dallasjustice
Major Contributor
I have a stereo playback setup with four subs. My room is rectangular. Each of the four sub subs are placed at each midwall. IOW, a Welti four sub setup. Of course, each sub is mono and the crossver is a 2nd order NT.
The challenge is to find a method to best time align each sub to the R/L speakers. The following video demonstrates a few different methods to accomplish time alignment. The first method used was to simply line the impulses up by applying delay to various speakers.
The second method used is probably best called the "sine wave method". The goal of this method is to line the subs up with a theoretically perfect sinewave at the crossover. In theory, this method offers the greatest precision. As you will see, this method didn't workout that well. In the end, this method assumes that if a sub is precisely time aligned at the crossover point (which they were), the same sub will be time aligned overall throughout the low pass. As anyone can see from the group delay plots, that is not a valid assumption when it comes to very low frequencies. As Uli said, this was a good learning experience. It separates the theory from actual practice in room.
Finally, Uli was able to achieve excellent time alignment by playing each sub with the R/L speaker. He then rotated the delay for each sub based on the step response. In my setup, all subs play before the R/L. Without going into too much detail, my DAC over AES introduces enough latency that all subs need delay applied to be time aligned to R/L (including frontwall sub which is about 12' further away from MLP than R/L).
Uli and I tried this 4 sub setup a few weeks ago. It didn't workout that great. The reason was that I didn't take care to balance all subs and level match all four together to R/L.
All methods demonstrated herein require, in the end, all four subs be measured along with the R/L speakers. So it's important that all four subs play equally and combine to the same level as the R/L speakers. Before the video, I used REW preference tab to send low frequency pink noise to each sub and balanced them all with the volume knobs on each JL audio fathom sub. I then matched level for all four subs played together to the R/L. This preparation made a huge difference.
Overall, the bass is unassailable. I feel like I can listen to anything and the system won't break a sweat or show a flaw. Thanks Uli!
The challenge is to find a method to best time align each sub to the R/L speakers. The following video demonstrates a few different methods to accomplish time alignment. The first method used was to simply line the impulses up by applying delay to various speakers.
The second method used is probably best called the "sine wave method". The goal of this method is to line the subs up with a theoretically perfect sinewave at the crossover. In theory, this method offers the greatest precision. As you will see, this method didn't workout that well. In the end, this method assumes that if a sub is precisely time aligned at the crossover point (which they were), the same sub will be time aligned overall throughout the low pass. As anyone can see from the group delay plots, that is not a valid assumption when it comes to very low frequencies. As Uli said, this was a good learning experience. It separates the theory from actual practice in room.
Finally, Uli was able to achieve excellent time alignment by playing each sub with the R/L speaker. He then rotated the delay for each sub based on the step response. In my setup, all subs play before the R/L. Without going into too much detail, my DAC over AES introduces enough latency that all subs need delay applied to be time aligned to R/L (including frontwall sub which is about 12' further away from MLP than R/L).
Uli and I tried this 4 sub setup a few weeks ago. It didn't workout that great. The reason was that I didn't take care to balance all subs and level match all four together to R/L.
All methods demonstrated herein require, in the end, all four subs be measured along with the R/L speakers. So it's important that all four subs play equally and combine to the same level as the R/L speakers. Before the video, I used REW preference tab to send low frequency pink noise to each sub and balanced them all with the volume knobs on each JL audio fathom sub. I then matched level for all four subs played together to the R/L. This preparation made a huge difference.
Overall, the bass is unassailable. I feel like I can listen to anything and the system won't break a sweat or show a flaw. Thanks Uli!
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. Interesting.
