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PA Department - Random Thoughts

Microphones

 - Aren't all mics basically the same?......  Microphones can be divided into two types. The most common is dynamic (which is similar to a tiny loudspeaker working in reverse). Most stage microphones are dynamic types. They have the advantages (in general) of being less prone to damage, need no power supply of any kind, and more consistent in their performance in different environments. 

The other type is condenser (sometimes called "capacitor") microphones. These are capable of higher performance than dynamic mics., but need a power supply, can suffer from condensation on the diaphragm resulting in muffled distorted sound, and are usually more expensive. Condenser microphones are to be found in professional recording studios almost exclusively.

(There are other types of microphone, but you are not likely to come across them in this type of application)

"Phantom Power" is a feature on some desks and amplifiers that enables the use of condenser microphones.

Condenser microphones need 48volts (sometimes less) to operate, and "phantom power" supplies this. 

If you don't have condenser mics, you don't need phantom power.

Conversely, if you don't have phantom power, your condenser mic won't work. (unless the mic is battery operated of course - but that's another story....)

Cardioid? ..... Cardioid microphones are directional (the pick-up pattern is heart shaped - hence the name), that is they pick up sound better at the front than the side or behind. This helps control feedback and increases how loud you can be. Cardioid microphones also exhibit what is known as "bass tip-up". This means that the closer you sing into a mic., the warmer and bassier the mic will sound. This is generally a good thing, used to effect by experienced singers with proper microphone technique. 

A hypercardioid (or supercardioid) microphone is directional too, but, unsurprisingly, more directional than the cardioid version. They exhibit a greater bass tip-up (i.e. nearer to the mic the "bassier" it gets) too, which generally makes them sound warmer than cardioid mics. Often especially good for female singers.

Omnidirectional microphones are not generally used on stage or studio.

Which Mic. is for me?......   A microphone for stage use needs to be cardioid or supercardioid (see separate tip in this section), to isolate the voice from the other instruments and monitors. 

The sound of the microphone is up to you, ideally try it (set the mixer EQ flat), also take into account handling noise - the quieter the better.

Generalising (again), American mics are brighter sounding, European mics are warmer. More expensive mics have lower handling noise.

Monitors

Firstly there is the speaker size - 10in, 12in, or 15in. Generally speaking bigger is better for sound, but less easy to store and transport.

Then there are powered and non-powered varieties.

A powered monitor has an amplifier built in, this will therefore work directly from the "monitor out" of a desk or amplifier. Otherwise you need a separate amplifier to drive the (non-powered) monitor speaker.

The amp in the powered monitor will generally also run an additional non-powered monitor if required.

 

 

  PA Department - Frequently Asked Questions

These are some of the basic general questions we have been asked, we hope you will find them helpful. ALL the letters on this page are genuine!

  Dear Rock Factory,
Quite possibly due to the fact i am a drummer i know nothing about PA and such thngs. Could you please inform me on the basic knowledge needed for example.
what do PA systems have
What do they do
WHAT ARE THAY!?!?!?!?!?!?!?!?!?!

Please help

Cheers Paul Sergeant


Good place to start Paul.

A guitarist has a guitar and a guitar amplifier, a bass player has a bass and a bass amplifier, a singer has a microphone and a PA (Public Address system).

So a PA is basically a microphone, amplifier and speakers. Of course, we can have amps that will allow for more than one microphone, by having more than one input. Also we don't necessarily have to stick the microphone in front of a person, we could place it in front of the bass drum say, then we say the bass drum is mic'ed up through the PA. Some bands just put the vocals through the PA, some mic. up the entire band - maybe half a dozen mics on the drums, guitars, bass, keyboards, whatever.

This lot can the be controlled from a mixing desk in the audience, and the on stage amps are mainly for the musicians to hear. We can also send all the sounds to dedicated speakers on stage for the performers to hear what everyone else in the band is doing - this is called a monitor system. This is the basics, it is as simple or as complex as you need it to be. (and can afford!).

Hope this helps

John (PA Dept)


I was browsing your site and got confused with some of the power ratings you gave - My system needs to be a minimum of 400W a side but ideally I would like to have up to a 1KW system depending on the price!
- Stef


You've really put me on the spot with this one, Stef! I'm sure lots of us are confused about this. The problem is that unlike most measurements, a watt can be a pretty vague thing. For instance, if we were told that a bag of apples weighs a kilogram, there is no room for misunderstanding - a kilo is a kilo!

