'small wonder' fullrange mini monitor (beginner's luck)

I'd like to share something I built for and with my son a while back for a pair of small desktop/nearfield monitors.

First off, I know that the number one rule of successful speaker design and construction is to _not_ just pick some appealing parts and bolt them together and expect good results. But that (with some trial and error along the way) is what I did, and got results that far exceeded my expectations. Beginner's luck.

The driver is the 2" Fountek FR59EXE, which look nice, seem well made, are moderately priced, and have the advantage of a built in grille.

The enclosures are a PVC weatherproof 4x4x4 inch junction box commonly called "JB444" sourced secondhand unused from ebay. Different makes of that sort of generic JB444 box have slightly different shapes and vary in how much their covers do or don't protrude past the edges. I picked some with a shape I liked.

Fitting the driver into the front baffle is a bit fiddly- the speaker's frame has arms that, if you make a hole of that diameter, you have nearly nothing left for the bolt circle around the front flange. A 2" cutout followed by some very specific filing of narrow recesses for the geometry of the frame and terminals works out nicely (you still have to be careful to leave enough for the bolts)

Initially tried as sealed enclosures and, no surprise, had a big fall-off at lower frequencies.

Tried some different diameters and lengths of PVC conduit for ports, using some calculators, with results better than sealed, but still underwhelming.

Drilled a 2" hole in the back of the enclosure and dropped in a Dayton DMA58-PR 2" passive radiator. Suddenly, wow, a really astonishingly well-rounded response, even at the low end. Started with the stock set of three washer-weights supplied with/on the PR "as delivered", played around a bit, and the sweet spot was two of the original washers plus one slightly heavier washer from the hardware store.

Tried several kinds and amounts of synthetic fibrous filler but they sound as good or better empty.

Finish on the outside of the enclosures is Rustoleum aerosol undercoating, goes on thicker than paint and is hard enough (but not brittle) to hold up surprisingly well with handling (after you let it harden for a day or more). The undercoating has an appealing "matte luster" appearance. Applied after sanding off the mold marks and scuffing the PVC everywhere with Scotchbrite to give the coating some 'bite.'

Rack handles are, of course, purely for looks (though they do also protect the binding posts on the back) sourced from ebay and apparently leftovers from some high-end Watkins-Johnson surveillance receiver.

Feet are screw-on silicone feet that someone on ebay was selling for use in making homemade wood cutting boards.

These are powered by a Tube Cube 7 single ended EL84 amp and the results really amaze me, both in terms of clarity and the extent to which you can really fill a room to satisfying (though not extreme) levels and truly enjoable clarity and tonal range with 3 watts to a 2" driver.

Not shown in the photos and added afterwards on the back of the enclosures were some small wire 'fan finger guards' to protect the PRs from errant fingers.

To get the lowest lows, we added a (housed separately) Tang Band T3-2190S 3" Subwoofer Module, powered by a Tang Band KIT0060 30 watt subwoofer amp module - but, to be quite honest, the main speakers themselves are remarkably satisfying for many kinds of music, even without the sub. I've listened to speakers of far more substantial physical proportions than these FR59 + DMA58-PR concoctions that did not actually seem to give as rich bass as these little gems. I don't have any instrumentation but the
FR59 + DMA58-PR in the 4x4x4 enclosure is very enjoyably listenable all by itself. I picked up the parts to build a second set and want to (when I find time) assemble some for my desk at work.

The FR59EXEs don't yet seem to have any reviews on either the Parts Express or Madisound sites, but I am very impressed. I bought a few more that I want to use to upgrade some of the smaller speakers in my Jeep.

Hope this provides some degree of enjoyment or inspiration to others. I am amazed at all of the knowledge, and generosity in sharing that knowledge, in this forum, definitely the more I learn, the more I realize how much still waits to be learned.
 

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Thanks for the feedback! I wish I had a better understanding of how it actually worked out that I got such great results. The Fs of the Fountek driver is 139 Hz and the listed Fs of the DMA58-PR passive radiator, with the stock-supplied three washer-weights is 39.8 Hz- and since we traded one of the washers for a slightly heavier washer, the Fs "in use" is probably at least a little bit lower than the rated 39.8 Hz. The resulting speakers have a really nice tonal balance (going by ear) all the way from significantly low notes right up through (at least as high as my hearing goes, which is probably no more than 8-10 kHz due to a combination of exposure to loud sound of various sorts over the years)
 
Thanks for the feedback! I wish I had a better understanding of how it actually worked out that I got such great results. The Fs of the Fountek driver is 139 Hz and the listed Fs of the DMA58-PR passive radiator, with the stock-supplied three washer-weights is 39.8 Hz- and since we traded one of the washers for a slightly heavier washer, the Fs "in use" is probably at least a little bit lower than the rated 39.8 Hz. The resulting speakers have a really nice tonal balance (going by ear) all the way from significantly low notes right up through (at least as high as my hearing goes, which is probably no more than 8-10 kHz due to a combination of exposure to loud sound of various sorts over the years)
Embrace the mystery! Well done...it's very innovative.
Regards Johnno
 
Embrace the mystery! Well done...it's very innovative.
Regards Johnno


Thanks- part of why I would welcome insights as to the roots of the mystery of my success is that I am kicking around the idea of trying eight of these Fountek FR59exe drivers in a close spaced vertical line, flanked by 4 of the DMA58-PR passive radiators above the eight fullranges and another four of the passives below the eight full ranges. My thinking (wishing?) is that the PRs would have the effect of extending the effective length of the line for low frequencies while letting the center of the line concentrate on high frequencies. What I am wondering is whether I can sensibly (since it's basically just a multiple of eight of the same drivers and PRs as my existing design) just take the interior volume of my single unit and multiply the volume of the long enclosure to be 8x of the single enclosure... and still have the hope of similar characteristics as the single smaller enclosure. . . .