Balanced or un-balanced

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Permalink Reply by Mike Boltz on May 11, 2010 at 1:31am

I'm going to try to say this delicately without offending anybody as that is not my goal, but the truth is that there are a lot of people who run sound at their church who really don't have any training in actual sound engineering and don't truly understand how and why everything works the way it does.
As such, there are a lot of opinions out there among non-professional sound "engineers" (especially in the church setting) that are well intentioned but largely uneducated about sound engineering. Some come close to what is right and even sometimes find what seems to work even if they don't quite understand why. That said, having run sound professionally as well as in churches for nearly two decades, here's the skinny on your questions:

Balanced vs. Unbalanced.

Unbalanced cables are designed for high impedance gear like guitars. Microphones are not high impedance. They require additional amplification that high impedance gear does not. That is why there is a gain knob (which is also known as a "MIC" preamp) at the top of ea. channel on the sound board. In order to get the amount of input into the channel strip necessary to provide an adequate output, the signal from a microphone has to be amplified.
The problem with unbalanced cables is that they are really best when used for short jumps with high impedance gear. The longer an unbalanced cable, the more noise it will add to the overall sound. Even when playing guitar, it is better to use a 6 foot cable than a 20 foot, if possible. It would be nearly impossible to use really short UNbalanced cables for microphones unless everyone was huddled around the snake box. It's just not practical.
That being the case, it is simply better to use balanced cables for all low impedance gear and ANYthing if you run more than about 6-10 feet. If you have a guitar player and he stands 15 or 20 feet away from the box on the snake, then he should be plugged into a direct box, and then run a balanced cable from him to the snake. Balanced cables can be run even 50-100 feet and still be okay.
Can you run an unbalanced cable 20, 25, 50 feet across the stage with an XLR adapter on the end connecting to the snake? Yes. Will your sound be affected? Yes. Sure, you will be able to hear the guitar, but the signal will not be as clean, and as is the case with all sound equipment there is a signal-to-noise ratio which you want to keep as low as possible. It CAN be done the wrong way, and may seem to work ok, but the more things you do the wrong way, the more problems you can create and the worse the overall sound will be. It's kind of like the old saying, "the right tool for the job".

As for the feedback:

Feedback is actually caused by just one thing.. And that is amplifying an amplified sound. Said a different way, when a mic (or other device capable of picking up sound... like an acoustic guitar) picks up the amplified sound from the speakers and thus sends it through the soundboard to be amplified again, then picks it up again, and sends it through the board to be amplified yet again, and again, and again. It is a loop. That is why feedback is also referred to as a feedback Loop. it is just that... a loop. The way to fix it is to break the loop. There are several ways to break the loop.
First is to kill the input device (mute the mic/guitar). The second is to stop amplifying it (turn the output on the board down). These don't always fly when running live sound. So then you have to try other means...
Separation: make the distance between the mic and speaker greater, or... aim the speaker further away from the mic. These are often effective.
However, if these methods do not work, try to drop the frequency that is looping from the device picking it up by using the EQ of the channel on the board for that device. Better sound boards have EQ's that you can select what frequency is raised or lowered by the gain knob for that band. Cheaper boards have EQ's that are set to one frequency. Generally, the frequency that is heard the loudest when making an "S" sound is about 7-8 kHz. The bulk of sound in the average human voice is around 1-2 kHz.
Piano's and guitars compete for the same frequencies found in the voice. Thus, it helps to turn down (notch out) the 1-2 kHz range from the piano and guitar a little bit to give place for the vocals. The highpass should be used on ALL vocal channels if the board is so equipped, to eliminate unnecessary low frequencies in the vocals and keep them from getting muddy and competing with the bass and/or keys.
As far as finding what's feeding back... If you aren't sure where it's coming from... first, get the feedback, then mute one channel at a time until it stops. Once you know what channel is feeding, grab any sweepable EQ, (usually the mid on most average boards.) turn the gain knob about half way down (usually -8 to -10), then slowly sweep the frequency knob from as far left as it will go, to as far right as it can turn. Somewhere along the way the feedback should suddenly stop. When it does, you will know that you have found the specific frequency that is looping on the specific channel that is feeding back. Then the trick is to make the mic or instrument sound natural with that frequency turned down. One thing to note is to only turn down the EQ of the looping frequency as far as is necessary to eliminate the loop and no more, otherwise achieving a natural sound may be all but impossible.

Hope this helps
Mike

Permalink Reply by Cory Zipperle on May 11, 2010 at 6:34am

I think this is the best post here so far.

The troubles that you are having stem from a lot of different things, mostly inexperience. Feedback is an easy issue to resolve if you know what to look for.

Somebody already referenced the Yamaha book on sound reinforcement. BUY THIS BOOK, AND PRACTICE ALL OF THE PRINCIPALS IN IT. The book is an excellent resource for anybody who is running sound.

The next thing you need is budget. In my opinion, it is wrong for your church to have something but not want to pay for it. They want sound reinforcement but don't want to spend ANY money? This impairs their ability to make a worship offering to God what it ought to be. I'm not saying that they have to have great equipment, but to start a ministry and then deny it any funding will only hinder the ministry's work. For sound, that has a TON of consequences for your church. If you can't put your best foot forward on Sunday morning, just don't do it.

