Sloped baffle

Just saw this thread. Wonderful to have so many knowledgeable folks chime in, plus the links to very good past discussions.

I'm certainly not up to par with my two cents here, but Psag might find it useful. Uli Brueggemann, the man behind Acourate DSP/DRC software, wrote this article on crossovers you are likely to find enlightening. It is in layman's terms: http://files.computeraudiophile.com/2013/1202/XOWhitePaper.pdf

Not sure what your system configuration is. Mine is based 100% on a computer server as source, which allows a neat approach - in my view, of course:

One way to achieve time and phase alignment is to use a multi-amped system (someone already said this above), having one amp directly driving a driver (no passive crossover used), and having a multichannel DAC and DSP software such as Acourate. Acourate allows to set digital crossovers and set time delays. So you can achieve time alignment without a sloped baffle.
Here's a great setup article http://www.computeraudiophile.com/content/556-advanced-acourate-digital-xo-time-alignment-driver-linearization-walkthrough/

I'm starting to go down this route, although I'm still coming to terms with the notion of the benefits of a time and phase aligned system where the amps are driven directly by a DAC (with the drawbacks of the latter) outdoing the benefits of my Lamm preamp driving the amp.

BTW, would like to ask a side question taking the advantage of so many knowledgeable guys reading this thread: following the above, my thoughts are of eventually replacing my speakers with DIY speakers using premium drivers, without passive XO, and enclosed in a DIY cabinet (I'm rather skilled at that). It seems premium driver (top Raal, Accuton, scanspeak, etc) can be had for relative low prices (compared to speakers that carry them). Does this sound like a good plan, or am I missing a significant issue??

Great thread!

Lewinski... great post. I was impressed by the various digital analyses and corrections that the software was able to effect. Hopefully, speaker manufacturers will be able to achieve greater time and phase alignment, driver linearity and low distortion by designing better X-overs. It may be that the best solution will be an active crossover that can effect the various functionalities that were the subject of your post.
...
After all, not everybody is a former NASA rocket scientist or a Steven Jobs/Bill Gates computer genius.

Thanks Bifwynne.

Not sure if you were implying I'm a computer genius. But to clarify it just in case: I'm certainly not!!! Not even very savvy, honestly! It looks a lot harder than what it is. I just have a dedicated server with JRiver and the Audiophile Optimizer running in it. The hardware is optimized. Amazing sound. And it was a set it and forget it setup.

Cheers!

what is your definition of "premium drivers"? Cost of the driver? Cost of a commercial speaker using this driver? The marketing hype surrounding that driver that makes you believe it must be the best?
From the little I know, some Scanspeak drivers are very good performance that would qualify for time-coherence.
Accuton drivers need not apply for time-coherence.
I don't know much about Raal.
Be careful how you choose your drivers - don't let cost be the judge - look at their freq bandwidth & where you intend to cross them over.

Bombaywalla,

Very fair point. Honestly, I have not done much research on drivers yet. I was trying to provide examples to show what I meant and used the brands that are usually mentioned in reviews as premium. I did look into their prices, and in a way I was think along the lines of price. What would be premium brands sound-wise?

BTW, I never thought about drivers not being time-coherent. What does that mean? I thought time misalignment was between/among drivers.

I have not even started looking into building a speaker. I am now thinking through / coming to terms with moving away from a nice digital and analog chain (Audiophilleo with PurePower going into a Metrum Octave, going into a Lamm LL2) and into a multichannel DAC driving multiple amps directly and using software for volume control. I'm sure many can relate to having second, third, and forth thoughts on such a move.

The benefit of driver time and phase alignment seems to be significant. The benefit of multiamping I believe is well documented, but the challenge is on the implementation. Digital room correction also makes sense to me.

After taking this plunge next step will be thinking which amps to get to drive my existing speakers. And later I will look into building my DIY speakers. Nevertheless I wanted to chime in here to provide a different approach for achieving time alignment.

BTW, yes, in a way this is similar to the Meridian path. But I do like tubes!!! So my idea is a SS or class D amp for woofers and tubes for midrange and tweeters. And I also have two power subs. But you made me remember about Meridian's approach. I will look into it. I believe they deliver a digital signal to the speaker and then convert it to analog inside the amp. I'll check if they have processors that deliver multiple analog channels, but I'm also wary of spending big on digital components considering it is not yet mature and hence evolving so fast.

