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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).

128x128jaytor
deep_333
1,563 posts
 

The minidsp SHD (2 way digital xover) uses an ESS 9028 DAC chip......pretty good. The Audiophile Junkie (see his Youtube channel) uses this Minidsp SHD in his super system. I posted this on a couple of other threads.....but I cannot stop talking about this....so here goes again.

I have been quietly following this thread. have a feeling that the OP will be thoroughly disappointed with the minidsp SHD since he appears to be used to a Denafrips dac and whatever preamp he’s got.

For my attempted application, i tried to replace the Denafrips Hermes+Venus and a Yamaha C5000 with the minidsp SHD in pursuit of an active crossover. The SHD is awful in comparison and i just got rid of it.

To each his own....(with the theory crafting n all).

avanti1960
1,505 posts
 

I would be willing to bet that most active speakers with DSP still have some degree of passive crossover networks prior to the electrical connections on the speaker.  many drivers require a simple impedance flattening or notch netwok to rid the driver of response peaks. 

if your your active drivers need impedance flattening, notch filters or if the speaker has baffle step compensation you are fighting an uphill battle trying to use only DSP to address those issues. 

 

erik_squires
16,382 posts
 

if your your active drivers need impedance flattening, notch filters or if the speaker has baffle step compensation you are fighting an uphill battle trying to use only DSP to address those issues.

 

@Avanti1960, having built both, I can say this is not at all the case. In all cases, impedance flattening circuits such as a Zobel, increase power required for the sake of making the crossover work closer to an ideal state, like it would with a resistive load. I can categorically state this is completely unnecessary with a DSP based amplifier and crossover. It’s one of the major benefits of designing active speakers that you can ignore the impedance of the drivers.

Another way to say this is that in a passive speaker I only care about impedance flattening because of the effect rises and peaks can have on the frequency response. With DSP, any such issues I can deal with directly in the EQ.  THe point is moot though because with an excellent plate amp the impedance curve of the drivers just doesn't matter (so long as it's high enough).

There are hybrid speakers, which use both active and passive crossovers but I think these are becoming rarer with the common availability of 3-way plate amplifiers. IMHO, and not all speaker designers will feel this way, there’s no upside to a hybrid system if I can go fully active.

The baffle step compensation you reference is a frequency domain issue as well which is quite easily dealt with by a DSP EQ instead of with additional passive components.

Another great advantage for the designer of a fully active instead of a hybrid system is the ability to digitally delay each driver independently and achieve a quasi point source output with high order filters giving you most excellent on and off axis response which you’d have trouble with a hybrid.

The flexibility of a DSP based crossover sometimes causes bad choices though, such as picking bad sounding or poorly matching drivers and then hammering them into shape with EQ, as well as using global EQ to fix bad crossover choices.

You sound ready to take the next step in building speakers, so I really hope you get excited and build some for yoruself soon, either passive or active.

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