TB W8-1772 or Fostex FE206En

[Llewellen]

There are lots of general hits here and elsewhere but I couldn't find anything head to head.
I'm considering one or the other of these drivers for the Madisound BK20 backloaded horn kit.
To be powered by the Seductor in a  small listening room (15ft x 20ft).
There is also the Fostex FE208EZ but it's published freq resp indicates the need for a super tweeter and I want to avoid that.

Opinions?  Comments?  Experiences?  Thanks.

[EricS]

I have not directly compared these two drivers, but I have a pair of 1772's that I've been playing with for a while now.  They currently live in a 40L ported MDF enclosure.  I am trying to decide on a final build as either a 24" tall speaker on a stand, or a floor standing design ala Bob Brines...

The TB 1772 speakers certainly do not exhibit rolled off treble.  They have quite the opposite - a rising treble with frequency response.  Fortunately, this is pretty easy to correct.

I've attached some images, all are measured frequency response of my 1772's in a 40L ported box that is up against the wall in a small room (12ft by 14ft).  The first image is the raw response of the driver/box combination with no crossover.  The second shows a comparison between my crossover (0.56mH inductor in parallel with a 15R resistor) and the crossover that Bob Brines designed for this speaker.  The primary difference is the correction Bob adds to the 10kHz+ region. I happen to like the slight rise in response at the treble end and my network is more simple.  If you want to bring the treble response down a bit more, change 15R to 20R (see last image).  Measurements were taken on-axis about 4 feet away from the speaker and the graphs show 1/3 octave smoothing (cleans up the jaggies a little).  If you move off axis, treble response diminishes a bit (like most other speakers).  I wouldn't read too much into the the big peak and dip below 200Hz - these are likely due to the physical configuration of the room.  Also, don't go comparing absolute dB level output across graphs as these were made at different points in time with different volume levels.  The point is to compare the general shape of the response plots.

There are a number of designs for this driver published online.  Here is one design for a smaller speaker (0.75 cu ft): http://www.transcendentsound.com/Small_Tang_Band.html  There was another design published on this same web site for a 3 cu ft floor stander that now seems to be gone.  The details of the larger cabinet are: cabinet volume of 3 cubic feet (85L).  External dimensions 37.5" tall, by 15.5" wide, by 11.75" deep.  The walls are 3/4" thick plywood and the vent centerline is 8 inches off of the bottom.  The vent is 4" diameter and 4" long.  There are two window braces in the cabinet for reinforcement.

The L-Pad approach is a great way to experiment with the treble level.  I built mine this way, listened for a few days, made minor adjustments, listened some more, adjusted some more...  They produce plenty of bass, and if you're a purist, you'll probably be fine with these speakers on their own.  I like a bit of kick from my bass, so I run these with my DIY sub.

[Llewellen]

@EricS  Thanks for the detailed response.  Very helpful and appreciated.  From your report, it sounds like this driver can produce enough high and low end in a BL horn to satisfy my aging ears.  The fact that the highs may need to  be tamed a bit just confirms that I probably won't need to think about a super tweeter.

I had seen the Transcendent link previously.  Any idea which sub was used or recommended?  Thanks.

[EricS]

I'm not sure which driver they used as a sub.  There are plenty out there to play with.  I found the new link for the floorstanding version of the 1772:  http://www.transcendentsound.com/Full_Range.html

[Llewellen]

@EricS:  Thanks for the link.  Interesting that the enclosure is designed wide and shallow.  I would automatically think the opposite to go narrow and deep, to try to minimize baffle problems.

Anyway, it's a reflex and I'm trying to settle on backloaded horn design of some sort.  Maybe the Madisound BK20 or perhaps the Frugel-Horn XL.  It my small apartment listening room, corner loading would be useful.

[Paul Joppa]

There is some data indicating that the worst (psychoacoustically) box diffraction problems occur when the dimensions are in the 8"-12" range. Narrow boxes work when the driver is nearly as wide as the box - the driver starts to beam so the edge diffraction is smaller, while the other approach is to make the cabinet much wider - most often, I've see 20" to 24" as a good minimum.

My own experience is that the narrow box approach usually gives the better imaging. But I try to keep an open mind ...  :^)

[Llewellen]

Thanks Paul.  That generally accords with my naive and non-experimental understanding of the subject.  It still leaves me pondering these  backloaded horn designs and driver combinations, which I have no chance of actually hearing before deciding:

Madisound BK20: designed for Foxtex FE206En but will also accept TB W8-1772 (both nominal 8 inch).  Exterior baffle width 12.5 inches.  Conventional style horn fold.

Tang Band: designed for TB W8-1772 (8 inch).  Exterior baffle width 11.75 inches.  Olsen/Nagaoka style horn progression.

Frugel-Horn XL: designed for nominal 6.5 inch drivers.  Exterior baffle width 9.5 inches.  Seems to be almost a folded QWTP design.

Decisions, decisions.  Advice, clues, suggestions greatly appreciated.

[EricS]

Interesting details on baffle width, Paul.  Thank you!  I would have assumed the cabinet would be more narrow and more deep myself.  I suppose the 12" grill obscured the difference between the driver diameter and the baffle width when I first looked at this design...

I've been a bit interested in the back-loaded horn design that floats around for the Tang-Band, but that looks like a large undertaking.  I also have a set of Alpair 10.3 drivers breaking in at the moment.  Funny how the sound changes with two raw drivers on the floor with one of them wired out of phase from the other - all of the lows and mids goes away, leaving only the treble.  Interesting lobing as you move your head back and forth over the pair    My plan is to build a set of Frugal Horn XLs for the Alpairs some time this summer.   Then, I'll be able to compare the floor standing Tang-Band speakers (probably Bob Brines' design) with the Frugal Horn XLs.  This comparison is several months away at this point, though.