sound advice

dbx’s DriveRack series can help you optimize and align your sound system; the 260 model has up to 2.7 seconds of alignment and zone delay available. This month we

Sound Advice
dbx’s DriveRack series can help you optimize and align your sound system; the 260 model has up to 2.7 seconds of alignment and zone delay available.

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

Make sure to balance the system crossover so you have the balance of lows, mids and highs that you want, and then you can start tuning with the EQ.

For the last ten years I have been working with touring engineers and watching how they work to get their bands sounding so great. This month, I thought I would share with you some tips about what they do and why they do it.

The Tools to Use
Every touring engineer usually wants a stereo 31-band equalizer at the front of house rack on the sound system mains, and another 31-band equalizer on each monitor mix and any additional mixes such as delay towers and front fill speakers. They always want high quality units such as Ashly, BSS, Klark Teknik or dbx. Equalizer design has come a long way in the last few years, but, for analog units, these brands have been great performers and have the fewest problems.

Use Good Cables and Plug ‘Em in Right
Most engineers prefer to have the EQs plugged into the output channel input jacks, since this usually gives the best signal-to-noise ratio and takes advantage of unity gain design in the mixing board. This works your EQ in the optimum range. You can plug out of the outputs of the board, but if you drive your board hard, you can start to clip the inputs of the EQ unless you have set up a good gain structure or you manage your gain settings between mixer and EQ. Don’t cut corners on cords here, or in any part of the main signal chain (from mixer to amp), because it will be heard by everyone.

Start With a Flat Graph
Make sure when you begin EQing a room that you start with a 31-band EQ that is set at zero on the frequency faders all the way across the spectrum from 20 to 20K, and at unity (zero) on the output gain. Then, put on a familiar CD that will sound similar to what your band will be playing. Make sure to balance the system crossover so you have the balance of lows, mids and highs that you want, and then you can start tuning with the EQ.

Tuning and Techniques
When you start learning to tune your PA to the room, it will take some time. Don’t expect it to go fast; even a seasoned professional will take at least 10 minutes, and up to 30 minutes in a tough room.

Start by listening closely as you boost each band by +3 db, then drop it -6 db. Determine which way you prefer it: boosted, cut or unchanged. As a general rule, you want to have each band left at zero or cut by 3-6 db; in cases where there are feedback problems, you can cut as much as 12-15 db. You don’t want to cut too much yet, as you are going for tonality at first.

Listen to your favorite song tracks again, then plug in a good quality mic at the console and talk on it loudly and clearly. Make sure there are no ringing tones signaling a possible feedback problem – don’t be afraid to scrap everything and start again with different settings.

Once you get a good tone that gives you the sound you want with your CD tracks and voice, set up the band and all mics. Have the band play, and try to bring the volume up to performance levels. Without the band playing, but with all of the mikes at performance settings, try boosting each frequency band by +6 db, one at a time and see if it starts any feedback. If it does, you will need to cut that frequency by at least an additional 3 db or more.

Slowly raise your main PA volume up by at least an additional 25% or more and find out where feedback frequencies happen. Try to cut some more on those channels to help eliminate those feedback points. It helps to have a frequency analyzer to spot the tones that will give feedback if you are not familiar with what they sound like. While a good used one isn’t overly expensive, it is best if you can train your ears to learn the tones and how they change the way your sound comes through.

If you have a feedback exterminator, now is the time to use it to increase the gain out of your PA and to clean up your sound. You may even want to consider putting back some of the tones you previously cut; it is best to only have several severely cut frequencies on your EQ, as having many more creates comb filtering and tonal problems in your PA.

Now that you are armed with the knowledge of what the big boys do, go out and have a good time – I’ll be listening for you!

Andy Anderson
Concert Sound

We all know that in-ear monitoring units have been out for a few years now, and it seems like the thing to do for band monitoring. There are several positives

We all know that in-ear monitoring units have been out for a few years now, and it seems like the thing to do for band monitoring. There are several positives and several negatives for in-ear monitoring versus floor wedges and we will explore a few of those now.

You get what you pay for
Simply put, the better the unit the better it will sound. Why? It has to do with the companding circuitry used to transmit all that audio into wireless format. Companding is a form of compression that is used to make the sound fit into the bandwidth used for wireless transmission. There is also compression used to limit the dynamic range of the input of the transmitter (raw audio in) and the output of the receiver (output to ear buds). Different priced units have varying levels of this and the more you pay, the better it sounds. Done properly, you should have the effect of listening to your band like listening to a good recording on your Walkman or iPod.

Where to put your money
The best set of ear buds you can afford a good start. The sonic difference of having dual driver units or high output units will be instantly noticeable to the wearer. Next, you’ll want to invest in the best transmitter and receiver package you can buy. If you are just getting into “ears” want to find out if they will work for you, suggest getting a basic intro package planning on upgrading to better buds and transmitter as soon as it is feasible.

Who benefits the most
The musicians that get the most performance out of in-ears are lead and backup singers, drummers, bass players, keyboardists, and acoustic guitar players. I have seen rhythm and lead guitarists use them also, but in general, most electric guitar players don’t like the “boxed in” feeling and the tone coloration of their sound. Also, many high volume players who use the sound of the cabinet to make their guitar feedback prefer not to wear in-ears. Usually these are players that do not sing or sing minimally in the band.

Loud rock bands also seem to need augmentation in the form of additional floor wedges and butt shakers or bass floor pads for drummers, bass players, keyboardists and some lead singers. Groups that have become used to an “aural bath” of sound seem to use the in-ears to get better coverage and more “me” when they sing.

In-ears are pricey, compact and may require more gear to support them; however, they are extremely light and can save a band lots of cost in transportation – not to mention backbreaking lifting! Wedges are nice because, if need be, several performers can hear one wedge. If you have an in-ears setup fail, you might have trouble adjusting to your backup plan (wedges).

A wedge setup requires an additional EQ and power amp channel, plus a couple of wedges. That adds up roughly to $800- $1200 for one or possibly two performers, if you can share. Four monitor mixes with eight wedges, two amps and four EQs will run you about $4000-$7000, depending on the quality of the gear you buy; in addition, the setup will weigh about 500- 700 pounds.

A great in-ears setup may cost you and your band about $2500 per musician (i.e. a DBX IEM digital processor and a Shure PSM700 with good earbuds) and maybe another monitor mixer board and some special cabling from the front of house to your snake head. You can get into in-ears for as little as $400 per system (GALAXY system), and you might be able to have two receivers share one transmitted mix to save cost. Another way to cut corners is to buy the earbuds and to use a small mixer beside you to drive your ear buds – this works well for keyboard players, drummers and bass players.

Be aware that in-ear systems are not a cure-all, but just another tool that we can use to get our music across to our fans. Most systems out there are combinations of in-ears and floor wedges. So, get some cash together and start experimenting on what works best for you and your bands. The future is here, so get on board and have fun already!

Andy Anderson
Concert Sound