Amplifier, Speaker & SPL Calculator

To calculate the theoretical power requirement for an amplifier you need to know 4 values:

1) The distance from the speaker. This is normally the distance from the speaker to the last row of seats in the room.  Type in feet or metres (the metres is calculated from the feet – if feet is used). From this distance the Sound Pressure Level (SPL) loss over that distance is calculated.

2) The SPL required. This is how loud you want the sound to be at the distance specified. Some general levels are:

  • 70-80dB  for speech only
  • 80-95dB for light music
  • 95-110dB for heavy music

3) The speaker sensitivity. This is not an indicator of how sensitive the main (human) speaker is, but rather a measurement of the sensitivity of the loudspeaker. It should be available in the specifications for the loudspeaker. It is normally stated as the SPL measured 1 metre in front of the speaker with 1 watt of power driving the speaker. Hence the specification will read something like:

Sensitivity (1W/1m) = 91dB

4) Amplifier headroom. This is an allowance for the amplifier to cope with peaks without distortion. Note that for every 3dB allowance, the power requirement doubles.

Use the calculator below with different values to see the effect a change in any of these parameters makes to the amplifier power required.

Note: these calculation are for “open-air” where there are no reflections from walls, ceiling and/or floors. When reflections are present, the SPL losses can be reduced by up to 6dB.

For those who need to know, the formulas used for these calculations are:

\large{SPL\ loss = {20\times Log_{10}\left(\frac{Distance\, from\, Spkr\left(meters\right)}{1}\right)}

and

\large{ Amplifier\ power =  \large{10^\frac{required\,amp\,gain}{10}}

 

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27 COMMENTS

  1. Hello, I am looking for an amplifier to listen to music only, my speakers are Focus chorus 716 with a sensitivity of 91 db, in the manual recommend using an amplifier between 40 and 200 w, which suggests, thank you very much!

    • Hi Rafael,

      They look like nice speakers. As you have probably worked out from the calculator above, you don’t need much power for home listening. I suggest any of the brand name amplifiers with an RMS power rating of 60 -100 watts should be more than adequate. The bigger question on deciding which amp you want will be what features you want. Do you want streaming, bluetooth, phono? That will be the main difference between any of the brand name amps.

      Geoff

  2. Hey Geoff

    I am getting Klipsch SP 280 F speakers (specs at 8ohms@150/600 continuous/peak watts) and having difficulty making decision on receiver that would allow optimal functionality of speakers. Narrowed receivers down to: Marantz SR5011 at 8ohms/100w per channel. Yamaha RX A660 at 8ohms/70 watts per channel (I think), Pioneer Elite VSX 90 at 6ohms/165×7 watts channel. Not really sure what to do. Must the receiver Always match the speaker in ohms and watts? or the speaker match the receiver ohms/watts? I want some headroom too. Distance from components including tv will be about 15 to 20 ft. Thank you.

    • Hi Mark,

      The 280’s look a fine speaker. They are also very sensitive (98db@2.83v/m). This means with just one watt of power they produce 98dB of sound 1m away – that is loud. Even at 20 feet, and only 20 watts of power they will produce over 93dB of sound. So for normal domestic levels, I don’t think the power of the amp is going to be a major factor. Also remember that the difference between 100 watts over 70 watts is only 1.5dB – not much.

      So it probably comes down to other features. Do you need a headphone socket? do you need steaming capabilities? do you need bluetooth etc.

      You probably only need a stereo rather than a multi-channel amp.

      So, I probably haven’t really been much help. I would think any of the amps will work well. If you can, see if the store will set up the speakers with the different amps and see if you can hear any real difference, or which one you like the sound of the best – with your type of music. .

      Geoff

  3. Hi geoff,
    I’m glad i found this site and it will be useful for me. I changed my car radio stereo and install Aftermarket Car Stereo. after this installation the sound was not good, and i found Aftermarket Car Stereo is more powerful and doesn’t match with factory/original speaker.

    Aftermarket Car Stereo specifications
    55 watts 4 channel of 4 ohms each speaker ,
    how much is the power of the speaker that i should buy to improve the sound?
    Thank you

    • Hujambo Dastan, Habari wako?

      First off all we need to know why the sound is not good.

      When you say the sound is not good, does that mean it is distorted? If so, is it distorted just at loud levels, or all the time?

      Having speaker of lower power capability only matters if you overload the speaker. At normal listening levels it should not matter at all.

      If you have run it at full volume, you may have damaged your speakers, but you haven’t said you have done this so I’m thinking it is something else.

