Factory Direct: Inside Community T-Class Loudspeakers
Bucking the line array trend with a maximum utility approach

By Bruce Howze

This Factory Direct was submitted by Community. Live Sound makes every effort to eliminate any use of marketing inspired hyperbole.

 

Community’s new T-Class Series loudspeaker systems were primarily designed for the regional hire sound market. My intention was to design a loudspeaker system that would provide the maximum utility and maximum financial return for regional sound companies.

To accomplish this goal I felt that I needed to design a system that could deliver exceptional acoustical performance in a very wide range of venues. This new system would need to be extremely flexible so that it could address the great variety of tasks that a regional hire company is faced with.

The system would need to address each one of those tasks not just adequately, but in every case do the job so well that the company’s clients would be delighted with the result.

In my view, a speaker system of this type is a major tool for a hire sound company. It‘s also a major investment, and to be a good investment it must enable the company to be very competitive in their market, to operate profitably and to grow their business in smooth and logical steps.


TFR64 (left) and TFR31 mid/high horns, offering swappable choice of patterns.

DEFINING THE CRITERIA

My design process commenced with a defined list of goals:

Design Goal 1: Success-fully address the wide variety of jobs that comprise the work of a regional sound company, the speaker system must be easily configurable into an almost infinite range of forms. Whereas large national sound companies can be successful with speaker systems that only work for large venues such as arenas and stadiums, regional sound companies need a speaker system that can equal the performance of the national sound company in the arena one night, but the next night be broken down into something like five separate club systems and maybe one system for a corporate product launch.

To achieve this flexibility the new system would need some means of altering the coverage patterns of the individual cabinets. The primary difference between cabinets that perform well in a large array and those that are suited for a small system is coverage pattern. Small systems typically require wide coverage from single cabinets. Those same wide pattern cabinets in a large array would perform very poorly, causing severe pattern overlap and interference between adjacent cabinets.


Two T-Class loudspeakers, under cover, meeting the goal of easy transport.

Large arrays work best with elements that have narrow patterns, and typically large arrays require separate long throw and short throw cabinets, ideally with different coverage patterns and possibly different driver compliments as well. The new T-Class system should readily provide all of these coverage patterns, and several more as well.

Design Goal 2: The acoustical performance of the new system must be excellent at all times and in any of its configurations. Convenience and versatility are not substitutes for sound quality. The sound company is aware of the benefits of the system’s versatility as it relates to them, but all the client hears is the sound level and sound quality, and that had better be “spot on” every time for the company to be successful.

To achieve this sound quality the new system would need wide frequency range, excellent projection ability, and extremely high output capacity at low levels of distortion.

Design Goal 3: The system must be convenient to transport and convenient to use. The individual cabinets should be of a size that can be handled by two people. It would be desirable if all of the various cabinets that make up the system could be of the same size. Rigging of the system should be quick, versatile, and reliable. All of the accessories necessary to transport and rig the system must be available as part of the complete system package. The hire company should not be spending its time to design and fabricate the hardware necessary to make the system do its job.


TFR cabinet interior with 12-inch woofers and mid/high section.

Design Goal 4: The speaker system should be able to grow with the company in manageable and practical steps. The system should function effectively for a hire company that begins with only a few boxes, but it should be able to grow as the company grows and never become outmoded or obsolete. A system of this type must be a good long term investment.

Design Goal 5: To be a good investment, the system must also be cost effective. Too often tour sound systems are priced beyond the reach of many hire companies that can use them. Good tour sound speakers will not be cheap, but they do not need to be overpriced. The system should not only provide excellent performance, it should do so at a cost that is not out of the reach of its intended market.

SIZE DOES MATTER

One of the first steps was to decide on a cabinet size. The cabinet would need to be large enough to perform well and provide good pattern control when used alone, or in arrays of only a few units, but it should not be too large or heavy for two people to carry or set up. I settled on a cabinet with a face approximately 25 inches square and a depth of about 33 inches.

The cabinet would (of course) be trapezoidal. I selected a 22.5-degree pitch angle, which is typical of Community cabinets and has seemed to work well. This cabinet size would be large enough to permit the full-range TFR loudspeakers to be fully horn loaded, and would also be a suitable volume for the single 18-inch direct radiating TSS subwoofer, thus fulfilling the requirement of having a single cabinet size for all elements of the system.


TSS subwoofers, 18-inch loaded and sized identically to the main loudspeakers.

