TOPIC:

Hi all. First time posting. I’m sorry it’s long. But I can’t figure a way of shortening it.I usually Can figure things out for myself as I’m quite a technical person in honesty. But here goes.

I’m trying to understand how exactly the Dirac live gets implemented in to the 2 channel audio with regards to bass management with 2 subs.

My understanding is there can only be 2 options. Both with its advantages and disadvantages..

option 1 - digital (left) and digital (right) channels to DSP in SHD (full range) ...high pass filter is set to channel 1 and 2. (e.g 80hz crossover).... then channel 3 and 4 have a low pass filter set at say 100hz....then Dirac corrects channels 1 and 2 and then separately corrects channel 3 and 4 . Then they all get converted to analogue, and out to the amps.

Option 2 - everything the same as option 1 but crossovers and delays are set and then Dirac is run on the combined speaker and sub output and Dirac believes it’s hearing just 2 full range speakers.

Advantage option 1— every speaker and sub gets corrected individually. So no speakers get corrected combined with a sub.

Disadvantages Option 1 - are that the final combined output of speaker and sub is not measured by Dirac and it can’t be certain of the response in room once combined. and the corrected values individually may need further tweaking.

Advantage option 1 - actual response combined speaker and sub gets corrected .

Disadvantage option 2 - if there is a combined peak at 70hz but in reality this is the subs peak, and the speakers response is in fact fine, direct will correct and will end up with a speaker that’s bass lite, and a sub that’s not had it’s peak fully removed. If this makes sense

Similarly if a boost is required at 40hz then the booth will also be applied to the speaker which you obviously don’t want.

Hope this makes sense. If someone could show me the errors of may understanding, that would be great.

I’m also assuming that I would have to set delays first even though Dirac can do this, because it will only set delays between left and right channels and not set my subs delays for me as it only sees right and left full range speakers so to speak.

Set your delays first, I suggest using REW to calculate them as the acoustic centre of subs may not be where you think it is. REW sometines gives strange graphs but the delays it calculates seem good to my ears. Typically the delays are not terribly sensitive as the wavelengths from the sub are so long.

If there is a way that works properly other than option 2 I don't know about it. I didn't even bother with crossovers, unless you take great care the phase shifts can do more harm than good in my experience. I just set my sub low pass frequency to where REW suggested it would help and let Dirac take care of everything else. The disadvantage you list for option 2 where Dirac will reduce the output of the mains and subs when only one was theoretically necessary was actually a benefit for me because my mains amplifier was slightly underpowered. By setting the sub level to give a slightly bass heavy result Dirac turned the bass down on the mains which made the mains amp cope much better.

My mains were actually pretty good but I had a 15dB suckout between 40Hz and 50Hz probably caused by SBIR so I only needed the sub to fill that in. Dirac can typically only boost by 10dB so any dips larger than that will not be fully corrected. SBIR is also why subs should be placed in corners. The end result sounds very good to me, any remaining problems require further room treatment,

My understanding is that a later version of Dirac will support proper bass management but for now I find letting Dirac do all the driver management works very well.

thanks for the great reply.

I’m summary I think I will do the following.

1. Set delay between subs using rew.

2. Set LPF for subs

3. Set appropriate HPF for mains. (No delays) Think this is required in my case because I like to play loud and clean on occasions and they are small kef LS50’s

4. Run Dirac

Sounds like a plan

One more question though. Should I use the subs stereo and route the channel 1 bass to channel 3 and channel 2 to channel 4... or printers both 1 and 2 to bother 3 and 4. If this makes sense.. I’m assuming more often than not same bass goes to both channels in music?

If it doesn’t make sense then sorry as I haven’t actually bought the SHD yet. And I’m used to AVR bass management and room correction

The nearest drivers to you need delays, for me that's the mains since my sub is in a corner behind the mains.

More often than not the bass is mono, yes, but 1 to 3 and 2 to 4 is the correct routing since Dirac may need to do different things to left and right to actually achieve the same results on left and right. For me, my bass suckout only happens on the left channel for example.

Thanks again. You have been very helpful.

Coincidently I have a 40 to 50hz suck out at the moment due to the exact same reasons as you. SBI.

But it happens across L, C and R and the sub for me, as they are all on the front wall.

My second sub I’m building to go opposite corner will sort it out though I hope. Room sim seems to suggest it will.