Copyright 2009 BG Radia Igor Levitsky, VP of Research and Product Development 1 Why using multiple subwoofers in a room is the best solution for ultimate bass

2 Copyright 2009 BG Radia ROOM IS IMPORTANT COMPONENT OF AN AUDIO SYSTEMROOM IS IMPORTANT COMPONENT OF AN AUDIO SYSTEM Subwoofer in free field – ideal case Direct sound only Single subwoofer in room – real case Positive polarity Negative polarity 0dB 6dB -6dB -12dB SPL Standing waves in a room with rigid reflective surfaces Direct sound plus room resonances Two nearby listeners hear different bass

3 Copyright 2009 BG Radia Real-life exampleReal-life example LF frequency response in authors room with color coded seating positions and corresponding graphs 0 1/12 resolution, no spatial averaging, measurements were taken at each seat head position Applying EQ to green response (e.g.47Hz, 57Hz) would result in worsening conditions at cyan or magenta seat. It is clear that global EQ is impossible for one subwoofer - three seats system even if it is based on smart averaging. Such EQ has no effect on room modes since it is applied in global electronic domain.

4 Copyright 2009 BG Radia into something very different ROOM turns even prefect subwoofer Strong room resonances generate unnatural, one-note bass. Bass quantity ( total output) and quality (response smoothness) vary from seat to seat. What happens with bass in this room? For an action movie junkie put one or all subwoofers in a corner for maximum bass output. This will generate most of room modes BUT musical accuracy and seat to seat consistency of bass will be very poor. If there is only one listener who cares about sound and who will always sit in one position – one sub in the corner and use EQ. THREE MEASURES OF BASS PERFORMANCE IN ROOMSTHREE MEASURES OF BASS PERFORMANCE IN ROOMS Smooth and extended frequency response in a given listening position (+/- 3dB goal?) Minimal variation of response from seat to seat ( makes global electronic EQ meaningful and beneficial for multiple listener set up) System efficiency in 20-80Hz region ( overall total output or quantity of bass) These measures often are not correlated and sometimes even contradict (see below) ! An intelligent professional system set up is essential in choosing the best option for a a given customer. All three metrics must be considered and understood.

Foam/fiber absorbers located on room boundaries Not practical, not very effective at low frequencies Typical measures for room mode control and their shortcomingsTypical measures for room mode control and their shortcomings EQ + optimizing subs and listener positions for the best response Bass is different in each seat in the room. EQ works only for one seat. Acoustical or mechanical resonant absorbers (corner bass traps, panels resonators) Not always practical, difficult to tune properly, require tuning using hi resolution measurements in actual room 5 Copyright 2009 BG Radia Q. Is there a practical solution producing reliable results?Q. Is there a practical solution producing reliable results? A. Using multiple subwoofersA. Using multiple subwoofers The first step to a good bass is controlling room modes. For all other listeners who prefer quality of bass vs. quantity preferably in more than one listener position the solution is not as obvious. However it is understood that controlling room modes produces a better solution for such case

6 Copyright 2009 BG Radia 6 Room mode control with multiple subwoofersRoom mode control with multiple subwoofers Case A Single subwoofer Positive polarity Negative polarity 0dB 6dB - 6dB - 12dB SPL A B 1st order, SPL 8 Mode cancelled 2nd order SPL 68 3 rd order SPL 18 Mode cancelled Case B Two subwoofers Positive polarity Negative polarity 0dB 6dB - 6dB - 12dB SPL Odd room modes having opposite polarities at opposing walls are cancelled when using two subwoofers seat to seat SPL variation is dramatically reduced. Meaningful room EQ for multiple seats becomes possible. Seat to seat SPL variationSeat to seat SPL variation

7 Copyright 2009 BG Radia Starting points for multiple subwoofer locationsStarting points for multiple subwoofer locations An extensive research on multiple subwoofers [1] shows that for rectangular rooms and typical listening positions in the middle or at 1/3 of the rooms length several configurations produce good results in terms of all three measures related to good bass in rooms. These recommendations are valid for in-wall installation as well. Two subwoofers - recommended locationsTwo subwoofers - recommended locations These are general recommendations. You can also position subwoofers close to these locations for practical or other reasons. Use measurements for further optimization and validation. Use these two configurations only if your room measurements show acceptable results If room is not rectangular use measurements and try combinations of different corner or opposite mid-wall locations for best results.

8 Copyright 2009 BG Radia Four subwoofers - recommended locationsFour subwoofers - recommended locations These are general recommendations. You can also position subwoofers close to these locations for practical or other reasons. Use measurements for further optimization and validation. If room is not rectangular use measurements and try combinations of different corner or opposite mid-wall locations for best results.

9 Copyright 2009 BG Radia Real-life exampleReal-life example 1/12 resolution, no spatial averaging, measurements were taken at center seating position The effect of using multiple BGX-4850 in- wall subwoofer system. LF frequency response in a room with three configurations FASCINATING!

10 Copyright 2009 BG Radia References [1]Welti T T., Devantier A. (2006). Low Frequency Optimization Using Multiple Subwoofers, J. Audio Eng. Soc., 54, pp Call BG Radia at and we will be happy to help you to get the best sound possible for your project