The BGW Subwoofer Advantage
By Joe DeMeo
Sales Manager, BGW Systems

Sound systems for cinemas have come a long way in a relatively short period of time especially with the fairly recent advent of digital audio. These digital audio systems enable theater patrons to experience the soundtrack from a movie in a way never before realized. We've all been to a movie where we've been physically "moved" by the soundtrack itself, whether it be recent blockbusters such as Lost World, Twister, Volcano, Batman & Robin or older ones such as the Star Wars Trilogy. These sonic sub-woofer frequency "experiences" lend a high degree of realism to the movie itself and usually leave the patron with a strong sense of actually "being there". Along with the actual digital audio playback systems themselves, the amplifier/speaker/processor chain has also been affected and now must comply with the sometime heavy demands placed on them by the movie soundtrack in regards to explosions, dinosaur roars, gunshots, etc.

A few years ago, BGW Systems Inc. of Hawthorne CA, (a supplier of audio power amplifiers to cinemas for over twenty five years, starting with Unversal Studio's award winning Sensurround) recognized the need for a stronger, more comprehensive sub-woofer system for theaters. Reports received were that many older theaters simply did not have the capacity in their sound systems for the accurate reproduction of these sub-woofer frequencies generated by the current blast of high octane movie soundtracks. Working to satisfy this need, BGW set out to design a sub-woofer system that could not only accommodate current theater needs but the needs of ones built far into the next millennium. The results were the BGW M2200 and M1100 Self Powered Subwoofer Systems.

The BGW M2200 and M1100 Self Powered Subwoofer Systems are a combination of amplifier, speaker cabinet and related signal processing in an all in one "plug 'n play" unit that work together to provide accurate and highly formidable sub-woofer frequency reproduction. The M2200 utilizes four 15" drivers with a power output of over 2200 watts, while the M1100 utilizes two 15" drivers putting out over 1100 watts. Working closely together with a reputable speaker manufacture and cabinet designer, BGW was able to define the technical parameters that would result in the manufacture of a unit that would satisfy the theater owner's sub-bass needs.

BGW chose its' GTA - Grand Touring Amplifier - for the basis of the power supply for the M2200 and M1100. The GTA is a 78 pound amplifier with a stored energy capacity of 340 joules and a power output of over 2200 watts in bridged mono mode (over 3 horsepower). Two of these GTA modules are utilized in the M2200, one in the M1100, which are all housed in a custom 144 cfm, servo -controlled fan enclosure. The speakers used in both models were custom designed especially for these units. Each 15" driver uses a 4 ohm, copper edge would voice coil rated at 600 watts each which match the available amplifier power of 1400 watts IHF per module. Two speakers are driven in parallel from each GTA module in order to optimize the amplifier to speaker power transfer. A special rubber surround and rugged spider result in exceptional excursion capability. The M220 enclosure is fabricated using 1" MDF composite, with 2" MDF forming the baffle, while the M1100 uses Baltic Birch plywood. Generous porting reduces distortion and power compression while ample internal bracing further stiffens the enclosure and eliminates resonance. The entire amplifier/processor assembly is housed in a separate chamber on the recessed back panel. For safety, protective corners and 14 gauge steel speaker grills are included on both models.

Internal signal processing and protection features differentiate these units from conventional systems. The processor board common to the M2200 and M1100 includes a clipping eliminator circuit, excursion limiter circuit, additional limiter circuit and fixed high pass and adjustable low pass filters. The clipping eliminator circuit prevents square waves from reaching the speakers and causing voice coil overheating, the circuit is capable of handling input levels of up to 16dBm. The excursion limiter integrates the voltage applied to the speakers during each musical transient and reduces the gain instantaneously once the speaker's excursion limit is reached. A fixed frequency high pass filter is also used to prevent out of band (subsonic) signals from reaching the drivers and damaging them. An additional limiter circuit is added before the filters which prevents excessive signals from reaching the filters and destroying their bandpass characteristics. Lastly, in order to easily integrate these units into a wide range of additional speaker systems, a choice of user switch selectable adjustable low pass filter frequencies from 63-180Hz on 1/6 octave ISO centers are included on the panel.

Installation of the THX approved M2200 and M1100 is simplified through the use of XLR summing amplifier inputs. The hook up is made directly from the digital audio processor. Both units also include a high powered relay for remote control of system power. However, many theater users prefer to simply leave the units on behind the screen as they draw very little current when idle. With the elimination of long speaker cables between amplifier and speaker cabinet, high damping factors are preserved and power loss in cabling is eliminated.

When the M2200 was introduced to the market, Iwerks Entertainment, a major designer/installer of 70mm simulator "attractions", held a subwoofer "shootout" to determine the best possible subwoofer cabinet to meet their needs. Many major manufactures of both power amplifiers and subwoofer cabinets attended and the results were verified by an independent local sound company. After the smoke had cleared (literally!) the M2200 had outlasted the competition and was determined to be the best value for the price. Henceforth, Iwerks has been using two M2200s for every one of their large scale world wide theater applications. Many other major theater chains such as Century, Edwards, General Cinemas, Cineplex Odeon, and Manns are currently utilizing either the BGW M2200 or M1100 or both for their newer screens as well as in the upgrading of older screens. Twenty nine of the BGW M2200s will be utilized in the upcoming Century Theater Promenade 25 screen megaplex in Orange County California due to open by years' end which will be the worlds largest all THX screen complex. Based on a performance and price standpoint, the BGW M2200 and M1100 Self Powered Subwoofer Systems represent an enormous value to theater owners and one that helps in providing a complete and positive movie going "experience".