SEOS Project: Waveguides are here!

Since the last post I've been waiting for the compression drivers and waveguides to arrive so that I can get started measuring and modeling the speakers, but to pass the time I've been doing some research about constant directivity loudspeakers, and the kinds of tools I'll be using to help me design them.

The Pi Speakers Whitepaper was the first source I looked at to get a sense of what's going on in a constant directivity system. It starts off with some background on horns and waveguides, and what kind of advancements led them to their current form, then it gets into how to integrate them into a two-way loudspeaker system. There is actually a lot more to consider when designing the crossover for a constant directivity system than just passing the correct frequencies to each driver. Since the goal is, of course, constant directivity, that means matching the directivity of the woofer to that of the tweeter at the crossover frequency, which adds a considerable amount of complexity.

Thankfully there are lots of resources available when it comes to crossover design. Next up on my reading list is also from Pi Speakers, and it's referred to as the Crossover Document. At over 70 pages, it's a hefty read, but I'm hoping it will expand upon what I've already picked up from Leach's Introduction to Electroacoustics and Audio Amplifier Design.

In addition to reading up on theory, I've been scouting out some programs to help me measure the drivers, design the crossover, and model the final system before spending any money on crossover components. Here's what I've found so far:

Room EQ Wizard (REW): I've used this in the past for measuring the in-room frequency response of my subwoofers, but it also has the option to measure driver impedance and spit out parameters for use in modeling software.

WinISD: Using the driver parameters, this program models the transfer function of the driver in different enclosures.

Passive Crossover Designer 7 (PCD): This program takes in raw impedance and frequency response data from each driver, and allows you to design and model a crossover while providing graphs for frequency response (at any position in relation to the system) and directivity. This program will also model different enclosures and can use that data for the crossover design.

Finally, last but not least, my compression drivers and waveguides just arrived today. The waveguides are made out of extremely thick and heavy plastic, and feel incredibly solid, although next to the compression drivers, they're lightweights. The DNA-360 is a monster! These things are much larger and heavier than I expected, and I wouldn't be surprised if the CD/waveguide combo weighed more than the woofers do. For some size reference, here's a picture of me holding one of them.

SEOS Project: Getting Started

I actually started the research on this project a while ago, so for this post I'll be playing a little bit of catch up and getting everyone up to speed on the progress I've made so far.

Originally in my search for another speaker project to work on I came across this thread about "Econowave" speakers. The idea behind them is to use a compression driver with a waveguide paired with a large woofer, resulting in high sensitivity that allows playback at reference levels with low power requirements. Additionally, the waveguide controls the directivity of the tweeter, narrowing it to reduce unwanted reflections, especially in the vertical plane.

Another resource I found as I was looking at these kind of speakers was the Pi Speakers website which uses the same idea although arguably in a more polished form.

Once I had decided that the constant directivity (CD) speaker was the way to go, the next step was to start figuring out what I wanted out of them, and from there which components to use.

Really my only requirement is that the speakers play low enough to crossover to a sub at 80Hz, which even with a sealed design should be doable. Since I don't plan to listen at reference levels (peaks up to 105dB from the main speakers and 115dB from subwoofers), that is a secondary concern, but with the high sensitivity of constant directivity speakers, it's a very achievable goal. Finally, since my goal is to never have to replace these, I set the budget to around $300 per speaker for electronics.

With that said, here are some of the options I considered when choosing components for this project:

Waveguides
QSC PL-000446GP Replacement Waveguide Horn for HPR152i ($35)
SEOS ($30) (http://www.diysoundgroup.com/waveguides/seos/plastic-seos-matte.html)
Dayton H6512 ($7)


Compression Drivers
B&C DE250 ($130) (http://www.parts-express.com/pdf/294-605.pdf)
Denovo DNA 360 ($75) (http://www.diysoundgroup.com/drivers/tweeters/dna-360.html)
Denovo DNA 350 ($57) (http://www.diysoundgroup.com/drivers/tweeters/dna-350.html)
Selenium D220Ti ($50) (http://www.parts-express.com/pdf/264-270s.pdf)


Woofer
Eminence Deltalite-II 2512 ($150) (http://www.eminence.com/pdf/DeltaliteII_2512.pdf)
Eminence Delta Pro 12A ($135) (http://www.eminence.com/pdf/Delta_Pro_12A.pdf)
Eminence Delta 12LFA ($100) (http://www.eminence.com/pdf/Delta_12LFA.pdf)
Dayton Audio PA310-8 ($65) (http://www.parts-express.com/pdf/295-032s.pdf)

The Dayton woofer and Selenium compression driver were used in quite a few of the Econowave designs, which is why they show up here along with the QSC horn. That pairing would have been my initial choice based on their price and the success people have had with them in the past, but after looking around some more I came across the SEOS project. The waveguide measured very well, and the DNA compression drivers offered alongside them are very comparable to the much more expensive B&C DE250.

With the SEOS and the DNA-360/350 looking like the best option for the high end, I wanted to find a woofer that could keep up, so I finally settled on the Eminence 2512 which offers better sensitivity, power handling, and extension than the Dayton (or some of the other Eminence offerings).

As of right now I've ordered the SEOS and DNA-360 as well as the 2512s (which just came in), and I'll be starting measurements and modeling the speakers so I can begin designing the crossover.

That was a pretty dense post, since I had to cover a lot of progress all at once, but it'll be a little more broken up in the future (and there will be more pictures once I get my camera from home).