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Power Delivery : Relationship between Speakers and Power Amplifiers

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What is the ideal Power Amplifier for your Speakers?

 

When it comes to power amplification, i.e. driving high loads and high amplitude signals of speakers, the matching of speakers to power amplifiers is everything.  There is a theory and then there is practice.

In theory, there is a relationship between sound pressure level and required power:

Sound Pressure Level L (dB) = 10 × log (power ratio W)

This relationship translates into following:

Difference in dB = power factor required

3 dB = twice the power
6 dB = four times the power
10 dB = ten times the power
20 dB = hundred times the power

For best possible performance power amplifiers and speakers need to not only be matched but also be made for each other. Our power amplifiers are optimised for damping i.e. ability to control the cone of the driver, in combination to our speakers that are presenting a flat impedance to our power amplifiers. Therefore the ability of power delivery is at its maximum.

In practise there is a power loss (due to X over and other factors such as impedance relationship) and therefore power delivery i.e. the ability to deliver the power from amplifier to the speaker driver into sound waves becomes crucial. Here the relationship between impedances of power amplifier and speakers is the key. The less loss (in damping) while translating power into sound waves the higher the perception of power, articulation and authority when music is played back. So, the total damping ability (with minimum losses) of amplifiers to deliver power drivers is everything.

Sound pressure level in psycho acoustics as subjectively perceived loudness.
The human perception of the double loudness is specified with about 6dB.

This personal feeling is not an exactly measurable value and varies from human to human.

Everything else equal, the perception of loudness would remain the same if we apply the relationship above to sensitivity of speakers.

 

Speaker sensitivity in dB/W/m = required power

83 dB = 100 W
86 dB = 25W
90 dB = 10W
93 dB = 5W
96 dB = 2.5W
>100 dB = <1W

 

The above can be interpret as following: In order to achieve twice as loud sound pressure one needs 4 times as much power.

Or in terms of speaker sensitivity, the difference 90db and 96db (6dB) translates itself into 4 times less power required.

 

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See the videos for more insights on the topic.

 

 

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