Home theatre - multi sub calibration advice.

[Danimacl]

Hi folks,

I am finishing up a theatre renovation and am looking room calibration software and hardware implementation advice.

Feel free to yell at me if I’m not in the right forum.

Sorry if the post is a bit long but I feel like the more specificity the better.
I have a have what many people would consider a smaller home theatre 11’W x 15’L x 7.2’H. As many of us know the smaller the room the trickier the acoustics. I have done everything in my power to acoustically treat the room.

Now here’s the question:
I currently own a Denon x4400H and a Dirac live enabled MiniDSP DDRC-88a with BM.

Now I have multiple custom built subs that all perform best within certain frequency ranges. I’m simplifying the setup for the sake of brevity, I’ll also give you my ideal high and low pass filters.

Subwoofer 1 - built into a rear seating riser. HP 25hz @48db - LP 80hz @24hz

Subwoofer 2 - large front ported sub under screen. HP 18hz 48db - LP 60hz @ 24db

Subwoofer 3 and 4 - mid bass woofers behind acoustically transparent screen. HP 60hz 24db - LP 150HZ @ 24db

And I have smaller LCR speakers which I’d like to high pass higher than normal - 150hz.

Am I better off buying a newer Denon X3800 with Dirac ART and 4 LFE? do all the processing in one unit? Will I be able to set individual high and low pass filters on the subs?

Or

Keep my Denon X4400H and Mini DSP? route all the subs through the mini dsp and have mini dsp Dirac calibrate all of them into one cohesive system 18-150hz. Then run one lfe signal into the mini dsp and use the denon to crossover at 150hz into the mini dsp.

Or

Keep my Denon X4400H and Mini DSP?
Run LCR and all subs through mini dsp and have Dirac calibrate all of that. Then In the denon run LCR as full range with dedicated lfe.

 

[DVDdoug]

REW and a measurement microphone.

And then maybe Multi-Sub Optimizer.

As many of us know the smaller the room the trickier the acoustics.

Most rooms are "small" compared to a concert hall, auditorium, or real theater.

I have done everything in my power to acoustically treat the room.

I always say, "diagnosis before treatment".

 

[Danimacl]

REW and a measurement microphone.

And then maybe Multi-Sub Optimizer.


Most rooms are "small" compared to a concert hall, auditorium, or real theater.


I always say, "diagnosis before treatment".

My apologies Doug, I was writing this on my iPhone and accidentally hit submit on the post before I was finished writing the post. You can now see the edited original post.

 

[DaveBoswell]

If it were me, I would be using REW and MSO to get all the subs working very well together and phase/time aligned, then have this single virtual sub presented to your AVR for final polish using Dirac (not Dirac ART).

Reasoning is that your setup has subs with various port tuning frequencies, different slopes on the HPF and LPFs (which cause varying degrees of phase rotation), and presumably materially different output capabilities and efficiencies at different frequencies. There is a very strong likelihood that you are getting a wide range of phase cancellations and phase summations across the sub woofer frequency range as a result resulting in significant reduction in total output and efficiency along with potential smearing of the response in the time domain.

ART may or may not be able to take this complex setup into account but I would doubt it would do as good a job as REW/MSO and some learning on your part. I think ART or any waveforming technologies works best when the phase response of the speakers being used is the same for all speakers.

If you are game, post your results in the MSO thread and we would be happy to give advice. Check out MSO tutorial video on my sig below to get a flavor of what MSO can do to properly align multi subs in phase, eliminate phase cancellations, and simultaneously provide consistent and smooth response at multiple seating locations. Your setup will be more complex that the 3 sub setup I use as the example.

 

[andyc56]

From reading the first post in this thread, it's not clear to me what the strategy of this system is intended to be. I wrote a post back in 2018 about the technique of operating subs in mutually exclusive frequency bands, noting that this is not the type of system that MSO is intended to optimize. Although MSO is flexible, it's not intended to deal with arbitrarily-chosen configurations, especially in the case of subs operating in mutually exclusive frequency bands.

