Adapting mid-bass bins for bass in multi-sub setup

[zydeco]

I’m running a pair of SVS SB16-Ultra subwoofers alongside stereo speakers using a mini-DSP unit to do the X/O and Room EQ. The ultimate plan is to move to Dirac DLBC and Dirac ART.  My thinking is co-opting some sealed bass bins with 18” AE TD18H+ drivers from a previous project to act as an additional ‘subwoofer’. The thought is that this would both provide another bass source to further reduce variation as well as provide another set of speakers for Dirac ART optimization.

 

I’ve done some quick, nearfield, REW measurements of one bass bin with the resulting showing flat performance over the range 35 to 500Hz and, at 95dB, a THD distortion of 0.2%. Stacking a pair of bass bins should, as I understand it, provide 6dB more output. Also, an old WinISD simulation seemed to indicate that with a lot of power and EQ I should be able get more extension from the bass bins albeit with some distortion.

 

The set-up of these bass bins into the system will take a bit of effort so, before doing so, I wanted to check that I not missing anything. It seems that a pair of the bass bins – whilst not matching the dedicated subs – will go loud and low with moderate distortion. And that adding these will both provide another bass source with capacity to reduce variation as well as another speaker surface for Dirac ART optimization. Is this correct? Or am I missing something?

[zydeco]

Well, a bit more reading and it seems as if Dirac Live Bass Control has issues when different subs using “lowest common denominator” approach with, for example, the high pass filter on the subs set to that for the weakest sub. The situation with Dirac ART is unclear but it’s starting to seem as if adding the bass bins (which are weaker than the dedicated SVS subs) might not be such a good ideal.

[Guest]

I run 3 SVS  subs with DLBC, one of which is smaller, with no issues.  I did ask at Storm Audio DLART web seminar about unequal subs and got a vague response.   It leads me to suspect that Dirac do not (yet?) manage different sized subs?

 

Sorry, no experience with mid-bass bins...

[zydeco]

@Snoopy8

 

Any advice on placements for different subs? I’ve always followed the shedded approach of the most capable sub in a front corner near the main speakers and then less capable subs as ‘helpers’ behind the listening position. It’s not clear to me that this is the right model when the more modern DSP is employed with one obvious alternative being to place the least capable sub where room gain is the most significant. (The thinking being that it seems as if MSO starts with getting all the subs volume matched)

[Guest]

There are no firm rules for multiple sub placement because much depends on the room.  Helper subs are meant to reduce null points.

 

The aim of MSO is to even the bass across seating positions.  Spreading the subs in the room will help. You can compensate for weaker subs by reducing their filter gains. Please let me know if you want to try MSO.

[zydeco]

5 hours ago, Snoopy8 said:

There are no firm rules for multiple sub placement because much depends on the room.  Helper subs are meant to reduce null points.

 

The aim of MSO is to even the bass across seating positions.  Spreading the subs in the room will help. You can compensate for weaker subs by reducing their filter gains. Please let me know if you want to try MSO.

 

Thanks, @Snoopy8, for the kind offer of assistance. I'm slammed at work at present but should be able to set-up the subwoofers and conduct initial measurements in a couple of weeks. I'll reach out if assistance is needed. The plan is to use an old mini-DSP 10x10 to execute the filters.

[almikel]

On 21/02/2024 at 4:14 PM, zydeco said:

My thinking is co-opting some sealed bass bins with 18” AE TD18H+ drivers from a previous project to act as an additional ‘subwoofer’.

My experience with TD18s in sealed enclosures is they don't go anywhere near low enough to be called a "subwoofer" without seriously large EQ and amp power, even in a large sealed box.

TD18s excel at mid bass - that's where I use them - in my tiny 60litre sealed enclosures they still have a Qtc < 0.7, and I push them down to 40Hz or so to crossover to my sub at 60Hz.

Easily the best mid bass I've heard - amazing bass slam...

...but they're not sub drivers if mounted in a sealed enclosure....

...maybe there's a ported alignment where they can get low...?

 

My wife thinks my sealed TD18s sound so good she's taking them if we break up...she's dreaming...but they're not subs.

 

Mike

[zydeco]

On 27/3/2024 at 10:19 PM, almikel said:

My experience with TD18s in sealed enclosures is they don't go anywhere near low enough to be called a "subwoofer" without seriously large EQ and amp power, even in a large sealed box.

TD18s excel at mid bass - that's where I use them - in my tiny 60litre sealed enclosures they still have a Qtc < 0.7, and I push them down to 40Hz or so to crossover to my sub at 60Hz.

Easily the best mid bass I've heard - amazing bass slam...

...but they're not sub drivers if mounted in a sealed enclosure....

...maybe there's a ported alignment where they can get low...?

 

My wife thinks my sealed TD18s sound so good she's taking them if we break up...she's dreaming...but they're not subs.

 

Mike

Much appreciated. You’ve reminded me just how great these units are for mid-bass. I was using them with Unity Horns, and subs, in our open-plan kitchen living room but neither the aesthetic or system complexity suited the family. I’ve not had it in me to sell either the horns or mid-bass under the illusion that I might be able to resurrect.

 

PS What are you using as the X/O between the PSE144, TD18 and subs?

[almikel]

On 30/03/2024 at 7:35 AM, zydeco said:

PS What are you using as the X/O between the PSE144, TD18 and subs?

I implemented double DEQX in 2015 after I built my T20 sub for 4 way active X/O (single sub/stereo TD18s/PSE144 mids/PSE144 tweeters).

 

More recently (2021) I wanted to simplify my life, and implemented Paul Spencer's passive crossover for his PSE144 (I bought the "standard" version of Paul's passive crossover), which meant I could run a single DEQX, and this remains my current setup:

• Paul's passive 2 way X/O within the PSE between tweeter and mids at 1.25kHz
• DEQX active X/O between PSE and TD18s at 350Hz - I'm pretty sure I just configured a Linkwitz Riley LR4 XO
• DEQX active low pass on the sub at 60Hz with LR4 (my T20 sub is a tapped horn so nasty resonances occur above the pass band
• I don't think I've applied a high pass filter/XO to the TD18s to cross to the sub...just allowing the TD18s to get as low as they can in their enclosure without a X/O taking anything away
• some global room EQ has been applied < 200Hz or so

...actually it's been so long since I made any changes, your question has made me question what configuration I setup back in 2021...the above may not be entirely accurate...just what I recall...

 

Sort of relevant to this discussion, is that after I built my TD18s in their small sealed boxes (around 2013), and dialing in a bunch of EQ to push them lower, I thought I had reasonable low end extension in my room, because the bass sounded great, but I'd never actually measured it

 

2 things happened within a week of each other that convinced me I needed a sub operating below the TD18s:

• some friends came over and we played the Boston Philharmonic Orchestra's version of "Fanfare for the Common Man", and they said, "you're missing something in the bottom octave"!
• I listened to @Jiri's system and some of the low frequency content made the hairs on the back of my neck stand up !

I immediately commenced the build of my T20 sub...I'd had all the bits and the design for ages, but just hadn't made any sawdust.

 

I was running single DEQX HDP3 active 3 way back then and adding a sub meant going double DEQX to remain fully active...

...Alan from DEQX sourced me a 2nd hand HDP3 unit with digital outputs to integrate with my existing DEQX, and actually came to my house to help me set it up!

 

I'm a big fan of DEQX - I really hope they succeed with their next generation product!

 

Mike