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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. This calculator is a very good starting point ; https://myhometheater.homestead.com/splcalculator.html Orchard Audio’s high-performance Starkrimson™ Mono amplifiers produce 150 Wrms (300W peak) of power, and should satisfy most people.
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Refrences: (1) https://www.ecoustics.com/articles/ideal-spl-home-theater/
(Edited)
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WilliamJeremiah
1
Nov 2, 2021
I agree with Warmouth. As long as you're there listening, you're always better off with more power than you need. Whether the same amount of power is used is only relative between two identical driver/cabinet configurations. A professional audio subwoofer cabinet driven with what a typical home theater sub cabinet requires isn't going to work out. A transducer structure capable of handling two thousand watts pink (continuously) isn't going to function properly with a mere couple hundred. Power is heat. Speaker ratings are there to prevent meltdown and/or self destruction. Rms is relative to continuous (pink noise) and Peak is relative to dynamic levels (music). I like to hit the upper quarter of Peak or Rms and half again, when matching power to speakers. Damage is more likely to occur during clipping when underpowering than it is when more than enough power is available and clipping is avoided.
SuperFlyEDSguy
37
Oct 29, 2021
Phenomenal summary! Though you’ll never get a bunch of audiophiles to agree on every point (correct or not), I do believe that you did a fantastic job concisely and objectively presenting a fairly complex paradigm in terms that everyone will understand. Kudos! 👏👏👏
SuperFlyEDSguy
37
Nov 12, 2021
I just now checked it out (2 weeks later) as I saved it in my ‘Reading List’ until I could find a good time to read it. From a technical perspective, it shines, objective as hell, and surely a 10/10! Your product designs are amazing as well! Do you have an EE background? I even saved a copy of the article to a folder that I keep my amp resources in as it makes a great ‘go to’ document for when you really just need the numbers and no added fillers. 😆 Here’s my very few criticisms: You write well and concise. You really need to include buttons or some method to “Print,” “Save as PDF,” “Share,” etc. I liked the article enough that I copied it into Word and manually cleaned-up the formatting, just so I could make a copy! If you try to print or save it as a PDF from within your browser, the “Recent Posts” take up far too much space on the right. The result is 50% of the content is visible until you get to the footer, which subsequently take up an additional two pages. That was a bit of a let down. 😔 Take a look at where you listed loudness of {60,80,100,120}dB, you typed “120db” (forgot to capitalize the ‘B’), at least it’s a ‘two minute fix.’ (Sorry to nitpick, but I notice things others may not.) Speaking of those bullet points referenced above, they are a sub-list to item number 4. The bulleted list should really be indented (just by a single tab though). This one may seem like hardcore nitpicking, but I assure you it’s not as I studied graduate Digital Marketing at Rutgers. You see, I struggled to find your phone number on your site and that is very, very bad! It needs to be in the header, big, bold, contrasting, e.g. anything that will get a buyers attention within a couple of seconds or they are likely to move on! Studies also show that buyers return to sites several times before making a purchase, especially for a $$$ item! Do what you need to do that will allow you to stay in contact with anyone-and-everyone visiting, and then send sensible promotions and offers. You should see a pretty nice increase in sales, or at the very least not lose any! That’s all. Those are my thoughts. Seriously, I liked the content that much that I just spent 45-minutes or so writing this follow-up! Keep up the awesome work as I’m eager to see more!!! — — — Update - 3/13/2022 - I realized that a couple of small things needed to be fixed as the post picked up slightly in popularity over the past couple of days, namely: (1) Fixed any words that were bastardized by Spellcheck! And, (2) Cleaned-up formatting just enough to separate ideas and points. ~ JR
(Edited)
orchardaudio
96
Nov 12, 2021
Thanks for the feedback. I already fixed a few minor things. Unfortunately the website service that I have will not let me change the formatting its just a template and that is the way it is displayed. I have tried some other templates and this is the best one I have found. I have EE background, you can see my profile here: https://www.linkedin.com/in/leonid-leo-ayzenshtat-9a988061/
Warmouth
0
Sep 7, 2021
Get as much power as you can afford (with in reason), never heard of too much head room.
alvarg
233
Jul 29, 2021
I agree with everything except the "95-110dB for heavy music" Or the 80-95 for "light music" I recommend everyone go out and buy a SPL meter (sound pressure level) and never go above 85db for at home listening. 85db for prolonged use is already enough to cause hearing damage
HMike
0
Aug 4, 2021
Agree. I find even 80 dB prolonged to be very uncomfortable. However, speakers should be able to handle peaks 20-30 dB above the average with classical music. Recorded pop music is usually highly compressed, so the peaks and average would be much closer (ie, constantly loud instead of intermittently loud) -- so maybe 10 dB headroom is fine for pop. Also, if you use digital equalization, an amplifier needs more headroom to account for any digital pre-cut. Unfortunately, I can't remember ever seeing speaker specs separated into peak and sustained SPL -- maybe someone that knows something about speaker design can provide some clarification on this? Just wanted to add: 12 dB pre-cut is probably the most needed with equalizing. That's based on my personal experience as well as the maximum EQ adjustment on a DBX 31-band graphic equalizer I own.
(Edited)
MZKMXCV
18
Aug 4, 2021
85dB is for average, the SPL levels stated here are for dynamic peaks. Movie theaters typically use THX standards which call for 85dB average and 105dB peaks (so 20dB dynamic range from RMS to peak).
redboat
0
Feb 25, 2021
Sounds levels fall as square of the distance in free space (and hence fall by 6 dB each time distance is doubled) but this does NOT occur in living rooms, where reflections have a large impact. So you'll need less power than the above calculations indicate. Also, very few listen to music much above 90 dB.
(Edited)
HMike
0
Aug 4, 2021
Room gain depends on frequency and location in the room. In a well-treated room it can produce a boost around 6 dB in sub-bass compared to the highest audible frequencies. That is just an average -- peaks and valleys could be up to +- 12 dB and vary depending on listening position. Fortunately the brain tends to average out narrow peaks and valleys.
orchardaudio
96
Nov 23, 2020
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ed_focal_1
0
Nov 20, 2020
Very interesting post and simple rules to apply. Thank you. I am surprised that you don't mention how power hungry are bass frequencies as opposed to high frequencies. We know that the power requirements double when the frequency is divided by two (If I am right). Does your rule #3 (sensitivity of the speakers) include such principles. Do the increase of distance or the volume of the room influence in the same way how bass and highs are perceived ? My experience is that, in order to avoid distortion and allow clear and "sound" bass (I listen mainly Jazz, vocal and classical), the amplifier must be "serious". Even for regular SPL. Regards
orchardaudio
96
Nov 21, 2020
As long as the impedance stays the same at low frequencies the amount of power would be the same. 20Hz at 8ohm with 10Vrms is the same power as 1kHz at 8ohm with 10Vrms. There are more factors to consider but in general this will get you into a very good ballpark. Take a look at this calculator: https://myhometheater.homestead.com/splcalculator.html
(Edited)
Scharfschutzen
48
Dec 6, 2020
Bass impedance rise is more prevalent on subwoofers than headphones.
pliedtka
9
Jun 17, 2020
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.
Scharfschutzen
48
Jan 15, 2021
SuperFlyEDSguy
37
Oct 29, 2021
No disrespect whatsoever, but please tell me you’re joking?! 🙃
orchardaudio
96
May 18, 2020
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