 

[john61ct]

operating subs in mutually exclusive frequency bands, noting that this is not the type of system that MSO is intended to optimize

Is MSO OK if there is a Front L/R pair of "virtual floorstanders" comprised of

Main bookshelves HPF'd only

then a pair of stereo MBM Couplers, say from 180-200Hz down to 60-80Hz

then the trueSub pair, from as low as possible (but rumble HP bandpassed) up to blend with that low point above.

Uncertain if those last will be fed signal in stereo or mono, but let's assume co-located regardless.

Note that these sets will likely be crossed steeply via LR, thus close to "mutually exclusive frequency bands" but blended, no actual FR gaps.

If necessary, I'm willing to have MSO ignore all the above, treat them as if a pair of passively xover'd floorstanders.

...

Then there will be at least one trueSub - but 2-3 more likely - as needed to tackle room modes etc, and the main goal to get

strong bass / sub SPL, matching the midrange-up with full flattish coverage from as low as possible (but rumble HP bandpassed) up to 70 (maybe 90Hz) all in mono

happy to follow guidance as to overlaps vs blending.

Prefer to give envelopment a chance (sides placement?), and prioritising

tight bass transients (fast attack & decay), if need be will sacrifice wider-optimised LP

...

Is MSO well suited to one or more of these scenarios?

Any feedback / corrections on my misconceptions or implied questions would be most welcome...

 

[-Matt-]

Is MSO OK if there is a Front L/R pair of "virtual floorstanders" comprised of

Main bookshelves HPF'd only

then a pair of stereo MBM Couplers, say from 180-200Hz down to 60-80Hz

then the trueSub pair, from as low as possible (but rumble HP bandpassed) up to blend with that low point above.

Combining drivers in different frequency bands is the job of an active crossover (such as various MiniDSP devices).

MSO aims to combine multiple subwoofers (hence the name). The subs may have slightly different frequency ranges but MSO works its magic in the frequncy range where they overlap. It allows you to combine contributions from the subs with different time or phase delays to get the smoothest overall response. The wider the region of overlap, the better it is for MSO.

Subwoofer 1 - built into a rear seating riser. HP 25hz @48db - LP 80hz @24hz

Subwoofer 2 - large front ported sub under screen. HP 18hz 48db - LP 60hz @ 24db

Subwoofer 3 and 4 - mid bass woofers behind acoustically transparent screen. HP 60hz 24db - LP 150HZ @ 24db

And I have smaller LCR speakers which I’d like to high pass higher than normal - 150hz.

From the OPs description it sounds like they are using active crossovers to apply high and low pass filters to each sub, creating separate frequency bands with limited overlap. If that is the intent then it may not suit MSO very well. MSO would work better if all the subs were allowed to cover as wide a frequency range as they can, therefore overlapping more.

 

[john61ct]

MSO aims to combine multiple subwoofers (hence the name). The subs may have slightly different frequency ranges but MSO works its magic in the frequncy range where they overlap. It allows you to combine contributions from the subs with different time or phase delays to get the smoothest overall response.

OK, so set MSO to leave the six co-located boxen comprising the "virtual floorstander Front L/R pair" completely alone, their LF energy treated as a given, xovers tuned elsewhere as if via passive networks

whether their trueSub components are stereo or mono.

...

Only use MSO if there are in addition multiple trueSubs (for-sure summed-mono-signal fed)
to be placed freely for both added LF SPL, and ofc for the goal of wrangling room resonance / modes.

These ranging in type, some say from below 20Hz if possible up to 60Hz, others maybe 40-90Hz.

Any guidance on placement, enabling envelopment?

 

[janbth]

Am I better off buying a newer Denon X3800 with Dirac ART and 4 LFE? do all the processing in one unit? Will I be able to set individual high and low pass filters on the subs?

