How To Choose A Band PA System

Author: John Goldsmith   Date Posted:31 May 2016 

How To Buy a Sound System For My Band

It's worth mentioning at this point that if the following explanations get a little heavy going then be sure you opt to buy your system from a professional audio dealer. 

Most music stores will not have any real depth of knowledge in audio and will just be happy to sell you something that fits your budget, not necessarily your purposes.

A professional Audio dealer will quiz you on exactly what you intend to do with your system, where others will maybe ask you how much you want to spend, a dead give away.

I'm going to try and simplify what can be a very challenging process for all but the experienced and trained audio engineering folk.

Before embarking on specific system suggestions, some background on basic acoustics, audio power, and sound wave propagation will help you understand the reasons behind the suggestions I have for you.

The volume at which we hear is a product of the sound pressure produced by the loudspeaker. That sound pressure is affected by several things in the chain. Working backward, the efficiency of the speaker itself, the power of the power amplifier, the gain of the preamplifier, the type of microphones and the loudness of the source, be it a voice, guitar or recorded music.

It follows then that the first thing to check when selecting a suitable speaker is the sound pressure level (SPL) the speaker is capable of producing. A very common mistake it to look at the advertised power rating of the speaker. We'll talk about power ratings a little further on.
For most small entertainment venues an SPL of around 90db will be comfortable.

SPL ratings of speakers are usually quoted at 1 metre from the speaker.
Sound propagates in accordance with the inverse square law. Simplified this means that for each doubling of the distance from the speaker, the SPL will halve. 

As sound pressure attenuates logarithmically, this means a reduction of 3db with each doubling of the distance. To simplify even further, let's say we have a speaker that produces quotes an SPL of 110db, at the two metres from the speaker it will produce 107db, at 4 metres 104db, at 8 metres 101db, you get the idea.

 

Now A Few Comments On Power Without Overcomplicating The Subject.

There are many ways of measuring and quoting the power of a loudspeaker and amplifier. 

Average, RMS, peak, continuous, some manufacturers will quote it measured at one frequency, some at several, and there are a few others as well. Enough to say that not all speakers are created equal so beware.

The popular trend at the moment is to quote peak power where the old trend was to quote RMS. 

Neither of these is particularly relevant to music reproduction as we are dealing with a continually varying signal. Continuous program power is probably the most relevant but rarely quoted these days. Although not technically correct, if you halve the quoted peak power rating you are in the ballpark.

The important point here is that just because a speaker is rated at 1000 watts, don't think it's going to blow the roof off.

Just a side note here, you are much better off doubling the capability of the speaker compared to adding a second speaker. Quite simply unless you need a very broad coverage, then a single speaker will provide a  better dispersion than two where the wavefronts can cause cancellations. That means some listeners will miss out on certain frequencies.

 

A Short Word On Speaker Input Sensitivity.

Most powered speakers will have a variable input sensitivity suitable to accept a signal from a microphone or a mixer depending on the setting. 

Power amplifiers though usually have a fixed sensitivity. The main issue here is to be careful mixing different power amplifier models or brands. It can be done, but you will need different levels to drive them to their required power output.

Dispersion and speaker throw are also issues that need to be considered. There's little sense in buying a short throw speaker with a wide dispersion for a long narrow room. Equally using a long throw speakers in a wide room will throw the sound straight back at you, while the listeners to the left and right may not understand what is being said. 

Minimizing the amount of sound that finds its way to the listeners ears by way of reflection is a major challenge if you want the listener to understand what is being said. That is paramount in a conference facility or church. As a guide, if the speaker does not have any form of horn loading in the mid and high frequency then most of the time it will be a short throw speaker.

You can see that choosing the correct type of speaker is more important that the brand on the speaker, unfortunately, many stores have a limited brand selection let alone a range of products for different purposes.
To save unnecessary angst for those needing only a simple system, I've split systems into three categories.

 

Small Portable and Budget Systems
Suitable for solo artists and duo's working in small venues holding up to 100 people.

In this area, the powered speaker provides a simple cost effective solution where most of the technical issues are taken care of for you; all be it sometimes at the expense of a one size fits all solution. That is not to say that passive speakers with a separate power amplifier are to be dismissed. 

Sometimes it will be the better option. If your speakers are likely to be subject to weather or in an area where running 240-volt power is not desirable then the passive solution is for you.

Trying to buy a system that will fulfill all your needs will always be a challenge, instead, opt for something that will service 80% of your needs and hire extra gear for those 20% occasions.

There are many systems available now where the best option is to buy a couple of speakers that will handle small venues on their own, then by adding a Sub bass speaker allow performance in larger venues. Freeing up sight lines is another advantage of compact mid/hi speakers augmented with sub bass speakers. As low frequencies are less directive that higher frequencies there's no need to buy two subs, and no need for them to be co-located with the Mid/Hi speakers. 

Don't, however, put them too far removed as you do what the bass to maintain an acceptable phase relationship with the higher frequencies. Placing a sub on the floor will give you increased efficiency and putting it in a corner will win you some extra sound as well.

