Sound Design Live

Build Your Career As A Sound Engineer

  • Podcast
  • Training
    • My Courses
  • Archive

Dave Rat’s End-Fire Adjustable Arc Subwoofer Array Explained

By Nathan Lively

During my interview with Dave he explained a subwoofer array that he developed during a Blink182 tour. Here’s what it looks like.

Here’s where Dave explains it in the interview, starting at 45 minutes.

This came out of the sub testing that I did, primarily on the Blink 182 tour and then finished or got farther on the SoundGarden tour. I tried multiple arrays and out of it I came up with this fanned array.

The way to make it is, find your zero point, your rear sub location, the center of the grille. I would just have someone step on a tape measure there or put a road case on it. Then walk out 6.25ft for a 45Hz maximum rear cancellation. Then I draw an arc with the string.

Then you would place along that arc the front radiating points. One, two, three, however many you want. The 0ms point is your rear sub. Set your front ones at +6.25ft, which is about 5.8ms.

I see, so if you soloed up any of those front subs, they should be arriving at the same time as the rear subs.

Yeah, so the concept is the sound radiates from [the rear sub] and travels 6.25ft to sum with the subs in the front.

The closer these are together the beamier it gets. As you spread them out on the arc, the wider it covers.

[You have to put a sub stack in the back equal to the ones in the front. Each stack has three.] It’s making sound that will actually cancel out everywhere else and sum in the front.

The theory

Dave’s design is a combination of end-fire and physical arc. The end-fire takes care of the cancellation in the rear and the arc controls the coverage width.

End-fire array: an array of multiple subwoofers, placed in a line, one behind the other, with a specific spacing and delay strategy in a timed sequence that creates forward addition and rearward subtraction.

Bob McCarthy, Sound Systems: Design and Optimization

The array achieves summation in the front by delaying the front elements to the rear, causing everyone to arrive at the same time. It achieves cancellation in the rear through delay as well (output processing + distance offset), except in the rear everyone is arriving late causing a chaos of phase relationships.

Physical arced arrays exhibit a coverage angle equal to the segment of the arc segment of virtual circle whose origin lies behind the array.

Merlijn van Veen

A physical arced array turns a line source into a point source. Where all elements were arriving at equal level and time on-axis, they are now steered outward with a virtual origin from behind the array. As arc angle increases so does coverage width as the various spatial crossovers move away from on-axis.

The design

How did Dave come up with the 6.25ft spacing?

spacing = ¼λ

spacing = speed of sound / frequency * 0.25

6.2778 = 1130 / 45 * 0.25

Dave’s design breaks some rules, which is fun. Normally we avoid a two-element end-fire array because it is limited to a single cancellation in the rear and then comes back with a nasty peak an octave up.

It is for this reason that if you design this array in Merlijn van Veen’s Subwoofer Array Designer, it will recommend high and low-pass filters at 29 and 60Hz, respectively.

With preferred filters.

The model

Wide coverage

I haven’t tried this in the field, yet, but we can look at some models in MAPP XT.

I’ll start with the widest spacing to get the widest coverage.

Here’s a prediction at 44.2Hz showing an opening angle of 176º.

In the measurement viewer we have a nice F2B ratio of 50dB at 50Hz.

But why 50Hz? I expected to see it at 45Hz.

It turns out that I spread the subs out so far that the distance offset changed from 6.28ft to 3.77ft from the rear. This changed the combined phase of the front subs to 150º apart at 45Hz and 180º apart at 50Hz, compared to the rear sub.

I reset the placement and delay based on the outside subs instead of the center one and was able to shift the null down to 47Hz. Hurray!

Narrow coverage

Now let’s try the narrow coverage version.

Here’s the prediction at 44Hz. Looks like it’s 10º more narrow than the previous design.

Nice F2B rejection of 31dB at 44Hz.

An alternative?

Dave breaks some rules here, which is fun.

Never end-fire with just two elements. It’s a one-note-wonder on the back side. Use the gradient in-line instead (same physical, different settings).

Bob McCarthy

This make me wonder what an in-line gradient array would look like with the same design.

Gradient array: A cardioid configuration commonly used for subwoofer arrays with front and rear elements. The rear element is delayed and polarity reversed to effectively cancel behind the speakers.

Bob McCarthy

The gradient array has frequency dependent coupling in the front in exchange for broadband cancellation in the rear.

You can use the exact same speaker placement, with different output processing.

It looks very similar to the end-fire at 44Hz, but is quite different across its operating range.

Where we had a limited range of cancellation with the end-fire array, we now have broad-band cancellation with the gradient. You may be worried about the dip at 100Hz, but notice that that the expected response is already 20dB down, moving it into isolation if you are running a linear system.

What’s it for?

As we discussed on the podcast, Dave was looking for a way reduce LF interaction in the center of the audience and total LF energy behind the arrays.

Compare a traditional setup of left and right sub stacks…

To two of Dave’s end-fire arcs splayed 90º apart.

