General Questions

[Rich newby]

hey guys im only young (13) and am just learning the ropes, and am skipping some really basic stuff so I just wondered if you could fill me in on some basic questions. Can you give the awnsers technical and not technical replys.

 

why do we have wrms, whats wrong with normal watts, why do we need it and what dose it do?

 

 

what is a comperssor ?

 

 

what dose ohms do?

 

 

what is the difference and uses for different types of mics? (e.g dynamic, caloroid)

 

if you match a pair of say 500w rms speakers to a 750w rms amp what would happen?

 

with an amp and a speaker set, do you have to get a perfect match?

 

 

 

im sure have many more questions, I just can think of them at the minut. ill add them into the topic when I remember them.

 

cheers

rich

[PDD]

Because I'm in a question-answering mood, and you're from Gosforth which is where I went to school, here goes... P.S. I'm not an authority on sound so please don't assume I'm right!

 

why do we have wrms, whats wrong with normal watts, why do we need it and what dose it do?

RMS = root means square. Very basically, it is an 'average' measurement of the power, as opposed to the peak. It gives a more realistic assessment of how a piece of equipment will perform.

 

what is a comperssor ?

Again basically, a compressor is a piece of equipment which 'smooths' louder sounds in order to make the overall mix seem louder. (Actually, it's quite hard to write a basic description of what it does!)

 

what dose ohms do?

Ohms is the unit of measurement for impedance. You need to know the impedance of, say, a loudspeaker so you can work out how many loudspeakers can be driven from a particular amplifier.

 

what is the difference and uses for different types of mics? (e.g dynamic, caloroid)

I can't really answer that in a short post. I suggest you do some research (internet, Google, other posts). Basically:-

Dynamic - moving coil/diaphragm and a magnet, converts sound pressure into electrical signal.

Condenser - capacitor does the same job. More fragile, requires a power source (e.g. phantom power).

There are others.

~

Cardioid - is a polar pattern, which is the area in which the mic can pick-up sound. Cardioid means heart-shaped. Others include omni-directional (every way), bi-directional (2 way), super & hyper-cardioid (variations of the heart-shape).

 

if you match a pair of say 500w rms speakers to a 750w rms amp what would happen?

It would work quite well assuming the user knew what they were doing. I was taught to over-spec the amp to the speaker, so there is enough power 'in reserve' to drive the speaker. However, you could easily destroy your speaker if you drive your amp too high. That is, of course, assuming you also have matched the impedance of your speakers (see above).

 

with an amp and a speaker set, do you have to get a perfect match?

It depends what you mean by a perfect match. If you mean matching power ratings then no (see above). You've already spotted the RMS thing, which is good.

 

why is 3 phase lighting perfferable to 1 phase lighting. what is the difference and what is the advantage?

(You could make a new post under Lighting)

But... It isn't necessarily preferable, but why not have 3 for the price of 1, eh? Basically you get 3 lots of 1-phase power, so 3 times the capacity. Don't mess about with it though!

 

Hope this helps.

 

P.S. Please use the Spell Check function when posting!

[J Pearce]

To explain compression a bit:

 

It makes the peaks quieter, then makes everything louder so the new peaks are the same volume as the old peaks.

So in a roundabout way it make the quieter bits louder.

This has the effect of making things sound smoother, until it is overdone when things become tiring and lifeless.

[alqueenan]

IMO the definitive guide to learning theatre sound is the appropriately-named Theatre Sound by John A. Leonard (John's company's website is at www.aurasound.co.uk), which can be bought from Amazon.

 

Also, I wrote a couple of 'Intro to Sound' docs while I was the sound training guy for the performing arts section at my Uni. They were training session handouts so not all the stuff will make sense, but they might help a bit. The second one contains a bit of stuff about microphone types and patterns. They're sat on the server of a postgrad friend of mine who is still at the Uni.

 

Part I

 

Part II

 

Part III

[robloxley]

what is a comperssor ?

A compressor is a piece of audio equipment that compresses the dynamic range of the sound passing through it by applying gain reduction when the input exceeds a certain level. In other words, when the sound gets too loud, the compressor turns it down.