But what if we say a speaker will handle 100 watts?
Well first let's look at what a watt is. For our purposes it is enough to say it is a quantity of electricity going through the speaker, and, just like in a light bulb or electric fire, this will cause the speaker to get hot. Ultimately, it is the ability of the speaker to withstand this heat that determines its power handling.
So far so good.

But here is the difficulty: - unlike a light bulb or fire, the electricity going through the speaker is not plain mains electricity, it is the stuff that goes to make sound, and as we know sound comes in many flavours.
Usually, certainly in our case, this sound is in the form of speech or music of some kind, which is not constant over time, there are gaps between words and musical notes. Now these gaps (sometimes silence, sometimes just quieter bits) give the speaker a chance too cool before the next loud bit, and in general we say (fairly arbitrarily) that music is half as heat producing as, say, mains type electricity.

So, a 100w RMS (mains type electricity) speaker, can cope with 200w program (music type electricity), because the amount of heat involved is the same.

Furthermore, this same speaker will take a lot of heat so long as it is applied only for a very short time.
This is called peak power, and is usually double that of program rating (music power).

So our 100w RMS speaker is 200w program, 400w peak.

There are other ways of measuring the power capability of speakers, usually to give even bigger, more impressive numbers (eg in-car hi-fi) but these are the common ones in our application.

Increasingly the music industry is switching from RMS to program rating for loudspeakers, partly because it gives a bigger more impressive number, but also it is a good guide to the RMS power you need to match these speakers. (i.e rms amp power should equal program speaker rating, give or take 15 - 20%) All the ratings you see on our website are manufacturers music program figures, or best estimate based on the physical size of the loudspeakers and their magnet structures.

Power amps are usually quoted in watts RMS, we do the same fo the reason above.

Stef, I hope this has answered your question to your satisfaction,
 
John (PA Dept.)


hi, i'm in a rock band. we are in desperate need of a good pa system. were thinking about getting a 1000w one, for playing small pubs/clubs, etc. we dont know exactly what we need so could you try and work something out for us.

thanks a lot

Jonathan Folkard

 


Jonathan,

1) You need a mixing desk with enough channels to accomodate the no. of microphones you intend to use
- eg 4 vocal mics. 3 drum mics, guitar, stereo keyboard =10 channels.
this means you need at least 10 channels, probably have to get a 12 channel desk, as not many 10 channel ones around.

2) You need a power amp(s) of sufficient size for the no. of things going through the PA, the size of the venue, and how loud you want to be. (Probably between 1000 and 2000w for a rock band in pubs/small clubs, miking vocals and and back line/drums supported by dedicated guitar/bass amps).

3) You will probably want some kind of digital effects (eg echo, delay, reverb). For smaller PA's this may be built into the amplifier or desk, larger rigs will need a separate rack mounted unit.

4) You will need speakers of a size and power handling commensurate with the power amps.

5) That's it ! - apart from of course - microphones, cables, cases, stands, and probably a van!

John

(PA Dept)



Hi
I was just wondering about monitors, im a drummer and i was just wondering how monitors work and can they go through any pa system, also is it possible to use a guitar amp as a monitor?

Kieran


Monitors are just another PA pointing back at the performers. You need monitor speaker(s) and a power amp.The amp is sometimes built in to the monitor, when it is called a powered monitor. You link from the monitor output on the PA system into the amp, and then on to the speakers. Yes you could use a guitar amp, although it would not be ideal.

John (PA)



Hi guys, my son is in a band and they are wondering how they can record
their own stuff.

Can they use the desks listed on your web site? If so what else do they
need?

And what is the difference between powered and unpowered desks. I noticed
in another query that you suggest a 12 channel desk yet all the powered
desks seem to be eight channel only?

Its all very confusing!

Alan Gent
Business Consultant MEBP


 

Alan, let's see if we can clear up some of this confusion.

A desk (sometimes known as a mixing desk, or mixer) is a device to enable several sound sources eg guitars, voices, etc. to be mixed together into one output, which is then amplified for an audience to hear, or maybe broadcast as a radio program, or put on a CD or whatever. Each input source needs its own input circuitry on the desk, called a channel. Usually these channels allow you to alter the volume and tone of each input, and maybe add effects such as echo.

