Isolation Ward From ebony pucks to magic foil, mystical and controversial tweaks.

---

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Isolation Ward ]

---

[ Alert Moderator ]

---

RE: The question becomes

Posted by caspian@peak.org (A) on September 14, 2009 at 15:30:21

In Reply to: The question becomes posted by unclestu52 on September 14, 2009 at 12:09:53:

Hiya Stu:

With the normal/reverse polarity tracks on the Chesky test disc, I can hear some difference with headphones, though in a blind AB test I probably couldn't readily identify which is which. I can also hear some difference on the little speakers I built last year for outdoor listening, but only consistently so outdoors, when the neighborhood is quiet. Indoors, despite a reasonably well-treated and acoustically "dead" room, not so consistently. Room effects seem to overwhelm the subtle difference.

Like you, I prefer speakers where all the drivers are connected in positive polarity. The only situation where drivers NEED to be connected in reverse polarity is with a true 2nd (or 6th) order crossover: in that case, the filter-induced 180 degree phase shift necessitates reverse electrical polarity in order for the drivers to be acoustically in phase and sum flat AT crossover frequency. Put both drivers in positive polarity and you will get a huge response suckout, NOT a hump. Of course, you get a couple of octaves out, either side of xo, and they're out of phase, which means higher harmonics will be inverted 180 degrees relative to their fundamentals. Not really a recipe for natural sound.

With good, smooth, wideband drivers, I can usually achieve a quasi-LR4 response with a 1st order electrical filter plus Zobel on the midbass, 2nd order electrical plus L-padding on the tweeter, both down -6dB at the chosen crosspoint, AND keep both drivers in positive polarity. The slightly "relaxed" lowpass electrical transfer function somewhat alleviates the time-misalignment of having the drivers flush-mounted on a vertical baffle. It's also quite easy to work in baffle step compensation with this arrangement: you calculate an oversized series inductor on the lowpass that will be down -3dB at the frequency where the baffle diffraction step is up +3dB, and then figure your crosspoint to the tweeter about two octaves (-12dB down from the midbass driver's reference sensitivity) above that. Quite easy to model, even with basic design software.

BTW, do you know of a published impulse response on the Dahlquist DQ-10s? Those, to my ears, are among the most "natural" sounding speakers I've ever heard, other than Quad ESLs. John Dahlquist obviously put a great deal of effort into the driver spacing on those, apparently trying to optimize time & phase coherency.

This post is made possible by the generous support of people like you and our sponsors:

DIY Hifi Supply

[ DIY HiFi Forum ]

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2013, Audio Asylum, all rights reserved ] [ Take5 ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---