Overview

AN3340

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Doc ID 18453 Rev 1

amplifiers in total) and the crossover filters are implemented using the DSP already present

in the audio chain. Although this solution should provide good performance, the audio

quality which the viewer/listener perceives is not so good because the dimensions of the

speakers are very small.

Some clever and original solutions have been developed in the past, for example, speakers

with two or more coils placed side by side, but the effort was directed only to solve the

problem of the mechanical dimensions, with the sound performance being neglected.

So it seems that the simplest way to improve the overall audio performance of a loudspeaker

system is to tailor the audio signal sent to the speaker in an attempt to compensate for the

deficient speaker response.

2.3

How to compensate a loud speaker

In order to improve the overall audio performance we need to match the audio signal to the

speaker. A simple and effective way to achieve this is to use the equalization circuits often

incorporated in audio amplifiers. In this way the signal can be modified to compensate for

the poor loudspeaker response.

section of these devices is a very flexible equalizer that can be usefully programmed to

compensate the speaker frequency characteristics.

This procedure can be performed manually, for each filter adjusting the frequency, the gain

and the quality factor. However, this procedure needs time and the final result depends on

the operator ability, aptitude and experience.

Another possibility is to use the automatic feature now available in the APWorkbench

software: the ST Speaker Tune.

The final result is an equalization curve which reflects the inverse speaker frequency

response. Thus, the overall frequency response in the final application, in a flat-screen TV,

for instance, will be flatter than the uncompensated system and at the same time the

frequency bandwidth will be enlarged. But the most important effect is the viewer/listener

experience who perceives a positive improvement.

In the next chapters the speaker compensation process using ST Speaker Tune is explained

and acoustic improvements are shown.