The LS1s-dmf is a technological marvel. By applying ‘Digital Motional Feedback’, a control technology from the renowned Dutch high-tech industry, it became possible to achieve exceptionally low levels of distortion and full dynamic control. With an LS1s-dmf added for the bass frequencies, the LS1 system offers low distortion over the full audio band and redefines the term ‘transparency’. This is bass control like you’ve never experienced before.
Digital Motional Feedback offers bass control like you’ve never experienced before.
At frequencies below 100 Hz loudspeaker drivers need to move a vast amount of air and therefore have high excursion levels, while also the fundamental resonance - which is present in any loudspeaker - induces unwanted delayed effects. The result is that all conventional loudspeakers exhibit a rising distortion in the bass region with additional “thickening” of the bass by the resonance.
In electronics, feedback is used to minimise distortion. To apply feedback in electro-mechanical systems like an active loudspeaker, an acceleration sensor needs to be mounted on the cone to monitor its motions. This so called “Motional Feedback” technology has been presented a few times before in history but the precision and control as found in the Grimm Audio LS1s-dmf is unique. By adding smart digital processing and current drive, the low distortion of the already high-performance aluminium Seas woofer is further reduced by as much as 30 dB, solving all problems that are related to low frequency resonances and distortion.
"The LS1-DMF covers the frequency range where control is most needed"
Rob Munnig Schmidt, RMS Acoustics
The LS1s-dmf subwoofer was developed in cooperation with Rob Munnig Schmidt, who worked at Philips and ASML and was professor at the Technical University Delft. Rob explains his design motives:
"Being lifelong fascinated by precision control of motion systems and sound reproduction I never was happy with the unbalance in audio design between electronics and mechanics. On one side designers do everything to reduce distortion in electronics by means of feedback to almost unmeasurably low levels, while on the other side the real music is reproduced by electromechanical structures, called loudspeakers, without any control of their behaviour. Although many people agree that the loudspeaker is one of the most determining factors for the quality in an audio chain, strangely enough people accept that all loudspeakers have a well distinguishable character due to resonances, non-linearity, diffraction etc.
For this reason I immediately said yes when Grimm Audio asked me to design a motional feedback version of their LS1s subwoofer with a digital DSP controller, based on my experience with this principle. It covers the frequency range where control is most needed, the low frequencies around the fundamental resonance. By applying a sensitive acceleration sensor with low distortion on a rugged and powerful driver the real sound output is controlled such that the resonance disappears and distortion is significantly reduced. The effect is readily audible by its clean and dry bass where a base drum with damping blanket really gives short well controlled bumps, while organ tones to even below 20 Hz are reproduced faithfully such that you feel it rather than hear it. It is so rewarding to see people who hear the new DMF sub show real surprise when realising how much better bass reproduction can be."
Rob Munnig Schmidt