Considering the option of "DSP speakers"

“Go home or go big.”

I notice occasionally somebody would come in here and say something to the effect “go active” or “go DSP” or something as cryptic as “FIR”. I am more or less old fashion – big caps, big coils, and stuffs. But with all the DSP “come-ons” recently so I went lookup “what if I do DSP, what would it take, how much would it cost” … something like that. I also looked at some of the commercial self-powered speakers to see how they do it.

First of all, “DSP” is not bad as some would automatically think of it. It's the “cheap DSP” that is bad. Let's say it you were to do it, what are your options?

  1. The most simple way is to buy a “miniDSP 2x4” which is about $100 bucks. It has two analog RCA inputs, one for left and one for right channel, and four outputs, one for tweeter and one for woofer for each channel, and 2 channels as a 2way. You can download the software plug-in which is pretty simple to use for xover filter works. If you want 3way or 4way speaker, you just need to purchase two “miniDSP 2x4” modules – one module for left and one for the right speaker. The problem is you still need to purchase two 2-channel amps (or 3 or 4) that are small enough to fit inside the speaker cabinets. Most people would go with class-D amp since they are affordable and small enough to fit inside the speakers. Or if you already have an existing receiver with 7-channel amp for example, then you can use that for your amplification, albeit outside the speakers. The first problem is you still need an pre-amp and take the pre-amp output to connect to the “miniDSP” RCA input. But the REAL problem of the “miniDSP” is it would have to convert the input analog to digital by its built-in ADC to perform DSP then converting it back to analog using its built-in DAC, so it's kind of a double back and forth. For only $100, I guess the quality of the ADC/DAC probably have to be compromised. I am under no illusion to think a $100 unit will perform the same way as a $7K dCS unit. But for a low cost solution, I guess this is acceptable and if that's all you want. Personally, because of the serious compromise in sound quality, I would only use this setup for xover development.

  2. The next thing to improve is to eliminate the built-in ADC stage. Luckily, miniDSP has something called “miniDSP 2x4 HD” which is about $200, which can either take the Tos-Link digital output of your CDP or it can also take the USB output from your computer. For the Tos-Link input, I am not sure how you can control the volume control (unless your Tos-Link source has volume control), but at least you can use the USB input and control the volume from your PC or your streaming device. But even without the ADC stage, you you still have to deal with the DAC stage because the “miniDSP” still has to convert the digital back to analog, and again, being only $200 in cost, I have to assume the quality of the built-in DAC is somewhat compromised, but this time at least, you eliminate the build-in ADC stage. And same as in #1, you can either purchase a class D amp and install it inside the speaker cabinet, or using an existing 7-channel receiver. The problem with the “miniDSP 2.4 HD” is you can't buy another one to do 3way or 4way and also use the digital input, because you can't “split” the USB into two, and since the USB protocol can only allow one master, one slave at any one time, you can't “split” them. And if you use the “Tos-Link” input, I guess if your transport has two Tos-Link outputs (or your reciever has some pass-through capability” then you can purchase a second “miniDSP 2x4 HD”, then you can do 3way, or 4way speaker as long as you can provide enough amplifications.

    (BUT make sure the digital “Tos-Link” output does not have any difference in latency or delay within them. It is not something that can be sure of. If there is delay or latency between the two Tos-Link, it will definitely affect the sound since the timing of the left and right channel won't be the same.)

    Or you can just purchase a “miniDSP 2x10 HD” which has 10 outputs and has one digital input but the “2x10 HD” will cost about $500 but you only need one digital input so that would eliminate any possible latency issue. But still your digital source needs an ability for volume control to act as a pre-amp. I think if you have a PC connected to the “miniDSP” module all the time, then you can control the volume from the “miniDSP” software plug-in, but I think the point is not having any PC plug-in at all, so you can independently control the volume even without the PC.

