TOPIC: DDRC-22D with dual mono subwoofers

I will get two news subwoofers today and my system will be:

Digital source > DDRC-22D > Benchmark DAC2 > SVS SB2000 dual subs in dual mono config > High pass 80Hz from subs to Hypex NC400 amp > Dali MS5 main speakers.

I am in doubt that this dual mono configuration where both subs are connected identically to the Bencmark DAC2 is the right way of doing it when performing room correction with the DDRC-22D.

Quoting from [url=http://http://www.dirac.com/faq-technical/]FAQ[/url]
Question: I have a 2.1 channel system with one or several subwoofers. Do I need the Full Version (multichannel) of Dirac Room Live Correction Suite or is it sufficient with the Stereo Version?

Answer: The Stereo Version is normally sufficient. Note that Dirac Live Room Correction Suite does not include crossovers or bass-management, these functions need to be applied separately. While crossovers should be applied downstream of (after) Dirac, bass management or any mixing of source signals into speaker channels should be applied upstream of (before) Dirac. The main rule of thumb to follow is that one should not mix together two separately Dirac Live-processed channels into a common speaker channel.

On the other hand this application note multi-sub-optimization-with-the-ddrc-88a/ describes just using a Y-splitter and connecting multiple subs to a single output.

If connected in dual mono how can Dirac change phase/amplitude for each subwoofer to even out room responce according to a target curve?

Should I instead connect each subwoofer in a stereo configuration contrary to the application note for DDRC-88A?

I think the answer to your question really depends on where you have located the subwoofers. If they are each right next to the respective speaker, imagine that they turn each speaker into an N+1 way (where N is what the speakers are already) and you'll be fine. Otherwise and/or if you want to optimize your LF as a single channel, then you will need a different way to connect things.

john.reekie wrote:
Thanks for your reply John.

The subwoofers will be next to and slightly behind the main speakers, either in the corners or between main speaker and TV. Assuming that case, my question regarding stereo/dual mono still stands Am I correct in assuming that Dirac won't be able to perform ACR at subwoofer frequencies, when they are connected as dual mono (identical input to each subwoofer even though the room response at listening position from each subwoofer will be different)? Is the recommended setup connecting dual subwoofers in stereo when using with Dirac in stereo mode?

A further question I have not been able to find out an clear answer to:
Group delay. I have no way in the current setup to delay the signals to the mainspeakers by let's say 10ms. I've read in another forum (by user FLAK) that Dirac may be able to correct the time delays, but is limited to 10ms. Assuming 10ms is the time I need to delay the signals to the main speakers with reference to the signal to the subwoofers, will Dirac take care of that?

Otherwise I would have to insert a further processor delay the signal to the main speakers 10ms.

Annoying I bought a stereo Dirac before deciding to buy two subs

What's ACR?

should be ARC or perhaps more correct DRC

Connected as you describe, Dirac Live will optimise individual response, not combined. Only you can state what combined response is, either by measuring or listening.

I assume subs have a phase control. Set up and measure, adjust to get best result. 10 ms delay unlikely to be needed.

john.reekie wrote:
Thanks again for your time John.

Yes the subs have phase control. My plan is to setup the subs with regards to crossover (80Hz or lower) and phase (listening) and first then do Dirac.

Regarding group delay I've just read that a typical sealed sub has around 8-15 ms group delay + the increased distance compared to main speakers (small in this case), so the 10ms seem likely to be needed and even too small a value? Link: sounddoctor

I will then proceed with stereo setup. I just wonder why the application note for DDRC-88a says that the subs have to be connected in dual mono instead of stereo. I cannot be the only guy having this question/issue. Perhaps the dev team can elaborate?

A further question. I plan on having a kind of house curve as target curve where the freq< 150 Hz gradually increases to +6-8dB. Will it be an advantage to increase the gain in the subwoofers so freqs < 80Hz already are boosted and then maybe requiring less processing from Dirac or is it best to just level match the speakers and subwoofers and then do Dirac/target curve optimization?

I just said, connected as you describe optimizes individually, not combined. Please try and understand the answer before re-asking same question? (sorry! ipad typing)

john.reekie wrote:
I am sorry your one-liners may lead to further analysis/questions and you feel annoyed by that. I am not an expert in digital signal processing for audio, which I guess most of the people on this forum aren't.

Regarding that question I re-asked: I just fail to see how Dirac can optimize much with dual mono config as they recommend in the app note. When you run Dirac it sweeps each speaker individually and then at last the combined output. If you have a dual mono config the individually measurements are basically useless, since it cannot output different outputs to the subwoofers anyway. My question was directed to the dev team why they then recommend dual mono. Perhaps there is a good reason for that.

Regarding the group delay and my last question I hope someone can share some thoughts/experiences about these.

perhaps less confusing if you avoid introducing new terms like dual mono. the app note says drive all subs from one dirac channel, that is so dirac can optimize the combined response. at no point in that app note is there individual sub measurements , except the first one in method b.

group delay is not constant with frequency.

john.reekie wrote:

Well it doesn't really answer my question, but I'll take you word for it that 10ms limit is no problem at all.
Thanks for your help. End.

I said likely, not definitely. Essentially, it seems to me you already have what you need to (probably) get a good result, given some caveats related to positioning and sub response. But you have do it and measure it for yourself, bass in rooms is just not predictable enough for someone at a distance to tell you what you need to do.

So I'd suggest try working with what you have to start with. If you really do feel that another device is necessary for time delays, stereo/mono summing, steeper crossover, independent control of subs, etc etc, there are several device you can use for that - 4x10 HD, OpenDRC-DA8, even nanoDIGI 2x8.

Hope this helps, and that the additional word count makes this response more acceptable.

Thanks John for your replies. I will just experiment now and observe the results. Nice to have some suggestions on future upgrades if it's necassary.