As I said before, great thread!

Bombaywalla,

The DSP signal processing is touching your music signal in a very fundamental way in that the entire music signal has to go thru the DSP before you can hear it. Same deal with the passive x-over. But the difference is that you change the quality of the cap or the inductor or the hook-up wire & you can change the sound to your liking. It appears that it's not that simple with the DSP software - you cant go in there & change the code. Or, maybe I'm not thinking of this correctly?

I think you have it right; at least from my perspective. However, I don't have the skills to change caps or wire...so I'm basically stuck with what I get. Actually, software provides more flexibility here, in my case.

So, if I'm envisioning this correctly - computer digital out runs into the DSP software which breaks the audio signal into highs, mids, bass. You get 3 digital streams now. You feed these 3 streams into 3 identical DACs or 1 Pro quality DAC able to output 3 analog streams (one box would be better as everything sits in 1 chassis & has a better chance of being matched to the other analog stream). Then 3 analog streams into 3 power amps - you need to match these very well too: same input sensitivity, same gain, same sort of clipping algorithm, same dynamic headroom extension, same power output capability, same current source/sink capability.

Here I would say, not exactly. Inside the computer being used as audio server the DSP software runs as well. On the DSP software (eg, Acourate) you set up XO frequencies, slopes, delays, etc, and perform the driver measurements, do the adjustments, etc, perform digital room correction, and eventually get a sort of digital filter. Then you apply this through a convolver to the audio player software (eg, JRMC). Now the computer is outputting through USB several channels. Eight in my case/plan. A multichannel DAC, such as the exaSound e28 takes USB in and decodes into the 8 channels and outputs 8 analog signals. Simple 1-box solution!

Also the amps don't need to be identical. You adjust gain at the software level. Take a look at the article by Mitchco I linked before. It's an easy read and provides a nice view of his setup.

I have in the past toyed with the idea of multiamping, but always in the analog domain. It always seemed it was too cumbersome, needed too many boxes, and was creating new problems. This newer technology seems to be bridging that gap. Or maybe it's me convincing myself?

Thanks for the clarifications regarding driver time-coherency. Conceptually I understand it. My gut feeling is, though, that lack of coherency is at least one order of magnitude smaller than that introduced by passive XOs. Right? If so, most of the issue would be solved with said software/approach.

There is also some chatter on DEQX on computeraudiophile.com. Actually, I've been looking into it as well, along the lines of my posts above (waay above).

The DEQX HDP-4, the most expensive unit, has good DAC inside, 3-way crossovers, and digital volume control. And room/driver correction. What I researched was for use instead of my DAC and preamp, so getting the signal from my computer server and running 3 amps per side to drive speaker drivers directly, avoiding passive crossovers. I found a guy in Texas with very nice and expensive system, such as YG speakers, say he replaced a $30k DAC with it, so the DAC section must be good. He's using it in the same fashion I'm interested, so can't speak to the ADC section - but that has been clarified by Psag above.
He's only caveat was the unit only allowed for one subwoofer out and he's using two in mono but needed different time delays on each to address a room mode so he uses a Xilica unit for that.
BTW, he also uses Dirac room correction software on his server. That piece I don't fully understand why as the HDP-4 does room correction too...

The HDP-4 is very interesting to me. Where I start wondering if it is the best path is for people like me who only use a computer as server. In that case you could use a Lynx Hilo plus Acourate software to achieve the same, but for $3k instead of 5, or use an exaSound e28 plus Acourate for $4k and have 8 channels available (hi/mid/bass for L&R, plus 2 subs) and be able to time/phase align all of them.

But I realize the majority of users here aren't running servers as their main source. Yet the HDP-4 can take 2 analogue inputs and several digital inputs, so you could still connect a phono section and a CD transport.

BTW, Psag, how good is the HDP-4 volume control? When bypassing your preamp, what changes do you notice?

Roy,

Thanks for your fantastic contribution here. We can only hope for more really knowledgeable folks like you to take the time and educate us hobbyists.

On the 1st or 2nd page I posted about a way I was intending to get at this. I have, at least for this purpose, the advantage of having only an optimized computer as audio source. My plan is to use Acourate software on the server, a multichannel DAC, and independent amps connected directly to each driver, without passive crossovers. Acourate allows the use of a variety of digital crossovers, and allows for time alignment of the drivers. BUT it is limited to a single time delay between any pair of drivers, much like the limitations you describe for DEQX (which I previously considered too, but a needlessly expensive option if the only source is a computer).
Clearly this will not solve 100% of the problem - something I learnt from you. But what's your very educated guess: will it solve maybe 80% of the problem vs a non-time-aligned 3-way speaker?

