I get this question quite often. Although we don’t mind the business we would rather have our customers understand how to not blow up their equipment.
The Problem: Blown Highs
Why does this happen? A simple answer is excessive heat…we see a lot of burned voice coils. Excessive heat on a voice coil is the result of distortion or clipping in an amp or mixer. Usually we find that the customer has not matched the amp to the speakers. I know this is a common mistake; even the sales guy at the music store doesn’t know how to match an amp to your speakers…a good reason to do some homework before you buy a sound system. Improper gain structure is also to blame in many situations. When you have poor gain structure starting at the mixer then everything else in your chain is going to get an ugly signal. The speakers are the last component in the signal chain and therefore will suffer the most. The woofer is a bit sturdier than the high frequency diaphragm so that is why it probably didn’t blow…yet. If you are coming close to the clip light coming on then it may be time to reconsider your current setup.
The Solution: Match the amp to the speakers.
There are other scenarios that can blow your speakers but we’re going to focus on amp and speaker matching in this article. This problem seems to be the biggest one.
The incorrect way… you buy a speaker that is 800 watts program and a 700 watt amp and you figure the extra 100 watts is a cushion. Well, I thought that too at first, but your amp will clip long before the speaker reaches its peak power handling. The peak power handling of a speaker is usually twice the program watts. So this speaker that is 800 watts program and 1600 watts peak will handle peaks of up to 1600 watts. Back to the amp: it is clipping at 700 watts. Whether the clip light is on or not you may be sending peak signals to your amp causing clipping. That will start to overheat the voice coils in your speakers.
The correct way is to find out the program watts and peak watts of the speaker. Then multiply the program watts times 1.5 or 2 to find out how much amplification you need.
Speaker Program Watts x 1.5 = Amplifier Watts
For example: 800 watts program (at 8 ohms) x 1.5 = 1200 watt amplifier (at 8 ohms)
The impedance or ohms is extremely important. If you can’t find the specs on a speaker, don’t buy it. I get my info from the people who make the speakers, they do tons of research. Here is some info from JBL on this subject.
“All loudspeakers are capable of sustaining short peaks of power much higher than they can sustain on a steady, continuous basis, and the proper choice of amplifier is quite dependent on the loudspeaker’s ability to do this.”
– Speaker Power Requirements by JBL Pro
Some real world examples:
Peavey SP4 – 2000 watts program/4000 watts peak
2000 watts program (4 ohm) x 1.5 = 3000 watts
This means you will need a 3000 watt per channel amp if you have two speakers. The Peavey CS3000 produces 3100 watts at 4 ohms in bridged-mono.
JBL SRX722 – 1600 watts program/3200 watts peak
1600 watts program (8 ohm) x 1.5 = 2400 watts
This means you will need a 2400 watt per channel amp if you have two speakers. The Crown XTi 4000 puts out 2400 watts at 8 ohms in bridged-mono.
It’s no surprise that the amps match up so nicely, they are designed this way. If you run your speakers with the correct amp they will sound better too. Here are a couple places that have good information and advice for powering your speakers effectively:
JBL Professional has very good information on this subject.
Danger: Low Power (PDF File) (PDF file)
Speaker Power Requirements (PDF File) (PDF file)
Peavey also has some great info on this subject and many others.
Crown Audio has some great online calculators for this as well.