The next step in the process was the detail design of the full range systems. I decided to rely on a general format that had been very successful in another Community product, the R2. This format is a three-way horn system with a pair of 12-inch drivers in the low end. Cabinet and throat dimensions would permit the low-frequency horn to have a flare rate slightly below 60 Hz, which would give good horn performance down to 65 Hz or 70 Hz with multiple cabinets.

The mouth of the LF horn would be large enough to accommodate a coaxially mounted mid/high horn section which could operate comfortably down to 500 Hz or 600 Hz. With a crossover frequency that low, the mid/high section would govern the pattern of the full range system. This proved to be the key to the goal of system configurability. If the mid/high section was the element that set the coverage pattern of the full range cabinet, all I had to do was make it very easy to swap mid/high sections and the pattern of a full range cabinet could be changed at will.

The only requirement would be that the hire company stock an assortment of mid/high horns in addition to their full range cabinets. Because these mid/high horns would be relatively small and relatively inexpensive, the need to inventory a few of them would probably not be terribly burdensome.

THE DRIVER DEBATE

Driver selection for the mid/high section was fairly simple. Our M200 driver was the natural choice for the mid range horn. The M200 is a low-compression ratio, low-distortion two-inch throat midrange driver capable of very high performance in the 400 Hz to 4000 Hz frequency range.


A look at T-Class flybar module and joiner plates.

For the high-frequency section I decided on the UC-2, a newly developed two-inch throat high-frequency driver. The UC-2 employs a non-metallic ring-shaped diaphragm and is capable of very high output levels without the sort of metallic diaphragm breakup commonly associated with two-inch throat high-frequency devices. The combination of the M200 and the UC-2 gave me exactly what I was looking for in terms of high output capacity at very low distortion levels.

Because the mid/high sections in TFR cabinets can be easily swapped, there was a temptation to develop a broad assortment of coverage patterns. I seem to have succumbed to this temptation, and we are now up to nine mid/high sections. The assortment can be broadly divided into two categories, those intended for use in arrays and those best suited for individual use.

Beyond their intended applications in tour sound, TFR cabinets are also expected to be employed in distributed systems at large sporting venues. In distributed systems each speaker is required to cover a zone of the audience, and the optimum patterns are often quite different from those that work well in arrays. For distributed systems, TFR mid/high sections offer two asymmetrical patterns that provide both long-throw and short-throw performance in a single device.

Additional patterns best suited to distributed systems include a 50-degree by 20-degree unit employing dual midrange drivers to provide maximum vocal performance over long distances, and also a 70-degree by 70-degree unit and a 90-degree by 40 degree unit providing wide-angle, short-throw coverage.


A scalable PA.

Mid/high sections designed for array use have either 30-degree or 60-degree horizontal coverage. The 30 degree units are designed to be close packed, and the 60-degree units are intended to be alternated with TSS subwoofer cabinets. There are two 30-degree models, a high intensity long throw unit employing two HF drivers and providing only 10 degrees of vertical coverage, and a 30-degree by 40-degree asymmetrical unit that has a vertical pattern that is 0 degrees above axis and 40 degrees below axis.

There is also a 60-degree by 40-degree model with this same asymmetrical vertical pattern, and also one with a symmetrical 20-degree up and 20-degree down vertical coverage. The asymmetrical models are very useful in providing downfill coverage from a dead-hung array.

CONFIGURATION ISSUES

Another design element to resolve in the TFR systems was the input configuration. There were clearly three choices: all passive, bi-amp with a passive mid-to-high crossover, and full three-way operation. In keeping with the goal of system flexibility and versatility, the answer was clearly to offer all three. This has been accomplished with two readily interchangeable input modules, one that is switchable to passive or bi-amp, and another that is a three-way unit.

Like the mid/high sections, the input modules can be exchanged in a matter of minutes, thus enabling the sound company that is willing to stock a few extra input modules to reconfigure the powering of their TFR cabinets to suit specific applications. Typically smaller systems would want to be operated passively or be bi-amplified, whereas larger systems would be better off being tri-amplified.

Design of the TSS subwoofer was straight forward. It would be a direct radiating 18-inch driver in a ported cabinet. Because the dimensions of the cabinet face were a bit tight, I decided to employ a molded fiberglass faceplate. This would enable the ports to be wrapped around the woofer frame, thus providing the port area I wanted within the confines of the face dimensions.

