FYI I edited my previous posts to correct some sp/grammar mistakes and revise some of my (really bad) date guessing. My memory just ain't right these days!
As I'm waiting for the compression drivers to arrive, here's an issue I'm having. It sounds like at least one of the 15" drivers is producing a sharp, loud ticking on louder passages, like it's bottoming out. I measured the drivers and they're all around 6 ohms. The amps run fine. The lf main is wired for 8 ohms and fed from the Foreplay through a lo-pass@800Hz. At the time, the 15" drivers were wired in series. I haven't investigated past this point. The probable answer is that I was inadvertently overdriving them by using the wrong Foreplay input, but I don't know for sure and the system is disassembled now. Are there any other possible causes I should be looking at?
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Post theme: "Look Ma, no wings!"
Researching OB designs again, I found information indicating that I could just wrap the baffle around to the sides
Well this was news to me! I hadn't seen nor considered this before and got very excited about the possibilities, as some of the more functional OB designs I've seen (half sheets with a 3" driver) leave me a wee bit tepid. That being said, I do tip my hat to those adventurous souls who do partake and I can only imagine the WAF conversations that took place over having not just one, but TWO half-sheets of plywood dragged into the living room and left "Just three feet off the wall, honey, please!"
Anyways, I really like the "no wings" concept and already have a basic design in mind, see pic. It's really just a rather pedestrian "form follows function" progression of the basic and popular <lf driver> <hf driver> <lf driver> OB layout with some custom design features included.
Unless things change radically, I will use 48" 14ga perforated shelving steel as the frame. This makes vertical adjustments easy.
To hold the drivers more securely, I'll cut up the old baffles, rotate them 90 degrees, screw them to the steel frame and use them as cradles to mount the drivers. This may leave a small space on either side of the horn that I'll fill with wood. The width of the cabinet will be ~16".
Since the new baffles will be folded to the sides, I'll attach some horizontal shelves to them to isolate the lf drivers. The backs will obviously be left open.
I want the top of the cabinet to follow the curve of the 15" driver.
I may want the bottom speaker to have a curve-following bottom section instead of making it flat.
For testing, I'll enclose the front and sides right to the floor. It'll probably stay that way.
As far as the base itself goes, I'll just be temporarily screwing a couple pieces of 2x4 to the steel frame for testing. I'm still debating final design, but I have some 1" thick marble pieces to play with or I just may stack a few pieces of mahogany for a stepped look.
That's enough info for me to get the old baffles cut up and attached to the steel frames. For mounting the wood baffles to the frame, I'll install threaded inserts and use machine screws.
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Compression Driver/horn (Heil replacement)
I ended up deciding to replace (instead of augmenting) the Heils, but replace them with what? I eventually chose a compression driver over another coaxial mostly because I thought that it would make cabinet design easier. I've also looked at cds in the past and and for a long time lusted after a set of TAD 2001s or updated JBLs with beryllium diaphrams, but couldn't afford them. When I started looking again recently, I found the Eminence N314-X driver that uses Textreme as the diaphram. Apparently it doesn't have the shrillness that's prone with titanium or the brittleness found with beryllium. Their waterfall plot shows they recover quickly with very little decay time. They have a recommended xover of 800Hz, just like the Heil does. This works well, as I have an ESS 800Hz xover to work with. The horns are Eminence H14EA 60x40 Exponential. I'm a little concerned that the the dispersion pattern may be tight, but they were on sale
*Update:
The Eminence N314x-8s are out of stock, but the factory does have the 16 ohm version available, so I ended up canceling the 8 ohm order and special ordered a 16 ohm set through Parts Express. Josh@PE was very helpful with the process. As far as differences go, general concensus would say that the mids on the 16s will be slightly less forward then that of their 8 ohm counterparts, and that may be a good thing. The drivers should ship sometime in the coming week.
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Building Materials
Perforated 14ga shelving steel
3/4" t&g mahogany in 5-7-9" widths
Mahogany trim
(2) 16"x56"x1" marble slabs, busted in half
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Hardware List
Digital Source:
RPi streamer, but that's a different story.
DAC:
Oppo UDP-205
Foreplay III:
Vanilla build. I have the extended kit, but I like the looks of the tube rectifier too much to swap it out :/
StereomourA:
2A3 Integrated build
Eminence N314X-16 hf compression driver
StereomourB:
2A3 Mains-only build
PAP OB-A15NEO lf driver
Subwoofer:
JTR Captivator 2400
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Signal path
RPi > Oppo UDP-205 > analog out > Foreplay III >> Subwoofer >> StereomourA >>> hf driver >> StereomourB >>> lf driver
Not shown are HT rear speakers, for now filled by Yamaha HS 50M studio monitors
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Initial Crossover frequencies:
hf <800Hz> lf <80Hz> sub
Available Crossovers:
1) ESS 2241 AM Electronic Crossover
Hard wired 800Hz
-10dB hf/lf shelf
2) miniDSP/Umik-1
The system will be bi-amped for testing and REW used for tuning. I'm shooting for an 800Hz xover. I'll start with #1 because it's easy and use #2 for further tuning. I'm planning to eventually build proper crossovers and move to a single mains for simplicity.
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At some point, I think I'll want to convert the hf amp over to 45 tubes and use the power decrease to help with SPL matching.
I'll post again once the compression drivers get here and I get everything mounted. Thanks!
