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SPECIFICATIONS ?



There have been a few errors crept into the use of some technical terms dealing with audio products, many due to a misunderstanding of the terms, even by professionals, but mainly by marketing bods in the ever quest to make their product sound better than the rest without actually being any different. These include dubious power rating claims, and the many figures given in the 'Technical specification' section that in reality mean very little. Some of the most common and incorrectly used terms are given below with the correct terminology and definitions.

THE DECIBEL

Of the many misunderstood terms, the decibel has to be the most prolific, incorrect or missing references or making assumptions about the levels with respect to specific instances, for example assuming 0dB is equal to 0.775V. The basic but correct definition and references are given below.

The decibel (one tenth of a Bel) expresses a ratio between two values and is logarithmic in scale.

The ratio of two signals in decibels is:

                                                              20 log     V1
  V2

for power the expression is:

                                                              10 log     P1
  P2

The decibel has no intrinsic value, but by providing a reference it can be used to give a absolute value, this reference can be a specific value eg. 10V, or a recognised designator eg. dBm (see below). In other words and without exception 'Without a reference the decibel can have NO absolute value'.

dBm is referenced to 1mW into 600 ohms (The original).
This is commonly and incorrectly taken as a reference to 0.775V, the derived voltage from 1mW into 600ohms.

dBv is sometimes designated as a reference to 0.775V.

dB-SPL (Lp) is referenced to 20u Pa (0.00002 Pa) or 0.2n bar.

dB-PWL (Lw) is referenced to 10E-12W (metric) or 10E-13W (US).

dBV is referenced to 1V rms.

dBA is a weighted SPL ratio (rolling off from 500Hz up); dB-SPL can also be refered to as dBC ie. unweighted.