"What a refreshingly honest blog about listening to music through hi-fi. So happy to see views based upon the enjoyment of music rather than so-called sound 'quality'." - Peter Comeau, Director of Acoustic Design at Mission / Wharfedale

Wednesday 8 June 2016

Linn Exakt and PMC Twenty.26. World First Review Part One - Background

Part One of a Three Part Review

Part Two Here

Sometimes, a technology arrives that makes the previous technology instantly seem hopelessly inadequate and it makes you wonder how we ever put up with the older version. For example, DVD picture quality compared to VHS video tape. Or the jet engine compared to the turbo prop.

I'm not one for hyperbole, but there's a chance that Linn's Exakt is nearly there, but the World doesn't seem to have noticed. Lets hope its not superior in the way Betamax was superior to VHS.

Let's wind back about 2.5 years and see where we go from there. Back then (Meridian's DSP series not withstanding), the normal way to improve a Linn system was to go active. Active, in Linn terms, used to mean taking the output from a pre-amp, splitting it into the appropriate frequencies for the drive units in the speakers, feeding that driver specific frequency range to a power amp and connecting that directly to the drive unit. This is more accurate than using big clunky passive crossovers found inside traditional passive loudspeakers. Everything else being equal (sources, amps etc.) Linn's active systems sound better than their passive systems.

But on their 40th Anniversary in September 2013, Linn launched Exakt - a very different architecture for active systems.  The launch event is reported here:




So what's different? Well, in a traditional system, using a CD or network player for example, the digital signal is converted to analogue in the player and is then analogue through the pre-amp, power amp and speaker crossover (either active before the amps, or passive inside the speakers). Exakt keeps the signal digital for longer, with a proprietary protocol connecting sources to the digital crossover called Exaktlink. So the combined network player and pre-amp (called a DSM in Linn speak) plays network and internet music, accepts digital signals from other digital sources and converts analogue inputs (such as a turntable) to digital too.  It then converts these inputs into Exaktlink format and passes the signal to be played along to either an Exakt processor integrated into a pair of active loudspeakers or to an Exaktbox which includes Exakt processing and digital to analogue conversions (DAC) to send information to a power amp dedicated to a single driver in a loudspeaker.

For the purposes of this post, I'm going to ignore loudspeakers that have built-in Exakt processors as they are unique to Linn.  Of interest here are the Exaktboxes as they can be software configured to drive Linn's extensive range of speakers both past and present and they can be software configured to drive speakers from other manufacturers too, which is why this is about PMC and not about Linn.

So, an Exaktlink digital signal is sent from a DSM to an Exaktbox. Exaktboxes are available in the usual Linn hierarchy of Majik - Akurate - Klimax. The Majik Exaktbox-i has integrated power amplifiers, the Akurate and Klimax Exaktboxes need external amplifiers. To simplify here, I'm going to write about the Akurate Exaktbox 6, a system that can support speakers of up to 3 drivers per speaker (2x 3 channels = 6 of the name). This is very relevant here as the PMC Twenty.26 has 3 drivers in each speaker. What does the Exaktbox do with the incoming Exaklink signal?  A number of things:
  • Splits the signal into its right and left components
  • The Exakt processor also applies phase correction which corrects for phase errors between drivers AND within each driver
  • The Exakt processor applies a time adjustment to ensure the music arrives in sync at the listeners ear
  • For each of right and left, that signal is then sent to 3 separate digital to analogue converters (DACs) - 3 for the right, 3 for the left
  • Each of those DACs is dedicated to one driver in one of the loudspeakers
  • Each DAC applies the correct filtering for its allocated driver
  • For Linn drive units in the Akurate and Klimax ranges, individual drive units are measured at build time and Exakt corrects for any errors found to bring left to right matching to levels not seen before, regardless of speaker quality and price.
  • The Exakt processor and bass channel DAC also apply SPACE Optimisation+ room node adjustments to the output of the bass channel, inserting sharp dips in the output volume at the frequencies where the listener's room is known to have bass "humps", hence flattening out the low end frequency response

The effect of the calculated frequency dips on the under 100Hz signal (no changes are applied above 100Hz) plus a little manual tweaking
  • Each DAC then applies the volume control level before finally converting all of this into the analogue domain and passing the signal along to a power amplifier that is dedicated and has a direct connection to the appropriate drive unit in the speaker.
So for a pair of PMC Twenty.26 loudspeakers, a 6 channel Exaktbox is required, along with 6 channels of amplification, and the removal of the standard passive crossover inside the speakers to allow the amps to be directly connected to the driver units.
The really key thing about how the Exaktbox operates is that it is configured by software, using Linn's Konfig application run from a PC or MAC attached to the same network as the Linn DSM. This means that the same Exaktbox process0r / multiple DAC unit can be software programmed to support any speaker that Linn has provided profiles for - from their own range, from the ranges of others and from speaker manufacturers who have developed Exakt profiles and submitted them to Linn. So upgrading speakers is now possible without upgrading hardware crossovers - just load up the appropriate profile for your speaker, connect up and you have your system amended to suit. Very clever. Konfig also allows the input of room dimensions, listening position, speaker position and building material types to allow for the correction for room bass nodes to be applied to the music and for the time of flight to the listen to be adjusted.

