Subwoofer Management System (SMS-1) Release 2.1.3
Release Notes
This document discusses the latest release of Velodyne’s Subwoofer Management System (SMS) firmware – release 2.1.3. This firmware addresses two issues related to the low frequency management of the SMS. First, it allows the subsonic filter to be set low enough that the only remaining rolloff in the low frequency is restricted only by the hardware, and secondly, corrects some distortion that previous versions of the firmware introduced to the audio spectrum.
Figure 1: SMS-1 Frequency Response
Please refer to Figure one. This graph shows actual output from the SMS-1 with the subsonic filter set to 5 Hz. The various curves shown reflect the subsonic filter as set to 6, 12, 18, 24, and 30 dB/octave -- the steeper the slope, the higher the subsonic slope setting. As you can see, the actual point at which the curves converge is 5 Hz, and at 5 Hz, the audio frequency is down about 5 dB. The typical 3 dB down point is about 8 Hz. This point is a limitation in the hardware and the low frequency response of the SMS cannot be extended any further without changing components in the hardware. In release 2.1.3 the subsonic filter can be set as low as 1 Hz., but any setting below 5 Hz. has negligible effect on the frequency response.
Note that the low-pass crossover in this example is set to the default of 80 Hz and 24 dB/octave.
Some users of the SMS measured the low frequency performance and discovered that the SMS was adding some distortion to the lowest frequencies. Most users did not notice this added distortion due to the low frequencies affected. The distortion was inadvertently introduced as the frequency processing software, which was based on Digital Drive subwoofers, was rewritten for the SMS. The 2.1.3 firmware corrects this problem.
There was some confusion that this distortion was also present in the DD series. This is not and was never true – the distortion was introduced in the SMS only, and has now been remedied.
If you have any questions on this information, please contact Velodyne customer service at
techhelp@velodyne.com.