The output from the desk is fairly low powered, about a volt or so, not enough to drive a loudspeaker, so you need to connect the output (which is often stereo) to a power amplifier to drive speakers. A powered desk has a power amplifier built in, so it will drive speakers.

The low output is enough however, to connect to a tape deck, so to record on to cassette or whatever you don't need a powered desk.

You can get powered desks with more than 12 channels, but usually if you are using so many input channels you would use a separate power amp, or amps, hence we tend not to stock them.

So yes you can use the desks listed on our website, but you would need a recorder of some kind -(these days it is usually a computer.)

John (PA)
 


Hi, I am a drummer and i have a dilemma. When me and my band play live we use a 150 watt P.A and hundred watt guitar amps and a 200 watt bass amp. I'll get to the point, - the rest of the band can't hear the bass drum. i have tried taking out the muffling in the drum and taking the front skin off, But it still isn't loud enough. i am not too keen on buying single mics because i will inevitably buy a set one day. But what can i do until then, mic wise. Can i use a standard vocal mic or doesn't that pick up the the low frequency of the bass drum?

Please help.

Cheers Joe Miller


 

Joe,

You can use a normal vocal mic for any drum with the possible exception of the bass drum. The bass drum is very loud and, well, very bassy. This can overload a normal mic, and it can sound bad. However, I would give it a try, you have nothing to lose if you have a spare mic lying around, everyones case is different, you may get away with it. Not sure the PA is big enough though, again try it and see, it may swamp the vocals. Try it.
If it sounds bad you need a better mic.

John (PA)
 


Can you help?
 
I currently have a PV1500 amp
 
I have some old (but very good) Peavey cabs (15"BW+ horn) which are 8 ohms and are rated at 350 per cab
 
I want to add some subs
 
I have seen some subs which match (cosmetically at least) they are Peavey Megasubs, they too are BW drivers and 8 ohms, but only 250W?
 
Now then, this is where I get lost, if I took an output from the amp L output into the sub and then linked the sub to the top( xover at 150hzts), then did the same out of the R output, does this bring the impedance down to  4 ohms?
 
Therefore does the Amp naturally compensate and throw out more wattage? does this mean that I actually get more wattage than the speakers can take?
 
This is my cheap option and I want to know if it will work without buying another power amp to power the bins.


So I want to know
 
a) will it work?
b) am I doing the right thing ( I have to steer clear of a 4ohm sub as that would drop the impedance down below 4 ohms and I have been told that PV dont like it? is this correct?)
 
If you can help I would be very grateful, sorry for being so thick but as much as I read up on it, the more confused I get!
 
Gary


 

I think we can clear this one up Gary.

First the power handling of the BW subs.
If they are an older model, some of the stuff (glue, coil former etc) used in their construction will not be as heat resistant as modern materials, and since it is heat that destroys speakers, the power handling will be correspondingly less. The latest Black Widows, for instance, are 500w.

Secondly the impedance question.
The answer to this can be very complicated, but to simplify it, the total impedance of the bin and the top together will be the same as the bin alone. This is because the amplifier is actually connected to the crossover in the sub, and it will be an 8 ohm crossover in an 8 ohm bin.

Ideally you should have a 4 ohm top with a 4 ohm bin (and 8 with 8) for the crossover to work as specified, but in practice it is not very important.

So to summarise, if you use the 8 ohm bins with your 8 ohm tops, you will end up with 8 ohms per side.

John(PA)


Hi,

I'm trying to learn about live sound, and I'm just totally confused about the whole ohm thing. Speakers have ohm ratings, and the power amps say that they can run xxx watts at yyy ohms. They give different power ratings for different ohm levels. I'd assume that if you hook 1 8-ohm speaker to 1 channel, then you're running at 8-ohms. I guess I'm not sure what ohm rating you're running at when you daisy-chain more than 1 speaker.. so 2 or 3 speakers are running off of 1 channel. I've seen guys do that with monitors.
Can you mess something up doing that, and/or how do you know what ohm rating you're running if you do that?

Thanks,
Marc



Marc,

What you need here is a basic physics text book on electricity, but in brief, the ohm rating is the resistance of the speaker, the lower the resistance (Ohms), the easier it is for the amp to push electricity through - the more power you get.

If you connect two speaker cabs, you are allowing two paths for the electricity to go through, so the total resistance is half that of one cab. (i.e. two 8 Ohm cabs is the same as one 4 Ohm). Three cabs would be 1/3 of the resistance of one i.e. 8/3 = 2.666.

