This project has been in the works for a while, but I have only recently gotten down to brass tacks... Up until now, I've been listening to my Fertin 20EX on the JELabs open baffle and been pretty content. But, as one sage put it, you can't ask a 8" 'chinless' wide-range driver to do justice to large-scale music. I suppose I could simply add a high-pass filter at around 200Hz, find something to fill in the bass and then be done with it -- but what's the fun in taking the easy way out?
This then but begs the question: What to replace the Fertin 20EX with? I genuinely enjoy the Fertins, but they possess a couple of shortcomings that needed to be addressed in the next speaker go-around. First, as I mentioned, the Fertins don't do macro-dynamics. They pull out all the small details of the music, but mezzo-piano to mezzo-forte is about the best they can do. The next speaker had to be able to handle the swell from pp to ff and not just gloss over it. Second, the Fertins aren't particularly high efficiency. I figure they're around 94dB/1W and the subsequent speaker iteration necessarily had to be in the ballpark of 100dB/1W. I have a fairly small room and for the most part mid-90's efficiency is fine, but to my ears low mass/ high sensitivity speakers simply sound more real.
At this point, I think it's clear I've moved on to a multi-way of some sort, dividing duties between a mid-bass and a tweeter. Around the time I started wondering about a replacement for the Fertins, a great thread popped up over at diyAudio: Large midrange for OB??? ScottG?. It generally confirmed that the direction I was headed in could turn out to yield a pretty decent speaker. Namely, I was thinking about pairing up a vintage pro-sound driver on an open baffle with a compression driver/ horn. I really like the open baffle 'house' sound so I stuck with that, and horns are essentially the only way to cover the treble at the required efficiency. Since then there have been a couple of other relevant threads: Lynn Olson's behemoth Beyond the Ariel and Magnetar's continued attempt at excess in sound reproduction Sensitive Wide Range Open Baffles.
For the mid-bass, I quickly settled on Jensen A12 12" field coil drivers. These speakers are ubiquitous on eBay, as they were used in Hammond organ cabinets for years and years. From a quick glance, they looked like they would do the job quite well, and I'm predisposed to liking field coil drivers anyways. There aren't many comments on the Internet about using them in hi-fi speakers, but the ones I found said that the drivers are wonderful and under-appreciated. I listened to the A12s full-range, and they do an awful lot right so I had high hopes for integrating them into my setup. I measured the theile/small numbers with WT2 and, for the sake of convenience, got Meniscus Audio to measure the frequency response. I'm planning on getting a speaker-testing setup of my own put together using ARTA, so I'll post revised measurements once that happens.
For the treble, I hearkened back to a set-up I heard a couple of years ago at VTV in northern NJ. I didn't hear much at the show that was particularly memorable, but one setup that really did it for me was Bill Woods' room. His enterprise is Acoustic Horn Co. and he was showing a 700Hz conical horn + a small back-loaded horn. I came away absolutely impressed with the effortlessness and clarity of the compression driver/ horn combination. I haven't heard much in the way of horns, certainly none of the big Altec multicells nor any of the 'salad bowl' Tractrix horns by Bruce Edgar, but the conical horns sound awfully nice to me. Because I didn't need extension to 700Hz, I went with his smallest model the AH!1000, a 1000Hz (obviously) conical horn. They're extremely well made, and Bill has been very generous with his time throughout the process; we've had several long phone conversations covering the two different crossover networks he included with the horns. Keeping with the vintage theme, I picked up a pair of Altec 802-8D 1" compression drivers and had them checked out & re-magnetized by Bill Hanuschak at Great Plains Audio.
So, we've got a 2.5 way with the Jensen A12 pair doing sub-1500Hz and the Altec 802-8D/ AH!1000 covering from there up. For a first pass, I'm unreservedly happy with the results to date. The Jensens only reach down to about 100Hz, but that's to be expected. I'd rather have sensitivity than extension and consequently I've always assumed that I'd need to add some sub-woofer support. The compression driver/ horn combination is excellent, but it's clearly still very much a work in progress to get the transition from one driver to the other nailed down. I don't expect that with my choice in drivers the overall frequency response will closely resemble 'flat', but vintage drivers have a reputation for making up for less-than-stellar numbers -- so let's keep our collective fingers crossed. As an aside, if I were to think about using some current production drivers, I would probably start with these and these. I only have one channel up and running as I'm still building a DC supply stout enough to handle all four drivers; let me state categorically and without reservation that listening in mono when evaluating a new speaker is just ruthless -- every flaw is writ large.
This project is still in the early stages and I intend to update this page as I make progress, which I hope will be frequently. In the near-term, I need to build new baffles; as can be seen in the picture they're a couple of inches too short as-is. Once I get ARTA up & running and with Testing Loudspeakers & Loudspeaker Design Cookbook in hand, I'm hoping to take another look at the crossover. And, of course, I need to finish the new, beefier DC supply. Beyond that, I might look into bi-amping with some passive line-level crossovers (PLLXO), but that's a ways off. And last but not least, a couple of sub-woofers to fill in <100Hz will finally make an appearance -- I've had the drivers for a couple of years, waiting patiently in the attic.
[7 Jan 09] At last, some news... This version has been superseded by these. I had some issues with a number of the Jensen speakers developing voice coil rubs, so I started over using current production drivers, specifically the ToneTubby 12" AlNiCo and Beyma CP380M 1" compression driver.