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, 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.
These manufacturers all agree that:
- Alignment is important. You deserve all of the decibels that you paid for.
- 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 are not appropriate for an audio analyzer, 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.
This alignment method is again 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.
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.
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.
The biggest challenge here is sunlight. Here are some of my favorite tips to get accurate measurements:
- Get closer. If you calculate your alignment position with Merlijn’s Sub Align calculator, you will often find that the best alignment position is a lot closer than you thought. This will make a distance measurement a lot easier to do.
- 3D design. If you can get the distances from a 3D model ahead of time, that’s the best.
- Target. Many laser distos come with a little mirror that you can attach to the speaker. Anything reflective will work.
- Camera. My laser disto has a camera on it. This makes it much easier to aim. You still need something shiny to aim at, though, and for longer distances you’ll need a tripod for accurate aim since your hands will never be still enough.
- Right triangle solver. If you can’t get a lock on the speaker, you can put the disto on the ground and aim at a target on the ground below the speaker. Then measure the height of the speaker. If it’s an array you’ll need to figure out the distance from the bottom of the array to the center and add that on. Then use a right triangle solver (just google it) to find the hypotenuse. This will also save you if there are obstructions like chairs in the way of your sub measurement.
- Range finder. I keep a golf range finder as a back-up. It’s only accurate to within 1m, but it’s better than nothing and can be used to verify questionable laser disto readings.
- Alternatives: tape measure, measuring wheel, or proxy loudspeaker. You can use an audio analyzer in conjunction with a proxy loudspeaker to get the time to subwoofer time of flight.
Delay finders struggle with subwoofers because subwoofers reproduce only a fraction of the audible spectrum leaving too little data for the delay finder to lock onto.
The proxy loudspeaker’s sole purpose is to add the frequencies which are missing from the subwoofer, allowing the delay finder to detect arrival time again.Subwoofer Alignment: The Foolproof Relative / Absolute Method
I wish there were some glasses you could wear that would highlight the laser dot or some kind of scope or sight. I see that the firearm community has a lot of cool toys like this, but haven’t found one that would actually help us.
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?