In addition to the book, I strongly suggest ownthemix.com. It isn't expensive and you'll get some really great training specifically for the church environment.

To provide a little more commentary here: We would never ask a piano player to lead our worship offering if all they knew how to do was bang on the piano. Yet, that is almost exactly what we do with our sound crews. This creates problems in every category with our corporate worship offering to God. I don't expect every church to bring the best equipment to the table with real engineers. But I do think we should expect our churches to equip and educate its sound ministry people to do the best that they can with what they have. In a church that has a sound system, none is more important than the sound guy.

Permalink Reply by John Earnshaw on May 11, 2010 at 12:14pm

Thank you for the great advice .You have all been positive as my usual expieriance is either with Ham radio gear or guitar and a Marshall stack .The points you mentioned have been going round in my head before I read this post about frequencies and the cables used.We hope to recreate the feedback on Wednesday and see what happens all depending on when we can get together as others have day jobs etc.
About the clean signal well I plan on bringing in some ham software to detect what is happening in each channel. Poor clarity is a complaint of the singers who are using the un-balanced lines and as I have said all the cables are different lengths which does not help with signals arriving together at the same time.
Basically I have been thrown in at the deep end with a system that is up and running but not right.
Again thanks for the help and if I continue to stay on the sound I shall be looking at a course in September pending health issues.
God Bless
John M0JFE

Permalink Reply by Cory Zipperle on May 11, 2010 at 8:52pm

For clarity, knowing how to set and use EQ is very important. If you really know what you are doing with an EQ, you can make pretty lousy speakers sound pretty good.

Hopefully this works out for you!

Permalink Reply by John Earnshaw on May 13, 2010 at 11:16pm

Just like to say a big thank you to all who have posted on this matter . Church has been really busy during this week so hope to make a start next week or so. I will be buying a copy of the Yamaha book and also see about enrolling on a course at the local collage.
Again I can't thank you all enough.
May God continue to Bless you and others with your talents.
John

Permalink Reply by Cory Zipperle on May 14, 2010 at 7:45am

If you don't mind my asking, what kind of cell phone do you have?

Permalink Reply by John Earnshaw on May 14, 2010 at 4:14pm

lg cookie kp500
Just had a look at the collage and local education places and no sound technicion courses been run so its the Yamaha book and online study I guess.Hope to start next week once I've seen the pastor on Sunday.Our church is busy so just got to sort out when I can go in to do things.
Thanks for the help
John

Permalink Reply by Wayne Pau on May 14, 2010 at 5:00pm

John,

Yamaha also re-did a copy later (it's got pink letters instead of the white on blank) specifically for churches:

http://www.amazon.com/Guide-Sound-Systems-Worship-Eiche/dp/079350029X

I personally have not gone through this edition, only the 1st & 2nd Ed. of the original. Not sure if it's better for you (if you haven't already ordered it).

Just thought I'd throw that out there.

Permalink Reply by John Earnshaw on May 14, 2010 at 5:57pm

Thanks a lot I've not ordered it yet I've got to buy a gearbox first the car has died .I will proberly order them both so I can study at home and use the equipment at church to learn from.
Thanks
John

Permalink Reply by Cory Zipperle on May 15, 2010 at 10:01am

Hm, too bad. I was hoping that you had a droid, windows, or iPhone. They all have applications for sound analysis that are pretty good and will help you find the source of the feedback.

ownthemix.com. Subscribe, NOW!

Great learning tool that is specifically geared towards people doing sound in churches.

Permalink Reply by John Earnshaw on May 15, 2010 at 1:39pm

I have a spectragraph on my computer and other test gear I use for ham radio gear. I will take a look at that site now
Thaks
God Bless
John

Permalink Reply by John Earnshaw on May 20, 2010 at 12:34am

Well guy's thanks for the help and I have been into church and nearly finished the system.I found out that at the rear of the DI rack on one of the XLR jacks there where a few strands not soldered properly.(manufactured lead) These where shorting out and causeing the system to fall over it's self and thus resulting in a HR straining the phantom's output power causing about a 15v drop which explains why the sound would drop in volume then recover.Amoungst other things the microphones are wired to the XLR on the mix desk ,Instruments to the line in and NOT the XLR as was previously done for everything. Accoustic guitar is through an amp using the line out to the line in on the desk. The keyboard is direct to the line in on the desk.Preliminary tests show no feedback ,a big increase in all microphone and instrument levels .The gain on the desk is now turned down to 20-30 as oppose 70 .Noise levels have been eliminated also when a noisey channel was found I fault found and corrected this so now noise is almost non audiable at max headphone volume.Full band set up and test is on Thursday night (UK)
I thank all for the inspiration and advice.Now comes the time to finish it off and pimp the system with those little extras.
How much extra did we have to spend £5. Not bad considering I set myself a brief of £0.00 or as near to.
May God Bless you all
John

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