DIY - Orient Express
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ATTENTION: the Vifa Logic AC25 tweeter is No Longer Available. This project is displayed for reference and archival purposes. Please do not ask me to substitute in another tweeter at this time.
A friend of mine asked me to build him a pair of bookshelf speakers for his in-home office. These were intended as actual bookshelf speakers (eg: speakers that actually would sit on a bookshelf, and not on a stand in the room). Although I had a good stockpile of drivers on-hand, two in particular nagged at me to try them. They both looked to be of excellent build quality, but how well could they perform? Could they perform together? Well, why not build a box and try it out?
Here is a quick rundown of the Crossover Diagram and Bill of Materials. All parts available at Madisound:OrientExpress BOM.doc
The tweeter is the Vifa Logic AC25SG05-4, available as an OEM buyout at Madisound at the irresistible price of $11. It was manufactured in China, but appears to be of good build quality. It has an aluminum faceplate, which is pretty much unheard of anywhere near this price point. Its FR is definitely not the easiest I've worked with, but at this price, I didn't feel bad about using a few extra parts to get it to cooperate.
The woofer is a real hidden gem: the Silver Flute W14RC25, which Madisound sells for $17.50. Silver Flute is a Chinese company who manufactures a lot of drivers for other driver and loudspeaker companies; I'd say they're in the same boat as Hi-Vi and Tang Band. These particular woofers are wool-coned, which you gotta admit is pretty cool. It's like, "Paper cones are so old hat. What else can we throw in the mix? Leather? No. Feathers? No. Wool? Sure, why not. It works well for this cozy sweater I'm wearing." What the wool actually contributes to the performance of this driver, I cannot say. But they have an Fs of 42 Hz, which I think is great for a 5" woofer, and they can be used up to a pretty high XO point, depending on how you like your cone breakup. They have cast aluminum frames, and just plain look really nice. In my book, they're taking the win over the Dayton Classic DC130--which itself is a really great driver for the money.
Since both of these drivers are priced so ridiculously affordable, and seem to be of such high build quality, the challenge naturally ensues: how good of a speaker can one create using them? Well, after putting in some honest effort coaxing the drivers, listening and tweaking, I have to say that they are capable of a pretty damn good small speaker system. I'm not going to kid myself or anyone else and say that these will rival boutique, high-cost, high-fidelity speakers. But they definitely can hold their own against most "mid fi" speakers commercially available. They pack a very clear, satisfying sound into a relatively small package that would work well in an office, a dorm room, small living room, or wall-mounted satellites in a 5.1 HT system. And at the price, well, what have you got to lose?
As mentioned earlier, the parts and drivers can be purchased at Madisound, and will come to a grand total of about $95 for the pair! Yes, you can substitute in some GE buyout caps and save yourself a few dollars. But heck, you could splurge and use the nice Solen capacitors and still come in under $100.
The cabinets are 8"W x 13"H x 11.5"D. They have a slot port in front that is 6.5"W x 1"H x 3.75"D (remember these are meant to go on a bookshelf, so the port has to be in front). The enclosure volume is 11 Liters, and is tuned to about 45 Hz. I built it using 3/4" MDF, and lined the sides and back with 2 layers of carpet padding. The crossover is actually mounted on the inside top of the cabinet, because I didn't feel like putting it on the back wall. I'm sure you could though, without any problems. The tweeter is offset because in simulation, it helped tame some diffraction artifacts. (so be sure you build these in mirrored pairs!)
I painted the cabinets using good ol' Appliance Epoxy. I guess this stuff has made a comeback, because it's very easy to get now. Makes a thick, hard finish that looks passable for real furniture. If you're okay with semi-gloss, it requires no sanding and clearcoating. If you want high gloss piano finish, well, you'll have to put in the elbow grease just like everyone else.
To the left is the cut sheet. It calls for 3/4" stock. In my case, I used MDF, but high-quality plywood would also work just as well.
This crossover is definitely the most complicated I've done so far, but that's not saying much, since mine tend to be very simple. The tweeter network is a 3rd order electrical filter with an L-pad attenuation. The 1 Ohm resistor in series with the .3 mH inductor is necessary, and provides proper shaping in the tweeter's acoustic rolloff. The woofer network is a quasi-2nd order electrical. The .47 uF capacitor across the 1.1 mH coil acts as a notch filter and takes out the cone breakup of the woofer.
