The L-Acoustics Preset Guide is not only a valuable resource for subwoofer alignment, but is also one of my inspirations for creating SubAligner. If L-Acoustics can create alignment presets for their speakers then I should be able to scale the same method to any other speaker pair.
It also provides a quality check for results from SubAligner: Do they match? Why or why not?
A majority of the Preset Guide deals with loading the appropriate preset into the amplified controller for a particular speaker.
The Preset Guide describes the recommended loudspeaker configurations for each system, with the corresponding factory presets and the main resulting acoustic properties.
But there’s a big section at the end called Pre-alignment delay values.
For some loudspeaker enclosure combinations, it is necessary to adjust the delay values for time-alignment. Refer to section Pre-alignment delay values (p.66).
This is where a method for crossover alignment is described to be used “If no acoustic measurement tool is available,” or if I might add, if actionable data is otherwise unobtainable. When might actionable data not be obtainable? Please see Don’t Align Your Subwoofer to a Room Reflection.
The procedure goes like this:
- Measure the path difference
- Geometric delay = path difference / speed of sound
- Alignment delay = geometric delay + pre-alignment delay
Let’s see how the results from SubAligner stack up against the official guide.
K2 + SB28
If you were to attempt to align these two speakers with a distance offset only, you would have a pretty bad day.
The preset guide recommends a polarity inversion and 0.5ms of delay in the K2 output.
SubAligner recommends a polarity inversion and 0.92ms of delay in the K2.
A difference of 0.42ms is only about 4% at 100Hz (or 14º). I haven’t interviewed the person who created the preset guide, but I’m happy to see that the human and robot result are in good agreement.
Is there an alternative solution?
If you would like to use less delay or create a crossover region with less overlap you can open the Filters pop-up in SubAligner. The first solution you’ll see is a 4th order Butterworth filter at 73Hz.
Kiva + SB15m
These two speakers are only about 80º apart out of the box so I wouldn’t worry about the alignment too much.
The preset guide recommends 1.4ms of delay on the SB15m.
Meanwhile SubAligner recommends 1.8ms of delay.
It’s interesting to see a difference of 4% again. My assessment, they agree.
SubAligner does give some recommendations for filters, but they provide no significant reduction in delay or overlap.
dV-DOSC + dV-SUB
When equidistant, these guys are ready to party.
Notice that 4% difference again? If I had to guess while splitting some hairs, I would say that the SubAligner results are giving more weight to the lower frequencies of the crossover region while the L-Acoustics recommendations give more weight to higher frequencies. The L-Acoustics result will produce a tiny bit more summation at the top of the crossover region and will allow you to turn your sub up louder in relationship to the main with less misalignment. On the other hand the SubAligner result gives a tiny bit more summation at the low end of the crossover region and allows you to turn the sub down lower in relationship to the main.
It’s also interesting to note that all of these alignments produce a crossover bandwidth of 1.7-2.1 octaves and if you average all 220 L-Acoustics alignments in SubAligner you’ll get 1.44 octaves.
Have you tried any of these presets in the field? What were your results?