[FredT300B]

This isn't a new design but a different version of a very successful existing design. It's a very low cost experiment based on an enclosure design first suggested by Greg Monfort on the DIY Audio forum, and later adapted by Jim Griffin for use with the Creative Sound Solutions FR-125S drivers. This might be considered a frugalphile version of Jim's design, because it uses two $27 Tang Band W4-1052SD drivers per enclosure instead of the pricier CSS drivers. Of course there's no free lunch, and the CSS drivers are better built and better sounding than the Tang Bands in several ways, but the TB's still sound very compelling in this enclosure. 

The drivers are four ohm impedance and are wired in series for an eight ohm nominal load. Unfortunately their sensitivity is relatively low, and they have a rising response curve much like the Fostex Fe-167E that requires a network for any semblance of balanced sound. Consequently the sensitivity is about the same as I recall from a pair of Magnepans I used to own. Low power SET tube amps are not recommended. My 200w/ch Krell drives them just fine. For the network I used a 2mH air core inductor with a five ohm resistor because that's what I had in the parts bin, but I believe a 1.5mH with a four ohm resistor might be adequate.

I auditioned these speakers for the most critical listener I know, my wife, and she said "they sound good". No audiogeek-speak from this chick, either they do it for her or they don't. These do. My impression is that the bass is very good for such small drivers and the treble is clear and extended enough that you don't sense any absence of air. The big plus feature of these speakes is the open airy soundstage - not as precise as with a monopole speaker, but more like live music actually sounds in a music venue. These speakers are very easy to listen to.

The enclosures are built of 3/4" birch plywood. This is a fun project that can be built for less than $150. I wish somebody who has test equipment would copy this verion and determine the best tuning. I use the same 3" by 3" port that's recommended for the CSS version. I'm in NW Houston, and anybody who would like to hear them is invited to stop by for an audition.

http://fredt300b.smugmug.com/gallery/132721_wacsQ#416183572_Y8n2X

[Duke]

Hi Fred,

Well I'm something of a fan of bipolars, you may recall...

Anyway, glad to see this oft-overlooked format is getting some attention.  I think it does some things better than any other, provided you can give it a bit of breathing space. 

Can I ask you a question about the cabinet?  I can't tell from the photo - is it wider than it is deep, or vice-versa, or about the same?

Thanks!

Duke

[FredT300B]

Hi Fred,

Well I'm something of a fan of bipolars, you may recall... Anyway, glad to see this oft-overlooked format is getting some attention.  I think it does some things better than any other, provided you can give it a bit of breathing space.  Can I ask you a question about the cabinet?  I can't tell from the photo - is it wider than it is deep, or vice-versa, or about the same?

Duke

You are so right about bipoles. I listen to live music at least three nights a week, and the first characteristic of bipoles I noticed is how much they sound like the real thing. These are positioned 36" from those stained glass panels behind them in the picture - I would like more space but the room is small. I heard your bipoles, and they sound better than these 

BTW, if anybody is considering building a pair and isn't as budget-constrained as I was, I strongly recommend using the CSS drivers instead. It's not that the TB's sound bad, just that the CSS drivers are the smoothest small full range drivers I have heard, they can be parallel wired for four ohms, giving them quite a bit more sensitivity, they have greater treble extension, and they don't require a correction network. The CSS drivers' sound and build quality is more comparable to the TB titanium cone cast frame drivers, but smoother through the treble range. The CSS version is easily driven by a small tube amp. For enclosure dimensions see the link to Jim's enclosure plans below.

http://homepage.mac.com/tlinespeakers/FAL/downloads/BipolarMLTLDesignPak.pdf

[chrisby]

Fred - a couple of observations if I may on your comment re "the CSS version is easily driven by a small tube amp";

Several years back we built a variety of designs with FR125 and WR125 drivers, and found that the combination of low power / low damping factor SE tube amps and these drivers didn't always work well.   Even with 2 drivers in parallel, the sensitivity was low enough that 3-4 watt SETs are easily clipped, and the drivers really shine with higher power/damping factor amps.

I'd suggest a 25-30 watt push pull (i.e. EL34 triode/ KT88, 6550 etc) would yield far better results.  When feed accordingly, and provided a vented or MLTL design is not tuned below their comfort zone, the CSS drivers can deliver stunning performance value. If there are any issues with low end extension in a particular application, low passing to SDX7 woofer per side,  even in very small sealed enclosures (i.e. starting at less than 1 ft^3 ), can relieve all the heavy lifting. 
 

