or mobile device with a browser. So you can just sit at the sweet spot and set the levels in comfort.

You also need to set the delays, which are in milliseconds. That means you need to measure the distance from the sweet spot to each of the speakers using a tape measure, or in my case a laser measure, and then convert them into milliseconds. The manual suggests that 0.3m equates to 1ms of delay for ear-level speakers; although for the overhead speakers, it suggest subtracting approximately 40% from the delay settings to serve as a reasonable starting point to account for the extra distance high-frequency height information travels due to ceiling reflections.

If you're thinking that this set-up sounds very hands-on and manual, then you'd be right. Very unusually for a sophisticated multichannel processor at this price point, the ACT 4 does not have any automated set-up or room EQ system.

This means that to actually do any room correction is going to require a calibrated microphone and some appropriate software. I use Room EQ Wizard (REW), which generated frequency sweeps that allowed me to EQ the response below 300 Hz using the four bands of parametric EQ available for each channel. It's probably more than most consumers would be prepared to do, but the chances are your dealer or installer will handle the set-up, and the results can be quite impressive once completed.

However, there's no denying that the lack of any automated room EQ does put the ACT 4 at a disadvantage to competing products like the Datasat LS10 which uses Dirac Live, or the incredible Trinnov Audio Altitude16 with its amazing proprietary EQ software. Thankfully Acurus will be releasing their own ASPEQT proprietary automated room EQ system, so this won't be an issue for much longer.
The ACT 4 is simple to set up, but the lack of a built-in room EQ system is a surprise at this price


Once you've set up the Acurus ACT 4, you'll be amazed at how easy it is to operate. You simply turn it on, select the appropriate input using the touchscreen and then set the volume. The processor will do everything else for you, especially if it's in the Auto setting.

This will intelligently auto-detect the incoming signal and apply the appropriate processing. So a Dolby Atmos soundtrack will be processed according, a 5.1 or 7.1 Dolby soundtrack will be upmixed using Dolby Surround. Conversely a DTS:X soundtrack will be delivered according to your speaker configuration, and 5.1 and 7.1 DTS soundtracks will be upscaled using DTS Neural X.

Alternatively you can use Direct, which matches the incoming signal to the corresponding speaker configuration, so 5.1 uses that configuration, while 7.1 uses all seven channels and the sub, DTS:X would use up to a 7.1.4 configuration depending on your available speakers and Dolby Atmos could go up to 7.1.6.

There's also a Stereo mode, which delivers a basic two-channel configuration and will automatically down mix multichannel audio to those two channels. The Analogue mode is for the stereo analogue inputs, and bypasses any digital processing, thus utilising the ACT 4 as a pure two-channel preamplifier. This mode is ideal for critical listening with large, high-performance left and right loudspeakers.

The Party mode is a variation of the Auto mode, in which any signal is upmixed or downmixed to 2.1 channels. The resulting left and right channel signals are then routed to all available left and right speakers. This mode is intended to provide party music that can fill a room with sound.

Finally there is the Night mode, which is also a variation of the Auto mode in which dynamic compression is applied to the signal to reduce its loudness. In addition, the subwoofer signal is automatically attenuated. This results in an overall quieter signal for listening at night without disturbing other members of the household.

The ACT 4 allows for on-the-fly adjustments to the DTS Dialogue Control to boost the audio, as well as the Treble and Bass. The Dolby and DTS engines are always running and available, so whereas a normal processor will take four to ten seconds to switch, the ACT 4 can switch between upmixers in a tenth of a second. That means you can instantly switch between the two modes to determine which of the two upmixing algorithms you prefer. I did try this but to be honest I couldn't hear any perceivable difference between the two, both were excellent at creating a greater sense of immersion.


In terms of its performance, the Acurus ACT 4 was rock solid with no problems in terms of operation. The processor was fast, responsive and stable, with no issues in terms of stability. It also performed extremely well as a pre amp and using the touchscreen was an absolute joy.

As a processor the ACT 4 is superb, decoding and rendering both Dolby Atmos and DTS:X very effectively to deliver an open but detailed soundstage with precise steering of effects and plenty of surround presence. Of course I was partnering it with exceptional amplification and speakers in the shape of the dARTS Theatre System, but even so the ACT 4 remains a great processor regardless.

As always I started with the Amaze trailer from Dolby's Atmos demo disc. The ACT 4 did an excellent job of delivering the multitude of effects such as birds, thunder and rain, resulting in an impressively immersive experience. I then moved on to the Atmos soundtrack on the Blu-ray of Gravity, which has a highly directional sound design making it ideal for testing a system's steering and tonal balance. The ACT 4 steered the voices and effects around the room seamlessly, resulting a very three-dimensional experience.

