Gandhi wrote: > Interesting. I have read the PDF files and must say that most of his > points och conclusions are quite surprising to me. It's not how I have > interpreted other sources. I'm not questioning him, he seems to have > done his homework, I'm just surprised. His views are also very strong.
It's hard to answer your concern without more specific information (what specific sources are you referring to, what contradictions you are encountering, and so on). Regarding his strong views, I know what you mean. It seems to be a quirk of his style that when asked a question, he will answer unequivocally. I've found that if asked a follow-up question to test just how strongly he holds these views, he will often equivocate. Gandhi wrote: > Do these views represent common knowledge? These are somewhat new developments. There are other workers in the field who have reached similar conclusions, with products based on them. Harman seems to be active in this area. Todd Welti and Allan Devantier of Harman wrote an article a while back called "'_Low-Frequency_Optimization_Using_Multiple_Subwoofers_' (mkloudspeakers.com/pdf/todd-welti-white-paper.pdf)", which is worth a read. The basic idea is this. Let's say you already have a multi-sub system, and you measure the bass response at multiple listening positions. If you use EQ that's common to all subs, it causes the same change in frequency response at all listening positions. So it cannot improve the variation in frequency response with position. If individual gain, delay and EQ are provided for each sub, then it's possible to control how the subs interact with one another as a function of listening position to reduce the variation of frequency response with position. Welti and Devantier describe a technique they call Sound Field Management (SFM) which is now used in the JBL Arcos product, a super-expensive system not really accessible to most people. Here's how part of it works. They define a statistical measure called Mean Spatial Variance (MSV), which is a measure of how much the frequency response varies with position in the bass region. The software uses an algorithm that adjusts on a per-subwoofer basis the gain, delay, and the parameters of one PEQ per sub to find the configuration that minimizes the MSV, independent of what the resulting frequency response is. Then they use global EQ to clean up the non-flat response. This is all described in their paper. An earlier attempt by Harman to accomplish a similar goal was in a product called BassQ. It did not use SFM, but rather the so-called matrix inversion technique also described in the paper linked above. Here's a '_review_of_the_BassQ_' (http://www.avsforum.com/forum/90-receivers-amps-processors/1163240-jbl-bassq.html#post16916242) by Roger Dressler of Dolby Labs. Geddes uses a different approach. One reason is that Harman's approach is patented, so he's trying to avoid getting caught up in that. Also, Geddes is concentrating on getting equivalent results with commonly available low-cost EQ hardware, such as the Behringer DCX2496 and miniDSP. Not sure if I answered your question, but my goal was to provide more technical justification (which seemed to be at the heart of your question). These issues seem to be explored more in the AV realm than the two-channel audio world. ------------------------------------------------------------------------ andy_c's Profile: http://forums.slimdevices.com/member.php?userid=3128 View this thread: http://forums.slimdevices.com/showthread.php?t=101723 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
