'LGT' Construction Diary

[cph2000]

You have probably covered the topic some other place -
but could you please elaborate on how you control volume in your setup.

I would also like to know if you have tried doing your stuff using Vista and especially from Media center.

IMHO, The Media Center front end is a big plus when you have your familly using the system also.

I like your soundcard, but I think I will go for class D amps to save some enrgy

Thanks

[ShinOBIWAN]

Originally posted by m0tion
I see a real problem occurring with the center channels ribbon not being on the listening axis, what with ribbon's poor vertical off axis performance. Would you be tilting the tweeter upward a bit?

Good point motion. It did occur to me too.

If you notice I swapped out the larger RAAL for the baby one, the difference is a ribbon length of 14cm vs. 7cm, The little RAAL also now uses the foam deflectors as seen in the larger RAAL's. Alex promises that this now makes the design comparable to a 1" dome disperation in the vertical and a fair bit better in the horizontal.

The stand for the center could also be made a couple more inch higher to further bring it inline with the main drivers.

Center channel placement is very nearly always compromised but it might just work. From experience the large RAAL in the LGT's is more than acceptable off-axis when the deflectors are used. There's still plenty of HF content even stood up from a couple meters away, the little RAAL should be better.

[sq225917]

cph a decent switching amp will use as much as a linear a/b when sat in idle, the efficiency is greater when running, it's a bit of a red herring.

[ShinOBIWAN]

Originally posted by fgroen Here's another project that might need the input of someone who combines perfection with actually finishing projects.

The locals have been mucking around with it for approximately a century now...

Apart from that... impressive work Shin! I'm following your thread closely, although not posting a lot. Your stuff on PC based filters is very interesting. I'm using a DEQX myself, and am very pleased with it. For my it's hard to understand why people are still torturing themselves with caps and coils.

It is hard to argue with active but passive is still excellent IMO. Hardwork though!

[ShinOBIWAN]

Originally posted by terry j
I'd like to ask a few questions for my own understanding, if you don't mind Shin. And further to that, I suspect you will be the perfect guy to be able to explain it so I CAN understand ha ha.

I know that at some stage you too have used a deqx, and have now gone to a computer based solution.

(Please pardon my ignorance that follows)

From what i can gather from an earlier comment of yours, the current computer based solution you feel produces better results than the deqx, and if I followed you correctly that is due to the number of taps able to be employed??(not that I really know what that means mind), but I assume that it allows for more and finer adjustments on the measured signal??

Hi Terry,

Yes that's right.

In simplistic terms; If you imagine the sample rate of the correction filter as its bandwidth, the resolution is determined by the bit precision and the number of samples(taps) within the filter is the length.

More taps offer more flexible and accurate correction.

Concurrent with that however is a commensurate longer delay of the signal??(no free lunches in audio eh) which is less useful for movies I'd assume.

Yes for a filter with 65536 samples then your looking at a delay of around 1.5 seconds using Convolver set to 16 partitions. Partitions split the convolving process up into multiple parallel tasks which are reconstituted at the end of each cycle. This greatly lowers the convolution processing time (down from 1500ms to about 10ms) but the filter length cannot be reduced without affecting the level of correction and accuracy so this is where the primary delay occurs.

This is no problem for audio only tasks such as music playback but forget it for movies or any realtime application. In these cases you need minimum phase filtering and again this is possible on the PC so you don't have to start being selective about what your audio system can or cannot do because of latency.

At times I've looked at some of the types of systems you are using, but due to computer idiocy they go way over my head and unless I suddenly get some sort of dawning light I doubt I'll ever have the nous to implement any of them.

Don't be afraid of the computer! It should fear you

I'm writing a loudspeaker DSP guide right now that will really break down the steps needed to achieve the things I've been talking about throughout the latter part of this thread and much more besides. It should make it accessible to virtually all interested parties regardless of technical know how.

