DSP Active Crossover

@bdp24 - I don’t think Danny is a fan of active crossovers, but partly because a lot of his excellent skills in passive crossover design. But Richard Hollis from Hollis Audio Labs has had some good success (according to others) using DSP crossovers and a system very similar to mine. 
 

I’m using the Rythmik HX800 amps for my woofer towers. Each of the amps has two outputs, each of which drive a pair of 16 ohm speakers in parallel. With this load, they’re rated at 400w for each of the two outputs. 

Hard to say how complicated this will be without knowing your system, and what the passive crossover does.

@erik_squires - My system is described on my Main System virtual system page, but to elaborate a bit more - my speaker system is a dipole line array with Bohlender-Graebener NEO10 midrange drivers, and NEO3 tweeters, with dipole woofer towers, each using four 12" servo woofers. 

The BG drivers have a fairly smooth response, so the crossover is fairly simple - 12 db/octave LC filter for both NEO10 and NEO3 driver arrays, with an additional LC notch filter on the NEO10s. The woofers are driven by Rythmik plate amps that have their own active crossover (along with a simple parametric equalizer). 

I don't think it will be hard to set up a DSP to do the same thing, although I'd probably use a 4th order crossover since it's fairly simple to do with DSP and makes it easier to get a smooth phase response. 

The NEO line arrays are fairly efficient at about 98db/w. I'm currently driving them (using the passive crossover) with a 300B PSET amp (monoblocks). With an active crossover, I'd probably continue to use this amp on the NEO10s and build another SET amp for the tweeters. 

I may be able to bypass the crossover on the Rythmik amps when using the dsp. If not, I'll set it to it's maximum crossover frequency and work around it with the dsp.

I currently use REW with a calibrated UMIK-1 mike. I suspect this will be adequate to set up the active crossover, but I'm open to suggestions. 

@jwr159 - I talked to Al Clark on the phone for close to 40 minutes today (he likes to talk) and I'm going to go ahead and order the dspNexus from him. 

@arion - Thank you for bringing this to my attention. The Trinnov Nova looks like an interesting unit, but is considerably more expensive than the Danville dspNexus, particularly for the six channels that I need. It also seems to be focused more on room correction than on crossover use, but I assume it can do both. 

Since I'm not sure if going active is my long term plan, I don't want to spend too much to give it a try. If I like the results, I might consider spending more in the future. 

I spent a while researching the Trinnov Nova, but decided to go with the Danville dspNexus. 

The Nova would have cost $5500 ($3500 + two additional 2-channel licenses at $1000 each) compared to $3000 for the dspNexus. But even at the same cost, the Nova is really designed as a pro-audio studio calibration system and is not as well suited for my purposes. For example, it does not have an IR remote, and it doesn't have an easy way to control the output volume. The user interface is fairly slick, but is designed to be fairly automated and doesn't appear to have the programming flexibility of the Audio Weaver software used by the Danville.

The dspNexus has both a stepped attenuator (in 3db steps) to set the max output level, and digital based volume control that can be controlled by an included IR remote. It is very modular allowing the DSP and DACs to be easily upgraded. Al Clark indicated that they are working on upgrades for both, and a new (significantly more powerful) DSP board will be provided for free later this year. 

Also, the dspNexus will ship on Monday, while the Trinnov is currently backordered. 

@lewinskih01 

I received the dspNexus a few days ago, but I've been buried with work so haven't had a chance to do anything with it yet. I've got a measurement mic on order that should be here early next week. I'm hoping to find some time in the next several days to at least hook it up to a computer and download the Audio Weaver software.

Thanks for the info. I found Mitch Barnett's book on Amazon. I'll check it out. I'll also take a look at the Acourate software to see if this will work with my dspNexus. 

@jwr159 

What software did you use to create the filters for your dspNexus? Anything other than Audio Weaver?

I've made some progress with the dspNexus. This product is still considered an "early adopter" release. The main limitation is documentation. But I've had a couple of video conferences with Emilson, Danville's software engineer, and now have a pretty good feel for how most stuff works. 

I bought a cheap active speaker to use for testing so that I didn't risk damaging my main speakers while I learned how it all works. This has allowed me to verify that the filters are doing what I want. 

Danville provided a sample 3-way crossover design which I have modified to meet my needs, although I'm sure I'll make a lot more changes before finalizing my design. I'm starting out with the crossover points set at 180Hz and 1800Hz, using 8th order (48db/octave) filters. These are the approximate crossover points that my passive crossovers provide, although with much more shallow slopes. 