 

[basically it has a threshold control which sets the level at which the compression starts; below the threshold nothing happens, above the threshold it reduces the level of the signal by an amount set by the ratio knob. This actually makes the output quieter than the input, so the gain knob can be used to rectify this.]

what is the difference and uses for different types of mics? (e.g dynamic, caloroid)

As above, I think you mean between dynamic & condenser mics; cardiod is a microphone pickup pattern.

[James]

When used properly a compressor compresses the dynamic range of an electrical signal passing through it.

 

In reality you can go and listen to an orchestra. An Orchestra could peak in the loud sections to something like 120 dBA and the quiet bits be about 20dBA

 

The orchestra could be said to have a dynamic range of about 100dB then.

 

If you were recording this on to magnetic tape then you could have a problem as magnetic tape has only got a maximum dynamic range of about 50dB before you either over saturate the tape or the signal gets lost in the backgroun magnetic noise of the tape.

 

Therefore you would loose half of the orchestras sounds completly. If you set the tape up to record the loud bits you would loose the quiet in noise, and if you recorded the quiet you would hear the loud distorting when it peaked.

 

So Out comes a magic box called a compressor.

 

In its simplist form a compressor allows you to altar the dynamic range of something. Take the orchestra, If you recorded it with a compressor compressing everything with a ratio of 2:1 then you would be able to hear everything after recording it onto tape.

 

Or if you were radio 1 you would compress everything at 25:1

 

There is a bit or a roumor about that Radio 1 is never any lower than PPM5 meaning everything has a dynamic range of about 4db

 

how can radio 3 and 1 ever come from the same broadcaster.

 

James

 

Ps Apologies for pulling aproximate fixures out of thin air to attempt to explain one of the things a compressor can do, I don't care if your 1812 overture hit 150dB A weighted or your concert hall has a background noise of 15dB It's 23:15 and I should be in Bed.

[Carey D]

hey guys im only young (13) and am just learning the ropes,

what is a comperssor ?

<{POST_SNAPBACK}>

 

Hi Rich, you've got some great answers here!

I shall add something I wrote a while back for someone else who wanted a basic description. Just another take on what a compressor does:

 

' Well, a compressor... compresses, or 'squashes' the audio signal to reduce its dynamic range. As a singer you can sing sensitive parts quietly and then belt out the more energetic moments. This can present a problem for the sound guy who may be pushing up your fader one minute to get your quiet moment heard above the instruments, and then pull it back when you get close and loud on the mic. The wide dynamic range of the human voice is compounded by the variable distance you may sing from the microphone. Proximity effect (louder and more bassy) can make the close mic moments louder still.

 

So, the idea is to have the assistance of an 'automatic' hand on the fader. It can be quite subtle and simply pull back the louder moments, or bring up the low moments too, all done fast and seamlessly.

 

The compressor has several controls that need to be set. Some offer 'auto' modes that make it a lot easier to use. Here's how it works. The input signal level is measured. When it reaches the 'threshold' level you have set, it reduces the rate at which the output level rises by the selected 'ratio'. For example, a ratio of 3:1 means that a 3db rise in input level above the threshold would result in a 1dB rise in output level. It's a bit like pouring water into a glass that is straight most of the way up, and then opens out to a wider diameter to the top. The water level rises more slowly once it passes that point.

 

How fast the compressor responds is set using the 'attack' and 'release' controls. Different setting work better with different sources such as vocals, bass guitar, kick etc. If you have set the threshold quite low and a reasonably high ratio then the overall resulting level may drop significantly. In this case you can restore this by turning up the 'make-up' gain. The compressor then starts to provide the effect of 'bringing up' quiet vocals as well as squashing loud moments.

 

The 'gain reduction' meter displays how much compression is taking place. For example, you may want to adjust the controls so you average between 3 and 12dB compression on the louder vocals.

 

It is helpful to look at a graph of input versus output level. For no compression, a 1:1 ratio it is a straight 45 degree line. With compression the line tilts until it becomes almost flat at a very high ratio, say 10:1. At this point it acts more as a limiter. If you want to see and experiment with such a curve you can download (free) our iDR System Manager software from www.idrseries.com. Install it on a PC, run it off line and check out the compressor or 'ALL' window. Let me know if you need further info on this.