If you would like to play with these MAPP designs, you can download them here. Please let me know if you discover any improvements. 🙂

Have you tried something like this in the field. What were your results?

Dave Rat’s Simple Problem Solving Mindset for a Long Fulfilling Career in Pro Audio

By Nathan Lively

Subscribe on iTunes, SoundCloud, Google Play or Stitcher.

Support Sound Design Live on Patreon.

In this episode of Sound Design Live I talk with the president of Rat Sound Systems, Dave Rat. We discuss artistic solutions to technical problems, the best mindset for a finding work and a long fulfilling career, and the time Flea shouted in his face for missing an entrance.

I ask:

  • What are some of the biggest mistakes you see people making who are new to FOH mixing?
  • What is the biggest mistake you’ve made on the job and how you recovered.
  • From FaceBook
    • Roshan Malim: Ask him about his sub woofers configurations and which is his favorite and why? And what is his most common sub woofer configurations for gigs? His ideas between flown subs and ground stack subs.
    • Christian Michael Martinez: As an owner of one of the largest production companies, how did you cope with the possibility of failure in the beginning as a small shop? How do you cope with risk now that the company is a success?
    • Maurizio M. D’Errico: Ask him about his technique of tuning a pa using headphones as a reference and if he still feels the same way about it since he made the YouTube video: How to EQ a Live Sound Reinforcement System.
    • Craig Gordon: Balancing touring and family/health.
    • Stephen Mink: Since he has some videos on YouTube about sub placement/patterns/alignment, his thoughts on where in a room to align flown and ground subs.
    • Dave Gammon: Does he really see the M-Force driver as the future
    • Garrick Quentin: Has he seen or heard of anyone else not affiliated with Rat sound using the double hung array as he did with the RHCPs and perhaps any comments on the whole concept in terms of its popularity, or otherwise, within the industry.
    • Davide Bonetti: does he need an assistant? 😇
    • Steve Knots: What’s the worst setup disaster he ever recovered from to pull off a successful show in the end?
    • Marty America: How’s your dog doing?
    • Micah Muth: How’s the Tesla?

The way to be successful is to sell self confidence. Confidence that when you’re there it’s going to be as good as it can possibly be.

Dave Rat

Notes

  1. All music in this episode by The Funk Lives.
  2. See my deconstruction of Dave’s custom end-fire subwoofer array.
  3. Hardware: DBX 12xds Subharmonic Synthesizer
  4. Books: Surely You’re Joking, Mr. Feynman!
  5. Quotes
    1. We didn’t borrow money, take any loans or take on any debt until 1997. So, 17 years of business.
    2. We had no idea. Well, we kind of had an idea. Everyone told us we’d fail. “There’s no way you’ll ever survive doing this.”
    3. If I’m 100% behind it and I’m going to make it happen; it’s not whether it will succeed. It’s how long it’s going to take. So if you just don’t even let failure be an option then it’s just a matter of work.
    4. Avoid silver bullets. They don’t come.
    5. Avoid being giant. You want to be happy, stable, and profitable. Being giant is precarious, stressful, and makes you a target for people to come after you.
    6. Probably one of the most common things for green engineers; the kick drum is so loud! It’s distracting from the core purpose, which is to connect the artist with the audience.
    7. If you act like you have a problem, then you have a problem. If you don’t act like you have a problem, then no one knows you have a problem.
    8. The way to be successful is to sell self confidence. Confidence that when you’re there it’s going to be as good as it can possibly be.
    9. We don’t have any problems here today. We just have a big pile of solutions we haven’t found, yet. It’s Ok, because the ones we can’t fix, can’t be fixed. But if it can be fixed, we’re gonna do it.
    10. It’s that unphasability. Combine that with, “Gimme the tools I need to do the job and everything will be fine,” and you can write your own paycheck.
    11. The sub configuration I prefer is the one that covers the venue as best as possible.
    12. The worst thing you can possible do is run your subs mono.
    13. Having a separate L/R sub aux, I find to be extremely useful.
    14. No where in nature do you have two things that are perfectly in time and phase.
    15. No where in nature do multiple unrelated sounds radiate out of a single point in space.
    16. By trying to make it sound the same everywhere, you loose the ability to make it sound great everywhere.
    17. A world-class sound engineer has the ability to recreate a quality sound consistently throughout a variety of environments and challenges.
    18. One of the ways I kept myself happy and sane was to start an external project. One tour it was blogging. It kept me busy. One tour I decided to learn to weld.
    19. By spreading (the mix) out, you can beat the crap out of the bass guitar into the fifteens of one rig, but the low end of the vocals and the low end of the guitar would stay clean. And the guitar could beat the crap out of the sixes in that one rig, but the vocals would be perfectly clean.
    20. If you desire to learn everything you can.

Search 200 articles and podcasts

Copyright © 2022 Nathan Lively

 

Loading Comments...