The impedance load presented by the Orient Express is very benign, and don't need any sort of special amplifier. The lowest they go is 6 Ohms at 3500 Hz. You could pretty much play them through anything.
Now, since I have partially intended this project to be a quality "beginner" project to get one's feet wet with speaker building, I am reminded of my first project and how intimidated I was by trying to figure out how to read a crossover diagram and lay out the actual components. So I have included a drawing of the component wiring and suggested layout. Once you have the components wired together, you can shift them around so that they take up a minimal amount of space. To explain this better, I highly recommend Wayne J's article on crossover construction.
Here is a diagram of pretty much how I laid out my crossover. For a grounding block, I like to use the little European terminal strips from Radio Shack.
A few notes on how I designed the crossover...
I first built the enclosures, then measured the drivers in them, with the enclosures basically pushed up against the wall (as a bookshelf would be). Thus, when you look at the FR, you will see a bit of peaking and dipping below 1K; most of this is due to diffraction effects from the room. I'm sorry if it bothers you, it's just how I work. I'd rather measure the speakers in the room they'll be in, so that what I hear in the room matches what I'm seeing on the screen.
Once I had the measurements, I took them into Passive Crossover Designer and went through several different crossover designs. The first crossovers had a very low parts count, and sounded decent. Not fantastic, but a good start. After a day or two of listening, I noticed the overall sound just had too many dips in the Frequency Response. Female vocalists sounded especially bad: practically all sibilance with no real body or tone to the voice. At that point, I decided I might as well try some filter ideas I'd seen Roman B and Dennis Murphy use, but could never really figure out why. By adding a few resistors in key areas, I found I was able to manipulate the slopes of the woofer and tweeter in pretty much every way imaginable. In the end, the slopes are fairly shallow (something like a cross between a 2LR and 3BW, and they are somewhat "spread apart," which actually helped flatten the FR at the crossover point, and bring the phase into lock-step alignment for a very wide range. I also experimented with an "elliptical" filter, as suggested by Curt C, to tame the breakup of the woofer, which worked exceptionally well! So, not only is this my most complicated crossover so far, but it's also probably the best engineered. To my ears, the biggest benefits of having such good phase coherence are that the speaker tends to sound the same from a wide variety of listening positions, sitting and standing, and also the entire presentation is very clear (no "smeared midrange" as Dennis Murphy would say).
I am really pleased with how well these speakers turned out. Despite what one might imagine a wool cone might sound like, these are actually very articulate speakers. When everything finally came together, I was really shocked by how "clear" of a presentation they offer. They're not quite as "revealing" as metal-coned speakers, but this is not necessarily a bad thing, as metal-coned speakers have a reputation for making good recordings sound great, and bad recordings basically unlistenable. The Orient Express finds a comfortable middle ground, and would suit pretty much all musical tastes.
For soundstage, I have found that these can serve one of two purposes. When pushed up against a wall (as I originally designed), the Orient Express image very well, and the soundstage is extremely large and seems to fill the room; the speakers create a much larger sound than they look. On the other hand, if they are mounted on stands a few feet off the back wall and toed in, they become extremely accurate and the soundstage moves right in your face, almost feeling like you're wearing headphones.
Finally, a bit about the bass. Really, I have no complaints, given the driver. It's not a ScanSpeak Revelator, so it's not going to defy the laws of physics with mind-blowing, ultra-low extension. Instead, what you get is honest bass, solid down to an F3 of around 50 Hz, with a gradual taper after that (no "falling off a cliff" bass). You should know, however that these woofers need some break-in time. But once they've been played for a while, they deliver some kickin' bass, at pretty much any volume. I have cranked (and enjoyed) several selections of metal and hard rock through them, and the bass is all there. The only thing these speakers cannot do are the ubiquitous "sonic booms" that so many metal bands can't resist tossing in for Low Frequency Effects. The Orient Express are good until about 15 watts, or 99 dB, at least that's what simulation says. I'm sorry I won't test this one out for you, but I value my hearing and I have a hard time being in the same room with speakers above 90 dB @ 2 meters away. (yes, that's as loud as I tested them; sounded good!)
So do with this project what you will. For the price, I hope there are some curious parties out there, willing to give this a try. I do not think you'll be disappointed. Come on, don't you need some new speakers for your office ... or, doesn't your son need some for his bedroom ... how about your niece going away to college ... a 5.1 system for a friend ...?
by Paul Carmody | this page was last updated October 14, 2009