Entering room information into Konfig so the software can calculate where there will be bass humps in the room (there are many more dimensions to be entered not visible in this capture
In the Linn Konfig Software, selecting the appropriate loudpeakers from the drop-down list applies the correct profiles and filters to the Exaktbox
Right, if you've kept up with that lot, well done. Let's consider why Linn would support anything other than their own speakers. Surely this would impact on sales of their own speakers? Well I would suggest not. Linn speakers (with the exception of the Keilidh), probably don't sell in massive numbers, they appeal to a limited set of listeners (like lots of other speakers do too of course), and its fairly rare indeed to see Linn speakers used in non-Linn systems, whereas it is very common to see Linn electronics - particularly sources - used with all kinds of speakers from other manufacturers. Also, Linn probably see a market where they can massively improve the performance of other manufacturers speakers and generate a new group of buyers for Linn electronics. So it makes some sense to develop Exakt filters for third party speakers. There is also the possibility that a group of speaker manufacturers will see the benefits in Exakt making their speakers sound better and therefore make them stand out from the crowd - certainly Kudos have seen this benefit and grabbed hold of it very quickly.

Of course, modifications need to be made to these third party speakers to allow amplifiers direct access to each drive unit (although Kudos now include Exakt compatible connection options as standard on Super 20 and T-808), and that's the subject of part 2 of this review - how a pair of Twenty.26 speakers can be converted to work with an Exaktbox and multiple power amps.

So is this a game changer? Well back at the launch in September 2013 I have to say I was underwhelmed. Yes, I could hear some differences, but all that clever processing to correct phase errors, supposedly seamlessly integrate drivers and near enough correct all phase errors between and internal to each drive unit should really have been very obviously an upgrade. Subsequent demos of a variety of speakers (although, to be fair, mainly Akubarik and 350) over the following year left me uninspired. Enough to decide to look for non-Linn speakers (but ones supported by Exakt in order to keep options open). I auditioned Kudos Super 20 and PMC Twenty.26 speakers at home (both of which were on Linn's roadmap for Exakt) and settled on the PMCs as a major step up from my previous Linn Majik 140s. With Linn Klimax DS/2 streamer, Klimax Kontrol/1/D pre-amp and Klimax Twin/D power amp they were good, but eventually got a little tiring to listen to - more than 2.5 hours was too much.  So there was still some doubt about if they were right for the longer term.

What has changed since then? Well, I went to the launch of the Exaktboxes and Linn's lifestyle Series 5 speaker launch (these are Exakt only) in September 2015. It was a good event and some stuff was demonstrated that was interesting, but still didn't wow me in the way the technology is supposed to do. About 2 months later Linn quietly updated the Exakt filters for some of their speakers - a significant change to the way that they handle the bass roll-off and there was much excitement on the Linn forum about the effects of this change. This was the most obvious and major change on top of a gradual trickling out of small tweaks and changes.  An early 2016 visit to an integrated Exakt Akubarik owner in Canada allowed for lots and lots of listening to a system that was transformed. Now Exakt sounded significantly different and significantly better than the non-Exakt equivalent speaker. Instruments so clearly defined, located in 3D, no bass flabbiness, such clear highs and vocals with real texture and emotion. Suddenly, the technology seems to be delivering on the promise. Listening for 4.5 hours proved extremely enjoyable and not at all fatiguing. Was it launched too early? Have lots of people heard it once, were underwhelmed and never bothered again?  I don't suppose we'll ever know the answer.

Back in the UK I went for a visit to not-so-local Linn dealer House of Linn and had another listen to Exakt Akubariks, this time using the external Akurate Exaktbox and Akurate power amps to better simulate the way the electronics would work with PMCs. Initially I would be bringing the Majik 140s back into action as their Exakt filters were available at the time, whilst waiting for the filters for the PMCs. The plan was to run the Majik 140s whilst waiting, then find out if the PMCs could be tamed by Exakt when the filters were released. If not, the Majiks could stay a while longer, the PMCs could be sold on and I would save up for Akubariks.

Well going from Klimax electronics passively driving the M140s to Akurate level (theoretically one step down in the Linn hierarchy) was a big surprise. Driven by the Exakt Akurate boxes turned the M140s into something far better than I'd imagined. Faster, controlled, better imaging, tighter bass, quiet impressive. I would've been very happy to live with them whilst saving for the Akubariks. But then the PMC filters were released, but not the conversion kit to go with them. What to do? Wait? Take the plunge?  Check out part two:


  1. I was threatened with castigation (I think thats what Linn said) if I or anyone suggested Series 5 was a "Lifestyle" product. So watch your back (I think).

    On a serious point, although I have no interest in PMC speakers nor can I afford an Exakt system, I commend the effort you have put to producing this detail description. Well done. I commend to the House.

    1. Thanks for the feedback Bob, very kind of you. Whilst Linn might not describe Series 5 as a lifestyle product, perhaps it would be best to say they have a different balance of attributes which tips the balance towards looks over sound, relative to their price equivalent products from the "traditional range".
      Very much like Linn describe SPACE as "room optimization" rather than "room correction", perhaps Series 5 are aesthetically "room optimized" too :)

  2. Hello Neil followed your path and converted a pair of PMC twenty.26 Sound transformed but top end had an edge which became tiring. Bought a pair of Kef reference 3 and converted. Usual gains in performance and to my ears a much higher sound across the punchy deep controlled bass neutral mid and top end If you haven’t done so listen to these speakers the meta version offers big improvement at top end but not supported on Linn Exakt platform. Thanks for your very informative blog which gave me the confidence to do the two conversions

    1. Hi, thanks for the feedback. I assume you used Linn's own Exakt filters for your Twenty.26s? They followed the profile of the passive crossovers. The filters I use from speakerfilters.com are far more balanced and remove that aggressive top end. Glad you enjoy the KEFs. I've just moved on to PMC fact.12 and am using speakerfilters.com Exakt filters for those too.
      If you consider going to meta versions, you can reach me via speakerfilters.com and we can get some filters created for you :)