By Ray Graeff. Mr. Graeff is the contributing editor of the 'Soundman' column of iBluegrass, a neat on-line magazine. (For more info visit www.iBluegrass.com.) They have many articles archived from past issues by Mr. Graeff and the other contributing editors. Permission of the author is pending. He can be reached at E-Mail: graeff@cameron.net
iBluegrass Magizine Sep-08-2000
Question:
WE'VE BEEN TRYING TO USE OUR ONE MIC SYSTEM, AND ALL WE GET IS SQUEALS, WE CAN NEVER GET IT LOUD ENOUGH WITHOUT IT DOING IT'S THING. HELP...!
Soundman’s Answer:
I'll give it a try. I am also a musician (doghouse bass ) and one of the bands that I work for does indeed use the one mic system. One thing that will help is to understand what makes it squeal.
As you turn any microphone up it becomes more sensitive. Noises from farther away are more easily heard (the whole principal behind the one mic. thing). Ok...these microphones are.... cranked up...... thanks to a transistor amplifier built into the base of the microphone along with several other electronic components. Technology has developed what is called a FET transistor (field effect transistor), and that rascal is really good. Now, what initiates a squeal, is the microphone picking up the sound of, say, someone walking across the stage floor. That sound is caught by the microphone, sent to the mixing apparatus, and then on into an amplifier which boosts the signal dozens of times. This amplified signal then goes to the speakers where it is reproduced for the audience to hear. The only problem here is that the microphone also hears the sound coming from the speaker and reproduces it, again. This starts a self-sustaining circle that builds in an instant. From the speaker... into the mic...through the amplifier... to the speaker... back to the mic again, and this vicious circle is repeated hundreds of times a second to produce the pitch of that unwanted squeal that we hear.
Now, we must interrupt that circle in some way. The biggest wrong I see first time users make, in attempting to use a one mic system, is setting the speakers on the corner of the stage where the one mic is located. It's just too close to the mic. If the microphone can't hear the main speakers, it won't reproduce the offending squeal nearly as easily. It doesn't cost a lot to go to Wal-mart and buy two 100 foot orange electrical extension cords, cut the ends off, splice them into the speaker cables and extend the length of the speaker leads. Black wire to black wire and white wire to the white wire...It doesn't take a rocket scientist to do that. Any thing to get those speakers farther away from the mic so those sounds won't start that vicious circle. But, when you get them out into the audience farther you'll want to elevate the speakers so they are above the heads of the seated audience...this means setting them on folding tables or specially produced stands of some sort. As you lean more about sound, you'll understand...for now just consider that good advice.
Now that the speakers are further away you will find that you can run your amplifier 3 or 4 times hotter than you could before. Good deal, but still not quite loud enough, you say. Ok, the next most common mistake rears its ugly head. Most fledgling sound people have, for some unknown reason, determined that the speakers must be turned in toward the center isle of where the audience is seated... where the sound from the two sides cross in the middle...QUIT THAT!! If you point both speakers toward the rear of the audience, you'll find that you can again turn up your amplifier another notch, without it squealing...try it! I have been in narrow churches with our one mic and the speakers were actually turned to face the wall slightly. Sound will bounce off the wall and supply the audience with plenty of sound, and the slight detour the sound has to make to get back to that hot mic is just enough to interrupt that terrible circle getting started.
Once the speaker placement problem is taken care of, there is another helper that can make a big difference. It's called an equalizer, in various forms. Now, I strongly recommend that you use a equalizer with no less than 30 channels to it. You are going to be taking bites out of the audio spectrum and the narrower those bites are, the better. You do not want you sound quality to suffer any more than it must.