      There could be a fault with the aftermarket unit. If you can, test it with another (borrowed) speaker, or take it to person you got it from to test it.

      let me know what you find.

      natumaini haya ikakusaidia

      Geoff

    • Hi Prashant,
      It is not possible to connect seven 4 ohms speakers to a hifi amp and have equal power from each one. I suggest if you use a stereo amp to connect just 6 speakers, 3 speakers on each channel. I would wire them in series so that you don’t overload your amp.

      With a load of 12 speakers, just about any stereo hifi amp will work OK.

      Geoff

  4. Hello Geoff,

    Nice website, everything well explained, but i have a small problem..

    I have these 2 speakers of unknown wattage, 6 ohms each, from sony SS-D105 model, from the LBT-D105 HiFi of the 1990s.

    The question: how can i know which amplifier to use here, since i do NOT know the wattage the speakers support?

    The info i gathered from the manuals:
    – The HiFi manual says:
    Power Output and total harmonic distortion: with 6 ohm loads both channels driven, from 40-20,000 Hz; rated 12 watts per channel minimum RMS power, with no more than 0.5% total harmonic distortion from 250 millwats to rated output.

    – The Speakers manual says:
    Sensitivity : 89 dB/W/m
    Rated Impedance : 6 ohms
    Frequency range: 50-20,000 Hz

    Please help me find out which kind of amplifier i can attach to this pair of 6 ohm speakers, and what amount of power/ohm/etc is requested from the amplifier.

    Thanks loads,

    • Hi,

      It is likely your speakers are around 10-20 watts RMS.

      However the real question is how loud do need them to be? As you can see from the calculator above, you don’t need much power for normal listening levels in a domestic install.

      The speaker will work well with just about any amp from 5 watts to 80 watts. Whether the amp in under power or over power for the speakers, if you try hard enough you can always blow either the amp to speakers. The secret is to listen for distortion. Distortion is the warning sign that something is wrong and about to get a lot worse.

      Geoff

      • THAAAANK you very much geoff! Whenever i have to buy something from amazon, will always click on your link/ad 🙂 Also will tell audiophile friends about your website

        Will listen for distortion. Will buy Amp around 16W. I don’t need loud sound, just to be able to listen, 60 – 80dB at most at 2m from speakers.

        Thanks again 🙂

    • Hi Silmon,

      How powerful the amp needs to be depends on many things, including how loud you need the program, as you have seen in the calculator above.

      The speakers will work well with a 10 watt amp. But they won’t be as loud as they can go.

      For an idea on the best match for maximum power for your speakers, have a look at this note by Peavy themselves. Even they recommend you don’t use an amp which will allow the maximum power of the speaker without safeguards.

      Other manufacturers suggest using an amp with a RMS rating equal to the Continuous power rating of the speakers, or something similar.

      It is difficult to be precise because if you try hard enough, you can blow your speakers with too little power (feeding them with distorted signal trying to make them louder), and with too much power, making them distort. My line has always been to listen for distortion (and pay attention to the clip light on the amps and the mixer) because distortion is the warning sign of major trouble looming if you don’t turn it down.

      hope this helps some,
      Geoff

    • Hi Armando,

      It is difficult to say. It will depend on the impedance of the speakers, how they are wired and how loud you need it to be. I suggest they also need to be balanced with the rest of the speakers also. Not to mention how much money you want to spend.

      Geoff

  5. Thanks for your calculator. Can you describe how one should interpret a negative dB Amp Gain required, which provides a 0 Watt Amplifier Power? This can happen easily if the distance is small and the required SPL is 60, and the Speaker Sensitivity is above 100 dB.

    • Hi John,
      Yes, calculations can be interesting when using extreme values.

      This calculator is telling us how much gain we need in the amplifier to achieve the desired level at a particular distance, relative to one watt of power going into the speaker and measuring the output at one meter. So a negative gain is saying you need less than 1 watt.

      In your case, 60 dB is not very loud, and a speaker capable of producing 100dB with 1 watt of power is a very sensitive or efficient speaker. So to produce only 60dB from the speaker, you will need to measure the level a long way away, or have only a fraction of a watt driving the speaker.

      Interesting, thanks for the question

      Geoff

    • Hi Marty,

      Yes, the losses in the air due to distance is still the same. The power required is the same. However, because a powered speaker comes as a pre-configured package they often don’t tell you the sensitivity of the speakers inside – so it is hard to use the calculator – but the basic principle remain the same.

      Geoff

  6. Good Morning, Geoff.

    Thanks very, very much for this wonderful site. I’ve been puzzling through my home audio systems for years and this is the most helpful information I have come across. I will contribute to support immediately!

