Thomas Cornish Consulting

By TJ Cornish, May 2015

I read a post on a sound reinforcement forum recently of a user who purchased a lower-end passive “line array” system and was struggling to get it running.  After checking out the specs of the product the user purchased, this is a great example of the challenges of a non-integrated system.

The “Line Array”

The passive line array modules in question are from a manufacturer that caters to the lower-end DJ market, and they have the following specs:

• 2x 5” woofers, 1.375” tweeter
• 65Hz - 20Khz frequency response (levels unspecified)
• 125dB maximum output (measurement methods unspecified)
• 16Ω, 300w peak power (150w RMS)
• 22lbs
• $280 price per box

These are designed to be used in a system of several modules per side, and either flown overhead, or stacked on the stage or subwoofers.  For the following example, we will consider a set of four speakers and the flybar per side.  The cost for 8 boxes, flybars, and an amp (Peavey IPR7500 with DSP)  is approximately $3850, not counting speaker stands.

Based on manufacturer specs, a set of 4 boxes has a theoretical maximum output of 137dB if the boxes sum perfectly.  The manufacturer’s specs are very vague and the vertical angle isn’t specified, so we have to guess, but normally line array boxes have approximately a 10° vertical coverage angle.  Most events require more vertical coverage than that, which affects summation.  If 40° vertical coverage is required, the high-frequency section of the array doesn’t sum at all, limiting the output of a set of four boxes to more like 125dB - the output of a single box.

Self-Powered Conventional

There are many good self-powered speakers.  We’ll look at the JBL SRX812P, which has the following specs:

• 12” woofer with 3” voice coil, 1.5” exit compression driver with 3” voice coil
• 48Hz - 20KHz -3dB frequency response
• 90° x 50° pattern
• 136dB maximum output (whole space 1m)
• 2000w total power, bi-amped system with FIR phase-coherent DSP processing built-in, including speaker protection limiting
• Ethernet control: 20 bands parametric EQ, compressor, up to 2 seconds of delay
• 58lbs
• $1299 price per box (MAP)

This speaker is intended to be used singly, and has two pole sockets allowing a normal straight angle, as well as a -7.5° angle.

I have not heard the passive line array box I’m referring to in this article (I am familiar with the JBL SRX812P and it sounds great), but we can make a number of judgements based on manufacturer-provided specs alone.

Unless you’re hearing with your eyes where the line array system may have an advantage since it looks more impressive, the JBL box wins in every category, including cost. 

As an owner of a professional-grade small format line array box (that costs about 10X the cost of the example in this article) I understand the draw of a vertical array; a well-designed vertical array system can be very flexible, however it is important to not be sucked into the marketing.  Low-end systems such as the example in this article come with little manufacturer support, and in most cases will underperform both in terms of output and sound quality compared to a reasonable conventional speaker.