ment applications in permanently installed sound systems. Typical venues include cinemas, auditoriums, theaters, performing arts centers, night clubs and concert halls. The TL606DW is designed to serve as the primary low-frequency section in extended-response two-way systems with excellent bass perfor- mance to 40 Hz and controlled dispersion to 800 Hz—a typical crossover frequency of two- way systems. When used with the dedicated XEQ-504 crossover/equalizer, the TL606DW can be combined with appropriate Electro- Voice TransPlanarTM horns and DH series driv- ers to form a passive two-way system of unprecedented wide-range response and lin- earity. However, to extract the maximum per- formance from the TL606DW, a multiamp con- figuration using the XEQ-2 or XEQ-3 cross- over/equalizer units is recommended so that full rated power may be applied to the low- frequency system. With a half-power point of 40 Hz, the TL606DW can also serve as the subwoofer component in large, multiway sys- tems.
FREQUENCY RESPONSE
The TL606DW frequency response was mea- sured in an anechoic environment at 10 feet on axis with swept one-third-octave pink noise. The frequency response curve for the TL606DW are shown in Figure 1.
DIRECTIVITY
The TL606DW directional characteristics were measured by running a set of polar-response curves in EV’s large, anechoic chamber. The test signal was one-third-octave pseudo-ran- dom pink noise centered at the frequencies indicated in Figure 2. The curves show horizon- tal (side-to-side) dispersion when the enclosure’s long axis is vertical. The vertical (up-and-down) polar responses are also shown.
Additional typical information is provided in Figure 3 which shows 6-dB-down beamwidth versus frequency. Figure 4 shows the directiv- ity factor and directivity index versus frequency.
DISTORTION
Following AES (Audio Engineering Society) recommended practice, plots of second- and third-order harmonic distortion for 0.1 rated input power are shown in Figure 6. Figure 5 shows distortion at 0.01 rated input power.
POWER HANDLING CAPACITY
To our knowledge, Electro-Voice was the first U.S. manufacturer to develop and publish a power test closely related to real-life condi- tions. First, we use a random noise input signal because it contains many frequencies simulta- neously, just like real voice or instrument pro- gram. Second, our signal contains more en- ergy at extremely high and low frequencies than typical actual program, adding an extra measure of reliability. Third, the test signal includes not only the overall “long-term aver- age” or “continuous” level—which our ears interpret as loudness—but also short-duration peaks which are many times higher than the average, just like actual program. The long- term average level stresses the speaker ther- mally (heat). The instantaneous peaks test mechanical reliability (cone and diaphragm excursion). Note that the sine-wave test sig-
nals sometimes used have a much less de- manding peak value relative to their average level. In actual use, long-term average levels exist from several seconds on up, but we apply the long-term average for several hours, add- ing another extra measure of reliability.
Specifically, the TL606DW is designed to with- stand the power test described in EIA Standard RS-426A. The EIA test spectrum is applied for eight hours. To obtain the spectrum, the output of a white noise generator (white noise is a particular type of random noise with equal energy per bandwidth in Hz) is fed to a shaping filter with 6-dB-per-octave slopes below 40 Hz and above 318 Hz. When measured with the usual constant-percentage analyzer (one-third- octave), this shaping filter produces a spec- trum whose 3-dB-down points are at 100 Hz and 1,200 Hz with a 3-dB-per-octave slope above 1,200 Hz. This shaped signal is sent to the power amplifier with the continuous power set at 800 watts into the 3.5 ohms EIA equiva- lent impedance for the TL606DW (52.9 volts true rms).
Amplifier clipping sets instantaneous peaks at 6 dB above the continuous power, or 3,200 watts peak (105 volts peak). This procedure provides a rigorous test of both thermal and mechanical failure modes.
SUBPASSBAND SPEAKER PROTECTION Below the enclosure tuning frequency, cone excursion increases rapidly. Since acoustic output is also failing rapidly, there is no utility in driving the system with signals much below the tuning frequency. While such signals may be in the program material, they are often extrane- ous—such as from record-surface irregulari- ties (strong 5- to 25-Hz components) or a dropped microphone. The DL15W very-low- frequency reproducer is ruggedly designed and has a high maximum excursion before damage (±0.5 inch). However, high-output subwoofer systems such as the TL606DW should be protected by a high-pass filter with a 3-dB- down corner frequency of about 0.8 the enclo- sure tuning frequency. Below the corner fre- quency, a roll-off of 12-dB-per-octave is usually sufficient.
Without protection, subpassband signals may “bottom” the DL15W’s. Damage will probably result, especially after repeated occurrences. Even if bottoming does not occur, the subpass- band signals waste amplifier power and modu- late (distort) the frequencies which are within the TL606DW’s operating range. Much “woofer distortion” or “muddy bass” can be attributed to lack of subpassband protection.
The Electro-Voice EX-24, XEQ-2 and XEQ-3 electronic crossover/equalizers provide sub- passband protection. 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
TL606DW’s may be used in multiples to in- crease acoustic output. In the following discus-
sion, it is assumed that all speaker cones are operating in unison (in phase) when a common signal is applied. A 6-dB increase in maximum acoustic output results when two speakers are located side by side. For operation at very low frequencies, the woofer cones “mutually couple,” acting as one speaker with cone area and power-handling capacity twice that of a single speaker. The doubling of cone area doubles efficiency, providing a 3-dB increase in sound pressure level. The second 3 dB comes from the doubling of power capacity.
Mutual coupling occurs when the frequency is such that the center-to-center distance be- tween the two speaker cones is less than about one-quarter wavelength. For a given center-to- center distance, the highest frequency at which mutual coupling will occur can be calculated from the following formula:
3,000
f = —————,
Dmax
where Dmax is the distance in inches and f is frequency in Hz. When Dmax is greater than one-quarter wavelength, as would occur if
two TL606DW’s were widely spaced, the level increase tends to be limited to the 3-dB power-handling increase.
More than two TL606DW’s can be used for increased output. In general, maximum acous- tic power output ability increases as the square of the number of mutually coupled cones. For example, four cones would provide 42 or 16 times the power output of a single cone, an increase of 12 dB (10 log10 16 = 12 dB). Note that the associated increased efficiency (2.9% X 4 = 12%) approaches that of a fully horn-loaded design, but in a much smaller enclosure.
SYSTEM POSITIONING
Subwoofer systems such as the TL606DW are often located on the floor. This is both conve- nient and can provide a desired high acoustic impact when the speakers are, for example, placed near the periphery of a dance floor. In other installations, such as a theater or audito- rium, the audible location of a subwoofer oper- ating at a sufficiently low crossover frequency (below about 125 Hz) will not be particularly evident. The other system elements operating above the subwoofer range can be positioned for the desired locational cues and uniform audience coverage.
Floor location provides the acoustic half-space environment associated with the 5.8% system efficiency noted in the Specifications section. Location at a floor-wall junction (acoustic quar- ter space) doubles efficiency (a 3-dB increase in sound pressure level) and tends to promote the full excitation of more room modes, or standing waves, important in achieving maxi- mum overall bass output in the room. Corner placement (acoustic eighth space) doubles efficiency again and guarantees excitation of all room modes. (Such placement for maxi- mum efficiency and room-mode excitation is not necessary and may not be desirable or possible for a variety of reasons, including aesthetics and building design.)
