LIVE SOUND 101: Amplifiers
In review, we covered the correct ratio of tops to subwoofers and what is the difference between vented and horn loaded enclosures. Now we are going to go over amplifiers. Not all amplifiers are made the same and many of them have different features, such as:
1. Hi pass/Low pass Filters – Frequency Cut-off points so you can set tops or bottoms without a separate crossover.
2. Subsonic filters – Ususally are set at 30hz, to filter out frequencies below 30hz so you do not bottom out your speakers
3. Limiters – Protects amp from abnormal sounds that can blow out speakers
4. Bridged watts – When 2 channels are made to 1 channel
5. RMS – watts per channel
6. 2/4/8 ohm stable – how many ohms the amp can handle safely without over heating.
7. Damping factor – How much the amp can handle uneven signals in ohms.
8. RCA/Quarter Inch/XLR inputs – Different types of inputs
9. Banana/Quarter Inch/Neutrik outs – Speaker outputs
10. Signal to noise ratio – How loud the amp plays
11. Weight – How heavy the amp is.
12. Company who makes the amp.
All these factors go into picking an amplifier, it might seem a lot but if you understand each characteristic, you can pick the correct amplifier and save a lot of money in the process. So lets begin on how do you determine what amplifier to choose.
WHAT IS YOUR BUDGET? Is probably the most important question you have to answer, how much are you willing to spend? What I mean by that is in total, maybe not just at the time of being. Many people constantly add on to their existing system. A decent amplifier will cost a minimum of $600(USD) dollars for a 2 channel amplifer, it can be bridged to 2000 watts into 4 ohms, and it can go 2 ohm stable per channel. If you pay for anything less, I would be very careful with running the amp at 2 ohms stable or maxing out the amplifier. So you have to project into the future, which comes to our next question,
HOW MANY SPEAKERS ARE YOU PLANNING TO POWER UP? If you are doing a small, portable system, usually 2 amps is all you need for a 2-way system (tops and subs). This will usually handle 100-200 people. For anything larger, you will need more amplifiers, especially for the subwoofers. I have gotten away with running 4 dual -15 inch JBL SRX tops and 4 JBL SRX 728 dual 18 inch subs with two Crown CE-2000 amplifiers , but I had a dbx crossover, dbx 31 band equalizer, and a dbx compressor/limiter to make sure I did not over run my amps. You should always have double the power of the RMS of your speaker rating so that you do not overheat your amplifier. This extra headroom will also keep the sound nice and smooth, especially in the midrange and highs. An over run amplifier sounds very harsh.
Another aspect of an amplifier is how many ohms will you running the amplifier? Lower priced amplifiers usually state they can run at 2ohms or they state that it can produce so many watts. Don’t believe the hype, most amps will run 4ohm stable but very few will run 2ohm stable for an extended period of time I tried many amplifiers and I can assure you, not all amplifiers are made equally. You really get what you pay for, so this goes into the next question,
WHICH AMPLIFIER COMPANY’S ARE THE MOST RELIABLE? I am only basing this on personal experience, and my personal experience extends 21 years of pro audio. I have used a variety of different amplifiers, I either rented them, used friends, or the venue already had these amplifiers in place. I have extensive experience using CROWN, QSC, CREST, BEHRINGER, PRECEDENT, AMERICAN AUDIO, PEAVEY, YAMAHA, and MACKIE. My favorite amplifiers to use are CROWN, CREST, and QSC, for the reason that I have ran them into the ground, running 4 subs and 4 tops at 2 ohm stable to each channel and these amps have never went thermal on me. I was even surprised that these amps lasted 12 hours straight of Drum&Bass music, which is very demanding on the speakers and amps. I do not recommend this, but because I had a good processors, I was able to get away with it. Many of you who are budget conscious and want to buy the lower priced amplifiers, all I have to say about that is make sure you don’t push them to the limits because they might go thermal and not come back. That means your party is done, and you will get a bad reputation after that. I have seen that happen at various underground parties and it is not fun watching a rowdy crowd complaining about where the sound is.
The next segment will discuss various processors that will take your sound to the next level.