Multi-amplification and Active Crossover

[JackD201]

I'm agnostic when it comes to DRC even if analog is my preferred medium. If I were to go active XO it would be with the DEQX. I've spoken with Mr. Langford about his units. The thing is the XO is the easy part. Problem with analog active XOs is that settings can go awry when you clean the suckers not much peace of mind there. With a digital solution you have your settings file and you're all good, gotta love being able to back things up. Then there's driver correction.......

The rule of thumb is to get your room as good as you can get it so your DRC needs to do less work. Sounds logical to me. What most people don't know about SOTA passive loudspeakers is that there's more to the XOs in there than just chopping up frequencies. The closely guarded parts are the passive driver correction networks some of which include circuits that keep impedance as flat as possible. Not so long ago manufacturers didn't talk about their XOs, in a crowded market however that has changed. Driver correction is what I would really be interested in in an all active system. The fallacy is that if you get rid of the passive XOs all is peachy. The fact is that if your speaker has correction circuits in your XO and you bypass these you've got a heck of a lot of work to do, an XO that can do that job and you'll need a quiet open space to measure and program the said corrections. The DEQX manual gives a nice rundown of the procedure. Aside from lugging your loudspeakers outdoors it pretty much does everything for you. Nice!

Recently I've been tube rolling just my Mid and Treble amplifier. No other changes. What I observed is in line with what Tom Danley and Mark Seaton have been saying about subwoofer "speed". It ain't the subwoofers! Switching between Mullards, Telefunkens and Valvos it became clearly apparent that so called "speed" and "punch" came from much higher up in the range. Conversely one has to wonder just how attuned we are to changes in a narrow mid bass region and thus wonder how much one really has to spend if all you're after is a stiff amplifier. Like I said in the other thread quality, in my case where I am passively, horizontally, tri-amping takes a back seat to having input sensitivities lined up as close as possible because this will allow consistency over a wider amplitude range and not get you stuck at a few volume settings where the system hopefully gels. I reckon we will be to bothered far more with the non-linearities than we would be about the slight differences in mid bass only quality. I'm betting I could get away with a Crest or Crown amplifier with attenuator controls for mid-bass duty, it just wouldn't look as cool

This brings me to why I don't actually do it. I mean I do have an RP-1 that does 2+2. It has proven itself to hoodwink many a listener into thinking that the LPs being played were never ADC'ed, processed then DAC'ed. The Midbass amps are bought and paid for and since they are 4 years old I'd have to sell them for a lot less than their performance should dictate. No thanks! The short answer is that I don't have to. I am wasting electricity I guess but with Class A amps up top and A/AB amps that run the first 40+ watts in Class A that's a given. I also save on a pair of interconnects LOL.

Now why did I do what I did do? Short answer: big room. The M2.2 alone could blow the roof off, the M1.2 alone sounds strained when I get frisky but otherwise has a superior midrange and superior highs. So I married the two. Best of both worlds

 

[treitz3]

BTW, although I can sympathize with the idea when carried by an expert with the proper resources, IMHO none of your arguments seems to warrant " Much better sound " than the passive option. How would you check for coherency of flavors between amplifiers in such a system, as you suggested for the active X2? Using empirical knowledge about their sound type or measurements? Please note that I have nothing against such projects, but as I think that Audiophile resistance to them is well founded and very reasonable, I should support my point.

Hello, microstrip. I have been pondering going active or upgrading passive for some time now. Different amplifiers bring different things to the table. Both positive and negative. Upgrading the passive can bring from experience a considerable change to the sound scape and overall pleasure. My question would be....where and at what point would one decide which would be the best choice?

 

[Mark Seaton]

I run a set of active mains in my HT. It's a 4 way set-up with pro drivers. Lots of raw power with quite a bit of finesse. I also have 3 pairs of Biamp only speakers set-up in rotation in my stereo rig. I am a big active and biamp fan and from experience it really pays to do your homework. Yeah active is great and all however it can be very difficult to get it right. If you go this way you are going to need measurement capability to properly dial things in.

Rob

Agreed. This is why I think that for all but a very few, active should be an engineered solution, not a DIY one. This is also why it has failed to catch on with audiophiles, even as it has taken over pro audio. It takes away a huge chunk of what the hobby is all about.

