TOPIC:

Hi Everyone,

Love the forum and all the knowledgeable folk who take the time to post.

Here’s my challenge question for today. I’ve a pair or two way standmount speakers and a sub. With two power amps I could bi-amp my speakers and what’s more, have active crossovers (always wanted to try that!)

What is the best way to have (a) active crossovers for my main speaker’s tweeters-woofers and also (b) have sub integration?
....and... have Dirac correcting for my room! I want it all!!

The SHD seems an obvious choice for achieving either (a) or (b) but not both. If only the SHD had 4 outputs + a dedicated sub out.

Anyway who fancies the challenge of figuring it out.

You probably know but let me just double-check: you understand that to use a miniDSP as an active crosover you would need to remove the passive crossover from your speakers, right? I'm asking as doing this, and the associated work to set this up well, is more involved than many may want to get into. Which is not to say there aren't loads of people who have put the time in to do this and are very happy with the results!

Yes understand it involves removing the passive crossover in the speakers. I never mind being asked things like that though - no one is infallible, something potentially damaging can be easily missed.

asx77 wrote:

Yes understand it involves removing the passive crossover in the speakers. I never mind being asked things like that though - no one is infallible, something potentially damaging can be easily missed.

Great.

As for your main question there is no clear answer. One option would be to use a 2x4 HD for the active crossover and then have a DDRC-24 or an SHD to control to sub to main speakers crossover and apply Dirac correction to the combined system. This isn't something I've done myself though, although I do actually have all the hardware I'd need!

@Tony_J is one member who has done something like I described I think. Maybe have a search through his threads if he doesn't spot this.

Hi Ultrasonic,
Thanks for that. Would you have the DRC/SHD feeding the 2x4 or the other way around?

I’ve read Tony’s threads and he seems to have daisy chained smaller units. The thing I don’t like about that is the Digital-Analogue-Analogue-Digital-Digital-Analogue back and forth. Seems to me MiniDSP really want to be offering a Dirac plug-in to something like there 4x10!

asx77 wrote:

Hi Ultrasonic,
Thanks for that. Would you have the DRC/SHD feeding the 2x4 or the other way around?

The former, and critically a 2x4 HD not a basic 2x4, which I'd totally avoid. You have to have the Dirac capable unit controlling the signal sent to all elements of the combined system for it to work.

asx77 wrote:

I’ve read Tony’s threads and he seems to have daisy chained smaller units. The thing I don’t like about that is the Digital-Analogue-Analogue-Digital-Digital-Analogue back and forth. Seems to me MiniDSP really want to be offering a Dirac plug-in to something like there 4x10!

Sure, miniDSP simply don't make a product that does all that you want hence some form of compromise if you want to try. My likely long term plan will be to replace my main speakers with commercially made active speakers and to keep using my SHD as I do now for sub integration and then Dirac Live applied to the combined system.

Having said the above is a compromise it should perhaps be pointed out that I'm sure loads of people have made active speakers with 2x4 HDs acting as active crossovers and been very happy with the results.

Hi, a 4x10HD or C-DSP8x12 driven from one of the SHD digital outputs will work fine and without additional A/D/A conversions. Think of it as one unit being the speaker crossover, the other being room correction and sub integration (and in this case, the network and USB audio inputs as well).

Cheers Ultrasonic that looks like and option but...

Ultrasonic and John,
John’s post prompted me to look at the Car audio options. Have you seen there appears to be a new product? The C-DSP 8x12 DL. It accepts digital input. Has as many assignable channels as could ever be needed and has Dirac! I think that is the answer product right? Or is there an issue with the quality of a product aimed for use in the car? Will the components (importantly the DAC) be lower quality?

asx77 wrote:

John’s post prompted me to look at the Car audio options. Have you seen there appears to be a new product? The C-DSP 8x12 DL. It accepts digital input. Has as many assignable channels as could ever be needed and has Dirac! I think that is the answer product right? Or is there an issue with the quality of a product aimed for use in the car? Will the components (importantly the DAC) be lower quality?

That's not a product I've ever looked at before...

