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How much power do I really need?

Scott Bierfeldt

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How much power do I really need?

Probably less than you think.  It all depends on the design of your amplifier and your speakers.   

Not all watts (w) are created equal and we will touch on biasing wattage toward current rather than voltage in a separate post.  For these purposes, we will assume a watt is a watt and everyone measures it the same way.  We all know that is not the case, but it makes this conversation simpler. 

Look at the specs of your speakers and you will see a rating called SPL.  This stands for Sound Pressure Level (SPL) in decibels (dB), and is the volume produced by your speaker with one watt of power delivered via one meter in distance.  This is a rating of efficiency.  The higher the number, the more efficient your speakers-- and the less power your need to make them loud. 

Here are two scenarios.  A speaker with an SPL rating of 86dB and 91dB which is the range for most speakers sold in America.

The assumptions are:

  1. A normal size room no larger than 20 x 20 feet with an 8 foot ceiling
  2. Two speakers within 4 feet of the wall
  3. The listener sitting about 10 feet away
  4. Reference volume for music is 80 dB with a need for 15dB in headroom – To put this in perspective, normal speech is 65dB, 80dB is the volume of your garbage disposal grinding up food
  5. According to THX, reference volume for home theater should be 85dB with a need for 20dB in headroom – This would sound like you are in an IMAX

A speaker with an 86dB SPL needs 0.6w of power to hit our music reference level of 80dB and needs 2w of power to hit 85dB for home theater.  However, there are peaks in volume, in music or a movie, which is why we need headroom.  Headroom allows your amplifier and speakers to deliver those peaks in volume like a crescendo during a symphony or an explosion during a movie.    

To hit 95dB in output, that same speaker needs18w of power.  For music, 18w of power is fine for reference listening.  Alternatively, for home theater where you need to hit 105dB peaks in volume that same speaker needs 185w of power. 

For a speaker with an SPL of 91dB, you only need 0.2w of power for 80dB in volume and 0.6w for 85dB.  For headroom, you need 6w of power to deliver 95dB in volume.  60w of power will deliver 105dB in volume for home theater.  A 10dB increase in volume basically requires 10x more power. 

There are always exceptions.  If you want to turn it up to 11 and rock out, or you have a big room, you will need more power.  The more you want to go above these reference levels, the more power you need.  Consider this though: 85dB in volume causes temporary hearing loss and extended exposure to volumes above 90dB can cause permanent hearing loss.  It takes 8 hours of exposure to 90dB to experience permanent loss, 15 minutes at 115dB. 

If you take a little care in choosing your speakers, our lower output power amps will deliver all the volume you want or need.  Give them a try in your home and see.  That is why we have a thirty day, no hassle return policy. 


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