PhotographyYelloweye 2.1 speaker system: yellow eyes
I couldn't think of a simpler name for a speaker cabinet with yellow Kevlar cones. Looking for an idea to replace the not-so-good sounding Logo speakers, I tossed up the idea of building two bookshelf cabinets and a separate subwoofer, often referred to as a sub+sat or 2.1 system. The excellent, but huge -and moreover retired- Yellowstones would have been way too bulky for our living room.
After tearing apart the Yellowstone project, I was left with an excellent set of drivers. I fired up the good ol' cab sim (WinISD) and decided upon closed 2.5 liter enclosures for the sats, each equipped with a Monacor Monarch SPH-135KEP and a tiny Dayton ND16FA-6 dome tweeter. The subwoofer will house two SPH-300KE monsters, but at this moment I haven't decided yet whether it's going to be an isobaric ported cabinet or a dipole. A dipole subwoofer requires a very large space behind the cabinet to act as some sort of infinite baffle approximation. Obviously, one needs the space to do this, and I'm not sure our living room qualifies. So I'll sort that part out later.
One of the main aspects, and to me the most boring and time-consuming part, of building loudspeaker cabinets is the finish. I made a small list of requirements for finishing these cabinets:
- No visible joints or nail heads
- Looks like wood
- Durable and scratch resistant
- Doesn't take too much time
- No filler, no sanding, no polishing
- cheap
Adding it all up, this suggests the use of mitre sawn pre-laminated board. In other words: laminate flooring. I have plenty of it left from my last flooring adventure, so if I cut up a board or two, there's no harm done. It's quite obvious one can't construct a proper enclosure out of this stuff alone, because it's only 7 mm thick. It'll have to be heavily backed by inside bracing and/or damping material. And if visible joints are not allowed, the outer shell will have to be glued only.
Luckily I happen to own a very handy power tool called a plunge router. And a nice one at that. With a 45° V-shaped bit it can do all mitre work, and cutting the holes for the drivers requires nothing more than letting it roar for 20 seconds along a compass with a straight bit. The brace panels can be nicely fitted into slots along the insides.
But here's the real kicker: the Monacor SPH-135KEP drivers have a removable solid aluminium cone in their centers, where other drivers have a dust cap that's usually very hard to remove without damaging the sensitive cone. The Dayton tweeters with their 32.5 mm diameter are so small, they fit nicely inside the 35 mm voice coil of the SPH-135KEPs. Thus creating a coaxial system! So I made two plastic tubes to replace the phase plugs and fitted the tweeters inside it. Unfortunately the woofers have an extra ring magnet on top of their pole pieces, so there's not enough room for the tweeter to sit flush with the woofer cone, but I think the advantage of having it in the center would make a big enough improvement in itself.
Click thumbnails to zoom in. Click again to zoom out, or use cursor keys to walk through all images.
1. The original Monacor SPH-135KEP driver.
2. The phase plug removed. It's kept in place by a bolt through the pole piece.
3. A plastic tube replaces the phase plug.
4. The Dayton ND16FA-6 tweeter installed.
The Dayton tweeter really is a super tweeter. And I don't mean it's of some sort of superior quality or something. I'm saying it has a pretty limited range with its resonance frequency as high as 2.3 kHz. As a result, I will be crossing it over at 4 kHz, where the resonance peak and phase shift can't cause too much trouble.
... to be continued ...
Fuzzcraft.com comment system 1.1
2011-08-06 Damic
Hey nice tweets, I got the ND20FA-6 in my car :p
(There's no signing up, no censoring, no hassle, no nothing. You can just post a comment)