|Products like NTI’s AL1 Acoustilyzer can now put powerful audio analysis and testing tools directly in the palm of your hand, and are perfect for finetuning your PA system.)
At every gig we want to sound our best, and we want our fans to hear us at our best. The only way we can do that is to have our sound system in great shape at all times. To achieve this goal, we need to do some periodic maintenance and a little system optimization. So this month we’ll take a look at what it takes to make our gear rock!
First, check the condition of all your system interconnect cords. Use a cable tester to check all mic and 1/4” cords for correct wiring polarity and to reveal any shorts; I like Behringer’s CT100 Cable Tester for this task, as it’s cheap and simple. Once you’ve verified all of your connections, visually inspect of the length of the cord for any wear, and repair or replace as needed.
Visually inspect your speakers, looking for any tears or rips; you’ll be surprised at what you might find. I once discovered a monitor sans cone – beer had been spilled into the front of the grill, and it softened the paper cone around the dustcap and coil, wearing it completely away. Once you’ve verified that your speakers are all in one piece, listen to each driver carefully for buzzes or crackles while playing a well-mastered CD or mp3 – you’ll want to choose a track with piano or another “clean” type of music. Repair or replace anything that is giving you problems.
For the remainder of these tips, you may need to purchase some test gear or hire someone who already has it. You will need a speaker polarity tester, a digital or analog RTA (Real Time Analyzer) and a RTA mic with cable.
First, perform a polarity test on each speaker in your system; to do this, you will need a speaker polarity testing kit consisting of a “clicker” pulse generator and “reader,” which is placed next to the speakers and indicates if all the speakers are in phase and moving in the same direction during the pulse wave. If they are not, you will need to make the appropriate wiring changes inside the cabinet in terms of the actual speaker/driver connections in the cabinet (post-internal crossover, if present) which may require soldering.
Once that is complete, do a frequency test. To do this, you will need a pink noise generator and the RTA with a calibrated RTA mic – many units have this incorporated into their circuitry, such as the DBX DriveRack PA.
Set up your RTA mic in the center, or slightly behind center of the room in front of your speaker stacks. Make sure the room is quiet and find yourself a helper, have them unplug all of the main speakers and start with one sub/low speaker cabinet. Get a reading and then move to the next one and compare. All of the readings should be close to each other. If there are large differences, take the RTA mic and put it about 6 to 8 feet in front of each cabinet, testing each one separately and comparing the readings again. If there are large variations you’ll have to dig deeper and look for speaker/driver or amp/wiring problems – something beyond the scope of this article. If all is well, proceed to the main high speaker cabinets. Do the same process of comparing each cabinet with the others to make sure you have no major differences, and debug as needed. During this process you should be listening for any buzzes or noises that are associated with the cabinet while it is producing sound and do what it takes to remove these noises – from tightening/ replacing screws to regluing/caulking seams. Finally test all of the speakers together and adjust your crossover and EQ settings to get an even response in the room. Remember that all of the testing and checking will be good for all other locations, but you may have to adjust crossover output levels for subs to the high speakers from venue to venue. The EQ settings should also be adjusted for new locations and checked with an RTA for best results.
You can also perform the same test on all of the monitor speakers – simply place the RTA mic facing the speaker in the position where a performer would be standing. Remember, monitor speakers are not designed to perform like a main speaker and have been optimized to sound good in monitoring situations. This may mean they have less low end and high-end in their frequency range. Check one out that sounds good to you with the EQ controlling the speaker bypassed and compare it to other monitor speakers.
There are lots of other system tests that you can use to get more performance out of your system, such as time alignment and system delay, but we’ll stop here for this month. Now get busy, and don’t forget those earplugs!