There’s a limit to your love. So sings dubstep crooner James Blake before his song’s sub-bass wobble. It goes l o w – can your loudspeaker keep up? Blake’s “Limit To Your Love” is a soulful way to evaluate the bass output/quality of your loudspeaker.
Pushing dynamic driver designs’ bass extension in a southerly direction are France’s Devialet. The Expert Pro‘s (née Expert) Speaker Active Matching (SAM) correction utilises internal digital signal processing (DSP) to extend the connected loudspeaker’s low frequency mining but without the (bass) driver hitting its excursion limit (XMax) and perhaps meeting an untimely demise. Protection is executed in real time.
Each loudspeaker is measured, mathematically modelled in software, optimisations applied and a corresponding SAM profile created. This profile is then made available via Devialet’s web-based Le Configurateur and installed to an Expert/Pro using an SD card.
At SAM’s launch in 2014, the loudspeaker measurement process took place at Devialet’s Paris headquarters. It also took a while. Loudspeakers were shipped in and out of the HQ’s SAM Lab. The public were invited to vote for their favourites. Any loudspeaker attracting over one hundred votes was added to the SAM measurement priority list.
A year later, the SAM Lab was rendered portable – ergo SAMlab. Connected directly to the rear of any Expert/Pro, the ‘gold brick’ SAMlab box serves as an interface between the amplifier, the loudspeaker and bespoke measurement software. Engineering staff could now travel to the loudspeaker instead of the loudspeaker travelling to them.
This in turn led to SAMlab loudspeaker measurement tours in which an engineer would be dispatched in order to create as many new SAM profiles as possible. Speaker supply would come from dealers and their customers.
I joined a Sydney stop on this SAMlab tour of Australia at one of the city’s most prestigious dealers: Len Wallis Audio in Lane Cove. Here I met with Yann Wachten, Australia and New Zealand Area Manager – he introduced us to L’Original D’Atelier in Melbourne last November – and SAMlab engineer Maxime Dumont, who led the speaker profiling charge.
Dumont took several hours to plug six or seven holes in the SAM profile database. Chief among them were two Australian loudspeakers: the Axis Voicebox S from Sydney’s John Reilly and Brad Serhan, plucked from the shop floor, and the ML1 Reference from the Gold Coast’s Mike Lenehan, supplied by an Expert-owning customer.
Dumont hitched the SAMlab gold brick to the back of an Expert and connected its socketry to loudspeaker and Macbook. The modelling process for each model took around twenty minutes.
The process saw three measurements taken with frequency sweeps than ran from 1Hz up to 1kHz: firstly, an impedance plot (as a function of frequency) was read from the loudspeaker binding posts; then the mid/bass driver/s excursion (as a function of frequency) was measured by a laser, not a microphone; this laser was then used to ascertain the driver’s XMax in millimetres (usually 3 – 4mm but sometimes up to 7mm).
The trio of measurements were then combined in Devialet’s OS X software application to create a mathematical model of the loudspeaker’s behaviour. SAM optimisation was applied but only below 150Hz. Tweeters don’t feature in this story. Devialet’s intent with SAM is to increase the loudspeaker’s low frequency output without affecting the speaker’s audible personality.
Regular readers will recall how the DEQX PreMATE+ was used some weeks ago to confirm Devialet’s claim that KEF LS50 saw a bass frequency trouser drop from 45Hz to 29Hz once the SAM profile was applied.
Back at Len Wallis Audio, pre-SAM, the Axis Voicebox S bottoms out at 76Hz. Post-SAM, we get close to 36Hz. That not only spells superior bass wallop from James Blake but more weigthy satisfaction at lower listening levels.
The indirect repercussion of better bass handling is that some SAM users report a tidier midrange and better image focus.
It’s also worth remembering that SAM isn’t compulsory – if you don’t like it, you can keep it turned off; or dial in a preferred percentage. If your loudspeaker has yet to be measured, it’s Hobson’s choice.
Want a deeper detailing of the SAM measurement process? The following video takes us further into the SAMlab process than the written word. This one’s a whopping 18 minutes long, no interval, and possibly exceeds the limit to your love (for web videos). Refreshments are therefore advised.