    I have a couple of specific questions, if you have a moment. Here’s the context: I am buying home audio for an 8 ft. ceiling room that is 17 ft. x 21 ft. We listen to mostly jazz and acoustic music (blue grass, celtic, new age) and a lot of classical music — usually at moderate volumes. (We play some classic rock…but do not generally play deafening heavy metal.)

    1) How much headroom should I allow for in calculating amplifier power requirements?

    2) What SPL level should I allow for in calculating amplifier power requirements?

    On my own, I’ve been figuring on 10 db for headroom and 90 spl (although I think the usual listening level is probably 80 spl, in truth.

    Any suggestions you might give would be very much appreciated. This is a brand new room and nothing has been purchased. So I’d like to try and do this right!!

    Thanks again for this excellent site.

    –norm st. landau

    As a follow-up question, can you recommend resources for unbiased audio equipment reviews?

    • Hi Norm,
      Thank you for your kind words, I’m pleased the site is useful to you.

      Regarding your set-up, I would have thought speaker selection and location are your bigger issues. Indeed the sensitivity of speakers can vary 10dB between brands.

      My general rule of thumb on speaker sensitivity is the higher the sensitivity (more efficient) the lower the quality. For an extreme example, a PA horn speaker is very efficient (high sensitivity) but poor quality. Money does buy an exception to this rule of thumb.

      In regard to amplifier headroom, 3 dB would be a starting point. However headroom is only required if the amp is running at full power – which it generally isn’t in a domestic situation. If the volume is turn down even just a tad, it is likely to give you the 3dB headroom. Keep in mind every 3dB extra gain you want, is double the power of the amplifier. 10dB headroom requires 10 times the power.

      I think I am saying don’t worry too much about amp power and headroom at this stage. I would suggest finding some speakers which you like the sound of while listening to your type of music. Then find a series of amps with the functionality you want. Then with the sensitivity of the speakers known and the max power of the amp known, use the calculator above in reverse to see how much headroom you will have at 80 and 90 dB listening levels.

      It might be worthwhile looking a getting a self powered sub woofer too. This will make a huge difference to the sound, especially for the bottom end producing instruments. Again, I suggest listening to a combination.

      The other huge factor will be the acoustics of the room. While not my forte, I know it makes a huge difference to the sound quality and how much power you need (or don’t need). Normally soft furnishings are better to an extent. Be aware of the furnishings in any test room you listen to, as they are probably set up to demonstrate the best sound – which might be different in your room.

      In regard to Hifi gear reviews, I’m not into them that much. Most of them should do a descent effort on the technical aspects, but after that it is a very subjective view. I prefer to listen to various offerings, and then research for any reviews on those particular items. Again, I would be reading mainly for comments on build quality and functionality – most other opinions on sound quality should be your subjective impressions.

      Anyhow, don’t if this helps or raises more questions,

      Geoff

  7. I have 32 speakers all rated at 6 ohms indoor/outdoor how big of a amplifier would you recommend.

    • Hi Jeff,
      The required size of the amp will depend more on the sensitivity of the speakers and how loud you need them to be, not on the impedance. Let me know some more details on the speakers, and the requirements for them and I’ll see if I can help. For that many speakers you probably need to use a distributed speaker system. Have a look at this article and then get back to me with your thoughts and further details.

      Thanks

      Geoff

    • Hi Juan,
      I’m pleased your have found the site useful. Thanks for your clarification question.

      Normally all power for speakers and amps should be RMS.

      Geoff

  8. Geoff, Glad to have found your site! I love what you’ve done! My dilemma is this: You give the ability to calculate dB and amplifier power to reach the distant last seat with a certain dB level – which is great. If I am to set up 2 zones, with proper delay techniques, then at what point in the dB “fall off” do I install zone 2 to raise the remaining portion of the auditorium to the nominal level. What power then is required? If one is merely raising the dBs enough to compensate for partial dB loss then a smaller amplifier and smaller speakers could raise the level appropriately, could they not? Do you have such a calculator for this scenario? Is there such a calculator? Much thanks!

    • Hi Rick,
      It is a good question, but not one easily answered. There are so many variables including height of ceiling, throw distance, wall linings, speaker parameters etc. So there is no simple calculator. There are professional analytical programs, which do most of the work for you, but they are expensive and take some learning. A common one is EASE (Enhanced Acoustical Simulator for Engineers). For a complex building, hiring consultant with experience with EASE is worthwhile.

      A simpler “poor man’s” option is the free Yamaha Simulator. While it doesn’t take into account wall linings and reflections, it can give you some basic guidance. It only allows the use of Yamaha speakers, but you may be able to find one with specs similar to the speakers you want to use – or buy the Yamaha speakers – I guess that is what they are hoping for by giving it to you free.

      Hope this helps

      Geoff

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