Design Article
Loudspeakers: Objective evaluations - Part 2: Measuring the essential properties of loudspeakers
Floyd Toole
12/21/2010 10:29 AM EST
Frequency response is the single most important aspect of the performance of any audio device. If it is wrong, nothing else matters. That is a statement without proof at this point in the book, but that will come.
It is interesting to consider that for as long as anyone in audio can remember, all electronic devices had basically flat frequency responses. No manufacturer of an amplifying device, a storage device, or a music or film distribution medium would even momentarily consider a frequency response specification that was far from what could be drawn with a ruler from some very low frequency to some very high frequency.
Yet, when we come to loudspeakers, it is as though we threw away the rule book and suddenly tolerances of ±3 dB or more are considered acceptable. The measurements in Figures 17.2 and 17.3 show a few loudspeakers from the 1960s.
Some of these needed all of that tolerance, and more, to embrace even the on-axis digressions from flat. Yet, two of them, over substantial portions of the frequency range, behaved quite well. It could be done. Still, bad habits are hard to shake off, and the industry is still burdened with that embarrassingly inadequate descriptor for the most important specification.
20 Hz to 20 kHz ±3 dB is meaningless without seeing the curve that it describes. It could be a horizontal straight line that simply falls off sharply at the upper and lower frequency limits (perfection), or it could be a line that undulates randomly between +3 dB and - 3 dB, a 6 dB range (absolute rubbish).
But even worse than the uselessness of that description of frequency response is the fact that it is often assumed that a single curve is sufficient to describe the performance of a device that radiates sound in three dimensions - in all directions - into a room. When a manufacturer shows a specification for a loudspeaker frequency response in numerical form only, and the tolerance is more than about ±0.5 dB, ignore it. If a curve is shown, but there is only one, it might be correct, but by itself, it is not enough data.
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kinnar
12/23/2010 4:39 AM EST
This is a very good article about the Loudspeaker Essential Properties Measurement but simultaneously it also discusses important parameters to be considered while designing the loudspeakers and the place of installation. Truly this is a great article.
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kdboyce
1/3/2011 2:44 AM EST
This article is excellent both for its content as well as how loudspeaker performance is explained.
Of key importance is the fact that every listening environment is different and therefore every listening experience is different according to the environment. Engineers of audio amplifiers do strive for as flat a response as they can get over the audio band such that any "deficiencies" in the sound is caused somewhere else in the system.
As speaker sizes are reduced, and lower costs enter the picture, one could legitimately as if such a speaker had any real performance features are all? It is a fair purpose, however, to tailor a speaker to a specific application. For example, voice only applications do not need full 22KHz audio bandwidth, but they should be really good in the 100Hz to 4Khz range.
Compensating small speakers using EQ and similar means only goes so far, and also becomes difficult for speakers confined to a very small space with little physical volume behind them. It is an attractive area for research, as we see user devices take on audio characteristics of larger devices while still retaining a handheld form factor.
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Nic Cohen
7/27/2012 4:00 AM EDT
It gets to a point where you will require the use of a solid object like a table which has adequate reverberation in order to compensate for the size and increase the loudness... No?!?
Nic
www.kdweb.co.uk
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