Krix MX20 “Wall of Sound” Impressions

Introduction

Krix is an Australian manufacturer based in Adelaide. They have been in business for 45+ years and have about 25 staff. Krix started out as a manufacturer of commercial cinema loudspeaker systems and their speaker system is installed in more than 6500 commercial cinemas.

Sound Diffraction and the Baffle Wall

Krix was the inventor of the baffle wall (see below for an illustration). Since then, other companies have started using the same concept for their own commercial cinema – and more recently home cinema – installations.

One of the issues of loudspeakers is that sound wraps around obstacles, including the speaker cabinet. We call this speaker cabinet diffraction. As the sound wraps around the edge of the cabinet, it does two things:

1. It acts as a secondary sound source beaming back towards the listener. If you have read any of our Audio Pro Guides, then you know that early reflections muddy up the sound by interaction with the direct sound. This secondary sound source acts just like an early reflection point without the sound needing to hit any other boundaries.
2. The sound wraps around the cabinet into the space behind the speaker and bounces back from the front wall. This reflected sound has a more obvious phase shift compared to the direct sound causing interference with the direct sound waves which show up as dips and peaks in the frequency response.

The solution? What if the sound is forced to travel along an “infinite baffle” along the front sound-stage, or as infinite as we can make it based on our room dimensions? Then the only interference would come from the room – as it already does – without the speaker cabinet causing its own issues. This can be enough for the sound waves to feel like they are launched at the same time and in phase – literally creating a wall of sound coming at you, as opposed to bouncing around the speaker cabinet and the front of the room first.

To help minimise interactions with the room, horns are used for the high-frequency driver to give a wide dispersion, but also minimise floor and ceiling interactions.

Krix’s MX Range

Krix decided to bring the same solution to the home using their MX range, which they unofficially call “The Wall of Sound”. It consists of 5 different models including the MX5, MX10, MX20, MX30 and MX40.

They differ in the sound pressure they are able to produce for a particular room size as below.

The below images have been taken from the MX5 & MX10 installation manual – property of Krix.

As you can see, the MX5 and MX10 are not engineered to play back at full reference level, but 3dBs below it. This is likely due to the high-frequency driver. The MX5, MX10 and MX20 all use horn-loaded tweeters. It’s only the MX30 and MX40 that use horn-loaded compression drivers. I am guessing that the MX20 has enough oomph or cooling for the tweeters to play back at reference level for extended periods and not fry them in the process. This is an educated guess as the MX10 and MX20 use the same 8″ midrange drivers otherwise.

Each MX “Wall of Sound” consists of 3 LCR modules and two passive subs.

The idea is that these units are installed behind the screen into an alcove, so the sound can run across the rest of the wall as it leaves the speakers. This way, sound can’t get behind the speakers and interfere with the direct sound.

Below is an example of what the speakers look like behind the screen.

Impressions of MX20

A friend here in Sydney had an MX20 installation until a few months ago. I say had because he sold his luxury home recently and unfortunately, at the sort of luxury we are talking about, it is expected that the home cinema comes with, whatever it cost. No bother, as he is downsizing, so needs a completely new setup. The MX20 might not quite fit.

Before the sale, he suggested we watch Dune (2021), which – we found out – has an amazing soundtrack. After making a few adjustments to his sub level on his Anthem AVR, which was up a tad high for my liking, we settled in to watch the movie. ARC was left OFF for the movie, so only speaker levels were calibrated with the Anthem.

His MX20 system consisted of the front 3 LCRs, 2 Subs as well as 2 Krix Phonix for surrounds, 2 Krix Atmospheric for surround backs and 2 Phonix on the ceiling for Atmos effects.

As soon as we started the movie, my jaw was on the floor. It was the first home cinema system I heard that actually sounded like a commercial cinema – if not better – without any sort of EQ at play.

The audio didn’t sound like it was coming out of speakers. It sounded like it was literally everywhere: in front, above, below and behind. In spite of having only side wall and back wall treatments, I didn’t feel like there were major room acoustical issues at play. The sound reproduction felt smooth and well-balanced.

The soundtrack was involving and the sound was just floating. Even though his room was quite a bit longer than wider and we were sitting at the back of the room, the sound didn’t have discontinuity from the front channels to the back channels. This is because the front LCRs literally filled the room with sound that was as tall, as wide and as deep as the room.

Upper and mid-bass especially sounded like it had real weight. This is the area that is the most difficult in home cinema sized rooms exactly because of sound diffraction coming to the party to ruin it. Since this is also the place we normally cross over from the mains to the subs, it’s an absolute nightmare to get right. Not here, though. The frequency response seemed smooth down to around 30Hz – more on this in a bit.

Comparison to My Own System

I decided to listen to the same soundtrack on my own system at home to hear the difference. The comparison is both fair and unfair.

1. I use Audyssey on a Marantz AVR, not an Anthem receiver
2. I had Audyssey ON, while we had ARC off for our Krix session
3. My speakers (Jamo D500) cost me a lot less than the MX20 + surrounds. They cost me around USD 8,000 less in fact.

However, there were my observations:

1. Even though my speakers are wide-dispersion, they are certainly NOT as wide as the MX20s. I need the support of the Front Heights to bring height to the front sound-stage
2. My surround steering felt a bit more precise, but that is likely due to having the same speakers in all speaker positions and having run room correction to fully timbre match them.
3. My system is absolutely compromised with having the centre speaker below the screen. If that wasn’t obvious until now, it is bloody obvious after this comparison. This will need to be resolved.
4. There is slightly more detail on my system. This is likely because my system is EQ’d to an inch of its life to achieve reference playback at any volume. Not having dynamic EQ can sound like the system has less detail.
5. My system IS struggling with the weight of the upper-bass and mid-bass, especially around the crossover frequency. This is likely due to phase issues around this region more than lack of output. Again, isn’t as obvious until you listened to speakers in a baffle wall.

Limitations of the MX Line and My Room

So there are a few limitations of the MX line that is worth mentioning.

1. The MX5 and MX10 are not supported for reference-level playback according to Krix’s documentation. It is true through that 105dB peaks are incredibly loud, especially in a small room, so not a huge deal. But you have to be aware.
2. None of the MX series goes down below 20Hz. In fact, they are quoted to go down to around 25Hz in-room. However, you need to apply very steep filtering under 30Hz for MX5 and MX10, under 25Hz for MX20 and under 20Hz for MX30 and MX40. This means you won’t have meaningful output under the filtering frequency.
3. Only the MX30 and up offers compression drivers, which are the gold standard of cinema sound. Now granted, those horn-loaded tweeters in the MX20 sounded very good.

Next Steps

We have decided to re-build the “Simple Home Cinema” cinema. We will build a baffle wall. We are considering whether we should go the Krix route, but the issues are as follows:

1. We only have 25cms we can dedicate to it in the room. Any more and the projection and screen distance is not going to work.
2. With such a limitation, only the MX10 can fit into the room. Firstly, the MX10 does not reach reference levels, and secondly, why settle for horn-loaded tweeters when you can have compression drivers on horns at this depth!
3. While the in-build subs are a great idea, I am not sure I’d be quite happy with a 30Hz cut-off. I’d need at least 20Hz, but preferably 15Hz.

So what is the other option? Well, build it of course – compression drivers and all. Over the next year, we will be designing and building alternatives until we come up with a design that will match and exceed the MX20 without infringing on any patents. We will therefore only use this as an inspiration for the build. But if successful, we will publish the plans so you can build them too.

We are shooting at MX30-level performance but at only 22cm depth with 3cms of play! Let’s see if we can achieve this, or we have to resort to using Krix. Stay tuned!