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This month we will continue looking at ways to improve the sound of your PA system; we’ll begin with driver alignment. Driver alignment is a term that refers to the “time aligning” of your speakers so all of the sound comes out at the same time, which sounds a little weird until you think about it. When your audio signal is sent down the wires to your amplifiers and finally to your speakers, the electrical signal starts all of the speaker components vibrating at the same instant, which is called acoustic alignment.
This big phrase is actually a simple concept. If we were to look at a cutaway of your speaker cabinet, you would see that the horn driver and woofers of different sizes can have different acoustic centers. The acoustic center of an individual driver is the location where the sound is considered to start its acoustic journey to the listener’s ears. This is generally considered to be the front plate of the speaker. You can tell its location by looking at a speaker – it is where the magnet assembly of the speaker and the frame that supports the outer rim of the speaker meet. Unless you have some good speaker diagrams, you will need to estimate this location, which should get you to within a half-inch of its actual location.
You will also need to know the acoustic center of your horn drivers, which is usually considered the front of the horn driver where it bolts to the horn. This doesn’t seem very exact if you have looked at a horn driver closely, but it should be close enough for most situations.
The theory is that you need to delay any drivers (woofers) that may physically sit in front of other drivers (horns) so that all the sound exits the speaker enclosure at the same exact instant. This is intended to make things sound “coherent” and moving in a unified wave at all frequencies. To do this, all of your speaker cabinets should be the same model and arranged edge to edge when stacked on the subs. You also need an amplifier for each type of component in your speaker enclosure – your horns need to have their own amp, the 12” speakers need to have their own amp, the 15” speakers need to have their own amp, and so on.
All of these amps also need to be controlled by a signal processor with a driver time delay function. My favorite unit for this in the lower price range is the dbx DriveRack PA. There are other great units out there, but I have about a baker’s dozen of these and all the club sound guys in my area use them as well. This delay can be done in feet/inches, meters or milliseconds. In general, feet/inches works best for most applications.
Begin with the speaker component that is the farthest away from the front of the speaker cabinet as the starting or “zero” point. Every driver component in front of that zero point will need to be delayed to that speaker. Measure the distance between the acoustic centers of the different speakers and dial in the delay time (feet/meters/ milliseconds) for each driver group. You should also be able to do this for your subwoofers, although if you have horn subs this can be tricky and is beyond what we can discuss here. When you are done, your speakers will be “acoustically aligned” and should sound cleaner and punchier.
System Delay
The concept behind system delay is that you should delay the sound coming out of your speaker system to match up with the sound coming from the guitar amps on stage. I have worked with many bands to try to line up the guitar amps with the front of the kick drum head. In theory, this creates a coherent wave front from all the instruments in the band.
For this you need to delay your PA to line up with the sound coming off of the stage. Measure the distance from the front of the kick drum head, or possibly the guitar amp line, and measure to the “acoustic center” of your PA. Go into the proper section in your digital signal processor and set the delay of the PA for the distance you just measured. Remember, this value may change when you go from club to club and venue to venue. You will need to measure and input this value again every time you set up for a show.
Now have fun and sound great!
Andy Anderson
Concert Sound
515-291-0464
andent@lvcta.com
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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!
Andy Anderson
Concert Sound
515-291-0464
www.concertsound.org
andent@lvcta.com
They can turn a great night into a nightmare. They can make your performance or destroy it. If you haven’t guessed it already, I’m talking about those nasty monitors. Almost every band I’ve talked to struggles with their monitor system at one point or another. Let’s take a look at some different ways to take the headache out of your time on stage.
Most seasoned players are familiar with the basic monitor setup for a band – two to four monitor speakers, one or two amps, a 31-band equalizer on each monitor channel and all the cords necessary to hook everything up to the mixer. We won’t go into these basic elements here, but instead we’re going to focus on the solutions that many bands have found to their monitoring problems. The biggest problems that most bands have are feedback and the need for more volume for their particular instrument or vocals.
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You have several options for eliminating feedback: using wireless in-ear monitors, trying higher-end mics, using monitor cabinets with bigger amps, or adding digital signal processors and high-quality equalizers to your system. Some mics, such as Audix, feature reduced feedback right out of the box due to their proprietary design of the mic’ing element. Many high-volume bands have switched to these designs. The Audix OM3, OM5 and OM6 are all good choices, depending on your vocal style. There are also some less expensive models and brands available that produce good results, but skimping on your mics is generally not the best idea.
Better quality monitor speakers and larger amps are a good choice when trying to improve your system in a more traditional way. Larger amps can push your speakers more cleanly with less distortion and are generally the deciding factor in how loud your monitors will be while still sounding good. As a rule, an amplifier that clips constantly will blow a speaker faster than running too large of an amplifier on the same speaker.
This may start some arguments, but I have found that using an amp with a power rating about double of what the speaker calls for works pretty well. My clients are usually very happy and I have fewer blown speakers caused by amp problems. A technique I see performers increasingly turning to is the combination of in-ear monitors with a regular floor wedge setup. This usually works best for loud guitar bands where the lead singer has a hard time hearing his own voice over the band. Usually, the singers only have their voice through the in-ears and use ear buds that allow some of the stage sound to come through. When the singers can hear the nuances of their voices, they don’t have to work their voices so hard. This setup can be done easily without modification to the monitor system or adding any mix outputs on the board, by either “passing through” or using a Y-cable to feed the in-ear unit.
The ideal system would be to have the whole band on in-ear monitors with digital IEM processors (like the dbx IEM unit), but sometimes guitar players don’t care for this. The best setup, in terms of cost and performance, for a medium to loud rock band playing in a club would be to have the lead singer on in-ear monitors and sending the backup vocalists – usually the bass and guitar players – through monitors called “sidefills,” since they reside at the side of the stage. These could be older PA cabinets, but I suggest something like a JBL dual 15” speaker and horn cabinet on each side. This way everyone on stage can get plenty of kick and vocals, and vocalists on each side of the stage can hear their own singing with a smattering of the remaining vocals mixed in. If the stage isn’t too large even the drummer can get enough sound that he can forgo his own wedge and mix.
One last monitoring tip for the road: I have been using dbx DriveRacks religiously for the last few years on my monitoring rigs. They can be set up quickly once you learn the programming and feature compression for speaker protection, feedback suppression and an onboard equalizer (31-band graphic and parametric). You can even save programs for venues you play at regularly, so when you get it dialed in you can keep it for next time.
Till next time, be loud and be proud!
Andy Anderson
Concert Sound
515-291-0464
www.concertsound.org
andent@lvcta.com