As a rule, I generally try to avoid becoming too technical in my articles. But certain topics, such as specifications, make such an aim virtually impossible.
Speakers feature a range of detailed specifications – such as waterfall plots, step and pulse response, phase response and distortion characteristics – that are used extensively by speaker designers, but are very difficult to interpret by the general public.
So what is relevant and what is not?
Speaker specifications can vary greatly from one model or another. Typically, the efficiency and frequency response of a speaker are the first specifications people look for, and are possibly the most relevant.
The industry standard input for a speaker is 2.83V, which equates to 1W into an 8Ω speaker. This is an industry standard input regardless of the speaker’s impedance.
Efficiency should be an average output across the speaker’s stated response or output, measured from a white noise input.
Some unscrupulous manufacturers measure the frequency response peaks and quote them as efficiency. This gives an inflated efficiency rating that is probably even more exaggerated, as such products are likely to have a wildly varying response.
Efficiency is an important parameter, as it dictates how much amplifier power will be required. Achieving a satisfying volume with speakers of 90dB may require a 50W amplifier. If the speakers have an efficiency of only 80dB they will need 500W to achieve the same level, whereas 100dB efficiency speakers require only 5W.
Average speaker efficiency is about 87dB, measured at a distance of 1m. A speaker with an efficiency of 80dB is considered very low, and an efficiency of 100dB is considered high.
In terms of frequency response, care should be taken when assessing the range quoted.
A frequency response of 20Hz to 20,000Hz may sound impressive, but it is meaningless. Without dB limits, virtually any speaker will produce some sound at any frequency from 20Hz up to 20,000Hz and so claim such a response.
A meaningful frequency response should be qualified with dB limits.
The frequency response of a quality speaker may be 40Hz to 20,000Hz +/- 3dB. If this speaker’s efficiency is about 87dB, the output level would not exceed 90dB or drop below 84dB across its stated frequency range.
Generally, the wider the frequency range the better, but other parameters may have more effect on the overall naturalness of the sound.
I have heard many mini-monitors outperform much larger speakers even though the mini-monitors had restricted bass extension. Their lower distortion levels and a much smoother response is reflected in their more natural sound quality.
However, frequency response within dB limits can still be misleading. Two speakers may have a quoted response of 40Hz to 20,000Hz +/- 3dB yet sound very different.
Speaker A may be up by 3dB in the bass and 3dB down in the treble, resulting in a fat, dull sound. Speaker B, being 3dB down in the bass and 3dB up in the treble will sound more lively, but lean and aggressive.
The specification for the power handling capability of a speaker causes the most difficulties.
It is natural to assume that a speaker rated at 100W couldn’t possibly be damaged by an amplifier capable of 90W, but it’s not that simple. Although a 90W amplifier may produce 90W at very low distortion, it may produce far more than this when driven into clipping, where distortion increases considerably.
Music is by its very nature dynamic – that is, it has loud passages followed by quiet passages. During the loud passages, speaker voice coils heat up. When there is a quiet passage they cool down again.
Some music, particularly electronic music, has a very low dynamic range (it’s always loud) and doesn’t give the speaker voice coils a chance to cool down.
As a result, the voice coils get hotter and hotter and eventually start to burn.
Speakers rated at 100W will probably sustain permanent damage if subjected to continual power of 80W, but they will be happy with short-duration transients of hundreds of watts.
The situation with amplifiers and CD/DVD players is even worse. Most quality amplifiers have excellent frequency response and low distortion, yet they can sound very different from one another.
Even power output is not as straightforward as some people imagine.
Some amplifiers capable of quite high power still sound wimpy and gutless at any volume level. Other lower-powered amplifiers (usually with comparatively large power supplies) can sound much more powerful, or gutsy, until they are driven beyond their rated power and start distorting.
Complex response, noise and distortion plots may help electronics engineers and designers, but they are of little relevance to the typical consumer and for that reason are rarely included with specifications.
Generally speaking, equipment with poor specifications will not perform well, but good specifications do not guarantee good performance. The way to judge equipment is by listening and comparing.
With experience, your ears are more sophisticated than any test equipment available.
© 2012 Connection Online Pty Ltd.