Loudspeaker ratings and how to match them to your amplifier

Loudspeaker ratings and how to apply them to your amplifier

Key specifications The loudspeaker's sensitivity and nominal impedance are the two key specifications you need to take note of. The nominal impedance value is only of use when matching to your amplifier.

Sensitivity can be described as the speaker’s efficiency at converting power into sound. The traditional method of measuring loudspeaker sensitivity is by placing a microphone 1 meter away from the drivers and allowing 1 watt of energy to flow through the speaker. The resultant measured sound output (in decibels) is called the sensitivity. Looking at your loudspeaker specifications, you will see something listed like, Sensitivity 87 db w/m

Example 1 Perreaux Audiant SR35 loudspeakers

Looking at the specification sheet, the SR35 is rated at 90dB w/m. This means that the SR35 loudspeakers will produce 90 Decibels of sound pressure (SPL) when measured at 1 meter away from the drivers when 1 watt of energy is drawn from the amplifier.

To put 90dB in context, a full on rock concert can produce transients of 120dB.

The Decibel (dB) is a logarithmic unit of measure. If a sound is measured at 87db, then twice the sound pressure is 90dB and 93 dB is 4 x the sound pressure of 87dB.

Quick loudspeaker comparison If the specifications on your own loudspeakers states 87dB w/m, then the Perreaux SR35 @ 90db w/m will play twice as loud as your own speakers when 1 watt of energy flows through each loudspeaker. In other words, it can be correctly stated that the Perreaux SR35 is twice as sensitive (efficient) compared to your own pair of speakers @ 87dB w/m.

If you occasionally enjoy loud music in your home, it may pay to purchase efficient speakers as the tables below reveal.

 87dB efficient loudspeakers (amplifier ratings on the left)

1W 87dB (note each step below represents a doubling of sound pressure)

2W 90db

4W 93dB

8W 96dB

16W 99dB

32W 102dB

64W 105dB

128W 108dB

256W 111dB

512W 114dB

1024W 118dB

2048W 121dB

Using 87dB efficient speakers you will require an amplifier which can deliver a massive 512W to generate 114dB of sound pressure

90dB efficient loudspeakers (twice as efficient as 87db equivalent above)

1W 90dB (note each step below represents a doubling of sound pressure)

2W 93db

4W 96dB

8W 99dB

16W 102dB

32W 105dB

64W 108dB

128W 111dB

256W 114dB

512W 118dB

1024W 121dB

Using 90dB efficient speakers you only require 256W to generate 114dB of sound pressure

Loudspeaker impedance The impedance of a loudspeaker is its measure of impeding the flow of power. In other words a 4 ohm nominal loudspeaker represents half the impediment to the flow of power as an 8 ohm nominal loudspeaker.

Looking again at the specification sheet of the SR35 loudspeakers. The SR35 has 4 ohm nominal impedance. This means that it represents half the resistance to the flow of power than an 8 ohm loudspeaker and in the case of matching it to say the Audiant 80i integrated amplifier. The 80i has an 8 ohm rating of 80w and a 4 ohm rating of 130w.

Example 2 Matching the Perreaux SR35 loudspeaker (90dB w/m 4 ohms nominal impedance) to the Perreaux Audiant 80i amplifier (130W into 4 ohms)

1W 90dB (note each step below represents a doubling of sound pressure)

2W 93db

4W 96dB

8W 99dB

16W 102dB

32W 105dB

64W 108dB

128W 111dB

In theory, you can obtain 111dB SPL when you match the SR35 to the 80i. 

Example 3 Matching the Perreaux SR58 loudspeakers (87dB w/m 4 ohms nominal impedance) to the Perreaux Eloquence 250i amplifier (500w into 4 ohms)  

1W 87dB (note each step below represents a doubling of sound pressure)

2W 90db

4W 93dB

8W 96dB

16W 99dB

32W 102dB

64W 105dB

128W 108dB

256W 111dB

512W 114dB

 You should be capable of producing 114dB SPL when combining the Perreaux SR58 and 250i products.

Example 4 Matching the Perreaux SR58 loudspeakers (87dB w/m 4 ohm nominal impedance). Matched to Perreaux Prisma 750 (1300W into 4 ohms)

1W 87dB (note each step below represents a doubling of sound pressure)

2W 90db

4W 93dB

8W 96dB

16W 99dB

32W 102dB

64W 105dB

128W 108dB

256W 111dB

512W 114dB

1024W 117dB

You should be capable of producing in excess of 117dB SPL when combining the SR58 and Prisma 750 (note: the SR58 loudspeaker is not capable of producing 117dB SPL)

Conclusion We recommend that wherever possible, you purchase high efficiency loudspeakers. If your speakers are also of low impedance (4 ohm nominal) and you are paring them with a quality amplifier that offers published 4 ohm ratings, then potentially this is a win win situation, enabling you to maximize your speaker amplifier combination for a minimum of additional cost.

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