Is this the right amplifier for my speakers? - Rapallo New Zealand :: Home Theatre & Hifi | Design & Installation
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Some of the questions we get asked most often is: Do these Speakers pair well with this Amplifier? Will this Amplifier power my Speakers? How do I know these Speakers will sound good with this amplifier?

As speakers and amps are such an investment, you want to make sure they work effectively and sound good! There are a few points that we think are important to consider when calculating an amplifiers power. Unfortunately, it isn’t as simple as looking up a couple of figures on the amp specs and comparing it to the speakers you intend on using it with.


Amplifier power is crucial to an enjoyable listening experience and even more important, for the safety of your speakers. RMS power rating, decibel sound level, speaker sensitivity, the environment of the audio, and your personal listening preferences are important to consider in making sure your speakers will work with a particular amplifier. In the end your goal is to find out whether your amplifier will work with a particular set of speakers.


For starters, it is important to note that an insufficient amount of amp power can cause speaker failure, called ‘clipping’. Clipping is the noise/distortion generated when a speaker is pushed out side it’s frequency response. If your amp is not supplying enough power to enable speakers to reach a sufficient loudness level, an average Joe’s natural response would be to turn the volume to its maximum level. Any electrical energy within the amplifier output signal falling outside the frequency range of your speaker would not be converted to sound and will end up as heat. If this is sustained for a long period, this will result in speaker thermal failure. Ouch!


In short, if your system is not able to play at a volume you want without the signal distorting, you need a more powerful amplifier/AV receiver.


We kind of anticipate the next question: How much power do I need?


Sound is a wave and Power is expressed in Watts. You will often find amplifier power expressed in ‘RMS Watts’, which stands for average watts obtained by the RMS (root mean squared) method using a ‘well-behaved’ frequency sine wave signal.


However, in a real life application, the audio signal driving a speaker consists of a multitude of frequency sine waves that play all at the same time (all interfering with each other, therefore causing much higher peaks or a ‘not-so-well-behaved’ frequency sine wave signal), rather than a pure single frequency sine wave signal. This means that in real life, an amplifier will deliver less than its rated power. Therefore, your audio amplifier power needs to be larger than the speaker’s rated power.


A general rule of thumb is to allow for a 30% to 50% increase in amplifier power over the rated speaker’s average (RMS Power). For example, if your speakers are rated at 100W, the amplifier paired with it should be delivering a 130W to 150W power rating.


There is a direct link between the RMS Power rating your amplifier produces and the sound level produced by your speakers. The more power an amplifier generates, the louder the speakers will sound.


But there are further considerations to make other than RMS Watt ratings when deciding how much power your amplifier needs to have.


FTC and IEA are two common power rating standards that make it easy to compare amplifier output ratings. We highly recommend you to refer to those standards for a realistic representation of what an amplifier can do.



Sound levels are another consideration.


Sound levels are expressed in decibels or dB’s. One decibel represents the minimum perceptible change in volume by human hearing. Normal speaking sits at around 60dB while a concert climax may reach 105dB. In a home theatre, the THX reference level for loudness is 85dB for each of the audio channels.


If you are after a high-end audio system for your home theatre, ‘The Practical Home Theatre Guide’ advises to allow for an additional 20dB dynamic headroom.


Dynamic headroom refers to excess power reserves or capabilities available from the amplifier for use during those loudness peaks to avoid clipping.


With all being said, everybody has different preferences in correct loudness to watch films and listing to audio. The THX 85dB is therefore only a guideline and you may want to subtract about 3dB if you prefer to listen to lower levels, or add 3dB if you like your music or movie really loud. The environment has everything to do with volume levels. If the speakers are further away from the primary listening position you may want them to have a higher decibel sound level. But more on that a bit later.


Another factor to consider is Speaker sensitivity (also called speaker efficiency).


This is an important factor that will have a big play in fine-tuning your amplifying power. Speaker sensitivity is the level of sound you get for a specific level of amplifying power. Basically, sensitivity is calculated by measuring the sound pressure level of a speaker from one meter away, fed with 1 Watt.


Conventional speakers (think cones and domes with a magnet and voice coil) are reasonably efficient, usually in the range of 85 to 90 dB/Watt/meter. Although one would assume so, higher speaker efficiency doesn’t necessarily mean better speakers; it simply means that it requires less amplification. But in most cases, it is worth remembering that there is trade-off between sound quality and higher speaker efficiency.


Lower speaker efficiency or sensitivity of your speakers means you require more amplification power.


There is the size of your room as well as the environment to consider. Your room will influence the quality and loudness of sound you hear and therefore will have an impact on the required audio amplifier output to achieve a desired level of loudness. For example, too many heavy furnishings in the room will absorb more of the reflected sound than you may like.

However, while the environment within your room will impact the sound quality, it is the room size that is the key factor here when it comes to determining audio amplifier power. A large room will require typically twice as much amplifier power than an average size room, while a small room will require half as much power than an average size room.

There is a very practical calculator to help you determine the amplifying power for your room here. You can specify the listening distance from source, desired level at listener distance, loudspeaker sensitivity rating, and amplifier headroom, and the calculator will present you with the required amplifier power.


So, here are the questions you should answer to figure out the correct power your amp needs:


What is the sensitivity of your speakers?

What is the size of your room?

How loud do you like to listen?


We really like to think of it this way: your amplifier and your speakers are a team that is only as strong as its weakest link.


We hope you have a good starting point to work out a good amplifier for your specific situation.

As we started off by saying, sound loudness not only depends on the audio amplifier power output, but also on both speaker efficiency and the environment you are in.  None of these three should be ignored as they are all equally important in the set-up of your home theatre or audio room to ensure that the resulting sound loudness will match your desired volume level.


Always feel free to give us a bell, to check the power rating of your amp can match your speakers. Nothing compares to peace of mind!

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