Alpine DML

Designer:
Bobby Kinstle

Project Category:
Freestyle Speakers

Project Level:
Intermediate

Project Time:
20+ Hours

Project Cost:
$500 – $1,000

Project Description:
This project was to create a nice sounding and aesthetically pleasing speaker system in an alpine vacation condo near Lake Tahoe that would be used mostly for classical or ambient music, and TV watching.

Design Goals:
It needed to blend into the existing room, connect to the existing amp, and play full range at moderate volume levels but not annoy the neighbors or the kid’s bedroom downstairs. It also needed to be 8 ohm and connect to the receiver already installed. The interior is wood themed so I opted to used end grain balsa rather than the usual foam core.

Driver Selection:
295-240 Dayton Audio DAEX30HESF-4 High Efficiency Steered Flux Exciter with Shielding 30mm 40W 4 Ohm. Two in series on each channel for 8 ohm load

264-1678 Peerless DA32TX00-08 1-1/4″ Corundum Dome Tweeter for the center channel tweeter because of it’s proximity to the fireplace I was concerned about heat on the AMT tweeters.

275-095 Dayton Audio AMT Mini-8 Air Motion Transformer Tweeter 8 Ohm

½” thick medium density end grain balsa sheet

Enclosure Design:
Each panel has a radius on the corner templated from a quart sized paint can to control unpleasant high frequencies. Each main channel consists of 2 panels. One wide panel with one exciter, one AMT tweeter, and the crossover. The second panel is larger and has one exciter to strengthen the lower midrange registers. The center channel is one large panel with the tweeter and crossover mounted to the edge closest to the TV. I plan on adding a second panel below it to strengthen the male vocals more to my liking. Wires, drivers, and components are generously secured with hot glue and solder joints are extra heavy since this is a high vibration environment.

Enclosure Assembly:
I glued small squares of hardwood to the corners of the panels for the eyelet screws to bite into securely and hung them from vinyl coated steel cables. Electrical connections zip tied to the cables helped conceal them. Each tweeter sat into a hole drilled into the panel and then filled with hot glue from the back side. The AMT tweeters were light enough they didn’t need additional support but the big Peerless dome screwed into a piece of wood glued on the back of the center channel. Wires were secured to the panels with hot glue.

Crossover Design:
All panels use 2nd order Linkwitz Riley crossovers for the exciters and tweeters. 2.1Khz on the center channel and 6Khz on the mains. All tweeters are wired reverse polarity. The preprinted Dayton 2nd order crossover PCB’s sure came in handy. I mounted the crossovers onto a thin piece of wood glued to the panel so the high mass components wouldn’t shake off. The center channel is crossed lower because I wanted it to be more directional towards the TV.

Tips & Tricks:
1. Vinyl coated steel cable is super strong, attractive to look at, can be made yourself in any length, and has no rattles whatsoever. Just make sure you strip the coating off underneath the crimp ferrule or it may slip out.
2. A glue injector is handy for filling in the cracks on balsa panels.
3. End grain balsa sounds fantastic but it’s mechanically poor. Screws won’t stay threaded into it. However, you can glue a 1/4″ thick piece of hardwood to it for heavy objects that need to be screwed down. The panel will break before that glue joint fails. This worked for threaded eyelets for the cables and as far as I can tell had no impact on sound quality.
4. DML panels make great midrange speakers with a range of around 120hz for big panels and 150hz for small panels to around 7ish Khz on the upper range. You are definitely going to need a woofer for them to sound right and it’s going to go high enough to be directional. Two small subwoofers mounted under the main panels would be ideal to play frequencies below 150hz. You can use a single sub but it will be directional in some frequencies.
5. AMT tweeters are spectacular for picking up the high end since they don’t weigh much, have stable impedance, and the smaller ones are really only good above 6K anyway. The Dayton AMT-mini-8 is super small and won’t change the sound of a large panel when mounted by an edge. It’s super crisp and blends very well with the panel.
6. Make sure you low pass the panel at the tweeter frequency as they can have some mighty unpleasant high frequency breakups.
7. Always mix at least 2 different sizes of panels on each channel. This blends the characteristics of the panels together in a pleasing way. I’m going to add a second panel under the center channel as the vocals feel a bit thin in home theater mode.
8. The VHB tape is holding so far but if it fails, most folks use epoxy to glue them back on.
9. While a multi channel amp, active crossovers, and a DSP can significantly “correct” the sound, I think chasing the usual goal of flat perfection will be and frustrating process. Instead embrace the beauty and character of the DML imperfections. Expect to listen and tweak before finalizing the project.

Conclusion:
When the music plays, the entire panel vibrates and acts like a giant speaker cone. This makes a huge sound field that swallows up the listener and mimics the sound of very large instruments like concert grand pianos that you just can’t replicate with small speakers. It sounds like the entire wall is playing music. Almost as if you were sitting in front of the band instead of through 2 distinct points trying to blend together. The huge surfaces replicate the fullness of large instruments like concert grand pianos, strings, and horns with a presence I’ve never heard from a speaker. The panels have their own character, and the sound is smoother and mellower than most speakers. Adding the AMT tweeters brought the crisp details back in and contribute to a truly enjoyable experience. The bass comes from the end table subwoofer I posted earlier and has no trouble filling the room with lots of deep bass. Best of all the subwoofer is hardly audible in the bedroom below this room thanks to it’s non resonant chassis and spiked isolation feet.

Sip your favorite spirit and relax to something classical.

About the Designer:
I grew up in the Mojave Desert in a small community of scientists, craftsmen, and engineers. We were the kind of people who didn’t accept “it’s impossible” or “you can’t do that”. If I want something that doesn’t exist, I’ll just make one. Now I’m a thermal engineer in the computer industry and I currently hold 17 patents worldwide.

Project Parts List: