Matching Amps and Speakers - Do we Need to Worry?

Matching amps and speakers is a common issue for many people when they are looking to buy new speakers - or a new amplifier.

If you don't want to buy a home theater system package and would rather buy a separate amplifier and speaker combination, then it can be difficult to know what to look for.

Most of us have seen the specifications listed for speakers and amplifiers - but we aren't too sure how we go about matching the two together - and are there other important issues to think about?

The worry is we will buy the wrong amplifier for our speakers (or vice versa) and we have visions of blowing the speakers the first time we switch it all on.

So how much do we need to worry about this - and what are the important issues?

Do We Need To Match Amplifiers and Speakers?

Question mark: matching amps and speakers

The main thing that becomes clear when we look into this issue, is that matching our speakers and amplifier is not something that we should be losing any sleep over.

That's not to say we should ignore it completely and that we shouldn't give it any thought at all when buying new speakers and amplifiers - but it's more an understanding that you could ignore it and the chances are you would still buy a speaker and amplifier combination that would work perfectly well together.

You are very unlikely to find an amplifier and a set of speakers that are designed for home use that are completely mismatched to the extent that you will damage them by connecting them together and turning up the volume to a reasonable level.

Most amplifiers/receivers and speakers that are available for home systems are all going to be roughly compatible with each other - the question is do you want to study the specifications closely and get a better match so you get the very best out of your equipment?

There isn't really an exact science to matching your amplifier and speakers - you have plenty of room for error - and you won't have too many problems unless you try connecting equipment which are completely incompatible.

Speaker Impedance and Amplifiers

Amplifier speaker impedance rating
Matching Amplifier Impedance Ratings

One of the most important things to consider when you are matching speakers with an amplifier is the impedance of the speakers.

All speakers have an impedance (or resistance) and this will be noted in the specifications of the speakers - usually in the range of 4 to 8 ohms.

Generally, most amplifiers will support the majority of speakers available on the market today, but it is useful to make sure this is the case.

The main danger is that speakers with a low impedance (say 4 ohms) can put a strain on the power supply of an amplifier if the amplifier isn't designed to handle a low impedance.

For a more detailed explanation, go the the article on matching speaker impedance.

Power Ratings of Amplifiers and Speakers

Obviously the ideal match here is to get the rated watts per channel of the amplifier to match the rated power handling of the speakers.

If the amplifier outputs 100 watts per channel into 8 ohm speakers - then you can look for 8 ohm speakers that are rated to support 100 watts.

Speaker power rating - rms and peak
Matching Speaker Power Ratings

Simple.

However, the main point is to make sure that the ratings you are looking at are both comparable i.e. they are either both RMS (or average) values, or they are both peak (or music power) figures.

If you compare an average value with a peak value then they are not the same and cannot be compared.

For more information on this, go to the article on speaker power ratings.

However, you are not going to do much damage to your speakers if your amplifier is slightly underpowered or overpowered for your speakers - there is plenty of room for error.

Amplifier power ratings
Matching Amplifier Power Ratings

A 50 watts per channel amplifier will work fine with speakers rated at 100 watts. The biggest problem would be if the 50 watt amplifier didn't give you enough volume in your room and you were constantly running the volume control of the amplifier at maximum - you would then be in danger of sending clipped waveforms to the speakers which could damage them.

Similarly, a 150 watts per channel amplifier will work fine with 75 watt speakers. You'll only have a problem with these if you really turn the volume up very loud - and you'll hear if the speakers are starting to struggle with the power you are sending to them.

As long as the speakers are a good size for your room, then you will probably never need to send too much volume to them.

As a general guideline, it is probably better to get an amplifier that is slightly more powerful than your speakers are rated for.

Denon AVR 3310 7.1 Channel AV Receiver
Denon AVR 3310 7.1 Channel AV Receiver

In this instance you will have plenty of power to drive your speakers to the full, the amplifier will be have plenty of headroom for loud peaks - and you can just rely on your ears to tell you when your speakers are starting to get too much power!