The ports have deep ducts that are structurally joined to the cabinet walls. This, combined with extensive internal bracing, resulted in an enclosure that is quite rigid, even at maximum power levels.

MAKING IT FLY

The next step in the design process was the rigging system. I decided to do seat track top-to-bottom, as I had done on the Community Air Force cabinets. This arrangement has the advantage of routing all of the loads through the rigging track itself, rather than through the structure of the cabinet. It also locates the cable attachment points at the front and rear of the cabinets so the cabinets can be close packed in both rows and columns.

For the T-Class systems I elected to do custom aluminum extrusions for the seat track. This would enable the rigging tracks to really become part of the cabinet, rather than something that was just added on. T-Class cabinets employ three rigging tracks, one at each front corner and one up the middle of the rear panel.


Two flybar modules, assembled.

My original idea for flybars was to make different sizes for each array width, but everyone whose advice I sought thought that was a stupid idea. The clear preference was for a modular approach using individual flybars that would bolt together to form whatever width frame was needed. Part of the appeal to me of the one-piece design was the degree of rigidity that could be achieved across the entire frame. To retain that rigidity in a modular design I decided to use joiner plates to link the modules, rather than just bolting the modules together with single bolts.

As you can see in the drawing of the flybar and joiner plates, the plates provide a wide bolt stance, and this provides good strength across the bar-to-bar connections. The joiner plates also have multiple bolt patterns in the horizontal direction to enable the flybar modules to be spaced apart. This spacing is necessary when some cabinets in the array will be angled downward, and this portion of the design seems to have worked out nicely.

The assembly of the modules is fairly quick, and the assembled frame has sufficient strength to be connected directly to the chain motor for arrays that are only one or two rows deep. Connecting directly to the chain motor without the need for bridles can save several feet of trim height, a valuable commodity in venues with low ceilings. The T-Class flybars are made to our design by ATM.

PUTTING IT TOGETHER

T-Class cabinets are attached to the flybar and to one another with rigging cables. There is one standard length cable that is used for this connection. There are also two other specialized cables. One is the Skip-Space cable, which is long enough to skip over the top row of cabinets and attach the second row of cabinets directly to the flybar. T-Class flybars have an alternate set of cable attachment points that are offset by 11.25 degrees, thus permitting cabinets to be suspended between two flybar modules instead of directly under each bar module.

This feature is primarily used to create arrays with a narrow horizontal pattern for the long throw section and a broader horizontal coverage in the short throw section. For example, such an array might have two long throw cabinets on its top row providing 50 degrees of horizontal coverage, and have centered under it a three box short throw section that gave 105 degrees of horizontal coverage. Arrays with this configuration are well suited to long, narrow rooms where the long throw section needs to cover the rear of the room without putting a lot of energy on the side walls in the process.

The other specialized rigging cable is the Skip Five cable, used only on arrays that are more than five rows deep. Its function is to connect the rear of the sixth row of cabinets directly to the flybar, thus enabling hangs up to ten rows deep without compromising the safety factor of the rigging hardware.


Front-edge seat-track and rigging cable.

In order to keep the cabinets in correct alignment the tops are fitted with molded nylon recesses that mate with nylon feet on the bottom panels. The side panels are fitted with molded alignment pads, and accessory joiner links are available which will hold the front and rear tracks of adjacent cabinets together, thereby keeping the side alignment pads engaged. The result is the cabinets all lock together to maintain both vertical and horizontal alignment in a dead-hung array.

As a side benefit, the joiner links can be used to hold rows of cabinets on dollies together during system set-up. An array section up to three rows deep and of any width can be set up on dollies and connected by joiner links. The entire section can be completely pre-cabled, rolled into place under the flybar, connected to the bar, and be in the air in a matter of minutes.

ESSENTIAL STEPS & TRUTHS

How well these systems measure up to their design goals remains to be seen, but they seem to be off to a good start. I must admit that I had some concerns about introducing a horn-loaded modular system at a time when the entire pro audio world seemed to be stampeding in the direction of line arrays.

However, it is a design philosophy that I firmly believe in, and I think that its natural efficiency, versatility, and exceptional acoustical performance will make it a winner. My guess is that T-Class systems will solidly prove their worth, and further, will still be earning money for sound companies long after the line array infatuation has faded from view.

 

Bruce Howze is president and chief engineer for Community Loudspeakers, and is the holder of numerous loudspeaker technology patents.

June 2003 Live Sound International

 

Email this story to a friend.