PMC Twenty5 / Twenty5i Active Module Review

What's an active loudspeaker?

A passive loudspeaker has a power amplifier connected to a set of components inside the speaker cabinet that separate the music frequencies between the drivers. These components are unpowered and sap power from the musical signal - typically they need to be quite large components to cope with the power flowing through them which leads to lower levels of accuracy in their manufacture and performance.

Done properly, like this option from PMC, an active loudspeaker means a set of powered crossover components fed from a pre-amplifier which send the split signal to a power amplifier dedicated to each driver in the loudspeaker. The powered crossover components deal with low power signal levels so can be manufactured more accurately and better quality crossover designs are possible. Sometimes the powered crossover and power amplifiers are external to the speaker, sometimes internal and in the case of the PMC Twenty5 and Twenty5i conversion they're a module which fits into the back of the cabinets, directly replacing the standard passive crossover panel.

Above I say "done properly" because some manufacturers (usually in lower priced products) call a loudspeaker active when really its just powered by an internal amplifier that drives a standard passive crossover.

So what are PMC up to with active modules in the Twenty5 and Twenty5i speakers?  The first of the Twenty series speakers were called just that - the Twenty range and they were launched to celebrate 20 years of the company.  In the domestic audio market I would say that this was the range of speakers that turned PMC from a respected but relatively little known manufacturer into a much higher volume well known brand.  Five years later they launched a replacement range called Twenty5 which had different cabinets across the board and then a couple of years ago these were tweaked into the Twenty5i range.

The Twenty5i range consists of a very small 2-way standmount 21, a large 2-way standmount 22, a slim floorstanding 2-way 23, a larger floorstanding 2-way 24 and the range topping (far more impressive as a performer) 3-way 26.  More details at PMC.

What's in the box?

There are 2 options here - you can buy a Twenty5i 21, 22, 23 or 24 speakers with the active module already fitted into the speaker in place of the passive crossover, or, if you already have Twenty5, 21, 22, 23 or 24 or Twenty5i 21, 22, 23 or 24 passive speakers you can buy the active module to be retrofitted by the dealer.  If buying a brand new speaker the active version is approx. £1500 more than the passive equivalent.  As a retro fit to an existing speaker the cost is around £1800.

Note that only 2-way speakers are currently covered by the active module.  The Twenty5 and Twenty5i 26 3-way speakers and the C centre channel are not included at the moment (even though the C is a 2-way design - I would speculate that there isn't room in that cabinet).  It seems that there's no current plan to add these models.

Demo

In the interests of transparency, I've not been a fan of the Twenty / Twenty5 / Twenty5i models with the smaller bass driver - ie the 21 and 23 models, even though its the 23 that's the mainstay of sales.

The demo system featured 2x pairs of Twenty5i 23.  Front end source was a Linn Selekt DSM streamer with the Organik stereo DAC module (approx £10k).  Output from this was fed to an ATC CDA2 combined CD player / pre-amp acting as a pre-amp (approx £3k).  The passive version of the speakers were driven by a Linn Akurate 2200 stereo power amp (approx £3.4k).

Our host played 3 tracks on the passive system - "Hey Laura" by Gregory Porter, "Here Comes The Sun (2019 version)" by The Beatles and "Happiness Is Easy (12" Mix)" by Talk Talk. Resolution is good, bass weight is fine for the size of the speaker but it feels a little "lazy". This is the main characteristic of the 23 models that I find to criticise - it just doesn't boogie, the music doesn't drive the along the way you might hope for a £4.5k speaker. Vocals are nicely resolved and have the emotion you'd hope for but are a little polite and recessed in the mix.

We get the first couple of minutes of Talk Talk again and then we swap from the passive system to the active system - the speakers now being directly connected to the pre-amp and the Linn Akurate power amp gets to rest a while. The speakers were positioned in the same marked location in the room (more on this later) and we went straight back to Talk Talk.  It only takes half the track to hear the differences the active conversion brings.  Everything is much more clearly presented - treble is tidier - bass is fuller and vocals stand clearly in the mix. Any downsides?  Probably not. The only downside we discussed between us was that perhaps the bass was a little too full - to be fair it would probably be worth experimenting with room positioning as this is a significant system change at play.  Remember here that we're looking at replacing a £3.4k power amp with a £1.8k active module.  That's not to say the Linn is a poor amplifier, its a testament to how fundamental it is to move the crossover from sapping power in passive mode to replacing it with far more accurate circuits in front of the power amp.  And I've saved the most important change to last - each driver has its own power amp and they are connected directly together - no power sapping passive components getting in the way.  And that will be part of the biggest improvement this option brings - the starting and stopping of the notes is in a different league, as is the impression of the music driving along - there's pace, dynamics and enthusiasm.  But its not aggressive nor wearing - we listened to another hour's worth of music and it was far more enjoyable - foot tapping in action.  It made a big difference to enjoyment of the music.

Conclusion

So no hesitation in saying this is a significant improvement on passive - and in this comparison, significantly better value for money.

Oh, and I've now heard a 23 I can enjoy :)

Thanks are due to Rob and Phil at Adventures in Hifi, Chester for the demo.  I'm sure they'll be happy to offer a similar demo for you.

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:

http://audiophilemusings.blogspot.co.uk/2013/09/exakt.html

http://audiophilemusings.blogspot.co.uk/2013/09/exakt-photos.html

http://audiophilemusings.blogspot.co.uk/2013/09/more-exakt-info.html

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:

Part Two

Part Three