TL880D Very-Low-Frequency Speaker System
Specifically, the TL880D is designed to with- stand the power test described in ANSI/EIA RS-426-A 1980. The EIA test spectrum is applied for eight hours. The spectrum is ob- tained by filtering white noise (a particular type of random noise with equal energy per bandwidth). The filter applies a 6-dB-per- octave slope below 40 Hz and above 318 Hz. When measured with a one-third-octave con- stant-percentage analyzer, this filter produces a spectrum whose 3-dB-down points are at 100 Hz and 1,200 Hz with a 3-dB-per-oc- tave slope above 1,200 Hz. This shaped sig- nal is fed to the power amplifier with the continuous power set to provide 1,200 watts into the 4.8-ohm EIA equivalent impedance (75.9 volts rms).
Amplifier clipping sets instantaneous peaks at 6 dB above the continuous power, or 4,800 watts peak (151.8 volts peak). This proce- dure provides a rigorous test of both ther- mal and mechanical failure modes.
The TL880D has also been power tested with a two-hour sine wave, at minimum imped- ance, so that competitive comparisons can be made using consistent methods. Continu- ous program power is defined as 3 dB above (double) the continuous sine-wave power rating.
Subpassband Speaker Protection
Below the enclosure tuning frequency, cone excursion increases rapidly. Since acoustic output is also falling rapidly, there is no util- ity in driving the system with signals much below tuning frequency. While such signals may be in the program material, they are of- ten extraneous, such as a dropped micro- phone. The Electro-Voice EX-24, XEQ-2 and XEQ-3 electronic crossover/equalizers can provide the necessary subpassband pro- tection. The 3-dB-down points are 30 Hz (EX-24 and XEQ-2) and 16 Hz or 32 Hz (XEQ-3).
Other high-pass filters are available and one- third-octave equalizers can also be effective at providing the required protection.
Use In Multiples
Cone loudspeakers may be stacked for greater acoustic output and a narrower beamwidth. (It is assumed that all cones are
operating in unison or “in phase.”) This prin- ciple is already employed in the dual-woofer TL880D, and is responsible for the higher sensitivity and narrower vertical beamwidth (with the system long axis vertical) relative to similar single-woofer systems. In addition, two TL880D’s can be used side-by-side and their combined performance will be differ- ent from that of a single TL880D in the ways outlined below.
At relatively low frequencies, below about 150 Hz for typical TL series dimensions, stacking produces additional acoustic out- put without altering dispersion. When a com- mon signal is applied, a 6-dB increase in maximum acoustic output occurs. The cones “mutually couple” and act as one cone with twice the area (therefore twice the efficiency) and twice the power capacity. The additional cone area provides 3 dB more output and the additional power capacity accounts for the remaining 3 dB.
Specifically, mutual coupling occurs at fre- quencies whose wavelengths are longer than one-quarter the center-to-center distance between the cones. The highest frequency at which mutual coupling occurs is calcu- lated from the following equation:
3,000
f @ ————— ,
DMAX
where DMAX (inches) is the distance between the cones, and f (Hz) is the highest frequency at which coupling occurs. When DMAX is greater than one-quarter wavelength, which would occur if two TL880D’s were widely spaced, or at frequencies much above f even when closely spaced, the increase in acous- tic output is limited to the 3-dB power-han- dling increase.
Installation and Suspension of TL880D Enclosures
The TL880D is designed for typical cinema stage (behind-the-screen) applications where subwoofers are mounted on the stage floor.
The TL880D is not designed to be self-sus- pended from above, and if suspended, must be supported and hung in a way which does not depend on the structure of the TL880D itself for support.
Architects' and Engineers'
Specifications
The loudspeaker system shall be a dual low- frequency, bass-reflex design. Two 18-inch woofers shall be front mounted in an 15.5- ft3 enclosure. The system shall meet the fol- lowing criteria: power handling, 1,200 watts of pink noise with a 6-dB crest factor; fre- quency response, smooth and uniform, us- able at high output levels from 23 to 2,000 Hz; sensitivity, 98 dB at one watt, one meter, 100 to 800 Hz, on axis; impedance (woofers paralleled), 4 ohms nominal, 4.2 ohms mini- mum; dispersion angles 220° (horizontal) x 180° (vertical) at 200 Hz. The enclosure shall be constructed of black texture-painted poplar plywood . The enclosure will contain sound-absorbing glass wool. Each woofer shall have the capacity to be fed indepen- dently of the other. The input panel and con- nectors shall be side-mounted. An installed vent cover shall be supplied that, when re- moved, shall raise the box tuning frequency from 25 Hz to 30 Hz, for increased output in the 30- to 40-Hz range. The enclosure di- mensions shall be 47.5 in. high x 30.0 in. wide x 23.8 in. deep (121 cm x 76.2 cm x
60.5cm). Net weight shall be 160 lb (72.6 kg). The low-frequency speaker system shall be the Electro-Voice TL880D.
Uniform Limited Warranty
Electro-Voice products are guaranteed against malfunction due to defects in mate- rials or workmanship for a specified period, as noted in the individual product-line statement(s) below, or in the individual prod- uct data sheet or owner’s manual, beginning with the date of original purchase. If such malfunction occurs during the specified pe- riod, the product will be repaired or replaced (at our option) without charge. The product will be returned to the customer prepaid. Exclusions and Limitations: The Limited Warranty does not apply to: (a) exterior fin- ish or appearance; (b) certain specific items described in the individual product-line statement(s) below, or in the individual prod- uct data sheet or owner’s manual; (c) mal- function resulting from use or operation of the product other than as specified in the