Tim

Both points above are right on the money.

The best results come from a fully engineered solution, but most enthusiasts want to plug-n-play with various components. A passive speaker makes it easy to lock down a handful of variables from the owner and maintain some integrity of the design. Different characteristics of audiophile amplifiers can easily be significant enough to create readily measurable and audible changes, and that assumes we can get the gains matched to what the designer intended. Knowing just how sensitive we are to broad band response changes of well less than 1dB, this could get very frustrating for anything more than crossover below 100Hz.

Of course the best answer would be to allow the owner the room to tinker and make changes to the sound with various response shapes or other integration differences. Playing with products like Tact and Trinnov are a good example of this, where most will find that they can make much bigger changes with small tweaks to the response or other settings which are much more significant and beneficial than most component changes.

Of course we then circle back to the reality that crossover execution and driver integration in any well designed loudspeaker goes way beyond a textbook high and low pass filter... When designing a passive speaker I make very different design choices than for an active design, as the behavior of the filtering has to compliment that of the driver elements.

 

[Robh3606]

Sometimes I feel I would (also) be a happy man on that side of audio.

Then you should give it a try. It's a lot of fun and you learn a lot when things go well and usually even more when they don't. If you like hands on and challenges it can really be quite enjoyable.

Rob

 

[RUR]

Of course the best answer would be to allow the owner the room to tinker and make changes to the sound with various response shapes or other integration differences. Playing with products like Tact and Trinnov are a good example of this, where most will find that they can make much bigger changes with small tweaks to the response or other settings which are much more significant and beneficial than most component changes.

Say Hallelujah! Not to mention compensating for FR variation in recordings resulting from lack of standardization in the mastering process.

 

[JonFo]

I strongly believe in the power of total system design as a means of achieving he best. That means from the room on down and through every element of the system, designing and implementing to achieve a coherent whole. It is extremely involved and time-consuming, never mind expensive if using quality gear.
Few audiophiles have the combination of engineering and technical chops to pull this off, and I fully understand as it is a major commitment of energy and money to building a one-off just for oneself.
Sort of like expecting a writer to develop their own word processor / document management solution.

But, for those that are interested and willing to invest, it can deliver outstanding results.

As a fan of large electrostats, rolling my own crossovers and discreetly amplifying every driver made a significant difference over stock passives. But that required training and lots of experimenting guided by measurements. Here’s my post on ‘roll your own’ on this forum that outlines what I’ve done in my rig, or check my sig.

Friends do ask me if they should go down this route, and my first question is whether they have the interest (and time) in really learning the many skills required to design, implement and support such an endeavor. If not, then I steer them towards integrated designs and encourage them to use the DRC to its full potential.

 

[microstrip]

Then you should give it a try. It's a lot of fun and you learn a lot when things go well and usually even more when they don't. If you like hands on and challenges it can really be quite enjoyable.

Rob

Rob,
As pointed by other members, the key issue is time. If we do not have the time, best keeping away from it - an unfinished project is really frustrating. And all the nice DIY suggestions we find in WBF are enough to keep someone busy at full time for years!

 

[Robh3606]

Rob,
As pointed by other members, the key issue is time. If we do not have the time, best keeping away from it - an unfinished project is really frustrating. And all the nice DIY suggestions we find in WBF are enough to keep someone busy at full time for years!

As far as I am concerned life is a DIY project. There is no time table. Only the one you impose on yourself. Took me 2 years to finish my XPL-200's. I couldn't get the drivers. Was well worth the wait. If you don't have the patience??

Rob

 

[fas42]

As far as I am concerned life is a DIY project. There is no time table. Only the one you impose on yourself.

Rob

Hear, hear!!

As far as overall system design is concerned, there are at least two approaches. That expounded by Jonathon I would term the hard way, because here what one is doing is juggling the mix of subjectively audible distortion to achieve the most pleasing result: a little less of one colouration, a touch more of another; it's fine tuning, a balancing act, of a very complex stew of auditory flavours.

