Adding a third sub to cancel "Deep Mid-Bass Null"

[Richx200]

The configuration would go like this:

PC --> DAC 1 --> L, R speakers
--> DAC 2 --> Subwoofers 1 and 2

On the PC, download VB Audio Matrix. Enable the virtual ASIO channel. Set it up to output channels 1, 2 to DAC 2 (i.e. to the subwoofers 1 and 2), and channels 3, 4 to DAC 1 (i.e. to L, R speakers). Make sure the microphone is recognized by VB Matrix.

Open REW and set it up in ASIO mode to output to VB Matrix. Select the appropriate microphone channel.

Then you need to take some timing measurements. Set REW to use a timing chirp and set this as your left speaker (i.e. channel 3). Now do sweeps of the subwoofers at the listening position. REW will automatically tell you what the delay is with respect to the timing chirp, but you can check by overlaying the impulse responses (aligning all the impulses with the tweeter chirp) and measuring the delay manually that way.

Then you need to figure out how to make a filter that will delay the subwoofer appropriately. I use a different tool for this, so I can't talk you through the REW procedure.

Load the filters into the playback software of your choice. It will need a built-in convolver.

I'll try it. Thank you

 

[NTK]

The subs are on the floor and bringing up the ceiling, I have to say that the ceiling isn't flat all the way across; there is a duct chase that runs the length of the ceiling on the left side. The chase is 12" high X 24" deep, see attached. Could this be my problem, since Room Mode calculators cannot account for the chase?

The conduit is not going to make much of a difference. Below are the room mode calculations using the 3-D irregular room shape room mode simulator by member ylio. The ~72 Hz ceiling to floor mode is predominantly buildup by the reflections between the ceiling and floor parallel surfaces. The conduit in the ceiling has a very minor effect on this reflection, and will not have a significant influence on it. The mode frequencies are listed at the right, and are quite similar between the 2 geometries.

Room eigenmodes calculator

Hi all! I want to share this application to calculate and evaluate the natural frequencies of rooms modeled in 3D. At the moment, the application does not consider materials, only rigid surfaces, but it is a very useful tool to evaluate the eigenmodes in irregular rooms. It is recommended to...

www.audiosciencereview.com

[Edit] Corrected the orientation of the conduit in the model.

 

[ppataki]

I'll try it. Thank you

I am really curious to see if this will work out well
I have tried it in the past but for me there was a constant clock drift issue (i.e. the delay kept changing all the time) even when using two identical DACs
Hence I have an RME Digiface in my home office system and a miniDSP UDIO-8 in my main system in the living room

 

[theREALdotnet]

I am really curious to see if this will work out well
I have tried it in the past but for me there was a constant clock drift issue (i.e. the delay kept changing all the time) even when using two identical DACs
Hence I have an RME Digiface in my home office system and a miniDSP UDIO-8 in my main system in the living room

I had the same issue. Delays introduced by USB DACs were all over the place and dependent on DAC chip, selected filter and sample rate. Even using the same DAC models didn't resolve the issue, because they would drift apart. Using clock sync in macOS kept them from drifting but introduced a large-ish delay that was dependent on sample rate. The delays I'm talking about were anywhere in the 1-15ms range, which makes a mockery of Dirac's corrections down to 0.1ms.

In the end I also found salvation in a DigiFace to which my DACs (all the same model) are connected via S/PDIF, giving them all the same clock.

 

[DonH56]

Most pro DACs back when I was dealing with this (decade ago) used S/PDIF, AES, or a master clock reference. USB, along with the OS, is a mess. A friend of mine had a list of OS tweaks for Mac and Windows to get close but ultimately went to a master clock scheme using professional DACs.

Not something I have looked at in years; are there USB DACs that will synch now? The USB interface itself isn't designed for that...

 

[Digital_Thor]

I found out that a suck-out from one of my 4 subwoofers, was created by one along my side wall.
Went in and added EQ that fitted the overall suck-out on that specific sub - and then it almost disappeared, when measuring them all together. Turning on each subwoofer with no EQ, gives you quite a good idea, which one makes "trouble".
It can feel a bit silly to turn a sub down a lot, but sometimes it simply does not need to add much, to make the sum of all of them look better.
If one subwoofer always makes it a bit worse... then it needs a new place.
Preferably one in a corner, one in the free and one somewhere behind you. 2 or 4 can be placed a bit more symmetrically - 2 diagonally and with 4 I mostly have them 2 one each side, where one is behind me and one of them in front of me, is a bit elevated. This "attacks" as many modes in the room as possible, giving you a bigger chance of an over-all smoothness in the listening position.
Can't fully explain why... but sometimes leaving a single subwoofer playing close towards a corner or wall, seems to make it somehow smoother, rather than if it plays directly into the room. It can also mask our sense of detecting it, if crossed a bit high.

 

[ozzy9832001]

You may want to experiment with the height of the subwoofer. If you have a standard 8' ceiling, 35hz is a direct multiple of that. Also, you may want to experiment with 1 subwoofer and see where the response is good for that drop and then cross over the second somewhere higher. I do this with my 2 subs. 1 is crossed around 55hz and the other around 100hz. Gives the best overall response with minimal localization.