From a quick look the two most obvious potential issues are that firstly you'd need to find a way to power it (as it's designed to work with a car battery as power source) and that going from the spec sheet the 6 V rms output level is high compared to the standard 2 V rms output for in-home unbalanced audio signals. The output level issue could be managed with digital or analogue attenuation though, and the DDRC-24 runs off a 12 V DC supply from a 'wall-wart' power supply so I'm guessing there must be a way to use something similar here.

On the quality front, going solely on the info. on the chips used, it looks equivalent to a DDRC-24 to me (which for what it's worth is not at good as the SHD series but these cost a lot more). There is more to ultimate performance than just part numbers of course.

One feature the in-car option doesn't support is a USB audio input. And it obviously lacks the streaming capabilities of the SHD series too.

I've just had a quick look at the user manual and I'd advise you to do the same. The plugin is designed around a surround-sound configuration like you'd have in a home cinema rather than a stereo setup, with specific functionality around handling the signal sent to the subwoofer. At first glance I think it would probably be suitable for what you want but I'd need to spend more time going through all the details to be sure. Make sure you do this before spending any money!

You may want to have a read through the CDSP section of this forum to see if you can learn more.

Great shout! There are a few posts there regarding home use. Devteam chipped in to warm folk of a few things they need to overcome. One thing I didn’t understand was their comment about the analogue outputs

“All inputs are "differential balanced" = like balanced input. So it's not the same as a simple RCA.”

Does that make sense to you?

Anyway I raised a new post there asking if anyone has implemented it in a stereo setup with success. Let’s see if anyone has!

asx77 wrote:

Hi Ultrasonic,
Thanks for that. Would you have the DRC/SHD feeding the 2x4 or the other way around?

I’ve read Tony’s threads and he seems to have daisy chained smaller units. The thing I don’t like about that is the Digital-Analogue-Analogue-Digital-Digital-Analogue back and forth. Seems to me MiniDSP really want to be offering a Dirac plug-in to something like there 4x10!

Hi - an alternative that avoids the D-A-D-A problem is instead of daisy-chaining one of the cheaper miniDSPs, daisychain an analogue 2-way crossover instead.

Alternatively, you could do what I did very early on in my experiments with DSP:

I presume that your sub has its own low-pass filter, and can take high level signals as input. If that is the case, then use either a DDRC-24 or a SHD and configure it to feed the bi-amped 2-way speakers, with a suitable crossover point. Do any tweaking of the 2-way setup that is appropriate (with the sub switched off) so that the overall balance WITHOUT Dirac is as good as you can get it - adjust levels between the LF and HF sections, remove any gross peaks in the FR by applying PEQ filters, etc. Feed the sub with the high-level signal from the bass channels of the bi-amped setup (or split off a low level feed from the LF outputs of the DSP) , and deliberately set its level control too high. Then run Dirac and allow it to "tame" both the overall response and also the sub. What Dirac will do, because the setup is too bass-heavy, is to apply a bass cut in the region of the FR curve where the sub is operating, and where there will be some overlap with the bass drivers in the 2-way. The effect of this will be to reduce the sub's output, but also to reduce the LF output of the 2-way in the region of overlap. In effect, Dirac has created a bandpass filter for the LF section of the 2-way, and integrated the sub in the process.

I did a very similar thing to this with a pair of full range speakers, a sub, and a DSPeaker Antimode 2 DSP box to do the integration - it worked surprisingly well.

Hi Tony,

So in this case am I correct thinking Dirac can't independently correct the Woofer and Sub as they are being fed from the same signal?

But then would we want that anyway? Let's suppose for a moment I don't have a sub. My speakers are 2-way and I have active crossovers... If I had tweeters and woofers on separate dirac channels this would be no good since at the crossover point (although minimal) there is interaction between tweeter and woofer. Both contribute to create the frequencies either side of the crossover point regardless of how steep a roll-off there is. So I guess Dirac needs to correct the combined signal. Is that right?

If so then feeding the sub from the woofer's feed would also be logical except is there less control around the crossover point? The woofer's and subs gradient is what it is - i cant change it and I need to figure out where the roll-off of the woofers naturally occurs and set the max frequency of the sub accordingly. I suppose having the sub crossover too low and the woofer too high is preferable to too much of an overlap.

And what happen if they're out of phase? Wouldn't they be fighting each other? If dirac boosts then the cancellation is boosted. Finally if I only have 1 sub, I can only feed it a left or right signal unless i use the high level inputs and take a feed from each speaker, yes?

