Optimization of a Subwoofer Line Array with MSO

[hulkss]

I decided to give the Multi-Sub Optimizer (MSO) software a try: Multi-Sub Optimizer

 

I have a 7-meter-wide subwoofer line array consisting of one central Infinite Baffle (IB) Subwoofer, flanked by four Epik Empire Subwoofers, and two Klipschorn corner-horns. Fourteen 15-inch drivers in all, driven with 5 amplified input channels: one for the IB, one for each K-Horn, and two channels for the two Epik pairs.

 

 

The objective is to get this subwoofer array sounding good in the four seats pictured below.

 

 

I took the needed 20 measurements (5 subs x 4 seats) in the seat positions using Room Equalizer Wizard (REW) software including a loopback timing reference. All the subs are powered by external amps with no signal processing at full fixed gain.

 

 

It’s interesting to take note of the “Schroeder Frequency” in this mess of measurements at about 120Hz. You can clearly see the three types of subs separate in output level at the low end. IB subs go low, horns not so much.

 

I set-up an optimization as follows:

To help ensure maximum output there are no gain adjustments.

 

Ideally, the line array should behave like one big ass subwoofer so fixed delays were set to “time align” the five sub channels to “launch” a coherent sound wave across the width of the room. There are no resonant ported speaker enclosures that make timing challenging.

 

Three Robert Bristow-Johnson (RBJ) parametric equalizer “bi-quad” filters were set for optimization in each subwoofer channel, 15 filters in total.

 

Click on the optimize button……12 cores at 4 gHz made short work of this (about 15 min). Do set up a real-time plot to see the filters develop. Very cool to watch and when they stop changing it’s done.

 

 

Hmmm…a very weird looking solution, however, I do believe in the math behind it. It’s good to see I have not lost any gain below 30 Hz so this is as loud as it can get with flat response. It’s also good to see that all the filters attenuate - no boosting, which usually sounds bad and is generally futile.

 

I entered the filter values into the Digital Signal Processing (DSP) Parametric Equalizer of JRiver Media Center, the software that I use for playback. I then re-measured using REW with the filters in place.

 

Here’s a plot of the in-seat responses: combined measurements per seat before optimizing, as predicted in MSO, and as measured with the optimized filter set. No smoothing applied.

 

 

Wow! What allows MSO to work so well? Here is one of the four in-seat final measurements and the individual responses of each subwoofer with the optimized filter set applied to each.

 

 

The optimization is clearly focused, as intended, on the combined subwoofer response. The filters do some to improve the performance of the individual subwoofers, however, they are still pretty much a mess. It now seems that I have wasted a lot of time over the years trying to improve one sub at a time.

 

Here is a look a waterfall chart showing the spectral decay of the complete MSO optimized line-array subwoofer system.

 

 

There is an effective amount of bass absorption in the room, the biggest piece in the form of a large bass trap that you can see in the second photo above the seats.

How does the bass sound? It’s now the best that I have heard. And, in-case you are wondering, that octave below 20 Hz does make a difference.

QED

[hulkss]

Hear's a couple more Charts from REW measurements, SPL with Phase and Group Delay.

 

 

[blue2]

Very interesting. Could you describe your full system components please?

[hulkss]

On 1/19/2021 at 2:10 PM, blue2 said:

Very interesting. Could you describe your full system components please?

The subwoofer line array consists of a central custom built Infinite Baffle sub with four 15" drivers from Acoustic Elegance. Flanking the IB on each side are two Epik Empire subs with two 15" opposed drivers in each of the four cabinets. In each corner is a Klipschorn bass horn. The system is all controlled with a HTPC connected to a MOTU 16A audio interface.

The three horns in the photo are PSE-144's from Red Spade Audio. All three front main speakers are tri-amplified with digital crossovers in the HTPC.