Time-Alignment of Multi-Way Speakers with Group Delay Equalization - I

Bharitkar S, Holman T, Kyriakakis C. Time-Alignment of Multi-Way Speakers with Group Delay Equalization - I. In: AES Convention 124. Audio Engineering Society; 2008. Paper 7396. Available from: https://aes.org/publications/elibrary-page/?id=14526

@inproceedings{Bharitkar2008_14526,
  author = {Bharitkar, Sunil and Holman, Tom and Kyriakakis, Chris},
  title = {{Time-Alignment of Multi-Way Speakers with Group Delay Equalization - I}},
  booktitle = {AES Convention 124},
  note = {Paper 7396},
  year = {2008},
  month = may,
  publisher = {Audio Engineering Society},
  url = {https://aes.org/publications/elibrary-page/?id=14526}
}

TY  - CPAPER
TI  - Time-Alignment of Multi-Way Speakers with Group Delay Equalization - I
AU  - Bharitkar, Sunil
AU  - Holman, Tom
AU  - Kyriakakis, Chris
T2  - AES Convention 124
M1  - Paper 7396
PY  - 2008
DA  - 2008/05/06
UR  - https://aes.org/publications/elibrary-page/?id=14526
PB  - Audio Engineering Society
LA  - en
AB  - In this paper, a first of two-parts, a technique for time-aligning the driver responses (viz., woofer, mid-range, and tweeter responses) in a multi-way speaker system is presented. Generally, woofers exhibit a much larger time-of-arrival delay, at a listening position, compared to the mid-range and high-frequency drivers. Moreover, the time-of-arrival delay for all drivers is frequency dependent exhibiting a large variation over the audible frequency domain. Due to these differences, a two-part study was undertaken to understand the effects of these variations, quantitatively and qualitatively. In this first part, we present the motivation behind the system used for applying all-pass filters to process audio signals being delivered to the multi-way speaker and propose a time-delay difference equalization technique. We show that applying all-pass filters result in significant ``temporal-smearing' of the response, despite flattening of the group delay response. Thus depending on the amount of group-delay equalization, the smearing with pre-ring effects could potentially have audible effects depending on the content. However, despite the temporal-smearing (viz., response-dilation in time) for an arbitrary-order all-pass filter, we show that the time-frequency characteristics of these group-delay equalizing filters exhibit a uniform decay rate at all-frequencies allowing group-delay equalization without affecting the modal decay rates. Thus this enables other cascaded filter structures to be utilized for modal equalization in additional to conventional loudspeaker-room equalizers. We also propose group-delay flattening for the woofer and a small range of the midrange frequencies through a weighted approach at the lower frequencies for group-delay equalization. Future work will involve investigations using perceptually motivated variable-octave complex smoothing of responses (1/24-th octave smoothing at low frequencies and 1/3-rd octave at higher frequencies), and designing all-pass filters based on this phase-smoothed data. Quantitative results obtained will be presented in this paper, whereas the next part of the two-part paper will present results from listening tests.
ER  -