DSP Active Crossover
I'm considering trying a DSP-based active crossover in my system. I did a search to see how much this has been discussed, and most of the posts are pretty old or about active speakers. DSP technology has changed a fair amount in the last 15-20 years.
My system is digital only, and my speakers are 3-way, so it's not particularly complicated. I've been looking at the Danville Signal dspNexux 2/8 which has two channel in (with digital inputs) and eight balanced analog outputs. This appears to be available with AKM AK4499 DACs which are fairly well regarded sigma-delta DACs (although I don't know how good their implementation is).
This product has a fairly rich DSP software environment for programming filters, time delays, etc., so it should be fairly straightforward to set it up to replace my passive crossovers.
My biggest reservations are 1) giving up my Denafrips Terminator+ DAC and nice-quality DIY preamp, and 2) using the DAC's digital volume adjustments.
This unit is about $3K (maybe a bit more with the AK4499 DACs), so isn't terribly expensive. From the limited research I've done, this unit appears to be higher sound quality than the miniDSP or DEQX boxes, but I could be wrong. All my amps have balanced inputs, so I'd prefer to use a unit with balanced outputs.
So, what I'm wondering is if the benefits of active crossovers and dsp equalization will outweigh the lesser DAC quality (assuming this is the case) and lack of analog volume control (currently using a relay switched attenuator). I'm also wondering if there are other dsp audio processors that I should consider (digital inputs, at least six channels out, ideally with balanced outputs).
@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. |
@jaytor -- Kudos for venturing into outboard active configuration (it’s what I do myself). It will be interesting to learn of your findings (if you’re willing to share them) compared to your passively configured main speaker system once you’ve initiated the process and has gotten your head around it with actual impressions of the sonics to follow. Cool main setup, btw. - I’m sure it’s very capable.
Your main priority is using the digital input on the dspNexus, I see, which - as a simplified system, with all that may entail - is what prompts above quoted concerns of yours. While on paper/in theory I understand worrying about introducing extra conversion processes, as an outset at least I wouldn’t be too concerned about them. What do you gain by avoiding them, while at the same time losing out on your Denafrips DAC and separate preamp? Seems to me some effort of yours has been invested in sonically "shaping" the sound of your setup with these very components, so why not start with them remaining in the chain and instead use the analogue inputs of the dspNexus directly from your preamp? Yes, you’ll have an extra A/D conversion (the effect of which is blown out of proportion, if you ask me, if it’s even noticeable), but this way I’d argue you have better grounds for comparing the sound from the passive speaker config. and the one introduced with the active ditto on the basis of this alone. There’s also the option of a software-based DSP preceding the DAC, which then necessitates a separate DAC channel for each of the amp dittos - like from the Okto Research dac8 PRO. This to some can bring into question whether a theoretical lack of overall signal symmetry of the DAC channels may have an effect on perceived sonics vs. only using 2 DAC channels that are then branched out on the output side of the digital crossover. I gather it’s in the splitting hairs department, but I have no experience to speak of here - not via my own setup, that is. Regarding setting filter values good advice has been provided already. I’d experiment with steeper slopes than 4. order - myself I use 36dB/octave L-R throughout (BW slopestyle on the subs HP). Does the dspNexus use linear phase filters (FIR)? If not it’s not an issue, as I see it. In any case I gather you’ll be able to get even better integration between you sub and main towers fiddling with delay, although you may come about this by simply moving them back and forth to each other the way you've positioned them. With my speakers we used nearfield measurements of the MF/HF horns to set precise filter notches and make a light peak suppression. On top of that the real work was getting the delay right - not least between the woofer section of my main speakers and the tapped horn subs, where the "origin" of the front wave is somewhere inside the horn path, and not simply on the cone backside exposed at the mouth. With the tools at your disposal already I’d say you have a very good outset for interesting results. |
@erik_squires LOL @jaytor I believe the Trinnov Nova retails for about $3500 for 2 channels and $500 for each additional pair of channels so $4500 for a 6 channel unit. I view digital crossovers, room correction, time domain corrections and amplitude domain correction all very related. Trinnov units do more than simple digital crossovers. It maps the room and builds filters so Your drivers work in Your room. BTW, Nice system. It's somewhat akin to our Apollo system being light membrane technology and OB. Cool 300B amps. We typically use 300B mono amps in our showroom. During development we have gone through passive crossovers, analog active crossovers and several DSP systems. IMHO, you are on the right path going with digital crossovers. High quality room correction is something to seriously consider, IMO. |
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. |
Minidsp Flex's are way better than you think. You can use two 4 channel out ones ($500 each) in parallel and get 8 analog channels out with both digital and analog inputs.....I read that these newer units are using Burr Brown PCM1795 DAC chips....not confirmed. These units run at 32 bit 96K unless you are using the option Dirac thang which operates at 48k. The new Flex units run at higher bits and have better distortion, etc. than most of the older stuff. Built in digital volume control and remote with several presets. Here are some measurements: https://www.audiosciencereview.com/forum/index.php?threads/minidsp-flex-review-audio-dsp.30804/ |