You may have noticed that no matter where you are, that same pitch of ringing always seems to follow you. There is a good reason for that, you brought it with you. Follow along here, it'll make sense in a moment. Inside that microphone is a deal called the diaphragm of the mic It is an extremely light, usually gold impregnated disk that vibrates when sound strikes it to produce a electric current. The diaphragm is much like the cone of a speaker, that we are all acquainted with, of course. Now, this microphone diaphragm has a certain dimension to it (in the case of the one mic, about 1 1/4 inches). It is also glued into a supporting frame which is rigid. This means it has a certain amount of tension on it, too. (Ah.... the light begins to dawn....) So does a guitar string...what happens to a guitar string with a certain amount of tension on it, and of a certain length? You bet....it vibrates when it is struck, and it always vibrates at a certain note. In soundman jargon, this is called the "Sweet spot" of your one mic. Hey, this means if we could lower that one sweet spot frequency of that microphone, we could run everything else much louder without it squealing. RIGHT YOU ARE...and this is where the little sliders on the equalizer come in.
You insert the Equalizer in the microphone line fter the phantom power inserter box, (the 48volt phantom power that the microphone must have, will not go through the equalizer. It won't work), but the EQ should be ahead of the mixer board, if used.
Ok we have it installed, now what? We still must identify which frequency is squealing, so we can get rid of it. Here we go... On the equalizer, set ALL the little sliders in the CENTER of their range... there is a little detent there and you'll feel each slider drop into it.
Turn the system on and advance the volume levels so that it is barely below the point of squealing (register the pitch of that squeal in your mind, you're a musician, right). Next, go to the equalizer, about in the center of the little sliders and pick one. Grab that little slider and slowly raise it toward the top (you are turning up the volume of that particular frequency (pitch) in your system). As you raise that level, there will be a point where it squeals. If it is the same pitch as you heard when you turned the main volume up, you've already found the culprit...WAY TO GO,,, YOUR LUCK IS MUCH BETTER THAN MINE IS USUALLY... if it is not the same note/pitch, put it back where you found it and go to the right (up in pitch), or to the left on the row of sliders(down in pitch) until you locate the offending note.. Once you have located the sweet spot commit it to memory or write it down. It's going to follow where ever that microphone is taken. Wow... we did it. Now all we have to do is slide that same tab down.. into negative territory on the equalizer and for every db we lower that squeal frequency, we can turn up the over all sound of the one mic system... Double Wow...
Now that you are feeling all proud of yourself, I have another bomb for you. You are going to find that as you turn the volume up, another, different frequency is going to squeal on you. What the heck is this? "YOU SAID...." I know, I know, now for the rest of the story.
The microphone is not the only component in the system... and they have diaphragms, just like the microphone..... " THE SPEAKERS... " They have sweet spots too, and you find them just like you found the sweet spot of the microphone.. There will probably be two more of them... one for the bigger coned speaker in you mains and one for the tweeter driver in the horn you probably have mounted in the top of your cabinets.
Now, if you're sitting there reading all this and sayin to yourself. I can't cope with all this technical stuff... there is another solution. It's called a Sabine FBX... and it does the same thing automatically, with it's inboard programming, that we just went through with the equalizer. IT IS, an automatic equalizer that scans back and forth in the audio spectrum, like a police scanner looking for squeals. When it finds one, it automatically turns that EQ frequency down for you. But, get the ole' pocket book ready because that little dude is several hundred dollars, and it's about the size of 3 packs of cigarettes. But, it also doubles as a phantom power supply for you , so you can do away with that other piece of gear that came with your microphone.
Now that you have your speakers spread way out, and pointed in the right direction, with properly suppressed sweet spots of your system you can go out and hurt people with the volume that you can achieve with the one mic system. One little word of caution...You better watch out for the comments about that foxy little chick in the third row and what you'd like to do to her, cause the crowd is gonna be able to hear a mouse with a gas problem, anywhere on that stage.
By the way, this is the same principle used to suppress feedback on the monitor system of a standard multi-mike stage set up. I've revealed to you, one closely guarded secret of professional sound people, and I may catch heck from my fellow professional soundmen. But, I have also given you a little more insight into all the things a soundman that really cares, can do for you. Think about that, next time you climb onto a bluegrass stage. I reckon it'll be OK. There's still a lot more things we do for you that you don't even suspect, let alone know anything about, but, the one mic system used on a festival stage does away with several of them...that's the painful part for a soundman .
Lots of luck.. hope this has helped you.. come back and visit another day...