The Audio Weaver software is very flexible and powerful, but requires that the user set all the filter parameters. In other words, you can't just hook up a measurement mic and have the software automatically determine all the filter parameters to match a target curve. There is a lot more trial and error, but at the same time, you know exactly what processing is being done. 

I have to make some speaker patch cables to connect between my speaker drivers and amps (bypassing the passive crossover), and then I can start testing on my main speakers. I'm hoping to do this over the weekend. 

So far, I have no regrets going for the dspNexus. It seems like a well-engineered and powerful device. 

I've read a lot of posts over the past few years from audiophiles that have switched to active crossovers and I can't remember any cases where the poster didn't feel switching to active was an improvement. It's obviously more complicated, but has some obvious advantages. I'm looking forward to trying it out. 

@mijostyn - that looks like a nice piece of gear. Do you know what DSP it is using?

I think the Danville dspNexus 2/8 is an excellent value at $3K, but currently doesn't have software as simple to use as products like the DEQX. You have to be fairly comfortable with computers.

The HW is well built, but the casework is not as fancy as the DEQX Pre 8. The power supply seems to be the weak point and I suspect the DEQX is better (based on what I've seen for their previous products).

I was able to try out the dspNexus on one channel of my main system yesterday. So far, I have only set up the crossovers (96db/octave), adjusted time alignment between my main planar line arrays and my woofer towers, and added a bit of PEQ to the low-frequency channel. My bass response is fairly smooth without any equalization so I didn't apply a lot.

I haven't tried to create any convolution filters yet. And so far, I've only played it from my PC, not from my streamer. Next step is to set it up connected to my streamer and playing both channels to see how it sounds. 

@ricevs - Unfortunately I haven't had a lot of time to work with this yet. I've been buried with work (I run an ecomm business and do all the coding - getting ready for the holidays) so this has taken a back seat.

Setting up the dspNexus means I have to disconnect my passive crossovers,  set up an extra pair of amps and get everything plugged in, and change the settings on my subs, so takes a while. And then takes a while to switch everything back. So I have to be able to dedicate at least 4-5 hours to make it worthwhile and haven't had that much free time in one chunk in a few weeks. 

Once I get into November, I should have more time since I don't like to make changes to the websites during the holidays. I'm planning to attend CAF next month and look forward to discussing my setup with Al Clark and Richard Hollis. 

So far, I have gotten a simple crossover setup to work, with a limited amount of equalization to the subwoofer channel. It sounded ok, but will clearly require more filter tweaking before I can decide whether I like it better than the passive crossover.

@ricevs - I have been using the dspNexus as the DAC/preamp, so I'm feeding it USB audio directly (no conversion from analog). I don't think it makes sense to use my Terminator + and preamp ahead of the dspNexus. 

I agree that the dspNexus could be improved. I think the biggest weakness is the power supply - the simple SMPS that is currently used could be improved a lot with a good linear supply with shunt regulation. I think if I decide to go this route, I will probably implement my own power supply. 

The biggest advantage I see to use a DSP crossover is to be able to implement steep filters with no added noise. If I implement analog active crossovers, the steepest I'd probably be able to get away with is 24db/octave. This is still better than the 12db/octave passive crossovers I have now though. 

I agree there is a bit of room for improvement in my current crossovers, but this is clearly diminishing returns. Still, I may consider it at some point. I've just got too many projects going on in parallel right now, and I'm having trouble actually finishing any of them 😀.

As far as facing all the drivers in the woofer towers forward, I have not been able to discern a difference. I had them facing forward in my triple towers and I think the quad towers are just as tight and clean sounding - probably a bit more so - than the triples. There isn't an easy way to turn them around anyway. All the holes for the wires are only drilled on one side. 

With such a tall tower, I'd be a bit nervous about having all the drivers facing forward since the weight distribution would be heavily toward the rear. Even the triples were slightly tippy. 

@dsp - Al, I didn't mean to imply that the dspNexus isn't a well engineered product.  I would expect that replacing the SMPS with a linear supply that was good enough to provide a noticeable improvement to the sound quality would more than double the cost and significantly increase the size of the enclosure (also increasing cost).

As is, the dspNexus provides a lot of value for it's price point and is very nicely constructed, allowing easy upgradeability to the DSP and DAC modules. 

I look forward to meeting you at CAF.