Dazed and confused by power amplifier choices? We’re here to help. 

Choosing an amp for your speakers can be intimidating, and not to make matters worse, but it is an extremely important component of your sound system. In fact, not only can choosing the right amp maximize the sound quality and performance you can get out of your system, but choosing the wrong amp can damage or even destroy your speakers. So, no pressure, but choose wisely! 

When it comes to choosing the right amplifier, it’s not just about having the best amp, rather it’s about having one that’s compatible with your speakers. In order to determine compatibility, you’ll need to understand three key amplifier specifications: power, impedance, and sensitivity. 

The level to which compatibility extends is still a matter of debate, even among experts. Will a perfectly matched amplifier really boost the audio quality that comes out of your speakers? It’s unlikely, but the jury is still out in the audiophile community. If you’re just making sure that an amp won’t fry your equipment, it’s fairly simple, so don’t fret. And if you don’t want do all the reading, head to the bottom for some quick shopping tips.

Power

As you might have guessed, the power spec refers to the wattage output of an amp (or the wattage intake of a speaker). This number tells you how much power an amplifier is capable of delivering, and how much power your speakers can accept without suffering damage. Contrary to what many people think, a higher wattage does not equate to a higher audio volume.

To find an amp that’s compatible with your speakers, the wattage needs to be at least as high as the power spec on the speakers. If the amp’s power capability is lower than the speakers’ power requirement, you’ll be under-powering your speakers, which can easily cause damage to them. Under-powered speakers won’t be able to produce audio at full volume without clipping, and the audio distortion created when clipping is one of the most common causes of damaged speakers. So, make sure your amp’s power rating is equal to or greater than that of your speakers.

Although it’s considerably more difficult, it is possible to over-power your speakers as well, so to be on the safe side, avoid getting an amp with a power rating more than four times greater than that of your speakers.

When shopping for amps, you might see the terms ‘continuous power’ and ‘dynamic power’ or ‘peak power’. Don’t fret, these are just more meticulous descriptions of an amp’s power output. Continuous power (CP) describes the wattage that an amplifier can, as the name implies, deliver continuously; this is the amp’s output during typical operation. Dynamic power, in contrast, is the maximum wattage output during dynamic frequencies that occur with the highs and lows in an audio signal. For example, an amp with a CP rating of 100 watts is going to be delivering around 100 watts of power throughout its function, but during spikes in the audio signal it may deliver 150 or even 200 watts for a brief moment — that spike is dynamic power. You just want to make sure that your amp can deliver enough continuous power to safely avoid clipping.

When looking at the power specifications on your speakers, it might be a bit more confusing. Different brands will have different ways of specifying power — some terms you might see include maximum continuous power, maximum short-term peak power, or minimum recommended power. Some speakers will make it easy for you and just list the recommended amp power range. In fact, if that information isn’t directly printed on your speakers, you can most likely find it on the brand’s site by looking up the model number. 

Impedance

Impedance refers to a device’s electrical resistance and is typically measured in ohms (Ω). If you don’t know what electrical resistance means, don’t worry, you don’t need to understand it to compared impedance specifications. The most important guideline is that the impedance on your amp is lower than your speakers’ impedance, otherwise you could cause damage to the amplifier. 

While impedance is an important spec, it’s most likely not going to cause you any trouble, and the vast majority of amps and speakers on the market today will be compatible enough to not be disastrous. That being said, it’s still good to know that an amp will deliver higher wattage into a speaker with a lower ohm rating. For example, an amp rated to deliver 180 watts into an 8 ohm load may deliver 256 watts into a 4 ohm load. This means that if your speaker impedance rating is significantly higher than your amp’s, the amp is going to end up delivering much lower wattage than the power rating. If this is too confusing, simply try to match impedance ratings as closely as possible.

Sensitivity

Sensitivity is a spec that only applies to speakers and refers to the measure of volume (in decibels) that a speaker produces from 1 metre away when fed 1 watt of power. Higher sensitivity doesn’t necessarily indicate a higher quality speaker, rather it simply determines how much power a speaker needs in order to produce a certain volume level. The peculiar thing about sensitivity is that the required wattage scales exponentially with volume level. In other words, in order to increase volume by 3 dB, you need to double the amp power. This, combined with the fact that volume decreases so quickly as the listener’s distance from the speaker increases, leads to such high power output ratings on most amplifiers. 

Once again, most consumer amps with typical power and impedance ratings will have compatible sensitivity specs, but if you’re particular about your volume levels, you may want to pay extra close attention to this one. Check the sensitivity rating on your speakers to determine how effectively an amp will be able to drive them. If you like listening at a certain volume, some quick math will tell you the minimum power rating your amp needs. Generally, if you like “turning it to eleven”, then choosing an amp with a higher power rating than your speakers’ requirement is recommended. 

As long as you follow these general rules, you won’t run into any problems with whichever amp you choose. If this overview was entirely too much information, then here are some easy tips to make sure your amp and speakers will complement each other (because we want to leave you with confidence, not fear):

• Head to the product page for your speakers on the manufacturer’s site and look for recommended pairings.
• Buy an amplifier from the same manufacturer as your speakers.
• Browse forums to see which amplifiers other people who own the same speaker model are using.
• While shopping for amps, check for any recommended speaker pairings that are identical or a similar model to your speakers. 
• If you’re using equipment more than twenty years old, avoid mixing and matching with modern equipment. Standards change over the years and using vintage speakers with a modern amp may cause you trouble if you aren’t certain of the specs of each device.

If all else fails, don’t hesitate to contact customer support here at Selby and we’ll answer any questions you have about your home theatre or surround sound system.