The other way is to eliminate the impact of audible distortion, by reducing it to a level that then allows the benefits of psychoacoustics to kick in, the ear/brain is getting enough clean information for the mind to be able to "switch off" from the colourations, and the musical message of the recording overrides all the otherwise distracting audible sounds. Just like live music does, or should do, if it's performed well enough ...

Speaking of which, had an interesting musical experience yesterday: went to a get together organised for seniors, with entertainment thrown in, in a decent hall. First up, a female singer with operatic capability accompanied by piano, no electronics in sight. This was excellent, a chance to experience the renowned "live sound"! And it was pleasing, she had a big voice, capable of generating those powerful, piercing notes that seem to reverberate through your skull; I felt comfortable comparing that sound to what I was getting at home ...

Then, oh dear(!!), a choir accompanied by a miserable, "professional" Peavey sh!tbox, sourced from digital. This is the sort of utter crap foisted on people which puts people off audio systems in general: zero treble, bass, a frequency response with 20dB peaks and troughs all the way along the spectrum, at times it was almost impossible to recognise the melody, the beat was so mangled you often felt the choir was off time. People were desperately waiting for the agony to be over, thinking fondly of the root canal sessions from previous years to calm them down ...

Then relief! A demonstration of dance styles, accompanied by a plastic boombox straight out of Wal Mart. Yes, the electronics were clipping and compressing quite a bit, and the enclosure rattled badly with sustained bass notes. But it was music!! The sound made sense, it did its job well enough so that you just tuned in what people were doing on the floor, and the experience was enjoyable.

This is what gets me many times about so-called "professional" sound: often it seems that its main intent is to beat the listeners' ears into submission, to prove that the gear has enough balls to handle the occasion without showing weaknesses. The last item on the agenda is to create pleasant sounding audio it often seems ...

Okay, rant off, sorry!!

Frank

 

[JonFo]

here is some relevant input from Roger Sanders (ESL and Amp designer extraordinaire) on the topic of active vs passive crossovers.

"Passive crossovers have dreadful performance. This is another extensive topic that I cannot address adequately in this interview. So just allow me to summarize by saying that passive crossovers have the well-known problems of phase shift, hysteresis losses, group delay, inadequately steep crossover slopes, and distortion. Less appreciated is the fact that they insert inductors, capacitors, and resistors between the amplifier and the speaker's drivers. This isolates the woofer from the amplifier and prevents the amplifier from having tight control of the driver. Or to put it another way, the damping factor of the amplifier is degraded by passive crossovers.

Since it is essential to use the amplifier to control the woofer, the amplifier must be connected directly to its driver without any intervening crossover components. Therefore electronic/active crossovers are essential to obtaining good integration. The amplifier must have a high damping factor. This excludes the use of tube amplifiers for driving woofers because their output impedance is too high. Powerful, well-designed solid state amplifiers have incredibly low output impedance (typically less than 0.1 Ohm), and massive current flow capacity, so they have the high damping factor and power needed to really control a woofer.

It is necessary to use electronic/active crossovers to achieve the best from any speaker system. I continue to be amazed by all the speakers on the market with passive crossovers that claim to be "reference" quality or SOTA systems. The truth is that electronic/active crossovers and multiamplifier systems are superior to any passive crossover system. All speakers will be improved with the proper use of electronic/active crossovers. So any speaker that uses passive crossovers simply cannot be considered the finest available. I am unwilling to compromise and so do not use passive crossovers in any of my current speakers.

There are many diverse types of electronic/active crossovers with many different features. Also, both analog and digital electronic crossovers now are available. I consider digital crossovers to be one of the greatest advances in modern audio. They offer features that I have wanted crossovers to have for years, but which were unavailable. "

From this article: http://www.dagogo.com/View-Article.asp?bShowUnpublished=&hArticle=991&PageOfArticle=1

 

[Keith_W]

New member, first post.

I converted my speaker from passive to active. In the process I bought a DEQX HDP-3 and a Marchand XM-44 crossover. The DEQX was intended as a permanent solution, however there were a few issues with my system:

- anything apart from a low to moderate volume input from my preamp would cause the inputs on the DEQX to clip,
- the output from the DEQX was insufficient to drive my power amps to full volume

Both issues supposedly can be fixed by adjusting the sensitivity and output of the DEQX by opening the lid and adjusting some jumpers (an undocumented feature). I adjusted the jumpers but only gained moderate improvement.

