Sound travels at about 1100ft per second or 1.1ft per ms.
The closest speaker/sub needs the most delay.
So if the mains are at 10ft and the subs are at 15ft, then you need to add 5ft of delay to all of your speakers so that their bass doesn't arrive sooner than the bass from the sub.
If the sub is closer, then you need to add that delay to the sub(s) instead, so that it's bass doesn't arrive before the bass from the mains.
A lot of AVR's do this calculation for you automatically, but most of them can only handle 1 subwoofer (mono track), not stereo bass or even dual-mono discrete.
It's probably best if you can measure the response and make delay changes to see what is really happening to the response. I was remeasuring my 3 subs the other day, and was trying to get rid of a big dip at 40hz. I first delayed the closest sub, and the response got worse, so I removed the delay, and started delaying another one, and again the response got worse. I ended up only delaying the one in the right front corner of the room, the closest one to my mains, and the dip started going away. That, plus reversing the phase of the second sub, pretty much removed the dip, at least it went from over -10db, to about -1.5db.
Measuring the room over and over again, while making changes is the only real way to know what works and what doesn't. My bass as never sounded better than it does today.
I've taking measurements and used the miniDSP a number of times before, and the more I use it, the better I understand it, and the better my system becomes.
1) Measure CC+subs (all speakers set to small, AVR set to "Multi Channel In", REW HDMI output CH3, sweep measurement)
2) Note if there is a dip at the crossover point (could be just above/below crossover as well)
3) Adjust subwoofer distance setting in AVR in +1' increments (make sure to back out of the distance setting menu or the changes won't take effect)
4) Re-measure
5) Repeat steps 3 & 4 until the dip comes up to flat
If your system is mainly movies, step 1 should be CC+subs...if mostly music you should measure FR+subs or FL+subs. If it is an even split, you will need to find a distance setting with the best compromise between mains & center.
When using a miniDSP, I'd recommend measuring the subs alone while adjusting the delay on one at a time and observe what response changes happen. After you have them aligned together for the best response, then you can adjust the delay of the subs (as a unit) in the AVR to the mains for the smoothest crossover transition.
There are certain things in theory that "should" work, but measuring instead, ensures what does or does not work. You never really know what problems your room is creating and what change makes the biggest difference if you don't measure it.
When using a miniDSP, I'd recommend measuring the subs alone while adjusting the delay on one at a time and observe what response changes happen. After you have them aligned together for the best response, then you can adjust the delay of the subs (as a unit) in the AVR to the mains for the smoothest crossover transition.
There are certain things in theory that "should" work, but measuring instead, ensures what does or does not work. You never really know what problems your room is creating and what change makes the biggest difference if you don't measure it.
2. Time align subs with each other using Jerry's method & program this delay into the 2x4
3. Using the sub distance tweak adjust the delay of both subs the same amount via the 2x4 in increments and keep making sweeps to attain a smooth response at the crossover point.
2. Time align subs with each other using Jerry's method & program this delay into the 2x4
3. Run calibration routine
4. Using the sub distance tweak adjust the delay of both subs the same amount via the AVR/pre-pro in increments and keep making sweeps to attain a smooth response at the crossover point.
Question guys..... I have 4 subs. I left the delay for the front subs on "0" in the mini dsp but there Is a 7ms delay on the rear subs. Should I add a delay in the front subs as well and then tweak the avr distance settings to dial it all in together. I always thought putting a delay in the front subs that are on the same plane as the mains might throw things off? I guess I'm wrong?
You leave the front subs at "0" and add delay to the closer subs. It does not matter if the front subs are on the same plane as the mains or not, what matters is that you add delay to the closer sub(s). Then, you align the sub "system" (all 4 subs) with the mains/CC with the sub distance setting in the AVR/pre-pro (
What's weird is the general consensus is to add delay to the closest subs, but when I tried that, my response got worse, as I has trying to remove a big dip at 40hz and when I delayed the closest sub, then the second closest, the dip got worse both times. When I only added delay to the sub next to the mains, the dip started getting a lot less.
In the end, I had no delay on the two subs on the side walls, and only delay on the one closest to the mains, and the one furthest away. That plus reversing the phase of the sub on the left side wall, pretty much removed the big dip.
That's why I can't stress enough to keep taking measurements, because you just never know what's really going on unless you do.
Well, you may have cured a dip, but your subs are not time-aligned correctly. You should try time-aligning correctly and curing the dip with sub placement instead of using an unconventional "band-aid" solution.
Also, were you measuring the subs alone, or were there speakers included?
I will be using the unbalanced version and have read that using a USB power supply can cause noise to be generated and you should use a dedicated power supply to stop this.
The 2 way advanced allows up to 4 subwoofers. You have two inputs and 4 outputs, so it can be used as a stereo 2 way crossover, or the crossovers can be bypassed for 4 non filtered outputs which is how I use it for 3 subs so I still have one open channel, where you just use the AVR's crossover.
The 4 way still only has 4 outputs, because the miniDSP 2x4 only has 4 outputs, but the 4 way, is for a single 4 way active speaker.
The crossovers are on the outputs not the inputs, but you can bypass them all, or 3 or 2 or 1.
I believe outputs 1 and 3 have the option of a low pass or none, and 2 and 4 have the option of a high pass or none.
In your case, you could use output 1 for the kicker, with the low pass crossover engaged, then use, say 3 and 4 with the crossovers bypassed for your subs.
Basically it has two inputs, then out 1 has the option of a low pass or not, out 2 has high pass or not, out 3 has low pass or not, and out 4 has high pass or not.
Was just looking at the graphs again...what is really curious is that dip at about 14hz and the rising response under 6hz on the CC+Subs graph. The CC+Subs graph should look almost exactly the same as the Subs Only graph when you get that far below the crossover, this doesn't look to be the case here.
Are you absolutely certain nothing changed between the two measurements (mic placement, AVR settings)?
You time aligned the subs to each other. The delay that Dirac is setting is to get the "sub system" in-phase with the CC/Mains. You want to set that wherever it gives you the flattest response in the area around the crossover (ala the sub distance tweak).
Right so the 40Hz dip is my fault on my subs (PB13 ultras) I had PEQ enabled at 40Hz to tame a peak.
I set this before running Dirac but it looks like Dirac does not like it as it seems to turn it into a null so turning off PEQ results in this at 40Hz.
You can see why I had PEQ enabled at 40Hz when you look at the yellow line, but it looks like Dirac does not need it so I will just turn it off.
So the 60Hz null is still there but if you look at the yellow line again this shows a peek which is before EQ is applied. So is my null cause by Dirac?
You would think Dirac would be able to just get rid of that peak just like it did with the one at 40Hz.
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