“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?
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.
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.
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.