BTW, would love to get your thoughts about this XO white paper by Dr Uli Bruggemann, the guy behind Acourate.

As of now I'm using B&W 804S. Obviously not time-aligned. Probably not even phase-coherent. So the setup described above would first be used with these speakers. And eventually I'm thinking of building my own speakers using top-notch drivers, the Loudspeaker Cookbook as guide. I'm a mechanical engineer and handy building stuff. Assuming I do a good job selecting drivers and building the cabinets...sounds like I'll end up with very good speakers in terms of bang for buck...what do you think?

Bombaywalla,

Not sure what to take away from your post. 1st order passive crossovers are better than any type of digital crossover? That would be in line with Roy's explanation. But I wasn't arguing otherwise...

I'll take as given that Roy's approach is the best one could hope for. My question to him is how close to that would my described approach get me.

Cheers!

Hey Roy.

Thanks for the thoughts again.

Thanks for pointing out that mistake in the paper, about aligning start times vs peaks. Seems something easily fixable by setting different delays in the software. So the software approach still is limited by all the previously mentioned aspects, but not an additional one :-)

I spent good time reading your website, particularly the development of the Calypso HD. Very interesting too.

In reality my system would be 4-way, as I have a pair of subwoofers I intend to continue to use. They are 12" Rythmiks in a sealed, DIY and very heavy enclosure. So below 80Hz I wouldn't need the woofers to get there, hopefully making their selection easier. Maybe an 8" woofer in a sealed enclosure does it?

I have by no means studied this at all so what follows has the goal of providing real-world examples rather than representing what I think might be best. I spent some time at Madisound.com to skim over the drivers they carry. These 3 woofers, non-metallic, from known brands. Sure, price was a simplistic way of focusing...I know it's wrong, but for this purpose...

Scanspeak Classic
Scanspeak Revelator
Accuton Ceramic

None of them is really flat down to 80Hz, let alone well below that. But they are quite flat to 100Hz, so the "problem area" seems to be rather narrow in the 80-100 Hz...hopefully not a huge deal.
Both Scanspeaks seem to be able to work well for a crossover around 500Hz. The Accuton maybe at 1kHz?
None showing wiggles on the impedance curve within these ranges.

The midrange was more difficult than I expected. VERY few drivers are flat within their expected range. Here are two looking good:

Accuton. This one looks as it could be used higher up, up to 5kHz per their recommendation.

SEAS. This one is a lot cheaper, but good on paper.

What's your take on ribbon tweeters? Clearly, you prefer non-metal dome tweeters, and non-ring-radiators. But why not ribbons? Or AMTs, such as Mundorf's? Their frequency responses look very good, and they extend well beyond 20kHz pretty flat...

I realize A LOT more thought needs to go into proper driver selection. But I am taking away that such selection is critical. Since I won't have the skills to design a proper passive XO, it could make sense embarking in all of this if the Acourate approach was good enough.

I won't get tired of saying it: thanks for the fantastic food for thought, and taking the time!!

Hey Roy.

Surely enough, I have a gazillion questions, but I won't keep asking! Well...not the gazillion anyway :-)

Thanks for the names of the publications worth reading. I am in the process of getting the first AES papers to get started. Being in Argentina doesn't help in sourcing!!

I do want to ask back about two specific comments you made:

1) why do you advise to cross over the subwoofers at 40Hz? Wouldn't the Classic Scanspeak driver listed above, for example, have an easier time if it had to reproduce down to 60 or 80Hz instead of 40?

2) you state "the Acourate approach is not right". But WHY? I'm following you other advise: to understand why? ;-)
Seriously, I realize it is not "completely" right, like with your passive network. But doesn't it get me closer to "right" than a middle of the road, non-time coherent passive XO?

I carefully re-read your paper on the Calypso HD development. I would say I studied it more that just reading. Lots of fantastic info there. I can see myself following your guidelines to build my DIY cabinets (plus what I hope to learn from the books, of course), and to get it mostly right in choosing drivers. But it would be just too arrogant on my part to assume I will be that good with XO design, and if that's the only path then it might become a deal-breaker for me. That would be a pitty!