If the cabs are of differing resistance it gets a bit more complicated, but it is always going to be less in total than the smallest one.

Take care, you must not go below the minimum specified for the amp (usually 4 or 2 Ohms), or you risk damaging the amp.

Also, although lower Ohms gives you more power, you don't get anything for nothing in this world, you lose some quality

As you might expect, there are equations to work this stuff out, and I have simplified the whole story, but this is a good basic starting point.

Hope this helps,

John(PA)
 

 
Hi Rockfactory This a quiere about PA's, which hope fully you can help with.

I play in a pop/rock band and we are suffering from not enough power in our PA, so we don't get as good a sound as we should. Please could you help me by informing me and quoting me on what you think we should have, ideally we would like to keep our speaker, so here is all the bits i thing you going to need.

Speaker:s Top Cabs are rated at 150 Watts 8 ohms (home Made?) Bass bins are Peavey Hy-sis 115 ( i think their rated @ 300watts and have a built in crossover?)

Channels wise we need 3 vocals 4 guitars/bass (lead, rhythm, Acoustic & bass 1 Kick drum 1 Snare with the possiblity of micing up toms on larger venues + possible playing a cd during breaks so some where in the region of 14 channels
we also run 3 monitors ,1 powered the other two link in,
venue wise we play mainly pubs/ cluds and a few outdoors gig, weather permitting! Dont laugh but we are currenlt running all (kick drum is the only drum) through a peavey 800F (effects and EQ buitl in) so im sure you can see why we are having problems.

The other problem is that a couple of the guy in the band dont understand how by changing the pa it would make a big difference, and dont like the ideal of taking a truck load of amps/cabels etc to every gig, and they dont understand about power from amps with speaker ratings (how can you run 200 watts speakers from 1000 watt amp and not blow them up) so could you please help and get me some figures and specs for what you think would bets suit us and if possible any suggestion on why we should upgrade (for the guys).

Thanks for helping a very frustrated drummer! Matt Hi Matt.


Based on the info you have given me, you are going to need a 2000 watt pa (or more). This is to deal with the amount of stuff you want to put through it, and the type of venues you play

Speakers :- use the ones you have if you wish, see how they cope, but disable the crossover in the Hisys 115 bass cabs.

Amps :- You will need 2 x 500w per side power amps or similar (see website), and a crossover to sent mid/top to one amp and bass to the other. (some amps have crossovers built in) 
One will drive the tops, the other the bins.
4 x speaker cables will be required, maybe a case to rack up the amps.

Desk :- You tell me you will need 14+ mic channels and one stereo channel (or 16 channels).
Alternatively, you could use a sub-mixer, i.e. a mixer (say 6 channels for the drumkit), which will feed into 2 channels on the main mixer, along with the other stuff.


"how by changing the pa it would make a big difference,"
- how does a top of the range Marshall make a difference to a guitarist with a 10w practice amp?
A bigger PA will allow for bigger venues, with less feedback and more clarity.

(how can you run 200 watts speakers from 1000 watt amp and not blow them up)
The 200 watts is an average rating, the speakers will take more for short periods of time. The amp needs a higher capability to deliver those short transients (as they are called)

Ideally the rms rating of the amplifier should be roughly equal to the music program rating of the speakers 

any suggestion on why we should upgrade
If you want the band to sound better, ........practice more and use better equipment :-)


John(PA)

Attention:  PA Dept  

Subject: PA Dept  : Power Amp advice  

Message: Hi there.

We bought a powered desk from you a few years ago now and we are at the stage where we are pushing it to the point it is clipping and there isn't enough headroom.

We want to get a power amp to help this, but don't know how to buy one.

The desk is 500w each side and our speakers are Peavey which are also 500w and are 4ohm. We also have bass bins.

What size power amp could we get that would make a difference to the headroom and also not blow the speakers? Also I've noticed that 4R and 2R is mentioned. What does this mean?

Many thanks 

From: James

 

>HI James,


Sounds like a separate power amp to drive the bass cabs is in order. I suggest 500w per side (or thereabouts) at 4R.

4R means 4 Ohms. i.e if your speakers are 4 Ohms each, the amp will deliver 500w into them. We used to use the Greek letter Omega for the Ohms symbol ( Ohmega - geddit!) - but computer keyboards generally don’t have this symbol, so we use “R” (for Resistance)

John

 

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