Article: Integrating Subwoofers with Stereo Mains using Audiolense

[dallasjustice]

10 hours ago, dziemian said:

 Unfortunately none of these software can deal with multisubs in a proper way and I am forced to use Multisub optimizer with minidsp just for that.

What do you mean by that?  I agree that Dirac does a poor job of integrating subwoofers with stereo playback. However, Acourate and Audiolense can accommodate just about any configuration you want. 

 

MSO is very useful for getting smooth bass frequency response across a wide listening area. Some people believe that is all one needs for optimal results. IMO, time domain matters too. I agree with Mitch that linear phase crossovers and time aligned drivers are needed for best results. Either Acourate or Audiolense can accomplish almost anything you need. There are pros and cons between Acourate and Audiolense. I’ve extensively used both for multiple sub integration. 

 

There are are many different subwoofer setup techniques. I think there are 2 categories:

1.  Mono/summed arrays. 

2.  Stereo sub arrays. 

 

However, there are variations within each category. For example, some mono sub arrays are simply time aligned to seated position. Either Acourate or Audiolense can handle these arrays. All stereo sub arrays should be time aligned to listening position. When I say time aligned, I mean flat group delay throughout the crossover region. As you can see from Mitch’s plots, it’s just about impossible to get flat group delay down to 20hz. It really doesn’t matter that much as long as both subs are consistent and the group delay is consistent throughout the crossover. Stereo subs can get a little more complex though. I personally use a 4 stereo sub array (cascaded subs). I believe Mitch linked to another thread which shows how and why I do that. 

 

Finally, there are the non time aligned subwoofer arrays. These are mono/summed sub arrays. Some folks advocate the use of non-time aligned mono subs. I personally don’t see the advantage of using those types of setups. These include Welti. That’s a different topic.

 

However, there is a very effective mono sub array which is not time aligned. It is called “source/sink.”  It’s mostly done using only two mono subs. The frontwall/midwall sub is the “plane wave.”  It is time aligned with R/L speaker. The rearwall/midwall sub is set to opposite electrical polarity from front sub. It is also delayed so that the plane wave and the rearsub wave meet each other behind seated position. The phase rotation of the rear sub needs to be adjusted using RTA function in REW while both subs are playing a LF pink noise. The phase rotation is carefully dialed in until all the room length modes are eliminated. Source/sink has two huge advantages for those with rectangular rooms who have nasty length modes. 1. When properly setup, it can mostly eliminate all length modes, without any DSP using only two subs. 2.  It will eliminate any rearwall boundary interference at listening position. Most people in rectangular rooms sit behind the room length midpoint. In these cases, the rearwall will likely destructively interfere at a specific frequency based on its distance from listening position in relation to the front wave source distance to listening position. This is called the “Allison effect”. Others call it SBIR. Still others call it a “null.”  They are all the same thing. It is NOT a room mode. Because it is non-minimum phase, DSP can’t fix it. Only speaker placement can overcome this issue. Of course a rearwall sub setup in a “source/sink” array will eliminate this boundary interference. 

 

Back to your question about Acourate vs. Audiolense. The only sub array I know about that Acourate can do which Audiolense cannot do is this “source/sink” array. The reason is that Acourate Convolver can be setup to simultaneously measure two mono subs with delay added to rear sub. OTOH, Audiolense can not measure in this way. Audiolense can only measure one channel at a time. 

 

I’ve tried just about every subwoofer array I’ve described, except MSO.   In my room I’d rank the 4 stereo cascaded sub array first. Second place goes to “source/sink.”  Other rooms are different. There is no ideal or perfect setup.  You have to tryout different arrays in your room, measure them and see what measures (frequency and decay) best. 

 

Subwoofery done right can be a very iterative process. This is true for most any array. Because there may be a lot of move-and-measure, it’s important to have an easy/fast method to loopback measure each array. This is where Audiolense beats Acourate. From the time one setups up a speaker array with crossovers to the time the .cfg files and FIR impulses are in a folder for Jriver/Roon, it may take 5-10 minutes when you get the hang of it. Acourate won’t go that fast. You’ll need to create your own .cfg files, crossovers and the speaker setups in Acourate Convolver will take some serious practice to get really fast. I know Uli can do it very fast. But my brain works much slower. 

 

I think both Acourate and Audiolense are outstanding. I’d say buy both. That’s what I did. I still use both of them; best audio money ever spent. 

 

Michael. 

[dallasjustice]

1 hour ago, dziemian said:

I meant that Dirac Live, Acourate and Audiolense  deal with subs separately. The only software I know of which takes into account all of them is Multisub Optimizer and Dirac Unison. Both softwares use all available drivers to help each other in obtaining good frequency response. MSO works for subs mainly and improves  frequency only, improving phases' feature has already been requested by some users but it seems not so easy. Unison on the other hand work with full spectrum and deals with both frequency and phases. But  as you know it is not available yet. I recommend a good book about the subject i.e. "Multichannel Audio Signal Processing. Room Correction and Sound Perception" by Adrian Bahne. It is a dissertation from University of Uppsala written by one of the people who worked on Dirac Unison.

 Understood. Acourate can measure and apply correction to more than one sub. I described this above with regard to the “source/sink” array. 

 

I don’t believe that is a weakness in most cases. Audiolense and Acourate will accurately predict the result. It’s easy to test with loopback measurements. The only time this wouldn’t be the case is in the source/sink setup I described. Otherwise there’s no need to measure subs at the same time.

 

Dirac Unicorn has been discussed for many years now and still nothing in reality. I understand the approach.  I’ve only heard it in Volvos. I think it sounds wonderful. 

[dallasjustice]

Yes. That’s what I do. But you need to make sure the propagation delay through your R/L DAC is exactly the same every time. This is a big problem with many DACs. You should check with the manufacturer. Many DACs have goofy jitter attenuation that creates a variable propagation delay. These DACs will never work with this setup. My Benchmark DAC works perfectly. You can check the group delay in REW loopback. You need to take multiple measurements to make sure the R/L DAC isn’t drifting. That’s the only way to make sure.