WarrenM
02-06-2011, 01:39 PM
How Much Power Do I Need? Part 1 ©2011 Warren Marshall
When it comes to home hi-fi or car hi-fi there is no such thing as too powerful an amplifier. You cannot destroy your speakers because your amplifier is too powerful! If my speakers specifications list says 50W RMS, 150W Max, that doesn't mean that I have to use an amplifier with less than 150W Max output. I can use a 3000W/channel amplifier and never come to grief, as long as I don't force more power into the speakers than they can handle (150W).
Of course, if your amplifier is driven hard enough to deliver jet-engine volume noise through the speakers and your speakers are not designed for that, then bye-bye speakers.
The main reason you would not want more power than you need, is that power is expensive - more available power means more expensive and much larger components, more heat generated, more drain on the battery and charging system, etc.
On the other hand, trying to get more sound out of your speakers than your amplifier can deliver is a sure way to destroy the speakers and possibly the amplifier too! I bet most of you didn't realise that.
I'm going to leave issues like distortion, signal-to-noise, and other important considerations, for another article.
So let's get back to how much power do I need.
Let's think subwoofers (deep bass) as these are the speakers which demand most power (large speaker cones pushing large amounts of air around takes a lot of energy) and that means that differences will be most apparent.
There is a very important and rarely understood specification that good quality speakers include. This spec is called SPL (sound pressure level) or more usually Sensitivity or Efficiency. The SPL is the volume of sound achieved at a distance of 1 metre from the speaker, when 1 watt of power is put into the speaker.
So what the .... does that mean?
Two equally good sounding subwoofers may be on your short list. Sub1 has a sensitivity of 92. Sub2 has a sensitivity of 83.
Here's the critical extra bit of knowledge: If you double the power, you don't double the volume! You just add 3dB!!! Double the power: Add 3 dB to volume. Commit that to memory.
So, suddenly this Sensitivity measure is really important: Sub1 is 9dB more efficient or sensitive than Sub2. Double the power fed into Sub2 for an extra 3dB and double the power again for an extra 3dB and double again for an extra 3dB, just to get the same volume as Sub1. You need 8 times as much power into Sub2 for the same volume.
If you need 50 Watts for the loudest you want Sub1 to play, you'll need 400 Watts for the same volume out of Sub2. If you go with Sub1, you only need a 50 Watt per channel amp (or larger of course). If you go with Sub2, you'll need, at a minimum, a 400W/channel amp.
Let's look at another example.
Speaker1 (Cheap) has SPL=92, maximum power handling of 50W
Speaker2 (Expensive) has SPL=89, maximum power handling of 400W
To get the same volume out of Speaker2, you need twice the power. So, if 50W is enough out of Speaker1 for you, then you'll need a 100W amp minimum for satisfactory maximum volume out of Speaker2. But if it isn't loud enough, you could use a 400W amplifier to get an extra 6dB of volume out of Speaker2, while adding more power to Speaker1 is just going to burn it out!
Are there any other ways to squeeze more volume out of a speaker (or use a less powerful amp and get the same volume)?
There certainly are, but you'll have to wait for the next installment
Cheers,
Warren
When it comes to home hi-fi or car hi-fi there is no such thing as too powerful an amplifier. You cannot destroy your speakers because your amplifier is too powerful! If my speakers specifications list says 50W RMS, 150W Max, that doesn't mean that I have to use an amplifier with less than 150W Max output. I can use a 3000W/channel amplifier and never come to grief, as long as I don't force more power into the speakers than they can handle (150W).
Of course, if your amplifier is driven hard enough to deliver jet-engine volume noise through the speakers and your speakers are not designed for that, then bye-bye speakers.
The main reason you would not want more power than you need, is that power is expensive - more available power means more expensive and much larger components, more heat generated, more drain on the battery and charging system, etc.
On the other hand, trying to get more sound out of your speakers than your amplifier can deliver is a sure way to destroy the speakers and possibly the amplifier too! I bet most of you didn't realise that.
I'm going to leave issues like distortion, signal-to-noise, and other important considerations, for another article.
So let's get back to how much power do I need.
Let's think subwoofers (deep bass) as these are the speakers which demand most power (large speaker cones pushing large amounts of air around takes a lot of energy) and that means that differences will be most apparent.
There is a very important and rarely understood specification that good quality speakers include. This spec is called SPL (sound pressure level) or more usually Sensitivity or Efficiency. The SPL is the volume of sound achieved at a distance of 1 metre from the speaker, when 1 watt of power is put into the speaker.
So what the .... does that mean?
Two equally good sounding subwoofers may be on your short list. Sub1 has a sensitivity of 92. Sub2 has a sensitivity of 83.
Here's the critical extra bit of knowledge: If you double the power, you don't double the volume! You just add 3dB!!! Double the power: Add 3 dB to volume. Commit that to memory.
So, suddenly this Sensitivity measure is really important: Sub1 is 9dB more efficient or sensitive than Sub2. Double the power fed into Sub2 for an extra 3dB and double the power again for an extra 3dB and double again for an extra 3dB, just to get the same volume as Sub1. You need 8 times as much power into Sub2 for the same volume.
If you need 50 Watts for the loudest you want Sub1 to play, you'll need 400 Watts for the same volume out of Sub2. If you go with Sub1, you only need a 50 Watt per channel amp (or larger of course). If you go with Sub2, you'll need, at a minimum, a 400W/channel amp.
Let's look at another example.
Speaker1 (Cheap) has SPL=92, maximum power handling of 50W
Speaker2 (Expensive) has SPL=89, maximum power handling of 400W
To get the same volume out of Speaker2, you need twice the power. So, if 50W is enough out of Speaker1 for you, then you'll need a 100W amp minimum for satisfactory maximum volume out of Speaker2. But if it isn't loud enough, you could use a 400W amplifier to get an extra 6dB of volume out of Speaker2, while adding more power to Speaker1 is just going to burn it out!
Are there any other ways to squeeze more volume out of a speaker (or use a less powerful amp and get the same volume)?
There certainly are, but you'll have to wait for the next installment
Cheers,
Warren