How Much Amplifier Power Do I Need?
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I cannot tell you the number of times I have heard a conversation about amplifier power go like this: “I hear that B&W speakers need at least 400W,” or, “I heard that Paradigm speakers are very power-hungry.” The fact is, there IS a way to figure out how much power your speakers will need and how to pair an amplifier with the speakers you already own or are looking to purchase. To determine the amplifier power, you will need the following items:
  • Speaker sensitivity specification (typically dB SPL /1W /1m)
  • Number of speakers you are using
  • Distance from speaker(s)
  • How loud do you want your music to sound, for general reference
  • 70-80dB for speech only
  • 80-95dB for light music
  • 95-110dB for heavy music

Rules to Remember
  1. Every time you double power or double the number of speakers, you increase the sound pressure level (SPL) by 3dB.
  2. Every time you double the distance from the speaker, you decrease SPL by 6dB.
  3. A speaker specification of 95 dB SPL/1W/1m means that at 1W of power, the speaker will deliver 95 dB SPL when you are located 1 meter away from the speaker.

Power Calculation Example Let's use the B&W 703 S2 speaker, which has a specification of 89dB spl /1W/1m. Most people will be using two speakers. This means double the power so it effectively makes the speaker specification 92dB SPL /1W/1m, or 3dB higher, as per rule #1. Now let's look at how rule #2 works. Every time you double the distance from the speaker, SPL decreases by 6dB. The table below shows how our 92dB from earlier decreases with distance.
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Let's say we will be sitting 12 feet away from the speakers. We can see how power will affect SPL, using the table below.
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My personal opinion is that 100dB SPL should be more than plenty. Consider for example that movie theaters aim for an average of 85dB SPL (1). With this, you can see that an amplifier needs to be able to provide somewhere around 120W per channel. Summary Don’t just listen to somebody about how much power you need; figure it out properly. Orchard Audio’s high-performance BOSC GaN amplifiers produce 150 Wrms of power, and should satisfy most people. Refrences: (1) https://www.ecoustics.com/articles/ideal-spl-home-theater/
(Edited)
thumb_upD. Ford, foobar8, and 33 others
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pliedtka
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Jun 17, 2020
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From my own experience for 2way 88dB/2.83V, 4ohm impedance to drive to satisfying levels with high dynamic music like symphonic, organ, something like 100-150W (8 ohm) of clean power with good current drive should be OK. Once we listened to some piece with crazy dynamics, some decent lows and my friends little 60W clipped because the power supply couldn't keep up with current demands. There was a big crack while bass hit the low note: my friend jocked "ups we broke it". So, yes it's better to have extra reserve of clean undistorted juice than to clip the amp and fry voice coils. 400W per ch maybe for inneficient 83dB/2.83V spkrs, if voice coils can handle it, or large spkrs with demanding impedance characteristics in very large room.
Jun 17, 2020
orchardaudio
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May 18, 2020
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May 18, 2020
sup27606
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Feb 28, 2020
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I think, any discussion on sound pressure level should come with a disclaimer as to what is permissible for what duration to avoid hearing damage. For instance, above 85 db, the risk to hearing damage increases with increased exposure, according to the link posted below. So, heavy music at 95-110 db should be listened to for a only a few minutes at a time to avoid hearing damage. I think, these facts should be made clear in the article. http://www.sengpielaudio.com/PermissibleExposureTime.htm
Feb 28, 2020
roissy
45
Feb 28, 2020
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You have to fully understand the principles of sound to use that chart. They are using the "A" weighting for measuring sound levels, which cuts the lower frequencies as much as 30db over the "C" weighting. Also the standards listed are for workplace, in other words, everyday exposure... My overall standard, not hurting my ears, (sometimes they can clamp) and if there is ringing or a hearing change afterwards, IT WAS TOO LOUD...
Feb 28, 2020
sup27606
6
Feb 28, 2020
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You said, "Also the standards listed are for workplace, in other words, everyday exposure". Thats is actually similar to a home audio setup, which for a music lover could be used on a daily basis, hence the sound exposure limits are applicable. You obviously know more about sound science than me, but anything that measures over 85 db using a crude iPhone decibel measuring app, produces ringing in my ears and reduces my hearing temporarily, so the recommendations in that link are not too off, I would think.
Feb 28, 2020
cell201135
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Feb 28, 2020
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Thank you very much this is super easy to read and understand the basics of audio levels to the uninitiated and learners alike.
Feb 28, 2020