Furthermore:

- contrary to what many people claim, the DEQX is not as transparent as is made out to be. There is a massive loss of resolution and dynamics. Instruments sound smeared together and the soundstage is noticably smaller. I have a Playback Designs MPS-5 - the DEQX made it sound like a Samsung.
- the auto function on the DEQX produces unbelievably bad sound. A steep learning curve is involved, something I am still working on.

The DEQX does bring quite a few benefits. I used it for a while as a development tool before ordering a Marchand crossover. I could simulate the effect of various crossover points and slopes with the DEQX and see and hear the result. I simply copied the best settings to the Marchand. The improvement was breathtaking.

I know that my Marchand can not correct phase or group delay, but it plays nice with my system and sounds great.

For me, the issues with clipping and insufficient drive were real deal breakers. But even if I didn't have those problems, the unit still kills dynamics and resolution. I am convinced that any digital crossover is not a contender in any high resolution system. They are valuable development tools, but the real solution is an analog active crossover.

 

[fas42]

- anything apart from a low to moderate volume input from my preamp would cause the inputs on the DEQX to clip,
- the output from the DEQX was insufficient to drive my power amps to full volume

Both issues supposedly can be fixed by adjusting the sensitivity and output of the DEQX by opening the lid and adjusting some jumpers (an undocumented feature). I adjusted the jumpers but only gained moderate improvement.

Furthermore:

- contrary to what many people claim, the DEQX is not as transparent as is made out to be. There is a massive loss of resolution and dynamics. Instruments sound smeared together and the soundstage is noticably smaller. I have a Playback Designs MPS-5 - the DEQX made it sound like a Samsung.

It sounds like you are only using the DEQX to process analogue input. Is there any reason you're not sending the MPS-5 digital output to the DEQX, then routing the the output of that through your preamp?

Frank

 

[Keith_W]

It sounds like you are only using the DEQX to process analogue input. Is there any reason you're not sending the MPS-5 digital output to the DEQX, then routing the the output of that through your preamp?

Hi Frank, I don't do this because the DAC in the MPS-5 is far superior to the DAC in the DEQX. Also, the DEQX was designed as an active crossover - i.e. it has multiple preamp-level outputs to control multiple power amps. It has to be inserted after the preamp.

 

[fas42]

Hi Frank, I don't do this because the DAC in the MPS-5 is far superior to the DAC in the DEQX. Also, the DEQX was designed as an active crossover - i.e. it has multiple preamp-level outputs to control multiple power amps. It has to be inserted after the preamp.

Well, this doesn't make sense to me. As you're using the DEQX now, you have D/A in the MPS, then preamp, then in the DEQX, A/D, digital filtering and a last round D/A before it hits the power amp. 3 digital to analogue transitions, I'm not surprised you're losing quality ...


As an experiment, how about MPS digital to DEQX, then you only have a single D/A, in the DEQX, then preamp straight to power amps. Yes, I know you losing the MPS D/A, but what's the point if it still goes through the DEQX D/A anyway? At the moment this is equivalent to a 3rd generation tape you're playing back ...

Frank

 

[Keith_W]

Well, this doesn't make sense to me. As you're using the DEQX now, you have D/A in the MPS, then preamp, then in the DEQX, A/D, digital filtering and a last round D/A before it hits the power amp. 3 digital to analogue transitions, I'm not surprised you're losing quality ...

Actually, the recommended configuration for the DEQX is:

digital transport -> DEQX -> power amp

HOWEVER, given that I have an SACD player and a turntable, I was forced to use the ADC on the DEQX:

(source) -> preamp -> DEQX -> power amp

At the moment, the DEQX is NOT in the main signal chain. The main signal (from 80Hz and up) is purely analog. It is hard to explain, I need to draw a diagram. Perhaps in my system thread.

