PNW AES Meeting Report - Subwoofer Array Listening Workshop

Subwoofer Array Listening Workshop
Presented by
The Pacific Northwest Section of the Audio Engineering Society
Hosted by Dan Mortenson, Dansound Inc, PNW Treasurer

How is the efficiency of a large array of subwoofers affected by changing the shape of the array?

That was the question driving a recent joint listening workshop presented by the Pacific Northwest Section of The Audio Engineering Society (PNW AES) and the Washington Association of Production Services (WAPS). Held on January 29, 2001 at Seattle's Paramount Theatre, the workshop let attendees listen comparatively to a variety of recorded program material through two different arrays at a time. Considerable effort was made by the coordinators to keep all variables constant except the shape of the array. Close attention was paid to such factors as the output level of each speaker, having a consistent number of drivers in each array (or nearly so - more about that later), having the same make and model amplifier driving each driver of each array, and having the same program material.

31 EAW SB-1000 subwoofers were available locally (from Carlson Audio Systems and NAF Productions), along with ample Crown MA-5000 amplifiers, so they were the speaker and amplifier of choice. Test program material was compiled on CD-R by workshop co-coordinator Rick Chinn, error-checked by Rick Fisher (RFI Mastering), played back on a Denon DN-680 professional CD player, run into the Paramount's resident Yamaha PM-4000 console, sent to a BSS Audio FDS-355 used as a router and low-pass filter, and then to the amplifiers. One output of the FDS-355 was also sent to the Paramount's center cluster of 2 Meyer MSL-4's, which were lowered closer to the stage and used to provide mid-highs, so the listening would be more pleasant.

On top of all that, we were provided with 4 of Rhino Acoustics' BassMaxx cabinets, each of which uses one Seismic Systems 8196 18" driver in a very large horn-loaded cabinet; these were connected to a single QSC 6.0 amplifier, and driven from another output of the FDS-355. The last output of the FDS-355 was sent to a Crown MA-3600 amplifier, which drove 4 Servodrive BT-7 subwoofers, provided courtesy of Servodrive and Jake Andreason. As icing on the cake, we also had a center array of 8 Servodrive BT-7's, with their own complement of 8 Unity TD-1's used as mid-highs for comparison purposes and interest. These were driven by more Crown MA-3600's, and received full-range signal from a matrix output of the PM-4000.

Sound pressure levels were calibrated and monitored using a very large digital readout placed on the stage and connected to an AudioControl Industrial SA-3051 RTA, set in SPL (unweighted) mode, with its microphone hanging from the center of the balcony. Additionally, 6 more AudioControl SA-3051's were set up around the auditorium, 5 unweighted and 1 A-weighted, so that participants could observe the effect of distance on SPL. Beyond that, electrical levels were monitored at the outputs of the FDS-355 (via Y connections) so that consistent signal level could be guaranteed at all times.

Program material consisted of pink noise, a variety of tone sweeps and bursts, music from a variety of styles (chosen for its LF content), and at one point, a recording of an SR-71 Blackbird military jet taking off and then breaking the sound barrier. The 125+ attendees were encouraged to walk throughout the theater to listen to coverage and tonality. To assist them in locating themselves in the coverage patterns, angularity markers were placed relative to the centers of each array, and distance markers were placed in the listening area. The Paramount has a 3000 seat capacity, and the back wall is about 130' from the stage. Ideally, this kind of event should happen outdoors or in a VERY large space, but with Seattle's weather being what it is in January, The Paramount was a dandy place for us, and we very much appreciated being allowed to use it. The 31 SB-1000's were divided up into a group of 16, and a group of 15, and those two groups were used to create the arrays to be compared. (Why a group of 15? More below.) General array types which we planned to examine were: vertical line array, horizontal line array, and square (4 box by 4 box). There were variations within each type: 8 box vertical line array in the air vs. 8 box vertical line array stacked onstage; 16 box vertical line array vs. 16 box horizontal line array; and 8 box horizontal line array stacked on stage level vs. 8 box horizontal line array stacked on floor level. Low wattage clamp lights were placed near each array, and connected to a controller at the mix position, so there could be a visual indication of which array was in use at any given time.

Event coordinators and planners arrived at 10am (the event started at 7:30 pm) to begin the setup, with the able assistance of the Paramount's 4-man stage crew, and sound operator Mark Anderson. The first project was to examine each cabinet individually to be sure that all drivers were functioning and in polarity. As the first boxes were completed, they were assembled into the vertical array using a chain motor to lift. It quickly became apparent that the 16 box vertical array would be taller than could be safely configured (even with the SB-1000's unique end-loaded drivers making for a larger footprint than normal front-loaded boxes), so we decided to go with a 15 box vertical array. Even so, it was 26.5' tall, and made a very impressive display. The array was electrically split into two separately-controllable groups: the top 8 boxes and the bottom 7 boxes, so that we could hear that difference (it was decided by the coordinators that 7 vs. 8 was the best we could do, and was announced as such).

The other 16 SB-1000's were put into a 4 x 4 array, and at the right time, that array was broken up and turned into the horizontal arrays. While the stagehands were reconfiguring the arrays, David Lee of Rhino Acoustics gave a description and listening test of the BassMaxx speakers, using the same program material as used through the other arrays. The second time the arrays were reconfigured, Chris King, representing Servodrive, described the Servodrive transducers and played the same program material. After an intermission, we listened to the BassMaxx compared to the Servodrive, and also to the large array of Servodrive and Unity loudspeakers. Discussion followed.

How did it all sound? The event was set up so that each person left with their own impressions, and no official consensus was to be solicited or reached. You should've been there!

Thanks to: AudioControl Industrial (Tom Walker and Dennis Griffiths), Carlson Audio (Mark Carlson, Jonathan Stoverud-Myers, Allan Bagley), NAF Productions (Mark Naficy); Uneeda Audio (Rick Chinn); Dansound Inc. (Dan Mortensen), Northshore Marketing (Lew Barrett), Servodrive (Tom Danley and Brad Skuran), Rhino Acoustics (David Lee), UCI and www.live-audio.com (Dave Stevens), and especially the staff and crew of the Paramount Theatre and Seattle Theatre Group (David Allen, Mark Anderson, Mike Miles and the hands).

Especially notable were the attendance of Christopher Whitt from Newfoundland, Canada, and Josh Millward from Iowa, who participated (with others) via live-audio.com in the planning for the event.