Thanks

Hi -

You are right - Dirac applies to the combined (2-way + subs) sound that you can hear in the room, so it won't discriminate - it looks at the overall FR curve and acts accordingly. What I hadn't factored in to what I said before is that you absolutely CAN establish what is effectively a crossover between the 2-way and the sub, because you can set the low pass frequency for the sub and also, in the bass section of the DDRC-24, set the PEQ filters to give you something close to a bandpass.

So, to elaborate a bit on what I said before.

1. Switch off Dirac on the DDRC-24, and switch off the sub.
2. Do some measuring using REW and adjust the crossover from the 2-way's bass/mid driver to the tweeter as best you can - pick the frequency, adjust relative attenuation if necessary, fix any gross peaks/troughs using the DDRC's PEQ filters. Note that to get the smoothest response at the crossover you may need to reverse the phase of the tweeters (or woofers). When you've got it as good as you can using those techniques, you will also get a good idea of where the 2-way's bass starts falling off.
3. Choose that frequency for the sub's low pass filter - so you might (for example) end up with the bass drivers in the 2-way handling from 100 Hz through 2500 Hz.
4. Take high level feeds from the speaker terminals of the bass drivers to feed the high level input of the sub, and measure again, adjusting the sub's level so you get as smooth crossover as you can manage - again, you may find that reversing the phase of the sub is helpful; if the sub can't handle that, reverse the phase of all 4 channels of the DDRC-24. Note that to get the bass extension that you are looking for from the sub, you may (probably will) end up with a hump where the sub and the 2-way cross over; don't try too hard to fix that, leave it to step 5.

At this point, there are 3 alternative approaches for step 5 that are worth trying to see which gives best results:

5(a). Run DIRAC using your fave target curve. This should adjust any hump at the crossover from sub to 2-way, and also fix any other problems it sees as normal. This is the no-brainer version, but as you have observed, if the 2-way is producing significant bass in the overlap region, this may not be ideal. DIRAC reducing the hump will have the effect of reducing the output of both the sub and the 2-way in that overlap region.

5(b). Deliberately increase the sub's output before running DIRAC. This is essentially the same as 5(a), but because the sub's volume is set higher, the reduction in level that DIRAC will make will have proportionally more effect on the the 2-way's bass output in the overlap area, so in effect causing a faster bass rolloff for the 2-way.

5(c). In the DDRC, set a PEQ HIGH_SHELF filter in the channels that feed the bass drivers of the 2-way, at the crossover frequency chosen for the sub. Adjust the output Up for the sub to compensate - you may need to measure again using REW to get the crossover smooth. What this is attempting to do is to force the actual bass output of the 2-way to roll off more quickly, but without removing the LF signal reaching the sub. This may need a bit of iteration with the choice of gain and Q values in the HIGH_SHELF filter, and you may find that tweaking the frequency chosen for the filter will help too . What you are looking for is as smooth a transition between the sub and the bass of the 2-way as you can. Finally, run DIRAC.

5(b) was the approach I took with the system I mentioned earlier in the thread, and it worked very well. I suspect if you get it right, 5(c) has the potential to do even better as it is actively suppressing the 2-way's bass output before DIRAC gets to play with it.

Hi Tony,
I almost follow you but let me check step 3.

Understand I should measure with REW but let's work an example using my speakers specs which are as follows...
Frequency response: 60Hz-20kHz (@3dB, -6dB at 48Hz)
Crossover frequency: 4600Hz.

Dirac 1 (Left channel to Outputs 1 & 2)
Output 1: Tweeter
Output 2: Woofer + Sub

Output 1: Set high pass to 4600Hz
Output 2: Set low pass to 4600Hz
Set the sub's own low-pass filter to 60Hz

So now the Tweeter's amp gets everything above 4600Hz
The Woofer's amp gets everything below 4600Hz (woofer only starts making sound from 60Hz and up)
Feed from the Woofer's amp goes to the sub.

Have I understood correctly?

asx77 wrote:

Have I understood correctly?

I don't think so. I'll leave the details to Tony but in case it helps you to make sense of this yourself I'll say that the two Dirac channels will be left and right full bandwidth, not different combinations of drivers.

What miniDSP hardware are you now considering using? I've lost track...