 

[FrantzM]

Hi

I did ask the question in your system thread. I see your point now... Your experience with the DeQX is interesting and different from that of another member (Terryj), also from Australia IIRC. Another uses the TaCT in a system with VTL preamp and amp (Marty). According to Steve Williams , here, it is one of the best , if not the best system he's heard. I take your comment on the DeQX to heart though as my next move will likely be multi-amp and the two crossovers in the lead are the DeQX and the TaCT.

 

[Keith_W]

Frantz I will get around to answering the question in my system thread. I know TerryJ well, but I have not heard his system. You have to understand that he comes from what I call the extreme fringe of objectivists. He uses a $100 DVD player as a transport, feeding digital into his DEQX, and using a whole bunch of secondhand amps to power his speakers. By all accounts it sounds good, but ... you never know how good a piece of equipment is until you get to compare it against something else in the same system.

In my system, I have the ability to compare my DEQX against a straight wire. If the DEQX is really transparent, then doing an ABX, level matched, against straight wire would be a fair test? I have done this comparison and repeated the experiment for several visitors and they all heard the same thing. The DEQX was simply set up as an ADC-DAC and performed no processing on the sound. It would simply take the signal, convert it to digital, then convert it to analog. The ONLY processing was to level match the output to the cable. Compared to straight wire, the DEQX destroys the sound.

The purpose of doing that experiment was to do a cost-benefit analysis. What was the cost of the ADC versus the benefit of all that digital correction? This is the answer:

The cost comes from the ADC. If you feed the DEQX a digital signal, your cost would be far lower. Using the ADC destroys resolution and dynamics. Regardless of how it measures or what specs it claims, there is no arguing with the audible result - everyone could pick it and describe exactly the same thing.

The benefits are well documented - speaker and room correction, and a level of integration that is simply not possible with any other technology. The DEQX is a very purist solution for those of a particular philosophy - namely those who only listen to 16 bit audio, have no analog sources, and feed the DEQX digitally.

Obviously, the cost-benefit analysis will be different for different people, different systems, and different philosophies - which is why I am not exactly bucketing the DEQX. It is a very good unit, but for my system - it doesn't work.

 

[fas42]

Actually, the recommended configuration for the DEQX is:

digital transport -> DEQX -> power amp

HOWEVER, given that I have an SACD player and a turntable, I was forced to use the ADC on the DEQX:

(source) -> preamp -> DEQX -> power amp

At the moment, the DEQX is NOT in the main signal chain. The main signal (from 80Hz and up) is purely analog. It is hard to explain, I need to draw a diagram. Perhaps in my system thread.

Yes, I'm a bit confused: if you're using the DEQX to split the signal between the amps for the active setup, then I can't see you getting away from 3 analogue, digital transitions.

The recommended setup is the right one to my mind, I'm surprised that it's not possible to use the DEQX to switch sources, SACD and TT, after a phono stage on the TT, of course.

Frank

 

[Keith_W]

Yes, I'm a bit confused: if you're using the DEQX to split the signal between the amps for the active setup, then I can't see you getting away from 3 analogue, digital transitions.

Given that this discussion is of my system and how I have implemented it, perhaps we should continue discussion in that thread?

The recommended setup is the right one to my mind, I'm surprised that it's not possible to use the DEQX to switch sources, SACD and TT, after a phono stage on the TT, of course.

It is not possible. The DEQX only has one set of analog inputs. You would need an input switcher. In other words, a preamp

 

[fas42]

In my system, I have the ability to compare my DEQX against a straight wire. If the DEQX is really transparent, then doing an ABX, level matched, against straight wire would be a fair test? I have done this comparison and repeated the experiment for several visitors and they all heard the same thing. The DEQX was simply set up as an ADC-DAC and performed no processing on the sound. It would simply take the signal, convert it to digital, then convert it to analog. The ONLY processing was to level match the output to the cable. Compared to straight wire, the DEQX destroys the sound.

Keith, I take it that the DEQX replaced the IC between the pre and power amp for this test. To my mind this is not a fair comparison, because the volume adjustment would have varied the level of signal input to the ADC, probably most of the time to less than optimum.

Maybe you have done it this way, but a better assessment would be between the analogue out of the MPS and preamp ...

Given that this discussion is of my system and how I have implemented it, perhaps we should continue discussion in that thread?

OK, continue on that thread ...

Cheers,
Frank