Electro-Voice TL880D manual Description and Applications, Frequency Response, Directivity

		TL880D
		Very-Low-Frequency
		Speaker System
		• Designed for cinema subwoofer use
		• High acoustic output to below 20 Hz
		• Two EVX-180A woofers provide very
		high peak and long-term output that
		complements the dynamic potential of
		digital sound on film
		• 2,000 watts continuous program
		• Side-mounted connection panel
		facilitates hookup when depth behind
		the screen is restricted
		• High output ability in the 20- to
		40-Hz range is also ideal for
		very-low-frequency synthesized
		effects, down-tuned bass guitars
		or pipe organ
		• Approved for subwoofer use in THX®
		cinema systems*
Description and Applications	put below 40 Hz than the devices typically	relative value, at a point, of the TL880D
	used in these applications.	when compared to an ideal spherical
The Electro-Voice TL880D is a member of	Frequency Response	response. The directivity index, Di, is calcu-
the TL series of low-frequency enclosures.		lated by Di = 10 log Rθ.
The TL880D is a dual direct-radiating vented	The TL880D’s axial frequency response was	Power Hanndling Capacity
design that provides high efficiency, low	measured in Electro-Voice’s large anechoic
distortion and excellent low-frequency	chamber at a distance of 10 feet with a swept	To our knowledge Electro-Voice was the first
performance. The TL880D employs two	sine-wave input of 4 volts. Figure 1 has been	U.S. manufacturer to develop and publish a
long-throw EVX-180A 18-inch loudspeak-	averaged and corrected for 1 watt/1 meter.	power test closely related to real-life condi-
ers, in an 15.5-ft3, black-finished enclosure	Directivity	tions. A random noise input signal is used
without grille. It is specifically designed to		because it contains many frequencies simul-
meet the low-frequency demands of digital	The directional characteristics of the	taneously, just like real voice or instrument
cinema sound, in subwoofer applications.	TL880D were measured in Electro-Voice’s	program. The signal contains more energy
The TL880D’s high pumping capability, high	large anechoic chamber; the test signal was	at extremely high and low frequencies than
acoustic output ability and extended bass	one-third-octave filtered pink noise at the	typical actual program, adding an extra mar-
response (to below 20 Hz) make it par-	frequencies indicated. A full spherical	gin of reliability. The test combines not only
ticularly appropriate for the dynamic po-	measurement system was used, which is	the overall long-term average or continuous
tential of the digital cinema application. (The	compatible with the AcoustaCADDTM com-	level—which our ear interprets as loud-
TL880D is approved for subwoofer use in	puter-aided design program. All directional	ness—but also short-duration peaks which
THX® cinema systems.)* The side-mounted	information was measured at 20 feet.	are many times higher than the average, just
input panel facilitates behind-the-screen in-	Figure 2 illustrates the horizontal and	like actual program. The long-term average
stallation, where limited space between the		level stresses the speaker thermally (heat).
	vertical polar responses. Figure 3 shows the
screen and theatre wall often makes it diffi-		The instantaneous peaks test mechanical re-
	horizontal and vertical beamwidths.
cult to connect to the back of an enclosure.		liability (cone excursion). Note that the sine-
	Beamwidth is the angle at which the hori-
The TL880D’s performance characteristics		wave test signals sometimes used have a
	zontal and vertical polar responses have
also make it highly appropriate as the		much less demanding peak value relative to
	decreased in level by 6 dB when compared
subwoofer in large, multiway systems for		their average level. In actual use, long-term
	to the axial frequency response.
contemporary music playback and sound		average levels exist from several seconds on
	Figure 4 illustrates the total directivity of the
reinforcement. The TL880D has more out-		up. We test for several hours, adding an-
	TL880D. The directivity factor Rθ (Q) is the
_________________		other extra level of reliability.

*THX is a registered trademark of Lucasfilm Ltd.