The purpose of this (ongoing) project is threefold:
to explore a woofer box configuration that has little documentation as far as construction of working models;
provide a symmetrical dipole output in the lower midrange that compliments the output of the Heil amt;
create a speaker that has a classic, nostalgic sound from the 1970s but with some refinements....
Component raw drivers:
Heil amt from ESS labs (2),
SEAS A26RE4 H1411-08 10" woofer (4),
SB Acoustics SB34NRX75-6 12" woofer (2),
SB acoustics 12" passive radiator (2)
The 12" woofer boxes were originally built to be subwoofers, and are awkwardly large for this application, but they will serve the purpose of providing bass for my prototypes. The passives are downward-firing.
The SEAS 10s are mounted back-to back, out of phase, and wired in series. The box inner shell is 11" x 11" x 9.5" stuffed with polyester padding. After a few trials, I decided they sounded best running full range on top, using their natural roll-off. Their bass response is surprisingly good, and well-defined in the upper bass, but of course tapered off due to the out of phase connection. Mounted on stands as satellites and using a center channel subwoofer, they do quite well. But what I am going for is a full range floor standing system.
For now I am only considering passive crossovers. The 12" woofer is a 4 ohm unit with a single 5.0 mH coil wired in series.
An advantage of the higher impedance series connection is I can use much smaller capacitors where needed. The bass of the system is much better without a cap in line with the 10s. The problem is that I also play records often and sometimes loud, and the 10s respond to the subsonics. Even with a 200 mfd cap, the resultant response produces a dip in the 180hz region, and there is a slight peak at about 300hz.
For the Heil amt, I used series resistances to match output levels and the higher impedance of the 10s. The high pass section is a scaled up version of the original ESS Heil amt1, so it uses smaller caps and a larger coil, with an additional series cap to touch up the response.
Except for the area in the lower crossover section, the response is decently flat from 300hz to about 8khz. There is a peak at about 1.5khz on axis of the 10s, a slight lobing effect of the system. All forward facing drivers are wired in phase.
On music, the sound is open, forward sounding in general, but not really too aggressive. There is an amazingly "3-D" effect on some recordings, as you can imagine. All in all, a very impressive sound, even more so considering the bass-mid enclosure volume is about 0.4 cubic foot.
So far I don't see any downside to the acoustic loading technique of the 10s, and am impressed by the transient response in the middle and upper bass. If this method stands the test of time, I might even try a version with 5" fullranges like the Tang Bands mounted above the Heils.
-- Greg
The latest version crosses over at about 180hz from 12" woofer to the two 10" woofers, (1st order low-pass, 3rd order high-pass); then at about 1khz for the cross to the amt (3rd order high-pass, natural roll-off on the SEAS 10s).
I also put a section of 3" high density foam in the center of the 10" woofer boxes with a 1" layer of polyester in back of each driver.
I went back to 4 ohm loading of the tweeter for now, it seems to blend better with the 10s at the crossover point. R1 gets pretty hot at high volumes, though.
Sound is really good now, though I was hoping for more sensitivity in the low bass. So possibly dual poly 10s or 12s would work better here.
--Greg
Attachments
New bass enclosures
I went with dual poly 10s, 3 cu. ft. vented box. The crossover is now back to one similar to the AMT 1, with a 2nd order low pass in line with the two SEAS woofs, now wired in parallel. The two Misco poly 10s are wired in parallel, with a 2.5 mH iron core coil in line. The SEAS 10s are now allowed to roll off without a high pass filter for the initial listening tests.
I went with dual poly 10s, 3 cu. ft. vented box. The crossover is now back to one similar to the AMT 1, with a 2nd order low pass in line with the two SEAS woofs, now wired in parallel. The two Misco poly 10s are wired in parallel, with a 2.5 mH iron core coil in line. The SEAS 10s are now allowed to roll off without a high pass filter for the initial listening tests.
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