You don’t need expensive equipment or a PhD to set subwoofer delay time. In fact, all you need is:
Sound too easy? Consider that top brands like L-Acoustics, d&b audiotechnik, JBL, Coda Audio, RCF, Funktion-One and dB Technologies all recommend the same subwoofer phase alignment method.
- Create an alignment preset for two sources that are equidistant.
- Modify that alignment in the field, using delay to equalize any difference in distance.
For the rest of the article I’ll refer to this as the relative/absolute method.
These manufacturers all agree that:
- Alignment is critical not only for an exciting show, but also to accurately reproduce the performance, protect the equipment and audience health, and keep from pissing off the neighbors.
- If an audio analyzer is unavailable or inappropriate, use the two step method described above instead. Some people don’t own an audio analyzer, have not invested the years of practice to master its operation, or don’t have time to set it up. Additionally, some circumstances make an audio analyzer ineffective, for example when the reflections in a small room make the data inactionable.
Manufacturers differ on where to get the pre-alignment delay values and the exact workflow, so let’s take a closer look at each of them.
Here’s a selection from the L-Acoustrics Prest Guide v18.0. Notice that their method is to find the difference in distance, convert it to a delay time using the speed of sound, and then add the pre-alignment delay.
It includes pages and pages of pre-alignment delay values depending on which speakers you are combining. SubAligner works the same way, but is not limited to a single manufacturer. It will automatically calculate the delay time for any speaker combination.
The same method is recommended in an excellent training video from L-Acoustics.
Never forget that you still have the geometric measurement. If you are in a situation where you cannot ensure the quality of the measurement maybe measuring the geometric distance with a laser meter and calculating the corresponding delay time can give you better results than a bad acoustical measurement.François Montignies, L-Acoustics
Here’s a selection from the TI 385 d&b Line array design 10.6 manual. They recommend using their modeling software for alignment, or an audio analyzer, or the same method discussed above converting physical distance to time.
I attended a JBL VTX training here in Minneapolis at Paisley Park. Most people don’t know that the park includes a performance space where you can see some of Prince’s larger memorabilia like cars and pianos. That space includes a VTX rig installed by Farber Sound, who were nice enough to organize the training.
Let’s take a look at page 24 of the VTX user manual.
Additional time alignment delay should be added as needed to account for physical path length differences between suspended A6 arrays and ground-stacked VTX subwoofers. If no acoustic measurement system is available, delay values can be calculated based on the geometric path difference between a reference point (i.e. FOH position) and each system. This is an effective method, since all VTX presets include a factory pre-delay to correctly align all components. When the latency of a system is unknown, this method is not effective and should not be used. This can occur when the signal paths of different parts of the system vary in latency.VTX A6 | User Manual, Distribution Date: July 22, 2022
When I posted about this online I got a nice tip from the instructor of the workshop, Raul Gonzalez.
For the benefit of the readers, it would be good to let them know that my class comment about using a laser pointer to check distance variation between mains and subs, only applies when using speakers within the VTX family as these all share similar phase response. Or as I shared, if the VTX tops and subs are next to each other, the delay time for phase alignment is included within the DSP preset.
Either way, on site verification via system measurement is always recommended.Raul Gonzalez
This is a great one-two punch and what I consider to be the most effective sub alignment strategy in the field:
- Relative/absolute method
- Verification with an audio analyzer and listening tests
In NEXO’s amplifier manuals they start off by warning you of the dangers of a misaligned system, subs on an aux, and additional unnecessary filtering. Then they outline their subwoofer delay setting method, which is to convert the difference in distance from the listening position to time, then verify with an audio analyzer.
In the Coda Audio LINUS Control v2.2.33 Time Alignment document, they recommend using an audio analyzer, then defaulting to the same method we have been discussing, which is to add the pre-alignment delay time to that created by the difference in physical distance.
We can see that the RCF Pre-Alignment Delays v.1.1 – Guide makes very similar suggestions.
On the Funktion-One website they highlight the importance of choosing the correct crossover frequency range, time alignment, and limiter setting.
Then they provide table of pre-alignment delay values and crossover settings.
The settings on the website are a bit special as these are for ground stacked systems using our ground stack boards, which fixes the physical alignment of the speakers.
For other configurations, particularly larger and more complex ones, we also recommend the process you describe of finding the delay of the physical distance offset and using this as a starting point for an optimised alignment.
It’s really important to get right!James Hipperson – Funktion One
In this marketing video from dB Technologies they explain that, “The user can easily align the boxes just by using a rangefinder.”
This video should start at 2:31.
How do you measure the physical distance offset?
The short answer: User a laser range finder. Choose an alignment position. Measure the distance to source A, then source B. A – B = the physical distance offset.
Where do you get the pre-alignment delay values?
Pre-alignment delay is the amount of delay time necessary to align two sources when they are equidistant. These values are often provided by the manufacturer. If not, SubAligner offers 88,656 combinations or you can generate your own.
To calculate your own pre-alignment delay times, place main and sub speakers on the ground so that they are equidistant with your measurement microphone and then do whatever is necessary (polarity, delay, filters, etc.) to hit your preferred alignment target.
I’ve been using this method to prepare for every new show that I work on. I either go to the shop to measure the speakers and generate and alignment preset or I get it directly from SubAligner.
Sometimes I can even estimate the final delay by measuring the distances in modeling software.
On a recent gig here in Minneapolis I was responsible for deploying a NEXO sound system comprised of S1210 and RS18. To prepare, I:
- Designed the sound system in NEXO’s NS1 modeling software.
- Calculated the alignment position using Merlijn’s Sub Align calculator.
- Measured the physical distances to main and sub from the alignment position in NS1.
- Put these distances into SubAligner to automatically calculate the delay time.
Then, when I get into the field and all of the speakers are in place, all I need to do is measure the physical distances and add them to the alignment preset (or just re-run SubAligner).
Final step: verify with an audio analyzer.
Great success. 🙂
What about you? Have you tried using this method for setting subwoofer delay? What were your results?