diy-thegirlfromipanema

DIY - The Girl From Ipanema

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Someone on HTGuide asked if there was a small, sealed design using these two drivers. I was kind of surprised to realize that although there are like 10,000 designs using these drivers, I don't think something like this exists. And if it does, well, then consider this "my version of a standard."

I was waiting for the paint to dry on another project, and since I already had the cabinet built, I gave it a shot. I measured the drivers in a 7 L cabinet (one could also use the Parts Express .25 cu ft pre-built enclosures), sealed, pushed against the wall--this was meant to simulate actual BOOKSHELF speakers, that is, speakers that sit on a bookshelf, against the wall. (The dip you see at 2.5 KHz is a diffraction artifact because of nearby furniture (hey, I wanted this to be realistic!)) I then took the measurements into PCD and tried several different topologies.

This is definitely the simplest one, but it works extremely well, so I'm keeping it. At first glance, I know most will think that such a simple crossover isn't possible on the RS150, but they shouldn't be so hasty to judge.

The 2nd order electrical filters on the High and Low pass essentially create 4LR acoustic slopes crossing around 1700 Hz. Although pretty much everyone uses some sort of notch filter or 3rd order electrical filter on the Dayton RS150, I wanted to find out what would happen if I just went with just a a plain 2nd order. It actually gets the breakup mode out of the way better than I would have thought, and the breakup just isn't an issue off-axis (and since I voiced these to be set up on an actual bookshelf, that is, against a wall, chances are, the speakers will not be toed-in).

What was a much more significant issue to deal with was the shoutiness between 1 and 2 K. (Whoever said we can notice 1 dB differences in this area was not kidding!) Adjusting the inductor on the low pass for a few days while listening to lots and lots of music, I finally tweaked it to a very "pleasant" sound. I really focused on the midrange in this, and wanted it to sound right on jazz and acoustic music; I mostly left bass-heavy music out of the rotation while voicing these because I found it distracted me from my goal.

Listening

In the end, I'm really surprised that speakers shoved against the wall can sound so spacious. They also work well as Home Theater speakers, as my wife and I have been discovering while watching a lot of monster movies on them lately. They don't offer much low end, nor do they even fake it. However, from about 80 Hz up, these speakers are frighteningly accurate. Rock music would probably not be much fun to listen to after a short while, but any sort of jazz, classical, or adult contemporary will come across sweetly.

At the risk of sounding like an audiophile rag reviewer, while I was listening to Pat Metheny's "Speaking of Now," I could actually close my eyes and identify the placement of all the instruments in the 3D space in front of me! No, I'm not kidding. And I've been playing live music (with living, breathing musicians) for the last 15 years, so make of that what you will.

I don't honestly know what magic is going on that makes these speakers so articulate. Perhaps it is the metal cones. I'm also tempted to think that it's due to the extremely tight phase alignment from 1000-6000 Hz, which spans across the crossover point, and is also the region where we tend to pick up a lot of imaging cues.

So dis me if you will for my engineering methodologies, but I recommend you let your ears be the judge. I figure it's called "Do It Yourself" for a reason: I get to design speakers myself that I like to listen to.

-Paul Carmody

Completed versions by other DIYers

Ipanemas as built by [heffster]. Awesome job! Seven thumbs up!

Above: here are the Ipanemas as built by [woodworker jon]. Takes my breath away! You can read his build log here.

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