For my filers, I spoke to Bruce Thigpen at Eminent and pretty much copied what he suggested. For his next gen speakers, he is using DSP, so is aware of what works best. Yes Audio Weaver is what was used to implement the filters. I’m not aware of any other option that is compatible with the DSP Nexus.
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).
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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. |
@jaytor wrote:
It will be interesting to learn of your findings when finally bypassing your main speakers’ passive crossovers for a fully active configuration. Not many do this on this forum, i.e.: switching their passively config. speakers to active ditto, nor those who start from scratch with speakers that came sans passive crossover to begin with. You don’t just buy speakers at hifi retailers without passive crossovers as an intended package for outboard active config. - except the rare likes of JBL M2’s, Sanders Sound and a very few others - indeed for that you’d typically have to convert your passive speakers into active, go the DIY route or pro segment. The latter two is what I did with DIY (shared) sub designs and pro cinema speakers intended for active config. My main inspirational source for going active is a friend of mine who converted his passively config. S.P. Technology Revelation speakers to active ditto, and as it eventually turned out that switch was quite the, well, revelation. The passive S.P. Tech’s were power hungry beasts as few and developed on the Crown Studio Reference I amps, which are very powerful with a crazy high damping factor in the lower regions. However very few hifi amps can muster up that kind of speaker control and power delivery, and you’d wonder why the S.P. Tech’s didn’t come with the mandatory recommendation of being paired up with the likes of Ref I amps they were developed on. The bottleneck though proved not only to be about power requirement, but that bypassing the passively crossovers entirely - upon thorough implementation to active after a lengthy process - simply meant a massive upgrade in overall sound quality. Initially it was still very obvious that going active was the right thing to do - that was apparent from the very get-go. Myself I’ve now used about two and a half years steadily upgrading my Xilica DSP-based, actively configured speaker setup in stages, lately only a few weeks ago. Detailed factory specs from EV manuals were initially involved to get a bearing on the crossover point (2-way main speakers, + subs) and where to place some of the filter notches; soon after near field measurements came to the aid for more precise adjustments, and what followed was a bit of restructuring acoustic room treatment, main speaker placement, some horn damping, amps experimentation (using similar amps top to bottom is a must), and eventually the lengthy process of making filter adjustments by ear mostly involving delay and subtle PEQ corrections. Gain structure, filter slopes and types (36dB/octave L-R here) and crossover points are usually found and settled on fairly early in the process, but lately we found some rather critical improvement in overall coherency with asymmetrical crossover points over the main speakers and delay reconfiguration incl. the subs as well. Some may find it an impediment with the active speaker approach and setting filter values by yourself that it’s likely a never ending process, but once you settle on the rougher structure of your speakers, amps, source, cables and overall rudimentary implementation, what follows is the process of fine tuning all that into a progressively coherent whole in your acoustic environment in ways of specificity and accuracy that a passive speaker setup simply can’t equal. It’s not that much about swapping hardware any longer and being on that merry-go-round to find the perfect matches component-wise, but rather seeing the gains that can be made from a much better outset with a DSP acting as a digital crossover, and the many options that are offered here implementing the existing hardware components. To me at least that makes much better sense. |
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