Audio Systems: Audio Equipment Failure, mackie speakers, power amp

Question
QUESTION: Hello,
Our company was hosting a dance last night, we hooked up our 3 Mackie speakers and Mackie Subwoofer and our DJ's digital turntable (Numark) and our power amp. We ran an extension cord from the wall outlet to our power amp and then hooked up a few power strips to the amp and hooked our speakers and lights up into the power strips. Just before we started the dance we noticed the speaker that was hooked up through the subwoofer start clipping. We tried turning down knobs, volumes, limiting it, everything, but at the level we needed the audio, it would clip. Then the signal light on it start to cut out too. Then we looked at the subwoofer and the thermal light started to light up every now and then, not to mention the fact that half of our lights weren't working. About an hour into the show our lights and speakers and turntables cut out. We grabbed a new extension cord, new power strips, and everything we could then we realized that the back 8 outlets of our power amp were not working, we had to live off of one power strip with only 2 lights and 2 speakers (+ subwoofer) plugged in. However, everything worked fine after that. If you could possibly explain what might have happened here and how it could be avoided next time that would be great.
Thanks,
Ed Harrel

ANSWER: You overloaded the power strip and the voltages were too low in the amplifier to keep up with the current required by the demands of the music.

Subwoofer systems draw lots of current, especially when driving dance music.  It is likely the something failed.

If you look at the specs of the power amp and speakers you can determine if you were not, indeed, seriously overdriving the system.

Without knowing the model numbers of the units you had in your system (you did not give them in your question) it is impossible for me to give you a very specific answer.  However, the Mackie amplifiers draw bigtime power. If you have in your system the M-4000, for example, it is a 4,000 watt driving amp and will pull serious current off the power line.  In fact, it could melt the contacts and the switch on a medium grade power strip.  It is surprising that you did not blow a breaker in the house power system panel!

Let me know if you need more.

C



---------- FOLLOW-UP ----------

QUESTION: Thanks, that helps a lot.
The 3 speakers were: Mackie SRM-450's
The subwoofer was: Mackie SWA1801
The power amp, I don't think it was a Mackie, had an outlet to get power from the wall, then it had another outlet next to that which was and output and then it had 8 outlets in back of it and it displayed the voltage on it. I'm not sure if that is acutally called a power amp, maybe it is just a power strip.
So my question is that the subwoofer was getting too hot, which cause the signal of the speaker to cut out occasionally? And after a lot of hard work from all the power strips hooked up to the black box with 8 outlets the whole system fell apart?
That is what I do not understand.
-Ed

Answer
If the sub was cutting out it is from overdrive; too much power over along enough period of time to get the output transistors inside too hot.  The protection circuit is designed to cut out when danger lurks.

Dance music really eats up the current/power.

Now, if the sub is not cutting out but going into cone overload - which produces a clapping or breaking up sound - then the voice coil may be loose of the surround of the cone/diaphragm coming loose.

The speakers you mentioned are bi-amped and have their own amplifiers built in.  So, I think the 8 power outs were from a power strip.

The speakers being built-in amps doesn't change the picture much; it still means alot of juice is being pulled off the wall when the audio gain is up to full level  -  which it always is for dance conditions!

You probably need more/bigger speaker output for the dance hall.  If the hall is too big for the equipment and the number of dancers in the hall is too great you may be pushing the system too hard.  Even Mackie stuff cannot withstand hard hitting dance music for long period of time.  The kind of dances that I am familiar with - youth groups of 200 to 300 - in a hall the size of a high school basketball floor would require a greater system than what you have explained to me.

Your system as you have explained to me above would be good for maybe 100 audience at the most.  

What do you think?

C