I would say yes. And you will have full control of each individual sub. I am currently running Dirac ART on a Marantz Cinema 30 with two subs, and it’s much better than my previous setup with NAD M33 + miniDSP 2x4 HD. Your other options will also work of course, but I don’t think they will beat Dirac ART.

 

[thcdru2k]

ART is powerful, but with your segmented passbands and different sub alignments I personally would manually integrate.

 

[Flaesh]

Subwoofer 1 - built into a rear seating riser. HP 25hz @48db - LP 80hz @24hz

Subwoofer 2 - large front ported sub under screen. HP 18hz 48db - LP 60hz @ 24db

Subwoofer 3 and 4 - mid bass woofers behind acoustically transparent screen. HP 60hz 24db - LP 150HZ @ 24db

And I have smaller LCR speakers which I’d like to high pass higher than normal - 150hz.

Here's some good advice:

REW and a measurement microphone.

Subwoofer 3 and 4 - mid bass woofers - Maybe we may consider them as parts of the LR?..

 

[andyc56]

Guys, the OP of this thread that people are responding to hasn't been seen in this forum since early January of this year.

The thread was necro-bumped yesterday and the subsequent question answered.

 

[john61ct]

Sorry to everyone for that, and very grateful for the clarifications as to MSO's functionality.

 

[john61ct]

Rather than starting a new one...

Note to newcomers - the earlier posts of this thread do not need responding to, even if useful for reference, most of those posters are no longer around.

...

@andyc56

Since MSO FR filters are IIR / PEQ only, miniDSP or other low powered convolvers (say RPi4B) are OK?

...

> operating subs in mutually exclusive frequency bands, noting that this is not the type of system that MSO is intended to optimize

So I guess doing all crossovers separately ?

Also excluding the say 200+ Hz LPF'd drivers that are part of the co-located Front LRC stacks.

...

Is MSO well suited to this below scenario?

MSO ONLY managing integration of the LF units:

1x mono big trueSub under FR Centre, fed a mix of both L/R summed/extracted and dedicated LFE mono signal

...

2-3 smaller LF boxen in each stack of the Front L/R pair, mix of MBM augmenter / couplers and trueSubs, e.g one 15-35Hz another 35-80Hz, MBM maybe 80-200Hz

these L/R "LF stacks" fed stereo only? or some LFE also mixed in?

So if MSO not doing the crossovers, maybe treat these as just three separate LRC channels, since the frequency overlaps are only between those three LF-boxen-stacks not within each stack ?

One say miniDSP 2x4 HD unit can then handle all the Front units.

...

Furthermore, as needed for wrangling room resonances, mono-only trueSubs, freely placed, between one and four boxen. Likely a mix of different sub models but all fed the same source signal bandpasses separately from MSO.

If one convolver unit per four channels under MSO control, so maybe three units in total will be enough including FR surround pair(s) not touched by MSO filters....

...

Any feedback / corrections on my misconceptions or implied questions would be most welcome...

 

[andyc56]

Your questions are so unclear as to border on being completely incomprehensible. The amount of effort needed to decipher them is more than I'm willing to put forth, so I'll just throw out a few general observations in this post, then call it quits. You have clearly not done your due diligence, even to the meager extent needed to ask a comprehensible question. A good start might be to read the DSP Hardware Requirements section of the MSO homepage.

MSO is intended to be used in conjunction with traditional bass management. I can only guess from your post, but it appears you will be using some kind of "roll your own" bass management, but you either don't understand or are completely ignoring how traditional bass management - a requirement for MSO - works. Here's a simplified block diagram.

A few more points:

• IIR filters are not "convolvers". They do not and cannot use convolution.
• I don't do system consultation, and it appears that the questions you're asking are about system design, not usage of MSO.
• I'm willing to answer MSO-specific questions that are well-formed and indicate that the person asking them has done their homework. Example here

 

[john61ct]

Ouch 8-(

Yes, I am a noob to DSP, in fact I am still not 100% sure I will even put it into production,

and even wrt just my testing & learning process, I am still deciding which tools I want to bother learning with.

