The most common active electronic component used in audio engineering is an operational amplifier often referred to as an op-amp. The settling time of an amplifier is defined as the time it takes the output to respond to a step change of input.
An Audio signal requires a fast settling time due to the signal constantly changing. Errors due to settling time produce noise level, non-harmonic distortion, (not related to original signal). This noise level increases with slower settling time, this noise level is defined as a ratio between system settling time and the highest transferred frequency. The settling time of the system feedback loop must be less than 1µs (microsecond), to maintain high quality audio. If this is not maintained, the system creates and introduces noises that are not related to the original sound. This is an element of distortion added to the signal that is rarely talked about, but its effects are much more significant and dramatic in damaging the audio quality, than any losses due to harmonic distortion, a figure commonly published by most manufacturers.
The Settling time of common electronics systems used in most commercial sound systems is around 10 µs, ten times longer than it should be. The distortion, created by slow settling times is not commonly discussed by many manufacturers as they fail to understand its significance, often overlooking it in providing the technical specifications of products. Moreover the noise this distortion adds is very often mistaken for original high frequency, especially in digital technologies where it can exhibit itself as a bright, “fizzy” high end.
Settling time is less of a problem on simple signals because it occurs with addition to the higher frequency of the original signal. However, when introducing a complex signal, due to its long settling time there is now a high level of non-harmonic distortion from the many different, prolonged scrambled elements of noise, which then create a cacophony, masking the weaker original signal nuances.
That system has a low resolution.
Settling Time, Non-Harmonic Distortion
Settling time of Operational amplifiers therefore also has a large effect on a system’s ability to transfer information accurately, without non-harmonic distortion, particularly in the higher frequencies. SLA circuitry only utilizes components with settling times of 1 microsecond (1μs) or less to ensure a high definition, low distortion signal path.
This graph shows the amount of non-harmonic distortion present in circuitry with settling time is 1μs and 10μs.
Speaker Pulse response
The main parameter of the speaker is pulse response. Parameters of the speakers are almost exclusively measured by a continuous sine wave signal. But continuous sine waves are not identical with regard to music signals. Music consists of many signal types, basic tones, harmonics and noises and are best represented by pulse response. When a speaker is measured by continuous sine wave signal, it has time to swing at higher frequencies, although the speaker has no control over diaphragm mass and motions.
One of the most important parameters in transducer design for Super Live Audio Systems is the removal of unwanted resonances. These resonances are usually caused by the mechanical design of the speaker and its failure to control the diaphragm motions. Resonances reduce overall definition by masking smaller signals and producing tones not related to the original signal.
The figure below shows an original sine signal (red, top) with its sharply defined end and the same reproduced signal (blue, bottom), still oscillating after the signal stops due to poor control of speaker mass. Poor pulse response has a very negative effect on the ability of a speaker to reject feedback. SLA systems feature exceptional feedback rejection and this in part is due to their excellent pulse response.
Active Impedance Control
Additionally, control over the speaker mass can be very positively impacted by using an active impedance control, (trans-coil) speaker system. This system utilizes a secondary stationary coil, which reduces inductance close to zero and dramatically improves pulse response. Inductance is the main reason for odd harmonic distortion. Odd harmonic distortion is far more audible than even harmonic distortion.
Low Inductance = Low Non Harmonic Distortion
The Active Impedance Control or AIC is an additional fixed, multi turn coil, positioned in the loudspeaker magnetic circuit gap. This coil is almost as long as the gap height and being wound around the pole piece to be very close to the voices coil. A current flowing into this coil generates a magnetic field that is in opposition to the field generated by the moving coil. This cancels out most of the voice coil inductance and reduces the flux modulation and inductance modulation. The AIC device can be seen as an “active” shorted ring in the gap. The two AIC terminals allow driving the additional coil in many different ways according to specific application needs.
Producing very high quality speakers for audio systems with minimal distortion has created the need for enhancement of the electronics for an SLA system design. In reality few manufacturers are able to utilize AIC trans-coil technology, because upon testing they realize that it immediately shows up the fundamental flaws in their own electronics designs. Even greater compromises in audio quality occur when utilizing digital processing to try and correct their acoustic design.