PA Questions?

[SceneMaster]

Hi

 

I'm a lighting man so sound is not really my thing. :** laughs out loud **:

 

I am doing a small gig on Sunday for a church youth band and I am lighting and the sound man. We have all the lighting sorted and I am borrowing my schools PA. The gear is old about 6 years but seems ok. I understand basically how the system works and have read the mixer manual several times and rigged this gear for the music department before so I know how everything connects and where to place speakers although for a church could you tell me I was just going to stick them at the front about 5m in front of the band at the sides. I have just never operated a sound rig and I wondered if there were any tips you could give me on operating a rig. I know about feedback and sort of the how to stop it but could people give me tips and pointers on everything in general to do with my rig.

 

>The mixer I am using is Studiomaster Powerhouse 300 Series (8ch powered mixer)

>We have balanced mics (Can someone explain the difference between balanced and unbalanced? The desk also provides power (phantom power I believe 45-47volts) so the mics with batteries in will need these taking out and why can’t you use unbalanced mics with phantom power and can I run a show without phantom power? All our mics are general condensers I believe so this should be fin for vocal and some general sound pick up for the acoustic guitars (well its all we have)?

>We have a Horizon multicore 8in XLR and jack out for speakers used with speakon cable to the loudspeaker cabinets.

>We may or may not have a monitor for vocalists

 

Another question is what voltages and current do loud speakers receive from an amp. It just the speakon cable’s jacks got cut when hardwiring into and amp the only jack connectors I can find at school are not insulated so although the + connection will be inside the female jack socket the negative will be on the out side as the connection runs right through to the plug body. Would I be able to just put some insulation tape on the jack? Also my music teacher said that we would need new cables instead of soldering on new jacks I don't see why this would make a massive amount of difference in sound quality. (Ok maybe a little but noticeable as this is amateur event and I am good with a soldering iron) Will putting new jacks on the speaker cable be ok as they are fairly new only used once I believe?

 

Thanks for any help.

 

Scenemaster who feels very out of place here as my home is the lighting forum!!!

[dominicgross]

Write.... where to start.

(Can someone explain the difference between balanced and unbalanced

A balanced mike/device uses a 2 core twisted cable. which are placed out of phase, then reversed at the mixer end to cancel out noise. This basicly means that you can use very long cable runs without picking up any noise.

so the mics with batteries in will need these taking out and why can’t you use unbalanced mics with phantom power and can I run a show without phantom power

Most mikes won't need the batteries taken out: when phantom power is applied it normally bypasses the bat.

You can't use unbalanced mike cause the phantom power will kill them: there not designed to take voltage, and because they only use 1 core cable: there's nowhere for the voltage to go.

 

next person...

[James]

Hi

 

I'm a lighting man so sound is not really my thing.

 

Don't worry - we all have our cross to bear :** laughs out loud **:

 

I am doing a small gig on Sunday for a church youth band and I am lighting and the sound man. We have all the lighting sorted and I am borrowing my schools PA. The gear is old about 6 years but seems ok. I understand basically how the system works and have read the mixer manual several times and rigged this gear for the music department before so I know how everything connects and where to place speakers although for a church could you tell me I was just going to stick them at the front about 5m in front of the band at the sides.

 

Getting the speakers as high as posible

 

(+) - better more even ispersion over your croud (think of them like big fresnels and you are trying to do even house lighting with them, OK - so up and out then :** laughs out loud **:)

(-) - Stability, Safety, can only go as high as stands can go (Though stands safely on staging is often good... ) and can only go as far as speaker cable stretches.

 

basicaly place them and walk the room - see how even it sounds and if need be don't be afraid to move them.

 

Getting the speakers away from the band

 

(+) Less of a rock concert feel, more gain before feedback occours

(-) Less of a rock concert feel, can create a "hole" in the middle of the front of the stage.

 

Getting the speakers behind the band

 

(-) It's a bad idea!

 

I have just never operated a sound rig and I wondered if there were any tips you could give me on operating a rig. I know about feedback and sort of the how to stop it but could people give me tips and pointers on everything in general to do with my rig.

 

Practice, and keep it simple.

 

you will have enough to worry about if this is your first mixxing gig without trying to beclever with fancy equipment or cobbling together bits of other systms to make do coz someone says you need a bigger system....

 

>The mixer I am using is Studiomaster Powerhouse 300 Series (8ch powered mixer)

>We have balanced mics (Can someone explain the difference between balanced and unbalanced?

 

Simplified bit of physics here. Any long wire in the presence of electicity has a small current induced in it. Not a problem with huge currents like lighting but a big problem with tiny currents like computers telephones and Sound.

 

Simplified bit of maths here.

Unbalanced Microphone puts out a signal (s)

Balanced Microphone puts out a signal and it's inverse! (+s) (-s)

 

Unbalanced line picks up noise by the time it gets to the sound desk. (s+n)

 

Balanced Lined pick up noise by the time they get to the sound desk (+s+n) (-s+n)

 

Mixer puts out unbalanced mic with noise (It's all it can do)

Mixer takes one half of the balanced feed away from the other half. (+s+n)-(-s+n)

=(+s+n--s-+n)=(+s+n+s-n)=2xs +n-n So you get twice as much signal with the noise almost totaly canceling out.