The absence of any built-in room equalisation meant I had to rely on my own skills but thanks to a carefully designed home theatre, a degree of familiarity with the room itself, and plenty of experience in managing the bass response, the result was a suitably balanced and smooth low frequency presence. I used my go-to bass test disc – Blade Runner 2049 – and the ACT 4 handled the massive low frequency notes at the start of the film very well, delivering them with plenty of control and precision.

I recently picked up A Quiet Place, and this film has quickly become one of my favourite soundtracks. For a film that is essentially about not making any sound, the mix is incredibly active all of the time. There is an amazing amount of subtlety with the silent scenes punctuated by wind rustling through the leaves or soft footsteps on sand. However when someone accidentally makes a loud noise or the monsters arrive, the dynamic range of the soundtrack is incredible. The entire soundstage just bursts in to life, with plenty of use of the overhead channels and massive amounts of bass energy to give the scenes greater impact. The ACT 4 handled this amazing soundtrack with real skill and authority.

Moving on to DTS:X soundtracks, the recent 4K Blu-ray release of Jurassic World delivers a great example of what the format is capable of, and the ACT 4 handled it extremely well. This is an active and immersive sound design, especially during the jungle scenes. There's also effective use of the overhead channels, with dinosaur sounds emanating from the trees above the protagonists. The sound designers make full use the bass to give the dinosaur roars a more visceral impact, but within all the action and effects the dialogue remains clear and focused.

The ACT 4 includes the Dolby Surround and DTS Neural:X upmixing algorithms and using the 4K Blu-ray of Dunkirk, I was able to compare the two. Both delivered the impression there were overhead channels, even though I know the 5.1 soundtrack obviously wasn't mixed that way. As a result I felt engulfed by sounds, whether it's the rattling inside the Spitfire cockpits or the troop ship filling with water as it sinks. It's entirely up to you which of the two you choose, and if you have a 7.1.4 set-up it really doesn't make any difference, but if you have a 7.1.6 set-up then you might prefer to use Dolby Surround because it will make use of all the channels.
The performance is superb, with detailed audio, precise steering, and plenty of bass



  • Great sound quality
  • Dolby Atmos & DTS:X support
  • Easy to set-up and operate
  • Attractive design & solid build


  • Limited to 13.3 channels
  • Lacks automated room EQ
  • Expensive

Acurus ACT 4 AV Processor Review

The Acurus ACT 4 is a well designed and cleverly thought-out multichannel AV pre-amp and processor. It's attractively designed and solidly made, with a large touchscreen display that makes installation and control highly intuitive. For such a sophisticated product, the set-up is extremely easy but the lack of any automated room EQ is surprising at this price point.

There's an excellent set of connections that includes 8 full-fat HDMI inputs and two HDMI outputs. There's also extensive analogue and digital inputs, and a complete set of RCA and balanced XLR outputs. The ACT 4 can decode both Dolby Atmos and DTS:X, but although it can process 13.1 channels and handle 7.3.6, if you choose width speakers it is limited to 9.3.2.

Another strange omission on the part of the ACT 4, is the lack of any automated room EQ system. While it's true that the set-up and installation is surprisingly simple, with the levels and delay settings requiring no more than a tape measure and an SPL meter, things do get a bit more complicated when it comes to analysing the acoustical characteristics of the room. To do this you're going to need to use a third party software, and have a reasonable understanding of room dynamics.

It's worth the effort though, because once set up the ACT 4 sounds superb with both movies and music. This is an exceptionally capable processor that can decode and render object-based audio soundtracks with remarkable precision. The soundstage is wide, open and cohesive, with good tonal balance, plenty of bass and a great sense of immersion. Dialogue, effects and score are delivered with real panache and the result is a marvellous sense of envelopment.

If you're looking for more channels of processing, especially the full 9.1.6 Dolby Atmos configuration, then you'll need to either buy the Acurus ACT 4-20 at £13,500 or consider another processor like the Trinnov Audio Altitude16. The Altitude16 costs £13,000 and also includes Auro-3D support, along with incredible set-up flexibility and the most impressive room EQ capabilities of any processor I've ever reviewed.

The Acurus ACT 4 is definitely a great product and worthy of a Highly Recommended badge, but the Trinnov Altitude16 with is Optimizer and re-mapping capabilities remains the high-end processor to beat.


Sound Quality






Build Quality


Value For Money




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