If your act is acoustic and vocals most likely a couple of speakers with a 12-inch speaker and a horn with a peak power rating of 1000 watts will be quite sufficient.

There are certainly smaller units that outperform, but you will find when you want to reduce the size and maintain the performance the price will increase.

If you plan to introduce a drum machine, drummer or bass player, you will need either a sub bass speaker or at least a 15-inch speaker and horn system, preferably with an increase in power output.

Don't be frightened of power. Power is your friend. There's a lot to be gained in having what we call headroom in your system, or unused power available.

Keep in mind people's ears are on their heads, so aiming speakers at their feet or the roof is not the most efficient solution. Placing the speakers on a pair of decent quality stands, keeping in mind not to extend them too high where they will create a hazard We will cover fold back or monitor speakers in the next section as the concepts are similar.

 

Typical Small Band System
Electric Guitar, Bass, Drums, Keyboard and Vocals.

The first consideration here is that we will have a fair amount to acoustic sound level coming off the stage from drums, guitar and bass amps, etc. That is before we even start putting microphones on anything. 

Regardless of whether all instruments are mic'd or whether some mic'd and some not, the system will need to place the vocal volume above the stage sound. 

Using a mixture of stage sound and PA will save money in the system and also on the need for a sound operator, but it will also take cooperation from the musicians to get a reasonable balance. A powerful tool is to place a chart in front of the guitarist to control volume. (an old muso joke).

With some practice and experimentation, this can be achieved.

The best option budget allowing is to have a system that will allow all instruments to be mic'd and an audio operator in the room to control the balance of all instruments.

At a minimum, you will need a couple of Mid/Hi speakers. Either 12 and horn or 15 and horn and a couple of sub bass boxes either 15-inch or 18-inch. Each box being around 2000 watts is a good starting point. 

The choice of speaker size will to some degree be guided by the type of music being played. The lower the bass frequencies you want to produce the larger the bass speaker. Usually, a 12-inch speaker will have better dispersion that a 15-inch in the vocal range.

Once you are that this level, you will need a stage monitor or fold back system to allow the player to hear each other. 

As soon as you introduce foldback, you are introducing more sound to the stage, which will, in turn, find its way back into the microphones and reduce clarity and separation in your finished audio product.

A few tricks here, keep the stage monitors to a minimum, keep them pointing to the rear of the microphones where possible and better still have player use in ear monitors where possible. In ears take a bit of getting used to but the advantages for both player and listener are well worth the effort.

Using a specific speaker designed for stage foldback will be an advantage as they will be more controlled and spray less sound all over the stage. Having some equalizer capability in the fold back system is also going to help avoid feedback when trying to produce a level the players can hear above all else that's happening on stage.

 

Professional Working Rock Band System

You are now in the serious end of town, so be prepared to spend a substantial amount of money. You may to also buy a truck to move the system and employ a road crew to unload, set, operate and pack up at the end of the night.

The sound pressure levels increase here substantially and as you will remember increasing the sound pressure is a logarithmic adventure. 

That means a doubling of the systems capability for each increase of 3db. Obviously as you can see with major touring systems, the sky is the limit, but let's stay with something capable of producing that is expected for most clubs and small outdoor gigs.

It's important to note here that our ears do not hear all frequencies equally and in fact the way they hear also changes with SPL. The lower the SPL, the more the bass frequencies will need to increase. 

Our ears are also less efficient at lower frequencies, so you are going to require more sub-bass for your mid/high speakers. For simplicity, let's say two to one. We will not discuss the different types of speaker configurations here, like point-source, left centre right and Line array. That's a subject in its self which we'll keep for another blog.

There will be many aspects to be considered purchasing such a system and sitting down with a very experienced audio design engineer will be critical to the success.

One valuable thing to understand is that in audio, there is always going to be the odd compromise. Whether it be in size, SPL, projection clarity bass punch or price to name a few. Keep in mind just because you spend  a lot of money it does not guarantee great sound quality. An ill-designed expensive system will be as bad as an ill-designed budget rig.

There are obviously other components that are required to complete the system.

Mixers, Microphones, Stands, Cables and Cases.

We will save mixers and microphones for other blogs so we can address them in greater depth.

I trust this has provided some insight into the complexities of the audio world and if nothing else, it convinces you to deal with respected professional audio companies that have many years of experience and are up with the latest developments in the audio world.


Comments (1)

Could you recommend a PA package for a four piece

18 September 2016
Could you recommend a PA package for a four piece band (one guitar, bass, drums, two vocals), I used to hire sound production but these days most of the gigs are simply not paying enough to cover the cost of hiring and many of the venues are small and only need a vocal PA. That said, some of the venues are slightly too big to make a vocals only PA sufficient, so it would have to be capable of micing of instruments when necessary (guitar and bass, but maybe only 2-3 mics on drums). We play fairly standard rock/pop covers ranging from The Police up to Jimmy Barnes/ACDC heaviness. For larger venues I will continue to hire a full system and operator but need my own for the smaller and medium venues. Preferred budget is $2500 but can go to $5000 if I need to.

Kosmic Sound Response
Hi - Can you please email us at online@kosmic.com.au and we will send through a quote we prepared for you? Thanks!

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