Impulse accuracy

Frequency response

When measuring loudspeakers, the frequency response is usually considered the most important measure. In principle, this would be correct if it were shown according to magnitude and phase. Unfortunately, much often content with the level frequency response and leaves aside the phase response. This is surprising, because half of the truth is buried there. While the level frequency response primarily shows the static behavior of a loudspeaker, the phase frequency response can be used to show the temporal relationships. Both together are contained in the impulse or step response and can be interpreted wonderfully especially in the step response. Translated with www.DeepL.com/Translator (free version)

If a linear level frequency response is present, this unfortunately does not mean that the loudspeaker has an error-free transmission behavior. Especially passive multi-way systems (consisting of woofer, midrange and tweeter) are usually anything but perfect in their dynamic behavior. Due to the different response times of woofer, midrange and tweeter and the influence of the crossover, a conventional loudspeaker has to deal with three temporally separated impulses for each impulse. Our brain then tries to calculate a reasonably homogeneous result despite time differences between the different frequency bands. Translated with www.DeepL.com/Translator (free version) That this does not correspond to the musical truth seems more than obvious.

Constant group delay

The term constant group delay is equivalent to a linear phase and means that all frequencies are emitted simultaneously. The phase frequency response or the group delay is not easy to measure, because it requires a relatively large anechoic chamber, especially to measure lower frequencies as well. However, it is known from studies that humans detect phase shifts in dynamic signals, of which music mainly consists, especially in the range of about 150 to 10,000 Hz. Translated with www.DeepL.com/Translator (free version) The phase frequency response or the group delay is not easy to measure, since it requires a relatively large anechoic chamber, especially if lower frequencies are also to be measured. However, studies have shown that humans perceive phase shifts in dynamic signals, of which music is primarily composed, especially in the range of about 150 to 10,000 Hz. This behavior, on the other hand, can be assessed very well in the step response.

With a step response a signal is given to a loudspeaker, which immediately jumps from zero to e.g. 2 volts. In the two graphs above, the input signal is shown dashed white. The closer the response of the loudspeaker is to the input signal, the fewer errors are present in the transmission range.

In the left graph we see the step response of a passive 3-way high-end loudspeaker, on the right that of an airplain phli during the development phase. While the passive loudspeaker shows three different, successive reactions, only one reaction can be seen with the phase-linear loudspeaker. By the way, both speakers could have identical level frequency response and the step response could still be so much different.

Which system now produces fewer errors or is closer to the original is obvious.