Need DIY help building filter for Vandersteen 2wQ

Howdy all, I have a home audio project issue that's a bit esoteric, but thought maybe someone here could point me the right way.

I have a subwoofer in my AV system, the Vandersteen 2wQ, an overall solid performer. This is not for a LFE channel, but rather offloads the low-end from my stereo front mains (a rebuilt pair of Dahlquist DQ-10's that really need the help even more than the Vandy's I originally bought the sub for). It connects to the power amp output terminals for my mains, and, this is the important part, requires a high-pass filter to be connected to the power amp inputs.

Filters are theoretically available from Vandersteen, but these range from dubious quality (I have a pair of X-2's I've been using) to ludicrously priced (the M5-HP, an adjustable crossover designed for one of their higher-end speakers, is both hard to acquire and costs nearly as much as the subwoofer). The filter itself needs to be matched to the input impedance of the amplifier, which usually means getting new filters if you change your system.

There was some discussion several years ago, mainly on the Planar Audio (I think) forum, about these filters being a fairly simple DIY project, though the details are a bit sketchy. I'm still pretty handy with a soldering iron, but the last filter I built was out of a cookbook in school some twenty years ago, so I'm a little rusty on the theory.

As far as I know, I need to make a first-order (-6dB/octave) high pass filter with a crossover frequency as close to 80Hz as I can get. Getting from theory to the workbench raises a couple of questions for me:

1) For a standard (unbalanced RCA-cable) hookup, I believe all that I have to do is connect a "high quality" capacitor to the hot lead of each of my pre-out/main-in cables. Let's pretend I can do the math to get the right capacitance I need (it's a function of the input impedance of the amp), as calculators are pretty easy to find online. Is that all I need? Some posts also refer to linking a resistor in parallel to the input, but I don't think this is right.

1a) For that matter, anyone have an opinion on what constitutes a "high-quality" cap? I've seen some brand names dropped (Auricaps, Teflon V-caps), but spending hundreds of dollars to trial-and-error different brands defeats some of the DIY purpose.

1b) I doubt I can find a cap that will map out to a crossover at exactly 80Hz, and using multiple caps seems needlessly messy. Knowing the right answer is "try different values and see what sounds right," see 1a, I'm going to assume that a cut off a little lower (like 73Hz) is better than too high (90-100Hz).

1c) Incidentally, when picking a cap, how important to me is the voltage rating of the cap? A lot of the ones I've seen are 600V. Is this reasonable for an audio application? Way higher than needed? Going to melt when I crank the volume?

2) I'm planning to replace both my amp (a Dunlap-Clarke Dreadnought c.1973 that's a monster, but way past it's mandatory retirement age) and my processor, with a new system that supports balanced (XLR) hookups. This means new filters (the unbalanced and the balanced are not interchangeable -- some of why I don't want to spend a ton of money on the factory filters). I don't have a lot of experience with XLR cables. What do I have to do different? Is it as simple as using two caps, one for each hot lead? What value caps do I use (one post said implied half of the capacitance of the single cap in the unbalanced hookup). Is there more to this one? Is working with XLR beyond what is reasonable to DIY?

If anyone out there has experience with the 2wQ's, or at least enough knowledge of circuits to tell me I'm doing it right, I'd love to hear from you.
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  1. I am willing to bet that a simple RC filter will not be enough. I also doubt if a simple first order filter will be enough.

    There's a lot of good stuff here:
    http://sound.westhost.com/projects.htm
  2. The beauty of home audio is that nothing is ever enough :)

    A simple RC filter (provided by the manufacturer) is what I'm using now. You can second-guess Mr. Vandersteen's designs all you want, but when an engineer tells me that a given device is designed to operate with a first-order high-pass filter applied to the amplifier input stage, that's pretty much the hand I have to play.
  3. I built myself a pair of filters and have been using them for about a month. They seem to work fine, and should be starting to break in by now. I've not been able to notice a huge quality jump from my old filters from Vandersteen, but I haven't really taken the time to do a lot of manual A-B testing to figure it out. I replaced my old amplifier just before doing this (to an Emotiva XPA-2) which subjectively made a much larger difference. More importantly, I don't "notice" my filters, which kind of means they're doing their job.

    Time to spend my XP and answer my own questions:

    1. Basically I made a short cable (about 8-10") from some triple-braided silver wire (http://www.homegrownaudio.com/), a good RCA male jack on one end (also one of their products), and a female RCA that I cannibalized off of an old Monster Y-connector (female jacks seem a lot harder to shop for than males). I just soldered one wire to my grounds, one to the hot leads (which I cut mid-length and spliced in my cap), and left the third wire unconnected as an insulator. Once done, I wrapped the whole thing in heat-shrink tubing.