  3. At this point, if for whatever reasons you hate the “miniDSP” corporation, you can simply purchase a set of Hypex modules, either 2way or 3way from Madisound and it has everything you need, including a built-in class-D amps and DSP processing. They are small enough that you can build them into the speaker cabinets. You still need to provide some kind of pre-amp control though, and just as with “miniDSP”, it takes analog RCA input and Tos-Link input and it also has a Tos-Link pass-through so you can connect that to the second speaker. This would eliminate the ADC stage, but you still have to deal with the built-in DAC. And of course you have to be mindful of the class D amp. Looking at the amp, it has a few tiny capacitors for power supply bypass compared to some huge caps on my separate amps and everything looks puny :-) And these things are not that cheap. A 2x4 module is about $500 and you need two so total is about $1000. That's definitely not CHEAP! (And that not including the speaker drivers).

So far, everything is simple enough. The only real reason to worry is with the built-in ADC and DAC, and therefore the sound quality could be compromised, but if you're looking at an affordable solution, then I guess all is good or good enough. Again, personally I wouldn't go with either 1, or 2, or 3 either unless I use them purely for my own speaker xover development works. Some commercial DSP speaker only use class A/B amp for the tweeter since the tweeter is sensitive to the noise of the digital amp.

4.  So what if you want to go DSP, but still want some really good quality sound? First off, at least you have to eliminate the built-in ADC/DAC all together. Use external DAC. Use external quality amplification. Luckily, miniDSP does offer a nice little “miniDSP NanoDiGi 2x8”, which does everything in digital domain. It has a Tos-Link input and has 4 digital SPDIF channel outputs (or 8 channel total). I believe miniDSP also offers a balance version so all inputs and outputs are balance, but being digital it's not that big deal. There is still a concern of the jitter of the SPDIF outputs and that can affect the sound quality on the downstream equipment. MiniDSP does offer more expensive “all-digital DSP” processing solutions but it costs quite a bit more (about $500 I think).

But still you have to provide some type of external DAC and amplification. At this point, things start to look a bit complicated (which ironically DSP promises the opposite). For a 3way speakers, you need 6DAC's, a 6-channel amplifications. There are off-the-shelf purely DAC modules that can provide multiple channels, and of course the good one will cost quite a bit of money. Or if you have purely digital amp, that is class-D amps that take the SPDIF input directly so you can actually eliminate the DAC stage all together. Just plug the SPDIF outputs of the “miniDSP” outputs directly to the amp. Again, it's the cost again. And I wouldn't be surprise if you want a better SPDIF amp, the more it will cost. Another practical thing to consider is how will these amps will fit inside your speakers or if you decide to have all the amp outside? Finding a plate SPDIF powered amp that will fit inside the cabinents can be difficult – a practical consideration. I can already imagine a bunch of cables criss-crossing!

At this point, it's no longer a straight forward “plug-and-play” but you probably have to do some research, but still it's probably not that bad.  As for sound quality, as for the performance vs cost trade off, if you just go with some run-of-the-mill external DAC, class D amp, then it why just go with option 1, or 2, or 3 and save your money.  Sure you can get the best external DAC or amplifications but then again it all comes down to cost, and if you go all the way with these, I assume it will cost a lot of money and gets complicated indeed, which goes back to the beginning, that is , is it worth it? Then why not just go with good old analog? I think you can only go so far with “plug-and-play” off-the-shelf solutions though (unless you want to turn your living room into an equipment rack). Which leads to #5.

5.  I think truly to have good DSP system is if you go “Meridian” way, that is to go “BIG” and I mean it as both figuratively and literally. Figuratively, you really need to have some real R&D, a real lab, and hiring real engineers to develop the hardware from the bottom up and everything is custom made – from the digital stage, DAC and amplification and electronic xover works with the drivers at hand. Literally, “Meridian” was referring to some of the stuffs from Meridian and I think those are the only true high-end DSP speakers. And if you can develop your own hardware in-house, then you can scale up your design and in the process, save cost but having optimal performance. But this would exclude any chance of DIY.