 

[win]

All this work when you could just easily solve it with MSO...

 

[Digital_Thor]

All this work when you could just easily solve it with MSO...

I have a friend who swears to it. Never worked in my system.. that's why I do it manually. Another friend uses Dirac, which my system simply doesn't have.
But no matter the means... As long as it works

 

[SorenTyson]

You could try to send bass both to the speakers and the subs, free to try if your avr allows it. If the speakers reach low enough they may solve the issue

 

[theREALdotnet]

Not something I have looked at in years; are there USB DACs that will synch now? The USB interface itself isn't designed for that...

I suppose a multi-channel USB DAC would solve the problem, at least all channels stay together timing-wise and have the same delay. I had looked at the Topping DM7, but it was quite a bit more expensive than my current solution. Also, it only has balanced outputs, and none of my subwoofers have balanced inputs.

 

[theREALdotnet]

I have a friend who swears to it. Never worked in my system.. that's why I do it manually. Another friend uses Dirac, which my system simply doesn't have.
But no matter the means... As long as it works

I reckon even with MSO, Dirac etc. it is best to sort out acoustic issues using physical means (placement, room treatment) as much as possible first before applying DSP. That's my approach, anyway.

 

[Digital_Thor]

I reckon even with MSO, Dirac etc. it is best to sort out acoustic issues using physical means (placement, room treatment) as much as possible first before applying DSP. That's my approach, anyway.

Exactly. I've seen it time and time again, that a DSP is somehow given magic and hopeful properties, that somehow fixes things, that would be best solved physically.
My advice was, mostly, that if multiple subs and/or DSP doesn't seem to make it all better - then go back and re-check all the basics, before trying again.
It is quite tempting to add EQ sometimes, rather than building or moving/changing something in the system - even though - it's no surprise what will give the best result

 

[Richx200]

The configuration would go like this:

PC --> DAC 1 --> L, R speakers
--> DAC 2 --> Subwoofers 1 and 2

On the PC, download VB Audio Matrix. Enable the virtual ASIO channel. Set it up to output channels 1, 2 to DAC 2 (i.e. to the subwoofers 1 and 2), and channels 3, 4 to DAC 1 (i.e. to L, R speakers). Make sure the microphone is recognized by VB Matrix.

Open REW and set it up in ASIO mode to output to VB Matrix. Select the appropriate microphone channel.

Then you need to take some timing measurements. Set REW to use a timing chirp and set this as your left speaker (i.e. channel 3). Now do sweeps of the subwoofers at the listening position. REW will automatically tell you what the delay is with respect to the timing chirp, but you can check by overlaying the impulse responses (aligning all the impulses with the tweeter chirp) and measuring the delay manually that way.

Then you need to figure out how to make a filter that will delay the subwoofer appropriately. I use a different tool for this, so I can't talk you through the REW procedure.

Load the filters into the playback software of your choice. It will need a built-in convolver.

I'm having a problem with the REW I don't know if it is the Laptop or the speaker. I tried 3 different ways to measure speaker number one with REW; I load 2 different ASIO's Asio4All, FlexAsio and Java; Asio4All didn't work at all, FlexAsio gave me "Too Low" no matter how many dbs I added. Jave I couldn't configure the speakers. Still trying to figure out what is happening. I check all the settings, and they seem to be correct. I cannot get the DAC's or MSO until I get REW worked out.

 

[Richx200]

All this work when you could just easily solve it with MSO...

I have to get REW working

 

[Flaesh]

I have to get REW working

Did you?
Feel free to ask if the post #28 is not entirely clear.
Subwoofers can be placed on the floor.

 

[Richx200]

Well, I didn't get REW working on the laptop, so I'm back to walking back and forth between the computer and subs. I've tried to find a place that would be acceptable to the wife, but no luck, so I still have my null. Not only that, but I must have moved those subs all over the room and still the null absorbs all the bass amplitude; when I increase it too much the subs go into clipping and distortion. Also, when I moved the subs, I played ARC’s distance setting thinking it would change the timing and still nothing; I don't think ARC's distance setting changes anything. In fact, when I move the subs to some areas, the null frequency changes; it feels like I'm chasing my tail.

I please need help with my next move.

The plan would be to get a DSP so would I be ok with the included room correction software or should I go for better software like "Acourate"(more taps) If I cannot get the null corrected, then I would try a 3rd sub.

Which DSP would best suit the plan?
Should I go for the better software?
Can I use a cheaper, smaller sub?

I do realize this is going to cost a learning curve, time and money: I just want the subs to work properly. I don't want to fail because I didn't spend extra $$$$.

Thank you for your time.

 

[Richx200]

Did you?
Feel free to ask if the post #28 is not entirely clear.
Subwoofers can be placed on the floor.
View attachment 392633

Wouldn't the couch block the sub?

 

[win]

You can get used 2x4hd minidsp units on eBay for less than $200.

 

[sigbergaudio]

Wouldn't the couch block the sub?

The sub doesn't care about the couch.