Choosing a pa system

Whether your purchasing a PA system or hiring one, it’s important to first have an idea of your requirements & what options to look for. 

What is the PA System For?

This is the first question that needs to be answered.  Three different types of applications might include:

  • Vocals Only (E.g. Bingo Hall, Seminar, Meeting).
  • Recorded Music Playback  (E.g. Dance music at a wedding reception, party or club)
  • Live Music (E.g. Band)

 

A vocal system only needs to do one thing & that is produce clear vocals.  Vocals only need limited frequency response so this doesn’t require a lot of power.  Around 1 watt of power per person would be adequate.  The mixer  can be quite simple & only needs 1 or 2 channels.   A feedback eliminator or a graphic equalizer might be a good addition.

 

A system for replaying recorded music needs greater low frequency response (for bass instruments & drums) thus more power - around 2 watts per person. Again the mixer can be quite simple requiring 4 to 6 channels to handle connection of stereo inputs from CD players & Ipods & perhaps a microphone for a DJ.

 

A system for a band steps up quite a bit in power requirements & complexity.  It has similar frequency requirements as recorded music but is also subject to much larger transient signals that may damage an underpowered system.  Around 5 watts per person is required.  For vocalists to hear themselves accurately they will need  “monitor” or “foldback” speakers with it’s own amplifier.  The mixer will need to have “auxiliary” sends to route signals to the foldback speakers as well as to any special effects units.  The mixer will also need enough channels for all the vocalists & instruments that need to connected.  This can add up very quickly so at least an 8 to 16 channel mixer is required.  A “limiter” is a handy addition to protect the system. 

 

Amplifier Selection

Just because an amplifier is rated at a particular power doesn’t mean it can supply that much power continuously.  In my experience a good amplifier will deliver around 70% of it’s rating.   It may be thought that connecting an overpowered amplifier may damage speakers however the opposite is actually true.   An underpowered amplifier will “clip” the wave form being sent to the speaker causing a distorted sound & burning out the speakers’ voice coil.   My suggestion is to exceed the speaker rating by around 50%.  For example a 100 watt speaker would need a 150 watt amplifier.

 

Speaker Selection

The things to consider include:

·        The amount of power required.  A typical 12” speaker box can be rated anywhere between 100 & 300 watts.

·        Portability.  A solid timber speaker can give a nice sound but a plastic cased speaker may be much lighter.

·        Combo or split system.  If you need extended bass response it may be necessary to have some fairly large speaker with say 15” drivers.  Alternately it may be visually preferable to have smaller say 10” main drivers & a dedicated sub speaker on the floor.

·        Powered or un-powered speakers.   Many modern speakers are self-powered.  This can simplify PA set-up & you know that the amplifier has been matched to the speaker by the manufacturer.

 

Microphone Selection

A typical industry standard vocal microphone would be the Shure SM58 which costs around $AU150.  I mention this specifically to put things in perspective because there are plenty of sub $50 mics around.   The things to watch for are handling noise, popping with certain consonants like “P” &  uneven equalization.    This may be an area not to skimp on.

 

Mixer Selection

The things to look for in a mixer include:

  • The number of channels (and especially the number of microphone channels vs line in channels).
  • The number of auxiliary sends (for foldback & effects)
  • How many bands of equalization.
  • Does it have on-board effects?
  • Does it have a “Pre Fader Listen” button so you can monitor channels through headphones?
  • Does it have faders or rotary knobs?

 

A major question is whether to use a “powered mixer” which has the amplifier built in or a stand alone mixer.   A powered mixer can be more portable & easier to set-up & operate but often has fewer features & allows you less flexibility of configuration.

 

Quality

With audio equipment the rule is pretty much that you get what you pay for.   There can be budget equipment that sounds good but the sacrifice you often make is in reliability.   That said it’s important to consider:

  • The amount of usage
  • The sound quality required &
  • Whether the user is “mission critical”.

 

The amount of usage can vary considerably.   A PA system used at a school sports carnival might get used a few times a year so the usage is extremely light.   A system in a club might run 12 hours a day & therefore have heavy usage.

 

For some applications sound quality is more important than others.  A vocal only PA in a Bingo hall doesn’t need to produce hi-fidelity music whereas a night club PA might.

 

“Mission critical” refers to the importance of reliability.  The question is, what would happen if the system failed?   In the good old Bingo hall it may not matter that much, the presenter could just yell louder but for a concert event with paying guests failure might be a commercial disaster.

 

The goal then is to decide what appropriate quality of equipment is.   There may be times when budget equipment is completely appropriate & anything more would be a waste of money & other times when buying budget equipment would mean taking great risk or getting inadequate performance.  

 

When purchasing a PA my opinion is that it’s often better to buy quality used equipment rather than new budget equipment.  Complete used PA systems can also be bought for a fraction of the price of the new components.  It might then be viable to sell of unwanted components at a good price & add any extra components as needed.

 

Conclusion

There are more considerations than I can list here when acquiring a PA but this should be a good starting to point to allow you to evaluate.

 

Lee Wright.

 

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