    1a. I didn't feel I had the time, resources, and equipment (and maybe ears) to audition tons of capacitors, but after reading a pretty thorough report from someone who did (http://www.humblehomemadehifi.com/Cap.html), I settled on a fairly high end set of Mundorf capacitors, which were more expensive than the Auricaps, but still cheaper than the V-caps. Having nothing serious to compare them to, I will say they seem to be doing a fine job.

    1b. The closest I could come was a 0.1mcF cap which puts my crossover at roughly 68Hz (should be the same as my old X-2 filter). Theoretically, that means my low end is probably a little boomy, but the room is far from ideal and I have it dialed in to where I think I'm pretty happy.

    1c. My caps are rated 1200VDC, but I get the sense that pretty much anything I went with would be fine. I don't know what the critical value is, but I suspect it's much lower.

    2. Balanced filters are next year's project, but still looking for answers!
  4. what you want is a rane or similar electronic crossover. frequency and Q, gain adjustable, mono sub output. set it to any point, gain, Q your room needs. building one is experimental, and not worth the trouble, compared to spending $300 or less for a well built unit. I used one on my last setup, and was very happy. Another factor that really helps is time alignment, increasing efficiency by 3 db or more, less power, more accurate sound, but that is usually only used in professional live systems due to cost.
  5. Hi

    I just came across this post looking for something else & thought I'd try to be helpful.

    I own the complete Vandy System with 3A Sigs, TWO (Stereo) 2Wqs; VCC5 Center & VCC-1 Surrounds.

    I have have the subs for about 4 years now & always thought they were pretty good - but I struggled with finding the right setting for the XOver -

    Well, I was auditioning new amps (ARC SD-135 & Modwright KWA-150) and was persuaded to spring for the M5-HP XOvers that he sells for the Model 5s - Yes, I know - it IS a lot of money for "just a crossover" - but when I heard from more that one trustworthy source, that they would really have a profound affect on the sound of the main speakers (you are right, the Wx-2 and even the X-2s really suck in comparison - actually, there IS no comparison!

    The M5-HPs make a HUGE difference is the clarity & Imaging of the 3A Sigs! You'd have to hear it for yourself to appreciate what I am saying - the lesser XOvers just do not do the job - problem is people compare the cost with the cost of the subs, they figure the XOvers "cost too much" compared to the Subs themselves.

    The way you need to look at it is that the cost of the subs INCLUDES the XOvers! Actually, what you ARE doing with these excellent units, is UPGRADING THE SOUND OF YOUR MAIN SPEAKERS AND the Amp!! The Amp works less hard (no low BAss), and so does the main spkrs!! The result is astounding - you almost have the sound of Vandy Model 5s at a fraction of the cost - this assumes you use a stereo pair.

    All that said - it is only meaningful if you have a pretty good "Hi-Rez" System to mate them with - I had a Rotel RB-1080 Amp & the difference was far less noticeable than with the ARC or Modwright amps.

    The last thought I have, is that Richard Vandersteen is a VERY SMART man - and knows his *** when it comes to designing and making great products - he does things with those XOvers that no DIY person who does not THOROUGHLY understand Vandersteen's Design would even THINK of (one example is that the unit used 9-Volt Batteries - they last for 7 years - to keep the caps continuously charged - there are many other features, one of which is that there are dip switches that allow you to match to any amp, even if you buy a new one) - I would trust his product and either buy them or not - If you do, you won't be disappointed (BTW, there are explicit instructions about how to use them with what speakers (The Vandy Dealer can provide those instructions with the XOvers) - if your main speakers are not Vandys - you will certainly need to call Richard Vandersteen and get his advice on how to set things up. These 2Wqs are incredible subs, but they are designed unlike ANY other subs & must be set-up properly - if you do, the results are phenomenal! If you don't, it is worse that using a different sub!!

    By the way - I just checked AGone for used XOvers - only ad I found was a guy looking for a pair in the "Wanted" section. I would doubt anyone would ever sell them, except WITH the Subs &/or Main Spkrs - NOT separately.

    I would go visit a Vandy Dealer - speak with him & Listen - who knows, he may have a pair (they come with RCAs or Balanced - and BTW, you cannot take a pair of RCA's & used adapters to make them Balanced - same goes for the other direction!

    Hope this helps;

    Regards

    David
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