Harman International

Sales Primer

Demystifying Amplifier Specs – The Dummy Guide

Ravi Lakkundi

Product Manager, India

Harman International India (Pvt) Ltd

Published on: 20 Sep 2012

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Introduction

Choosing a right receiver/amplifier for one’s home is challenging and an immense task. The obvious

place to start is some review website, magazines and of course knowledgeable trusted friends – After all

you are making a sound investment on/for your ears for years to come! The task of selection finally boils

down to comparing the technical specifications of the receivers one has shortlisted.

Amplifier specifications can actually be quite deceiving, one must know to read and decipher them for

an apt selection of amplifier/receiver system. This paper provides basic level understanding of such

specification sheets, which at times are spurious. Intended for dummies and sales staff, avid readers are

highly encouraged to study the reference materials for technical details.

What to expect in Spec sheet?

Typical Amplifier specifications have

features like THD, Sensitivity,

Wattage/Channel, S/N etc.

An understanding of each of these

terms and how they are measured can

be helpful in selecting a good amplifier

for your home and also will help in

comparing different amplifier based on

price and specs.

A typical detailed AV Receiver specification

“35W x 7 RMS all channels driven continuously into 8 Ohms with less than 0.07% THD from 20Hz to 20 KHz”

All aspects of this specification are very important. Any missing information should be a cause for

concern. Below are examples wherein specifications are unclear and incomplete:

“35W x 7 RMS @ 8 Ohms from 20Hz to 20 KHz”

“35W x 7 RMS @ 8 Ohms, 1 KHz, 1%”

“35W x 7 RMS, 1 Channel driven, 0.07%”

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The Dissection

Watts refers to power. ‘35W x 7’ conveys that the

amplifier is of 35W and ‘x7’ means that the

amplifier has 7 channels.

Higher power is what a consumer expects but

one needs to be careful on how this power was

measured. The remaining part of the spec

explains how this 35W was measured.

Gyaan: Although ‘PMPO’ (Peak Music Power

Output) is a phased out term, but then it’s always

better to be cautious! More about this later in

this section

RMS is Root Mean Square and is a method of

measuring AC waveform. PMPO is generally 5 to

6 times greater than RMS.

‘All channels driven’ signifies that the power

measurement was made by driving all channels,

i.e. 35W measured across all 7 channels, driven

to their maximum level at same time.

Gyaan: There’s a potential for cheating here.

Measuring the power with only one channel

driven, results in obvious higher number for

Wattage!!

A continuous test signal must be used to measure

power of amplifier. An example of such signal

would be a sine wave. An amplifier which is

capable of giving higher power for short amount

of time will have higher power rating if its power

is measured with short bursts instead of

continuous wave.

Gyaan: Watch out for this term in your hunt for

Amplifier, this could be one of the money savers!

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Power generally gets measured across a dummy

resistor, in this case an 8 Ohms resistance load. At

times, the manufacturer measures the power

across a lesser resistive load and spec it as a 4

Ohms load. Measuring the power across a lesser

resistive load will boost the power.

Gyaan: A manufacturer who gives its amplifier

power rating for two different resistive loads, ex:

8 Ohms and 4 ohms is an honest manufacturer,

and if the power rating doubles from 8 Ohms to 4

Ohms, the amplifier is a good amplifier.

THD Stands for ‘Total Harmonic Distortion’. This is

one particular topic which can cover an entire

book on what and how it is measured.

This basically means the distortion that the

amplifier produces at the specified level.

Gyaan: The lesser the better!!!

Every amp has a rated power and a frequency

range within which it delivers its rated power. If

the range is between the audible range 20 Hz to

20 KHz, the amplifier has the ability to faithfully

amplify music.

Gyaan: A power specification which says 1 KHz or

has the frequency range completely absent should

be a contender for skepticism.

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Conclusion

Choosing an amplifier/AV receiver merely on appearance or brand could be a mistake by consumers.

One probably will not be doing justice for his/her own ears for years to come!

The best way to evaluate an amplifier is to listen to it because every amplifier might be tuned differently

for different regions also do have a look at the specifications. This paper tries to give an explanation of

such specification for dummies. This paper is intended to be informative and not completely explanatory.

References

Author is NOT an expert in amplifier technology. This whitepaper is inspired from lot of work which was

done previously by experts and author has tried to summarize such a work (for dummies). For the ones

who wish to read more here are some reference World Wide Web links

[1] http://www.rayfes.com/caraudio/ampspec.php

[2] http://www.buyingloudspeakers.com/Speaker%20Specifications.htm

[3] http://www.audioholics.com/education/amplifier-technology/the-all-channels-driven-amplifier-test-

controversy