Violet DSP Evolution - an Open Baffle Project

[Bratislav]

Originally Posted by cuibono

I ran the sims - 50W power in wrt 7ohms, 2m away, no floor, 4inch baffle. I got a rms deflection of .6 (out of 2.1 max calculated), but only 85dB SPL at 300Hz (pretty low efficiency!!). The good news is that its doing about 95dB SPL at 550Hz, and 100dB SPL at 1kHz. The low efficiency in the mid-hundred Hz is one of the reasons for going to a 4 way...

This is where adding a second W4 can make a difference. You will reach ~91dB @300Hz, and all you have lost is tiny bit of vertical coherence and a couple of bucks !
Better than going to 4 way trouble, IMO.

[cuibono]

Originally Posted by twest820

Is this where I get to say I told you so?

Yes, you did!

Bratislav - I'm still on the fence about whether I should change the mid setup - as far as I can tell, the mid's aren't actually having any issues. Adding another W4-1320 is one possibility - its all about cost versus complexity.

I'm leaning towards a 4-way, and the primary reason is because of the tweeter - it may need a higher XO point. It seems to be the limiting factor when it comes to max SPL output. I may make that a whole new design though. As it is now, the three drivers give plenty of SPL output (well, I guess it's 10 actually...).

[Antripodean]

Impressed by your listening impressions for linear phase eq and computer xo. Is there a budget way to do this? (the software)

[twest820]

Originally Posted by cuibono

Yes, you did!

Originally Posted by Antripodean

Impressed by your listening impressions for linear phase eq and computer xo. Is there a budget way to do this? (the software)

The Linux+BruteFIR+Octave solution discussed a page or two back is free in dollar terms. For Windows Allocator (USD 150), PLParEQX3 (USD 50), and some sort of host (USD 50-75) is the cheapest option I know. Don't know of any Mac solutions which I'd call low cost.

[Saurav]

What about sound cards, what are the minimum requirements? Any specific characteristics to look out for, beyond the 6 or 8 channels?

[doug20]

Originally Posted by Saurav

What about sound cards, what are the minimum requirements? Any specific characteristics to look out for, beyond the 6 or 8 channels?

I think its the card that costs the most. I haven't found one below $400 worthy of an active solution. Something with the quality of LynxTwo-B is going to be $900

Maybe the M-audio Delta 410 is good enough?

[twest820]

There's an M-Audio Firewire 410 lots of folks use and a Delta 44. Not sure about a Delta 410. Generally speaking I'd suggest an interface with balanced outputs. But you can cost reduce a bit if you're fine with unbalanced. My experience is USB interfaces are best avoided, but your mileage will vary.

I use a Focusrite Saffire Pro 40 I eBayed new for USD 350 shipped. As a DAC it edges out my Wolfson 8740 based Cambridge Azur 640C, so I'd say it's possible to get good results under $400. If you only need three way I've seen the Saffire Pro 24 routinely eBay new for USD 225 shipped. In comparision my software stack costs USD 275. Besides, you know you want a good interface for measurements, right?

If you really want to shave bucks and don't mind a bit of a wait, Thuneau tends to run Black Friday deals. If you have a bit more budget the Motu Ultralite has a box spec that suggests all warped phase operations can be offloaded to its DSP. Interesting option for reducing CPU load or running standalone without the PC if need be.

[cuibono]

I do things pretty cheap - but there is always a little sacrifice when it comes to usability.

I use the Asus Xonar D2 - 2 in, 8 out. Its about $125. The only thing is its quirky, and not quite meant to be used like other 'prosumer' cards.

For software, I use Reaper. Its basically free, and comes with the basic plugins needed to do XO and EQ. The only thing is the 'linear phase' EQ - I haven't found a free version, but I haven't looked. I'm guessing a thorough search might turn something up. But then again, using linear phase EQ might not be necessary to doing phase correction.

[twest820]

Reaper supports linear phase crossovers? I had the impression the plugins were all warped phase.

[cuibono]

twest - they seem to. What makes you think otherwise?


The last few days, I've been working on a tangent. I got a bug in my bonnet - my memory of the Orions were as a little on the warm side, with a pretty smooth character - almost too smooth in the treble. Listening to my Plutos, I get the same impression. But listening to the Violets, I feel like they sound relatively analytical, with some emphasis or hardness in the treble, and I was wondering why (if it is actually true).

In the past, I had postulated that the smooth/warm character of the Orions and Plutos was due to some aspect of the ASP (analog signal processor) - lots of opamps? Simple power supply? So what I've done the past few days was hack into one of the Pluto ASP boards, install a DPDT switch, and then recreate the ASP's filter function in my DSP (digital signal processor) computer. I can then switch between the ASP and DSP, and instantly compare the analog and digital versions.

After a bit of fussing, good news - no difference! I was concerned, but apparently there is no need to. I'm pretty glad - if there were differences, that would require a bit of reevaluation. I think one of the important points here is that, while both routes are doing a lot of signal manipulation, they are doing it fairly different ways - but the final results end up audibly the same. One less thing to worry about!

Of course the necessary qualifier - these results only apply to my listening under the specified circumstances - generalize at your own risk!

I did some measurements I could post, showing that the filter functions are virtually the same. I did learn one thing that is of concern - both types of filters have relatively limited S/N ratios - like 50dB. I'll probably try to address that at some point.