PERFECT YOUR PA
Posted on Sun 28 August 2011 in entries
Get to know the specs of your PA and you’ll find more power to play with, as Rob Speight explains…
MEET THE WRITER
Having spent the last 23 years honing his sound engineering skills, Rob is MD of Outpost Sound, offering recording, mixing, post-production and sound design services to music professionals.
PERFECT YOUR PA
Many people believe that the best PA system is the most powerful one, with the highest number of Watts, the biggest speakers you can find and of course, the cheaper the better! However, PA systems these days come in all shapes and sizes and the technical specifications behind them can sometimes be daunting. Nevertheless there are several simple ways in which you can make sure you get the right system for the right job and understanding what you actually need and what those specs actually mean in practice are often half of the battle.
WHERE DO I BEGIN...
For the purposes of this article we are assuming that you already have mics, multi-core, mixing console and outboard (if not, call our sales team for some advice.) Therefore, we are going to go through everything else, from system control and equalisation to crossovers, amplifiers, loudspeakers and mounting hardware to make sure you’ve got (or you get) the correct system for your needs.
Let’s start with the basics. We take the audio out of the mixer and pop it into your amps or powered loudspeakers. But before you turn it on you need to focus. One of the easiest ways to make your PA system work as efficiently as possible is to focus the loudspeakers towards the people who actually need to hear it. That means keeping the sound off of the walls and ceiling and concentrating it into the audience.
You want to keep the high and mid-high frequencies hitting your audience’s ears. Anywhere from about 1.5kHz to 8-12kHz contains the audio information that our brain interprets as definition and, in the case of lyrics or speech, this is where the intelligibility comes from.
I BELIEVE I CAN FLY
Put the speakers on a stand if possible or, better still, ‘fly’ them on specially made mounting brackets or rigging set-ups. Point them down into the audience and angle them so that their projected audio output will cross over slightly.
All loudspeakers have what’s called a dispersion angle and this is the angle at which the higher frequencies are controlled to come out of the centre of the box. If your PA is intended for smaller rooms and venues, you’ll be looking for a larger angle (i.e. wider dispersion) so the sound is spread shallow and wide in a smaller space. If you need to reach the back of a long-ish narrow venue, you’ll need a tighter dispersion angle.
For a larger room, to reach the first few rows you should use an extra speaker with a wider dispersion angle to fill the audio hole you get right at the front of a performance space. For an even bigger hall, you’ll need even more speakers to get even coverage to everyone. Dispersion really only applies to high frequencies, as soundwaves become less directional the lower the frequency.
POWER TO THE PEOPLE
Then there is power. Firstly, only buy a system that is right for the job or the kinds of rooms you’re using it in. You want to fill the space comfortably with a bit of headroom for transients. Of course you can ask the Absolute Music staff for advice (call us on 01202 597180) about what power will suit what kinds of venues, but while we’re here, let’s talk a bit about the specs.
For loudspeakers and amplifiers you need to consider power handling and provision, both of which are measured in Watts (W). Wattage can be measured in different ways. Peak power is the maximum power that the loudspeaker can handle or that the amplifier can generate. This is pretty meaningless though. I mean, who wants to drive their amps or speakers full tilt throughout a gig!? A better specification to look at is RMS or Root Mean Squared. In layman’s terms this is the power the system can handle comfortably.
AMPLIFIER STATION
These days many loudspeakers have built-in amplifiers, which can be both a good and a bad thing. On the positive side the amplifier will be matched to the loudspeaker, there is no additional cabling to worry about and you won’t need a flightcase for your amps. However, you will need to put in more effort to lift them and if the amp dies then you lose your loudspeaker as well as you can’t just patch in another amp channel.
DESIGNATED DRIVERS
You will also want to consider if you want an active or passive system and how many 'ways' it will have. In general terms an active three-way system is going to be best. This will have three drivers covering high, mid and low frequencies, driven by three separate amplifiers and crossed over by powered electronics.
Breaking it down, this means that each driver only has to concentrate on a small frequency range, making it more accurate and efficient; the amplifiers don’t have to work as hard to cover the entire frequency response and the crossover, because it is active, is more accurate and stable, i.e. it will send the right frequencies consistently and accurately to the correct driver.
If you need to be bass-heavy in your mix or you have a drumkit, consider a separate sub, but make sure that the crossover frequency works with the high-mid boxes you are thinking of buying. For example if you look at the specs of something like the Bose L1 systems you will see the top boxes cross over at 150Hz, whereas the sub kicks in down to 40Hz.
AND THERE'S MORE
These are the basics, but to make sure you’ve got the very best PA set-up for your budget and your needs, here are a few more final things to consider…
• Get a graphic equaliser to put between your mixing desk and the amplifers. It will give you so much more control and stability to your system. The DBX 2231S dual 31-band unit is a seriously ideal piece of kit but be prepared to spend some time setting it up for each gig.
• Put a compressor/limiter after the graphic EQ; it will help to control transients and protect your loudspeakers, especially if you are not using a powered system. Speakers with integral amps often have built-in overload protection. The DBX 160AD or DBX 166XL are ideal, or look at the DBX 2231S which also has a built-in limiter.
• If you are buying separate loudspeakers and amplifiers, make sure the amps can provide more power than the speakers can handle to allow for transients and give you headroom. It will make the mix sound better, but don’t overdrive the desk because you will blow the drivers!
• Make sure your system is lined up. If you can, send a 1kHz tone through the desk, get it to a 0dB level on the outputs and then make sure that it also reads 0dB on your amplifiers. This way you always know how hard you are driving you amps and ultimately your loudspeakers.
• Don’t just buy a system because it looks good. Listen to it! Bring a few tracks you know well (try to make them varied) on a CD (not MP3) and listen to them on the system. Check that they sound good at low and high volume levels and always push your budget to buy the best you can afford.
• Finally, if you can afford it, buy a loudspeaker whose cabinet is wood rather than plastic. They just sound better!
Come in-store and try out our range of passive and active PA speakers on our live stage or browse the large selection in our online shop.
WE RECOMMEND
This system boasts a dispersion angle of 180° and sits behind the performer negating the need for a separate monitor or multiple units. Try it in-store today!
You may also want to check out the Bose L1 Compact.
For just over £400 you get a pair of PA speakers, an eight-channel mixer with iPod dock and a built-in dual-150W amplifier.
You may also want to check out the Samson XP510i.
The black V2 of this classic PA speaker is still a fave in the Absolute Music office and on our PA testing stage. A pair costs well under £1,000.
You may also want to check out the Mackie SRM350 V2.
With the expertly made ART series you'll see and hear the difference in build and sound quality. The 750W bi-amped 722A has wide dispersion and comes in just under £1K.
This trio of powerful three-way active PA speakers includes the KW122, KW152 and KW153 with prices starting at £1,299. The series also comprises the KW181 subwoofer.
This 300W speaker with state-of-the-art design punches well above its £280 price point and boasts a versatile input section.