Another thing i haven't quite grasped yet, seeing as how it's all set up on the computer, does that also mean that the computer is now an integral part of the system??? I mean I use a computer (as you know) to set up the deqx, but after that the deqx is it's own standalone unit in the chain. But you need to continue to use the computer no? (I'm not saying it's good or bad, just trying to understand it).

By the way, I did try and follow your computer based guide...failed miserably ha ha. [/B]

That PCXO guide is pretty much outdated and was lacking a lot of information that would make it understandable to the casual non PC geek There are newer, simpler and better methods now.

In my case the computer does everything - its the music server, its the gaming machine, its the movie playback device and a its the loudspeaker DSP and crossover. But the methods used for the latter part of that equation are entirely flexible enough to take external audio and process that.

Aside from this you can use programs such as AutoIT to create scripts that accomplish anything you'd do with a mouse and keyboard within the windows environment. So on windows bootup you could load Console set it to activate and load a particular crossover preset and that would be it. To the end user this would appear as a box you turn on, wait a couple of minutes for it to initialise and then from there you play music or whatever.
Such is the power of this setup that you can even add an IR with remote as I've done. This then allows you to setup more AutoIT scripts that tie in with the IR software hotkeys. You can then very simply switch between crossover and correction setups as the push of a remote button ie. low latency minimum phase for movies, quality linear phase for music. The limits are endless here.

So a streamlined and silent PC box is possible that would operate just as the DEQX or any other standalone hardward would. Of course when you wish to tinker under the hood you'd need to rig up a keyboard, mouse and screen but once set you can forget and still have all the convenience of a modern standard alone device. Its amazing how far it has come even in the couple of years I've been playing with all this.

[ShinOBIWAN]

Originally posted by cph2000
You have probably covered the topic some other place -
but could you please elaborate on how you control volume in your setup.

I would also like to know if you have tried doing your stuff using Vista and especially from Media center.

IMHO, The Media Center front end is a big plus when you have your familly using the system also.

I like your soundcard, but I think I will go for class D amps to save some enrgy

Thanks

Hi cph2000

For the volume control I'm attenuating at the source(the PC) for now. But Russ White is designing a flexible remote preamp that is configurable and expandable to allow multiple inputs and outputs. Its an excellent solution for active loudspeakers and/or home theater.

[ShinOBIWAN]

Originally posted by Grumpy_Git
Shin

If you really wanted to do it properly you would just build a few more LGTs and use an acoustically transparent Projector screen!

Now theres a system!

Nick.

[tinitus]

http://www.groundsound.com/dcn23.html

[ShinOBIWAN]

Originally posted by tinitus
http://www.groundsound.com/dcn23.html

I've seen these before.

I would say they'd be excellent for inbedded solution or where the user doesn't need maximum flexibility or quality.

The feature set is comparable to the DCX2496 ie. min phase filtering with PEQ and software configurable. The added bonus is the EQ automation.

Downsides are fixed DAC's, limited flexibility and limited power. Certainly a great answer to some situations but its not comparable to the PC solution.

[BerntR]

Originally posted by ShinOBIWAN


This is no problem for audio only tasks such as music playback but forget it for movies or any realtime application. In these cases you need minimum phase filtering and again this is possible on the PC so you don't have to start being selective about what your audio system can or cannot do because of latency.

I agree with your main message, but I think more of the good stuff can be had in the DVD Video department.

I have done tests with 5.1 setup and linear filters on my 5 year old laptop. With a modest delay on the picture through AC3 filter - and 32 k tap filter length it seems to work pretty well. But who knows? Maybe my laptop is blessed with a very slow graphics processor .

There is a correlation between number of correction paths and processing speed, so it may be harder to get full lipsync + full stability on systems that are both multichannel and active. A vital Duo processor should be able to handle the task pretty well though. In any case a no-compromize solution may be trivial to implement pretty soon if it isn't already. All that is required is cpu power and video delay control with a little headroom.

A minimum phase solution is of course a good fallback strategy if the linear phase route fails. And it can be made to sound very good too.