 

In summary, the compressor is a great tool for keeping vocal levels in check. It can help the listener hear the words being sung. Insert one on your vocal channel. Set the ratio to around 3:1 as a starting point.

 

There is a huge resource of information on compressors on this and other internet sites. Try a search too.

Hope that helps,

Carey (Allen & Heath)

[Rob_Beech]

Carey will be an excellent help here on the board.

 

your information and help at alt.audio.pro.livesound is priceless.

 

Good to see you here!

 

PS my new GL2800 (32) is IMO the best thing since sliced bread. and unlike the ML's you dont have to worry about "MUTE ELBOW" B-)

 

 

 

Rob

[si pie]

Just a quick note on the microphone types. The shure website has an education bit. Very useful for explaining beck electret mics (condensers)

 

shure Kbase

 

Also a quicky about amps and speakers.

 

Impedance - If you have 2 8ohm speakers connected together the total load is 4 ohms. 3 8ohm speakers makes 2 ohms.

 

2 4ohm speakers makes 2 ohms.

 

You need to make sure your amp will run to the minimum impedance you want to put on it.

 

Also if you have a 500w speaker you probably want a 600 - 700w amp to give you some headroom so that you don't get a distorted sound. The peak output of a speaker is normally much higher than the rms output.

 

But you don't want to give yourself too much headroom because you run the risk of blowing up your speakers. Although a good game of "catch the cone" is always good fun!

 

Also extra wattage costs a lot more money!

 

Hope this helps

 

Simon

[Rob_Beech]

3 8 ohm speakers is 2.667 ohms 4 8 ohm speakers is 2 ohms.

 

just to correct your typogr..ty..yeah...

 

Rob

[Rich newby]

Ok guys, thanks so far, iv thought up a couple more

 

Why can running a system at 4ohms be dangurous? I have a 2 tops and 2 subs, so could I run the system of the size of amp I have already with just another pair of speakers?

 

 

what are the different uses for lots of different types of mics? (as many as you know please)

 

thanks for your replys

rich

 

just some bloke, thanks a lot, you really helped me understand the 3 phase bit and now I can understand the tech bit completly :)

[Bryson]

Right, I've attempted to split this topic into the power and sound related parts. It ain't perfect, by any means, but better.

 

Next time, ask unrelated questions in different topics! :D :) :P

 

So, try and keep these two new topics on-topic please! Ta.

[PDD]

Why can running a system at 4ohms be dangurous? I have a 2 tops and 2 subs, so could I run the system of the size of amp I have already with just another pair of speakers?

 

It's not, unless your amp isn't capable of handling a 4 ohm load. I think most decent amps can do. It's 2 ohms you need to avoid. From what I remember, the power can exceed the rating (=gets hot) and the frequency response goes all funny.

 

Without knowing the ratings of your speakers, I would guess with your current setup you won't be able to run anymore speakers from just the one amp. If your subs and tops were equally 8 ohms each, that would be 4 ohms per side. You would also need to know your speakers could take the power rating at the lower impedance.

 

what are  the different uses for lots of different types of mics? (as many as you know please)

 

Now that really is too big a question to answer succinctly! Very generally - dynamic mics for loud sounds/close miking/vocal/hand-held use; condenser mics for wider frequency response/distance pick-up. If you want model numbers I suggest you visit some websites as everyone has favourites!

 

P.

[Rich newby]

hi again paul <_<

 

ok my tops are 150w and subs are 300w. thats 450w per side. and my amp is 1.4kw so I still have a lot of extra wattage to play around with.

 

cheers

rich

[PDD]

Do you know the exact spec for your amp? Is it 1.4kW per side, or 1.4kW in total (700W per side), or is even mono? And more importantly, does it say, for example:- 1.4kW @ 4 ohms. (Of course we've already covered whether its RMS or peak as well).

 

How about the speakers? Are they 4 or 8 ohms?

 

P.