The JBL 518S is designed to add the sort of bass needed for any band wanting to mic up drums or bass, and also great for DJ's wanting some proper night club style bass end on their rig. Predominantly designed to be used with a pair of JBL Eon 515's, but can be used with any pair of active PA speakers. Stereo input with left & right outputs means that you can use just one bass bin for every pair of tops you have, or if you need the extra power use a pair of these & add 1000w (continuous) power to your rig. Pretty portable as far as active bass bins go - the JBL Eon 518S is half (yes, HALF!) the weight of the Mackie 18" powered bass bin.

Here's what JBL say about the Eon 518S

The EON518S is an 18-inch, direct radiating, high performance powered compact subwoofer system. Designed to extend low frequency performance of any EON system. It also offers the convenience of an integrated crossover and stereo loop-thru capability. The EON518S is comprised of a 460 mm (18") Differential Drive woofer driven by a 500 watt Class-D digital amplifier. 
 
Features :
 
500 watt High-Performance Powered Subwoofer System
True portability weighing only 29.5 kg (65 lb)
Compact enclosure
Designed handles with comfort rubber grips for easy transport
18" Differential Drive low-frequency driver with neodymium magnet for low-distortion and light weight
Efficient Class-D digital amplifier technology
Stereo balanced loop-through outputs
Integrated and switchable High Pass Filter on loop-through outputs
Easy daisy-chain connections for extending the system
Polarity reverse selector
Integrated 36 mm pole mount socket for sub/satellite applications
Rugged DuraFlex finish
 
System Power Rating    :    500 W continuous 1000 W peak 
Frequency Range (-10 dB)    :    36 Hz - 130 Hz 
Dimensions (H x W x D)    :    617 mm x 569 mm x 652 mm
(24.3 in x 22.4 in x 25.7 in) 
Frequency Response (+/- 3 dB)    :    42 Hz - 100 Hz 
Maximum SPL    :    129 dB 
Crossover Frequency    :    120 Hz (HPF selectable on outputs) 

Applications : 
Live sound reinforcement, speech and vocals, music playback in entertainment, A/V, and institutional venues, especially when ease of use and portability are important factors.
Extending the low-frequency output performance of powered and non-powered full-range speaker systems.
Optimized for complete compatibility with EON full-range speakers.

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