TI Information – Selective Disclosure SLOU
PurePath™ Smart Amp User Manual (TAS5766M/68M)
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5
Hardware Design
Smart Amp systems can operate at higher rail voltages than traditional systems while protecting
loudspeakers. This is possible because Smart Amp understands the speaker characteristics.
This allows control of excursion and temperature of the voice coil and the magnet while
preserving the music peaks. For products where the rail voltage remains unchanged from a
previous model, smaller speakers could be used to save cost and reduce form factor while
preserving loudness.
If the maximum output voltage limit of a traditional system is based on the average power of a
full-scale sinusoid, there is risk of voice coil overheating if a square wave is provided as an input.
This is due to the fact that a square wave has 6dB higher average power than a sinusoid of the
same peak amplitude as well as having the presence of higher frequency components.
Conservative designs may then have to trade off sound pressure level (SPL) with reliability.
More advanced methods to control load power include the use of limiters and dynamic range
compressors. These methods can protect the speaker however peaks may be clipped and/or
greatly reduced, especially on source material with high peak-to-average ratios (PAR).
The graphs below are actual song clips comparing the traditional method (left) against Smart
Amp (right) to control output power. The dashed lines correspond to the output limit of a
traditional system. Note that the average power (P
ave
) is increased while allowing peaks to cross
the output limit.
Figure 8. Audio Clip A, 22dB Peak to Average Ratio Source
Figure 9.
Audio Clip B, 9dB Peak to Average Ratio Source
