Distributed Bass Array in 4-way stereo, with Acourate

Lewinskih01
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Joined: 19 Oct 2019 22:12

Distributed Bass Array in 4-way stereo, with Acourate

Post by Lewinskih01 » 03 Aug 2021 13:01

I'm leaning towards implementing a distributed bass array and I'm interested in getting feedback.

My system is 4-way stereo active with digital xo and room correction thru Acourate. The top 3 ways are open baffle and using two sealed subs now playing in mono (12" sealed Rythmik kits in DIY box). I'm thinking of adding two additional sealed subs to even out bass response across the room.

Here's what I'm thinking in terms of implementation: Get a MiniDSP 2x4 or 2x4HD, feed it with the two channels carrying subs frequencies out of my ADC/DAC card, and connect the 4 subs to it. Then, before using Acourate, I would go through the 4 subwoofers integration (per Geddes, or miniDSP (https://www.minidsp.com/applications/su ... tiple-subs) using Multi-Sub Optimizer including time delays) and program the miniDSP to get the flattest possible response before applying Acourate. Then run the regular room correction routine on Acourate as if the DBA was a single sub in mono.

Some potential weak spots I see:
  • Doing DAC at the card, then ADC/DAC again at miniDSP. Maybe it's no so significant at these frequencies? Would it make a difference if it were the 2x4 or 2x4HD running at 96kHz?
  • It's probably hard to time-align the DBA to the main speakers. Is this significant?
Feedback? Am I missing downsides or are there better ways to achieve these results?

Thank you in advance!
Horacio
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UliBru
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by UliBru » 03 Aug 2021 16:40

Horacio,

setting up multiple subwoofers is not an easy task. The result heavily depends on the shape of the room and the furniture inside.
Beside the informations you have linked to you may also consider a double bass array, see https://en.wikipedia.org/wiki/Double_bass_array

IMO the arrival time of the sound waves of the subs should be the same to avoid cancellations. And of course you may apply equalizing filters as e.g. computed by MSO.

I do not see a huge problem with double AD/DA conversions because the frequencies are very low. So the miniDSP hardware should do the job properly. So also the time-alignment should be possible.
Stay well tuned
Uli

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Lewinskih01
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by Lewinskih01 » 03 Aug 2021 23:51

Thank you Uli!

I did look into double bass array thread in this forum. My understanding is that 4 subs are needed placed above ground against the wall, at distances per the graph on Wiki, otherwise the setup won't work. Unfortunately I can't place the subs up there. Actually, in his approach, Geddes also recommends lifting one sub from the floor (for very different purposes), and I can't do that either. Stuck with subs on the floor.

Do you think the MiniDSP 2x4HD would sound better in my application than a regular 2x4?

Regards,
Horacio
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UliBru
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by UliBru » 04 Aug 2021 09:24

Horacio,

IMHO for the subs the 2x4 is sufficient, no need to use the 2x4HD
Stay well tuned
Uli

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Lewinskih01
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by Lewinskih01 » 08 Aug 2021 16:34

Hello Uli.

I exchanged with another Acourate user about his experience with Virtual Bass Array, and I realized I was misunderstanding double bass and virtual bass array subs configurations. So I reread the VBA thread and want to understand if applicable for my setup.

The room is 10x4.8 meters, but there is a dividing heavy folding acoustic panel door in the middle, so effectively there is a 4.8x5m living room where the system is, and an opening to another similar space for dining room. The speakers are in one section where the back-to-from is 4.8m with both subs in the front wall corners. Therefore the right sub is against a section of the panel door that is usually closed. The front to back 4.8m is almost the same as your VBA example, and I have front and back walls covered with bass traps, mostly Helmholtz resonators tuned at 35 and 70Hz, and broader band bass traps. Also on the ceiling.

Since the system is fully active 4-way stereo I ran a logsweep with the digital xo (set at 70/275/1800Hz NT2). Subs in mono. Here's the uncorrected measurement:
10 to 300.jpg
10 to 300.jpg (92.07 KiB) Viewed 2363 times
Does this look like a good candidate for VBA? I'm not seeing the resonance at 35 and 70Hz, although there are peaks on L and R at 76Hz. BTW, the midbasses are 18" dipoles. At 76Hz the sealed subs are also playing though. There is a peak at 48Hz, but guess that's unrelated.

On the other hand, since sealed subs radiate in all directions I'm wondering if I should consider the 10m length at the 10x4.8m is the rigid brick boundary. That would lead me to 17Hz resonance, but I'm not seeing that on the measurements.

Do you think it's worth pursuing?

Regards,
Horacio
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UliBru
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by UliBru » 09 Aug 2021 12:16

Hello Horacio,

viewing the picture I believe you should more investigate in removing the dips in the frequency response instead of the peaks.
The room behaves pretty symmetric.
Stay well tuned
Uli

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Acourate system: JRiver/Roon -> AcourateConvolver -> miniDSP U-DIO8 -> TacT M/S2150 amps -> DIY horn speakers
Lewinskih01
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by Lewinskih01 » 10 Aug 2021 02:33

UliBru wrote:
09 Aug 2021 12:16
Hello Horacio,

viewing the picture I believe you should more investigate in removing the dips in the frequency response instead of the peaks.
The room behaves pretty symmetric.
This is great feedback Uli. You save me from going down the wrong rabbit hole! What comes to mind as potential ways to reduce dips? Are you looking at the dips at 30 and 95Hz? Or 200Hz on L?

