Calculating the Amplifier Power for a Room

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Calculating the Amplifier Power for a Room

Buyers have several decisions to make while shopping for amplifiers, and selecting a product with appropriate power levels is one of the most important. Although this process can require a little research, it can result in improved sound quality and diminished risk of damage to speakers and other components.

The power of amplifiers is listed in watts per channel, though buyers should be clear on how this rating is measured by the manufacturer. Matching an amplifier to a set of speakers is also important. Consider impedance levels, and the sensitivity of the speakers to find appropriate items. Lastly, the room itself plays an important role in the performance of an amplifier. Although there is no set formula for finding a product to match a room, it is worth taking a measurement of the space and considering the amount and type of furnishings in the room.

Amplifiers can be purchased from electronics retailers, department stores, and online sellers like eBay. Shop from the full range of sellers to find the best products and prices, and review sellers when buying online. With proper research, buyers can find the best amplifier for any room.

Choosing Amplifiers

The power of an amplifier is generally thought of in relation to the amount of volume it can produce. Volume can be a difficult thing to judge, however, and the same setup will perform differently from one setting to the next. Buyers should begin their search for an amplifier by determining the number of watts per channel products can produce, then consider the speakers and room it is being used in to obtain the best setup.


Watts (W) are the basic measure of an amplifier’s power. The watts per channel (WPC) indicates how much power the amplifier can provide to each speaker in a setup, and is listed on product packaging and specifications sheets. A simple WPC rating does not tell the full story of an amplifier’s power, however. When shopping, be sure to look for an RMS rating with all channels driven. It is also worth checking impedance levels.

All Channels Driven

Amplifiers must split their power up between the number of speakers used in a setup, and a unit that is not powerful enough for all the speakers will have a lower WPC than it would otherwise. For example, an amplifier that is capable of producing 100 watts per channel in a two-channel stereo setup might only put out 80 WPC in a 5.1 surround system. When shopping, be sure that the WPC rating is listed with all channels driven. This reflects the WPC it is capable of putting out with its maximum number of channels powered at once.


Amplifier power is commonly shown in one of two forms: peak power and RMS. Peak power is not always an accurate indication of an amplifier’s performance, as a product only needs to reach a peak level for a moment to earn the rating. When possible, look for an RMS rating instead. This indicates the maximum power an amplifier can sustain for extended periods of time.


Impedance refers to the speakers’ resistance to an amplifier’s signal, and is measured in ohms. Power ratings for an amplifier are listed based on the impedance level of the speakers it was tested with. To ensure accurate power performance, purchase amplifiers that have been tested with the same levels of impedance as the speakers that will be used at home. For example, if an amplifier is paired with 8-ohm speakers, choose a product that was tested with speakers that have an 8-ohm impedance.


Choose an amplifier with a power rating that matches the speakers. An underpowered amplifier is capable of harming a pair of speakers, as the resulting clipping and distortion falls outside the speaker’s frequency range, and is converted into heat instead of sound. Extended use of the speakers in this way causes the speakers to overheat, potentially resulting in damage to their internal structure.

Similarly, amplifiers that are too strong for a set of speakers can damage the diaphragm, create other mechanical troubles and can also cause overheating. The two key things to consider while shopping for speakers are the impedance levels and sensitivity.


Speaker sensitivity is measured in decibels (dB). This indicates how loud the speakers are going to be for every watt of power they receive. Most modern speakers range between 85 dB and 95 dB. The difference between these numbers is greater than it seems, however. Speakers rated at 95 dB can actually play twice as loud as ones rated at 85 dB. The amount of power required from the amplifier increases at an even greater rate. For example, every extra 3 dB above 85 requires twice as much power.


Amplifiers are designed for use with a certain level of speaker impedance, usually 8 ohms. Lower ohms ratings on speakers require more power from an amplifier, which can result in damage if the amplifier is overworked.


The size of the room an amplifier is used in has a large effect on the perceived volume and quality of its sound. There are no rules for determining the amount of power needed for a room, as the variables involved can be quite complex. For example, thick and padded furniture in a room can absorb some of the sound produced, and dampen the perceived volume. The shape of the room also affects its acoustics, and can change volume levels.

There are, however, some general guidelines that can be followed. Begin by finding a room’s cubic metre measurement. To do this, measure the room’s length, width, and height, and multiply the three dimensions.

For a room that is 90 cubic metres, an amplifier needs between 50W and 80W per channel with 87 dB speakers to provide sufficient power for loud listening. A room that is 28 cubic metres only needs around 25W per channel with the same speakers. A 150 cubic metre room may require as much as 150W per channel.

How to Buy Amplifiers on eBay

A wide variety of amplifiers can be purchased on eBay. These are available from both private and commercial sellers, and can be found in new or used condition. To shop for these items, enter keywords on the homepage. For example, to begin a broad search, type "amplifier" into the search field. Results can be narrowed by adding keywords to the search, or by clicking on any of the category options that appear on each page. Look for links to the most relevant sections on eBay. The numbers beside each category name indicate the number of items contained in that section that match your keywords.

Read item listings to ensure a positive buying experience. Be clear on the price of the item, as well as shipping charges and the shipping methods used by the seller. Look for a clear description of the product. In many cases, sellers provide a copy of the specifications sheet produced by the item’s manufacturer. If you are buying a used amplifier, look over available photographs and compare it with the seller’s description to verify its condition. Contact the seller with any questions you may have about the listing.

Research sellers before committing to a purchase. Positive feedback ratings and the number of transactions a user has completed are shown in item listings pages, and can be used to gain a quick estimate of the user’s reliability. Click on the seller’s name in item listings to view more detailed information. In the full profile, you can read comments left by previous buyers, and see average ratings based on aspects of the seller’s performance like shipping speeds, shipping costs, and the number of completed transactions.


Amplifiers for stereo and surround sound systems are produced with varying amounts of power, and can perform differently depending on how they are used. To find the best amplifier for a particular room, it is important to consider the amplifier, the speakers that will be used, and the size of the room. Amplifier power is measured in watts, though there are some variables in how this information is listed. Keep in mind the number of watts per channel, and the difference between peak power and RMS to find suitable products. Be sure to pair an amplifier with a speaker system. Match impedance levels, and be sure speakers can handle the appropriate decibel range.

Take the room measurement in cubic metres, and consider the amount and type of furniture present. There is no strict formula for calculating the amount of power needed for a room, so choose quality items in an appropriate range for the best results.

Amplifiers can be purchased from electronics retailers, department stores, and online sellers. Marketplaces like eBay have a high number of listings for these products, and are an easy way to shop for amplifiers with varying amounts of power. Research sellers when buying online, and be clear on the specifications of an item before committing to a purchase. With proper research, it is possible to find suitable amplifiers for any room.

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