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PA Speakers for Dummies
well, that wasn't the title of the article but I found it to be appropriate after I read it. It's called " A Guide To Live Sound Speakers And Amps " and was posted at [URL="http://www.ultimate-guitar.com/columns/gear_maintenance/a_guide_to_live_sound_speakers_and_amps.html[/URL]. I had to leave out a few paragraphs at the end of the article so it would fit here in this post but the most important stuff is here, intact.
Here we go ... Hey, you've made it. You're a real band doing real gigs in front of real audiences. Now you need a proper PA. This aims to be the first part of a guide which will help you set up and run a full blown PA. I've already written a guide to a simpler system and how to run it the links are at the bottom. You'll need speakers, amps, a mixer, mic's and all the leads and a guide to setting it all up and getting the best out of it. I'm going to start with the speakers because that will determine what amp you use and will in turn affect the rest of your choices. It's a great time to buy speakers as design has improved to the point where one engineering solution has evolved which works for 90% of our needs. Nearly all bands end up with a pair of smallish boxes on stands, each with a single speaker and a horn for the top notes. The speakers come in a range of sizes for different bands and if you need to be really loud you add a bass bin or two. All you've got to do is choose the speaker size you need and how you want to run your amplification. Choosing the Speakers There isn't a single PA system that solves every problem and you need to give a little thought to what you want your PA to do. What sort of music do you play? Are you a metal/rock band or a folk duo? Will your PA just carry vocals or the whole band including the kick drum and bass? Where will you perform and what volume levels will you need? You are going to need different stuff to do different jobs. There are also the little practical problems like can you lift it and will it fit into your vehicle. There is no point dragging round a much bigger system than you really need. Pretty much the whole range comes with a 8,10,12 or 15 speaker and a horn to cope with the higher frequencies. The smaller speakers will generally give you more clarity in the midrange and a better vocal and acoustic guitar sound but they won't go as loud as a big speaker and the bass will be limited. Move up to the 15 units and you have a speaker that may be able to cope with the volume of a full rock band, but unless you spend a lot of money you will lose the clarity of a smaller speaker, because neither a horn nor a 15 cover the middle very well. Even if you opt for a 15 unit it may still struggle with bass and kick drum if you are really loud or play in bigger venues. So, if you want to run everything through the PA then at some stage you should add a bass bin (or sub) to free up the main speaker to cope with everything else. 8 or 10 + horn Ideal for vocals in an acoustic band, or for voice and guitar. These speakers usually give good vocal clarity and are easy to transport. Limited sound output except for high end designs. A really high end 10 unit will match a mid-price 12 speaker but at a price, worth looking at if weight and portability are an issue and you can afford it. 12+horn Good all round solution for many bands especially if limited to vocals and guitars. These speakers can achieve high sound levels and can be used successfully for the whole band if you add subs. Vocals are usually fairly clean and you can often lift them unaided onto a stand. They'll also pack into the boot of a family car. Our band opted for this solution (Yamaha S112V's +S118 subs for bigger venues) 15+horn High sound output levels and will cope with bass and drums at medium levels. Any decent design will give enough output to fill a 200 seat venue for most bands though subs might be needed if you are very loud. You will need to be built like an ox to lift these babies onto the stands. 2x15+ horn designs are also available. These are big heavy speakers designed for disco's or for full on rock bands where their bass heavy nature is an asset. A single pair of these will cover most of your gigs on their own but you aren't going to fit them in many family cars. Another solution around is to add a mid range speaker (usually a 5 or 6 unit) to a 15+horn, like the Mackie 1530 which does give lovely sweet vocals. Adding a mid-range speaker is such a great idea for cleaning up vocals that it probably should be a lot more common. Active or Passive? An active speaker is simply one with an amp built in. Most speakers are passive and you need to buy an amp to drive them, but an increasing number have an amplifier built in. You can also buy active mixing desks where the amp is built into the mixer. So, your choice is active speakers with a passive desk, passive speakers with an active desk or passive speakers, separate PA amp and a passive desk. I'll concentrate on the arguments for and against active speakers for now but similar arguments apply to active mixers. Active speakers Having the amp built in means that the amp exactly matches the speaker meaning one less decision for you and less chance of a blown speaker. Protection circuits are usually built in too and sometimes even digital processing to exactly match amp and speaker. One less thing to carry and forget No speaker leads needed, though you will need a mic lead to run to the speaker. The speakers need to be plugged into the mains. Usually have an active crossover so potential for a better and very slightly louder sound. If anything goes wrong you've lost speaker and amp. Passive speakers You need to match amplifier and speaker. More flexible, you can change amp or speaker and upgrade in stages. Only one lead running to the speaker. Less impact if anything goes wrong. Lighter, but one more box to carry. To me it is fairly simple, if you are the sort of musician who just wants to get on and play and who wants to run a PA with minimum involvement with technology then get an active system. It's the plug and play solution with a perfect matching of amp and speaker. Some even have computers built in (DSP) which will sort out your tone settings and even some feedback problems without you having to do anything. For acoustic acts there is usually the chance to mix one mic and one instrument so you may only need the active speaker! If you are a technophile who is always looking to upgrade then go for separates; , as you grow in expertise and/or funds you can change components and upgrade at less cost and there are lots of add ins you can use. It really is more flexible. How much Power Do I Need? You are really asking two questions here, how loud do I need to be and how should I match an amp to my speakers? Loudness is measured in decibels or dB, not in watts and speakers vary greatly in their ability to turn watts into sound. Some speakers are just louder than others so you need less wattage. Using the most efficient speakers could easily be the same as using 4x the power in watts. This is why I suggest you choose the speakers first. If you are not used to thinking in terms of decibels have a look at my article Making it Loud' http://www.ultimate-guitar.com/colum...g_it_loud.html To give you an idea of what you are looking for I'd say 115-120 dB is enough for an essentially acoustic set, 120dB+ is enough for vocals with a band and 125dB will carry a fully mixed band so long as you don't push too much bass through. There is a word of caution here though. The manufacturers don't all rate their speakers in the same way, so you need to check before comparing figures or at least be a little sceptical about some of the claims. The most common trick is to rate the output with the peak power the speaker can take. Most speakers can handle four times their rated power for a second or so, especially if there is no deep bass and so the manufacturers give a figure their speaker will only give at four times the rated power. You won't achieve this figure without using, say, a 1000W amp with a 250W speaker. One example of this is JBL 305 Eon which claims a max. output of 128dB, enough for most bands needs if you can achieve it. In reality the Eon is a 250W speaker and it has good sensitivity. At its rated 250W though it will only give 122dB which isn't quite enough to cope if you have bass and kick going through the PA. To be fair most manufacturers such as Wharfedale and Electrovoice do exactly the same trick, but Mackie give a rating at the RMS (EIA) power so their 123dB speaker is actually a little louder than the 128dB JBL. Remember that you only get the manufacturers rated output if you use the same amp wattage and you may need to knock 6dB off the maximum claimed in the adverts. Some manufacturers give a one watt sensitivity figure. If they do you can work out the max output from this by adding 20db for 100W and 3dB for each doubling after that so a 200W speaker with a 98dB/W sensitivity will give a 121dB max. |