 

(Incedentaly that's how computer networks work without shielding, telephone wires wirk without shielding and it's verry usful indeed.

 

Beccause both core wires in a balanced cable don't exactly ocupy the exact same physical space as eaxh other there will be fractional differences in the noise induced in each wire so (n) isn't quite equal to (n) but it's close, You can get close by using starquad cable - this has 4 cores, which is split into pairs diagonaly oposite

connected together at each end and twisted along it's whole length - this means this is quieter cable than 2 core mic cable.

 

The desk also provides power (phantom power I believe 45-47volts) so the mics with batteries in will need these taking out and why can’t you use unbalanced mics with phantom power and can I run a show without phantom power?

 

OK, a normal dynamic microphone works like a speaker in reverse.

 

With a speaker you put volts in and you get sound out.

With a dynamic microphone you put sound in and you get volts out.

 

Condenser mics are slightly different. They turn sound into an electrical signal through a capacitor which needs to have a voltage across it to work.

 

This is why you need a battery in some condensors.

 

Phantom power works by essentialy putting a DC ofset on the balenced inputs of the sound desk. with a ballanced microphone you have a transformer connected to the hot side and the cold side. If both of these have +48v on them then the microphone's transformer sees only +48v - +48v ie it can't see the DC,

 

Of course if the microphone is sending it's signal back unbalanced then suddenly one half of the mic is lifted up by +48v - ie not nice.

 

All our mics are general condensers I believe so this should be fin for vocal and some general sound pick up for the acoustic guitars (well its all we have)?

 

Are you sure? what makes and models do you have, some are better than other for different purposes obviously. What isn't obvious is which ones - that's why you still see the same arguments about the same mics in auio forums for the last umpteen years. (LAB, r.a.p, a.a.p.l-s etc...)

 

>We have a Horizon multicore 8in XLR and jack out for speakers used with speakon cable to the loudspeaker cabinets.

 

This doesn't make a lot of sense Are your speaker cables speakon - speakon or jack to speakon. Speaker cable should be nothing to do with your multicore. Amps should be as close as is possible to your speakers. If you are talking speakers with impedances of 4 or 8 Ohms and you put even half or just 1 Ohm's resistance on the speaker cable then you are seriously loosing power from your ampifier.

 

(That's why the idea of a powered mixer FOH makes me a bit queazy, Oh - you said you have a powered mixer, Grr. bad luck... but make the most of it you can - get far enough away you get an idea of what the audience are hearing, but close enough to your speakers that you aren't using too much speaker cable.

 

>We may or may not have a monitor for vocalists

 

Another question is what voltages and current do loud speakers receive from an amp.

 

Do you want a serious answer to that question? Ok, 1dBu = 0.775v RMS, you can use Ohms law to work out the current draw using the power handling and gain applied at the amplifier.

 

Ok, It's not unknown of for big amplifiers to put out large voltages. Whatever you use for professional speaker connections should be capable of taking mains voltages and currents.

 

It just the speakon cable’s jacks got cut when hardwiring into and amp the only jack connectors I can find at school are not insulated so although the + connection will be inside the female jack socket the negative will be on the out side as the connection runs right through to the plug body.

 

Um, Again - I'm having problems decyphering wht you are saying here, (That is one hefty sentence)

 

If I understand you, correctly and you have a 300W power amp then you shouldn't have a problem with using Jack connectors - however I would only recomend Neutric ones for speaker use. If you are jack - Speakon with the jack being at the amp then you should be fine as there is no way you should be able to touch both + and - at the same time when the amp is powered.

 

Would I be able to just put some insulation tape on the jack? Also my music teacher said that we would need new cables instead of soldering on new jacks I don't see why this would make a massive amount of difference in sound quality. (Ok maybe a little but noticeable as this is amateur event and I am good with a soldering iron) Will putting new jacks on the speaker cable be ok as they are fairly new only used once I believe?

 

Don't need insulation tape, lead shouldn't need replacing, as long as it is fairly decent (1.5mm minimum preferably 2.5mm)

 

If you were thinking of using insulation tape for another similar aplication use heat shrink instead - It's much nicer when it ages... (and clear heat shrink over paper is a good way of labling up connectors)

 

Thanks for any help.

 

Scenemaster who feels very out of place here as my home is the lighting forum!!!

 

Don't worry - Try to read a copy of the Yamaha sound re-enforcement handbook - If your school or local library doesn't have a copy then try to request one. Hope I've been of some help. Ask again if you don't understand something (Oh and for the pedants, I appreciate I've been a bit loose with the truth is some cases but I wanted to simplify some of the explinations...)

 

Hey and welcome to the sound forum*

 

*I can't realy say this as I don't claim to know anything about sound.