On the other hand, an amplifier that is slightly underpowered can potentially be more harmful than a more powerful one.

If your amplifier hasn't got enough power for the volume you require, you will end up turning the volume knob right up. This can lead to the amplifier sending clipped waveforms to the speaker which can really do some damage.

Go here for more information on AV receiver and amplifier power specs.

Speakers, Amplifiers and Room Size

One of the most important considerations is room size - and the amount of volume you need to fill it.

Jamo C 401 Bookshelf Speaker
Jamo C 401 Bookshelf Speaker

The most important issue is that you have enough power from your amplifier to fill the room that you will be using - and it is only large rooms (or if you know you need very loud volumes) that require big amplifiers with a large output - say over 200 watts per channel.

Then, as long as you are sensible about the size of speakers you need for that room you will have a good match between amplifier, speakers and the size of your room.

For example, if you have very large room with high ceilings, then you'll probably be wanting a pretty powerful system to give you enough volume to fill the space.

If you do, then the chances are you won't be buying small satellite speakers to connect to your powerful 300 watt per channel amplifier.

Sony STR-DA5400ES AV Receiver
Sony STR-DA5400ES AV Receiver

It's logical that small satellite speakers won't be big enough to give you the volume you need in a large room.

However, if you did this, then it wouldn't be a great surprise if you eventually damaged the satellite speakers by turning up the volume too much to try and fill your room with noise - you would be constantly sending them much more power than they are designed to handle.

So in this example, you would be more likely to choose bookshelf, floor standing or in-wall speakers with a power rating close to that of your amplifier - and then you wouldn't have any problems.

Price Matching Amps and Speakers

Another good way to look at matching your speakers and amplifier, is to look at the price of the equipment you are going to buy.

Boston Acoustics RS 334 Floorstanding Speaker
Boston Acoustics RS 334
Floorstanding Speaker

If you really don't want to be bothered with looking at amplifier and speaker specifications (and understanding them!) - then this can be a good way to avoid those boring specifications completely.

If you look to spend approximately equal amounts on your amplifier and speakers, then you won't go far wrong.

For example, if you spend UK£2,000 (approx US$3,300) on an amplifier/receiver, then you might be asking for trouble if you connect them to UK£100 (approx US$175) speakers.

But who would do that anyway?

However, if you spend UK£800 (approx US$1400) on your amplifier and UK£600 (approx US$1000) on your speakers, then you can be fairly confident they will be fine together.

If you look to spend roughly similar amounts on your amplifier and speaker system (doesn't have to be exact!), then you are almost certain to be buying equipment that will be a close match and will work fine together.




Matching Amps and Speakers Summary

So as you can see, if you are buying a separate amplifier and speakers, it can be a technical minefield and it is easy to get confused about matching amps and speakers.

However, when we break it down to the important things, we can see that there isn't too much to worry about when matching speakers and amplifiers.

The main thing is that you buy an amplifier with enough power to give you the volume you want for your room size - and then get some speakers which are a reasonable match for the amplifier (impedance, power rating and size).

You don't want to be constantly running an amplifier at maximum volume in order to get the required sound level in your room. This can put a strain on the power supply and doesn't give you any headroom for peaks in the soundtrack (the loud bits!).

To summarise:

  • Impedance matching - make sure the amplifier supports the impedance of your speakers
  • Be careful when comparing power ratings between amplifiers and speakers - the numbers may be average or peak figures
  • If in doubt, choose an amplifier with a power rating higher than the speakers rating - this is slightly better than an underpowered amplifier
  • Think about the room size and speaker size. Larger rooms will need more powerful amplifiers - and speakers to match
  • For most home theater systems, 50-100 watts per channel (RMS) should allow plenty of volume for a reasonable room size
  • Try to match the price of your amplifier and speakers - they will probably work fine together
  • It's not an exact science - as long as you don't go to extremes, then most amplifiers will work fine with most speakers designed for home use

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