BTW my soundcard (Lynx Hilo) allows adjusting level on right and left of each channel independently so above 70Hz in the picture I have reduced the left channel by 5dB (IIRC) to make both channels match more closely. Below 70Hz it's mono subs therefore L & R look the same.

Regards,
Horacio
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UliBru
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by UliBru » 10 Aug 2021 11:48

Horacio,

please send me the recorded pulses
Stay well tuned
Uli

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Acourate system: JRiver/Roon -> AcourateConvolver -> miniDSP U-DIO8 -> TacT M/S2150 amps -> DIY horn speakers
Mister Cool
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Joined: 08 Nov 2021 13:59

Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by Mister Cool » 11 Nov 2021 20:12

Lewinskih01 wrote:
03 Aug 2021 13:01
I'm leaning towards implementing a distributed bass array and I'm interested in getting feedback.

My system is 4-way stereo active with digital xo and room correction thru Acourate. The top 3 ways are open baffle and using two sealed subs now playing in mono (12" sealed Rythmik kits in DIY box). I'm thinking of adding two additional sealed subs to even out bass response across the room.

Here's what I'm thinking in terms of implementation: Get a MiniDSP 2x4 or 2x4HD, feed it with the two channels carrying subs frequencies out of my ADC/DAC card, and connect the 4 subs to it. Then, before using Acourate, I would go through the 4 subwoofers integration (per Geddes, or miniDSP (https://www.minidsp.com/applications/su ... tiple-subs) using Multi-Sub Optimizer including time delays) and program the miniDSP to get the flattest possible response before applying Acourate. Then run the regular room correction routine on Acourate as if the DBA was a single sub in mono.

Some potential weak spots I see:
  • Doing DAC at the card, then ADC/DAC again at miniDSP. Maybe it's no so significant at these frequencies? Would it make a difference if it were the 2x4 or 2x4HD running at 96kHz?
  • It's probably hard to time-align the DBA to the main speakers. Is this significant?
Feedback? Am I missing downsides or are there better ways to achieve these results?

Thank you in advance!
Horacio
Hi,

maybe I am wrong, but there seems to be a "misunderstanding". I spend a lot of time experimenting with DBA and other Multi-Sub setups (and I am still in progress -> thats my real hobby :D ) and I believe, that there are two completely different approaches:

1. DBA (Double Bass Array) approach, which is based on "reducing/eliminating" the reflected sound/wave -> the rear subs act as a "active bass trap"
Pros: wider area for hearing position, Cons: works in rectangular room only

And newly i found Uli's VBA -> my next project !!!

2. SFM (Sound Field Management) approach, which is researched, described by Welti / Devantier, Geddes -> based on a sofisticated combination of delays, sound levels and frequency ranges for each sub (see calculation e.g. with Multi-Sub Optimizer
Pros: not limited to rectangular rooms, Cons: complex calculation

Which one do you try to achieve?

If DBA is the case...

Why do you want to use additional MiniDSP? Because of the limited number of output chanels of your soundcard? (only 8?)
Since the subs are allmost Mono, you could try to drive the two front ones from one soundcard output channel e.g. left (having the same level, delay, correction...) and the DBA/rear ones from the other (right) channel (again, both with the same settings). Then you can drive everything by Acourate w/o additional MiniDSP. All you need is just two differen XOs for the left (front subs) and right (rear subs) channel.

I have allmost identical setup, and however my Motu 828ES Audio Interface has 10 output channels only 8 of them are driven by volume control (because of 7.1), which I use. And therefor this is the way, how I will try to overcome the problem.

Image

The schema shows 10 channels, but in fact driven by 8 otput channels (splitted)
(some components and data are not up-to-date, because I am permanently rebuilding, changing the setup)

Image

BTW. I fully agree with Ulis hint to take care about the dips. In my opinion, most peple are to focussed on correcting the peaks (which is "easy" per EQ) but underestimate the importance of eliminating / filling-in the dips (which is much more difficult). The dips lead to "week", bloodless reproduction. I made some experiments with very simple, cheap 12" subwoofers as DBA placed in the bookshelf and the improvement especialy in the area of eliminating dips was amasing!

Upper measurements are with DBA, the bottom ones without

Image

It was one of the bigest improvements of my system to "close the gap" -> to get this missing, but so important, nice, warm, full bass 35-70Hz :-)
JRiver MC (Convolver) on iMac -> Motu 828ES Audio Interface -> 4x Hypex Power Amp -> 3-Way Open Baffle U-Frame -> 4x Subwoofer (DBA)
Mister Cool
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Re: Distributed Bass Array in 4-way stereo, with Acourate

Post by Mister Cool » 11 Nov 2021 23:46

I missed the picture of the mentioned DBA subs in the bookshelf, very simple

Image
JRiver MC (Convolver) on iMac -> Motu 828ES Audio Interface -> 4x Hypex Power Amp -> 3-Way Open Baffle U-Frame -> 4x Subwoofer (DBA)
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