DIY New England - Saturday Oct 22

[Michael P]

Thanks for putting up the pictures. I think Jon's speakers were using the 4 ohm Anarchy woofer. Build thread: http://techtalk.parts-express.com/fo...-rs100p-8-sb19

[johnnyrichards]

DIY speakers and dogs? Awesome - reminds me of DDIY 2013, the so-called informal debut event. Looks like a lot of fun!

[dlr]

Thanks for putting up the pictures. I think Jon's speakers were using the 4 ohm Anarchy woofer. Build thread: http://techtalk.parts-express.com/fo...-rs100p-8-sb19

Thanks for the info. I've updated the page and included a link to his PE build thread.

dlr

[jclin4]

Hi Dave, thanks for publishing the webpage and for your pics and comments on the builds. I much enjoyed being there. I shared the link with my wife to give her a peek into these gatherings. She liked the last pic of the three rescue dogs!

[Pallas]

DIY NE 2016 Pictures

dlr

Posting here to avoid "thread drift" on the DXT tweeter thread, even though I got here from there.

Dave, IIRC you've always held that between driver felt was highly beneficial. Yet the dipoles you showed here appear to me to have just two pieces of felt in an "open V" shape around the tweeter.

Have measurements or listening in the last decade-and-change since your eye-opening diffraction article changed your position on optimal placement? Does the waveguide change something with the tweeter/midrange interaction?

[dlr]

Posting here to avoid "thread drift" on the DXT tweeter thread, even though I got here from there.

Dave, IIRC you've always held that between driver felt was highly beneficial. Yet the dipoles you showed here appear to me to have just two pieces of felt in an "open V" shape around the tweeter.

Have measurements or listening in the last decade-and-change since your eye-opening diffraction article changed your position on optimal placement? Does the waveguide change something with the tweeter/midrange interaction?

Originally I had a small piece at the point of the V, it makes a measurable difference, but not a lot. The V shape seems to handle most of the diffraction, both the baffle edges and the midrange driver. I also just liked the looks of a simple truncated V shape and was looking for the least possible amount of felt. I had originally hoped that the DXT would obviate the need for felt other than between drivers, but was surprised that the edges required the usual treatment. The DXT waveguide loading just isn't sufficient to prevent baffle edge diffraction to the extent that I had hoped. I'm tempted to substitute another 1" dome to see how much difference there is. This was really only going to be a first try at a dipole system, I expected to go to a 4-way sooner, more like John K's approach. I still have plans for that and have a true dipole tweeter in mind.

The midrange itself doesn't have any appreciable diffraction insofar as the side edges go. But it did have an issue with the top edge diffraction, but that was related to the dipole characteristic. The midrange is operating almost fully in dipole mode in relation to the width, but the position of the driver below the tweeter on the rectangular baffle places the top edge too far away, so the dipole effect is in the transition range from dipole to monopole there. Raw baffle measurements showed a problem that I determined was the top edge. I experimented with felt and fixed it to some degree with felt at the top, but didn't like using that at all. I really wanted a more presentable system. So out of curiosity, I placed a thick piece of felt above the midrange on the rear of the baffle. This almost totally eliminated the bump measured on the front. This in essence cancelled out the additional depth of diffraction that is seen between monopole and dipole diffraction effects as seen from the front of the baffle. What this means is that the system is dipole primarily in the horizontal plane. Were it to be measured off-axis by rotating the system on the z-axis through 360 degrees, at some point the additional distance to baffle edges would slowly alter the response, lowering the frequency at which it is at the upper edge of dipole operation. But since this is not a coincident driver system, the change due to crossover integration off-axis will be far more detrimental than the small change in dipole range and that is all off-axis anyway, so I went for absolute best on-axis response that I could get with the geometry. Dipole, monopole, both are related to the distance to any point on a baffle edge, so the monopole diffraction changes as does the dipole interaction. My take from this is that for the absolute best, most complete dipole system, multiple drivers mounted on circular baffles is best (for round drivers anyway). Usually a dipole designer tries for a narrow baffle, but pays little attention to the vertical dimension. I suppose that the primary difference is not at the listening position direct response, it's in the total room radiation difference between monopole and dipole. Full dipole reduces the total energy vs. monopole by, what, 4.6db? I forget the exact number. To me this means that the vertical radiation (floor and ceiling portion) will be reduced with a full dipole, but that's only a portion of the dipole effect, so how much it may be perceived is anyone's guess. But I digress (a lot!).

At DIY NE I kept waiting for someone to ask about the big piece of felt (2" h, 6" w, 1" d) on the back, but apparently no one noticed it since it's not obvious. I also found that after installing the tweeter with the big motor sticking out in the back that the felt had much less effect, the tweeter already blocking a lot of the back wave from reaching the top edge directly. The impact of that really surprised me.

dlr