I've also looked at some sub-$1000 DSP speakers, and Harman Kardon “Citation Tower” for about $3000 and Elac Navis floor stander for around $2500. Some of them actually uses only class A/B amp for the tweeter, and the class D for the woofer so I guess they realize the difference in amplification quality. Anyway, the only truly high end DSP stuffs that I've have seen only come from Meridian. The others I would characterize them as “life style”, and I am sure they provide good quality sound but I wouldn't call them high end – at least not at the same level as Vandersteen or Sonus Faber, B&W, or Magico.

Most high end speakers are still analog, And I think the main reasons why there are not many out there because it costs a lot of engineering money to develop a good system and only a few big companies can afford it. You can't just plug-and-play and call it high-end. Of the off-the-shelf stuffs I've seen, I don't think they are up-to-snuff. But I also think more and more will have some type of DSP in the future and that is just inevitable.

I like the hybrid approach a great deal.  While Vandersteen doesn't use DSP, the built in sub with EQ works really really well.

Another approach that works very well is the digital-only DSP. miniDSP has them also.  Lets you use any DAC as your source, but the signal it gets will be room corrected.

Andy, if you want to take full advantage of digital sound processing it helps if you have a unit designed for that purpose, a digital preamp. The best available now is the Trinnov Amethyst. If you want to bi or tri amp you would get one of their multi channel units. Less expensive are the Anthem units. You can do it with computers and programs but the problems come when you want to switch sources and if you are multi amping it helps to have a unified volume control. These units have their own test microphones and programming built in. They also have built in DACs. The Trinnov even has analog inputs. It is just a much neater way of doing things. If all you do is stream then the computer is fine.
I use a TACT 2.2X which is a digital room control preamp which you can program with a PC. It has the best bass management I have ever seen allowing you to switch cross over points and slopes on the fly with a resolution of 1 Hz. Unfortunately the company did not survive. The closest to it is the Trinnov Amethyst.
Andy, wow you did quite a bit of research on DSP. There is a difference between budget DSP and quality DSP. Also, there is basically straight up DSP as used for crossover functions and DSP with room correction. How you design a DSP speaker system with or without room correction can be different.

When using DSP instead of passive crossovers you are basically designing the speaker system much in the same way you would be using passive crossovers (except using multiple channels and specific amps) but with much greater flexibility and obviously in the digital domain. You would design the speakers around the drivers and cabinet to the desired outcome and use instrumentation to test and evaluate the results. Using DSP with advanced room correction can be different.

At this point our entire speaker line is DSP controlled and uses advanced room correction. We have partnered with Trinnov and supply the ST2 with our systems. We intentionally designed the Arion speakers for this arrangement. Our customer receives their Arion speakers with the DSP unit containing a basic setup just to start with. Since we typically don't supply all the amps (4 channels are required) the system must be configured to work with whichever amps are chosen. We don't pre-load any EQ or alignment into the DSP unit. All the EQ and alignment is done by the room correction system specifically for the customers room. Our method is somewhat open ended and unlike some other systems that force you to use their amps and have their systems preset with only some adjustments. We like the idea of letting our customer choose which amps to use. It's mostly about system/room integration.

Good quality DSP crossovers have many benefits over analog active crossovers, one of which is a greater potential for success. There has been much written elsewhere about active (analog or DSP) vs passive. Same benefits apply to DSP. Anyone considering DSP should strongly consider good room correction. 
The only reason I could see designing any dsp speakers without their own amplification would be marketing. Bryston was showing their dsp xover at axpona with their 3 way and their own amps, the xover was $13,500! throw in a couple 7b's and a modest pair of 3 driver 3 way speakers and you have the dumbest waste of money imaginable. 

SO far dsp loudspeakers do seem to be pretty expensive to implement and then nobody will want them anyhow. 
Take a look at the DSpeaker X4 as preamp.
Active digital crossover, incl phase/time domain alignment, for subs and room correction across 16kHz.
I use it in two systems with excellent results.