And yes, I am on a very limited budget, spending more than a C-note or two per month negatively impacts the family grocery budget these days.

But I can empathise with the fatigue of expending mental efforts, I need to be careful in my own dotage, or I don't have any energy left by dinnertime to properly tend to my teen kids as a single dad myself.

Stereo bass is central to my testing plans, your "basics diagram" is helpful, but seems to imply that bass management means mono subs only?

Does MSO allow for blending / smoothing both stereo and mono-fed LF drivers servicing overlapping frequencies?

Note that, it would have of course been ideal to communicate with you as the project author, but I was not intending to impose my ignorance on just you specifically?

I am posing these question to all members of the forum, that might be more willing to guide me in climbing this very steep learning curve.

IIR filters are not "convolvers". They do not and cannot use convolution.

Yes, but my understanding is that is a pretty fine point as a technical distinction

From my notes:

> Convolution FILTERING is technically FIR filtering only, convolving the input signal with an impulse response (IR).

FIR filters are often referred to as "convolution filters" or "non-recursive"

vs IIR filtering, uses recursive difference equations

>> all are convolved, including both Finite Impulse Response (FIR) and Infinite Impulse Response (IIR)

> all Linear Time-Invariant (LTI) filters operate according to the principle of convolution, but only FIR filters are directly implemented using a finite convolution operation

Is convolution the only way to apply filters?

I've read about the discrete convolution and how it applies to filters, but is convolution the only way to apply filters (to input signals)?

dsp.stackexchange.com

Therefore I chose to use convolving and "convolver" as a general term for the realtime always-on "actual filtering" or "implementation" of DSP - to distinguish from the (occasionally used, offline) tools used to just CREATE the filters.

If this really is so offensively wrong, I welcome suggestions as to an alternative umbrella term for that audio DSP implementation concept, but that covers all types of filters.

Anyway, my apologies for failing to do enough homework on MSO specifically, before asking if it suits my usage goals.

Hopefully as I get up to speed in future, we can "let bygones be bygones" and communicate more smoothly.

Finally on behalf of the whole community, thanks so much for all the skillz and labour you have so selflessly contributed, MSO certainly has earned a fantastic reputation as a very valuable tool over the years.

 

[ernestcarl]

Stereo bass is central to my testing plans, your "basics diagram" is helpful, but seems to imply that bass management means mono subs only?

You can't have both easily. More configurations means additional complexity and possibly even cost/expense and time investment in system design.

 

[john61ct]

That last I very much look forward to.

I would not even consider tools like MSO unless I valued difficult challenges.

By "both" I assume you mean "stereo bass" on the one hand, and mono-only subs on the other?

I also infer trade-offs between multi-seat smoothing to reduce impact of room resonances

vs the possibility of enabling acoustic envelopment.

If necessary I plan to be able to switch my system between different configurations

Normal listening levels vs "dance party" mode

Background music vs "Critical listening" (single MLP mode) vs "film viewing" (whole couch)

Trying to enable acoustic envelopment seems to be a special edge case...

 

[ernestcarl]

By "both" I assume you mean "stereo bass" on the one hand, and mono-only subs on the other?

Yes, but you can already have adequate enough "bass" envelopment already esp. if you main L-R speakers extend down to 80 or even 40 Hz + a sub(s).

"Perfect is the enemy of the good."

Biggest hurdle I see for most folks is the incapacity to start/begin small and accepting compromises.

 

[john61ct]

Just to clarify, I intend for my "virtual floorstander" L/R stacks to include multiple limited bandwidth "subs" plus MBM couplers

so getting VERY full range altogether, possibly higher SPL to perceptually match the "main" pair up top - right down to the deepest frequencies **both fed by Stereo**

except for maybe the mono Center stack at higher SPL, for when watching films.

All these virtual floorstanders are blended-xover, only duplicating frequency ranges ACROSS the three channels not within each stack