Speaker SPL - How much power do you need?

I want more power!

Your speaker choices make huge difference in the way your amplifier uses its power. For example, a 512 watt amplifier coupled with an 86 dB speaker will be just as loud an an 8 watt amplifier with a 104 dB speaker. How can that be?

Moving air is not like moving a liquid or a solid, high end speakers are only about 1% efficent when it comes to converting the electrical energy into sound. You waste a lot of power in heat. Small increases in actual speaker effiency results in high sound output, this sound output is measured in SPL (Sound Pressure Level). Its measured using 1 watt of power at a distance of 1 meter. Its a very general reference of efficency, and not of anything else.

Note: SPL is often also called 'Sensitivity' - same thing, both are measured in dB

Some Color has been added to show what it takes to get 100 dB, 110 dB, 120 dB and 130 dB SPL.

Higher SPL = Louder

How does this relate to what you hear?

• 40 dB SPL - Very quiet living room.
• 60 dB SPL - Average Conversation 5 feet from person speaking.
• 80 dB SPL - Same person shouting.
• 90-100 dB SPL - Platform of subway station as train arrives.
• 130-150 dB SPL - 100 feet behind airplane jet engine.

Match the solution to the need

General Usage - Area

What are some area/volume considerations? How much air do I need to move? Here are some guideline sizes to consider:

NOTE: 1 foot = 30.48 centimeters, 1 meter = 3.28 feet

• Average Mid Size Car (in the USA) approx 200 Cubic Feet (5.66 Cubic Meters).
• Living room that is 12 feet by 15 feet with an 8 foot ceiling = 1440 Cubic Feet (40.75 Cubic Meters).
• Small Performance Space that is 20 feet by 20 feet with an 8 foot ceiling = 3200 Cubic Feet (90.56 Cubic Meters).
• Mid Sized Performance Space that is 100 feet by 40 feet with a 10 foot ceiling = 40,000 Cubic Ceet (1132 Cubic Meters).
• Large Performance Space that is 400 feet by 200 feet with a 15 foot ceiling = 1,200,000 Cubic Feet (33960 Cubic meters).
• Stadium = usually more than 10 million Cubic Feet (283000 Cubic Meters).
• Outdoors = Infinate space.

Many clubs and churches are Mid to Large in area/volume. Some places have very high ceilings, this needs to be accounted for (especially if the speaker cabinets are going to be mounted up there). A solution that works well in the Home or a Car will not scale to the volume of air past a Small Performance space.

Issues

Higher efficency often means that the actual sound interpretation is less accurate. This is why Home and Car Audio speakers tend to be lower SPL; they are better for sound reproduction than Musical Instrument Speakers. On the other hand, when you are making music, you often buy speakers that give you a unique tonality (ie. they interpret the sound by adding thier own coloration/distortion) - this is a desirable trait for Musical Instrument Speakers, but not for Home/Car Audio applications.

In my experiance, using good quality Home/Car Audio Speakers for Guitar or PA use are very poor choices. Conversly, Musical Instrument speakers are marginal for Home/Car Audio use, unless you are prepared to equalize the 'coloration' out of them (which may not always be possible). Rarely do Musical Instrument Speakers have 'foam' surrounds - this is an easy way to aviod Home/Car Audio speakers in the wrong application.

The highest SPL Musical Instrument Speakers I know of are made by Celestion - Marshall uses them to get their 50 and 100 watt amplifiers as loud as possible. The Musical Instrument Speaker lines of JBL, Electro Voice, Eminence, Pioneer, Altec, and Jensen are also quite capable (there are many other brands). Some sources of these speakers are: Parts Express, Carvin and your local music shop. Don't allow anyone to talk you into low SPL speakers for PA, Floor Monitor, Guitar or Keyboard use.

Also see: Speaker Design and how it affects your choices for more information.

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