[FredT300B]

Fred - a couple of observations if I may on your comment re "the CSS version is easily driven by a small tube amp"...
Even with 2 drivers in parallel, the sensitivity was low enough that 3-4 watt SETs are easily clipped, and the drivers really shine with higher power/damping factor amps. 

Thanks for the clarification. Now that I've thought about it, I drove them with an 8 watt 300B amp, which drove them to reasonable levels in a small room, but they did much better with my Ella KT88.

[JLM]

This design does offer a number of compelling advantages over any other design I can think of.  I have F200A MLTLs, but this could open the door to smaller drivers/cabinets with far greater higher frequency dispersion. 

Have you tried to pull them out farther into the room and listen nearfield (equalateral triangle, speakers to listening position)?  That's what I do and the imaging is fantastic, especially depth of soundstage.  I'd guess these would do even better.

[FredT300B]

Have you tried to pull them out farther into the room and listen nearfield (equalateral triangle, speakers to listening position)?  That's what I do and the imaging is fantastic, especially depth of soundstage.  I'd guess these would do even better.

I had not tried them nearfield, but I did after you mentioned it. I set them at a 45 degree angle 5' out from the corners, which places them 5' apart. Listening at a distance of 5' does increase the soundstage focus. I also listened at the sofa's normal position in the room, which is 7' from the speakers. The differences are not great, but there's a small tradeoff is between a more focused soundstage at the nearfield listening position and a more realistic "live music" ambience when the listener is farther out. It's a personal preference, which probably places me in the minority among audiophiles, but I prefer the farther-out listening position.

[planet10]

Fred - a couple of observations if I may on your comment re "the CSS version is easily driven by a small tube amp";

Several years back we built a variety of designs with FR125 and WR125 drivers, and found that the combination of low power / low damping factor SE tube amps and these drivers didn't always work well.   Even with 2 drivers in parallel, the sensitivity was low enough that 3-4 watt SETs are easily clipped, and the drivers really shine with higher power/damping factor amps.

It isn't even low power SETs, or SETs at all.... at an event at RAW in Vancouver, we had an opportunity to drive a number of FR125 speakers with a number of Single Ended amps including an 845 and a substantial Nelson Pass ZEN-family amp. Like the 4W EL84 amp they all suffered the same issue... on some passages the driver would "fart" ... we surmise that with no mechanical damping at the end of stroke, the SE amps were popping the voice coil against the back plate.

A good Push-pull amp recommended for these.

low passing to SDX7 woofer per side,  even in very small sealed enclosures (i.e. starting at less than 1 ft^3 ), can relieve all the heavy lifting. 
 

The largest sealed box you want to put an SDX7 in is 3/4 ft^3 (21 litres)

dave

[JLM]

Fred,

"Live music ambience" is what I associate with dipole sound.  Didn't realize we were talking about just a 5 ft vs 7 ft difference.  Thanks for trying.  The additional focus provides me with additional resolution (detail).

[TerryO]

Fred - a couple of observations if I may on your comment re "the CSS version is easily driven by a small tube amp";

Several years back we built a variety of designs with FR125 and WR125 drivers, and found that the combination of low power / low damping factor SE tube amps and these drivers didn't always work well.   Even with 2 drivers in parallel, the sensitivity was low enough that 3-4 watt SETs are easily clipped, and the drivers really shine with higher power/damping factor amps.

It isn't even low power SETs, or SETs at all.... at an event at RAW in Vancouver, we had an opportunity to drive a number of FR125 speakers with a number of Single Ended amps including an 845 and a substantial Nelson Pass ZEN-family amp. Like the 4W EL84 amp they all suffered the same issue... on some passages the driver would "fart" ... we surmise that with no mechanical damping at the end of stroke, the SE amps were popping the voice coil against the back plate.

A good Push-pull amp recommended for these.

low passing to SDX7 woofer per side,  even in very small sealed enclosures (i.e. starting at less than 1 ft^3 ), can relieve all the heavy lifting. 
 

The largest sealed box you want to put an SDX7 in is 3/4 ft^3 (21 litres)

dave

Dave's absolutely right. I was also at that RAW event and can testify that my FR125's mounted on a large open baffle was a very sorry sounding speaker on the majority of tube units at the event. However, when driven by higher powered SS amps they did sound much better, although they weren't as good sounding as I had hoped. This was my experience at home using my LM 7480 chip amp, as well as Scott's (SCD) mono blocks based on the same chips that he brought to the RAW event.
This problem didn't present itself with any of the Fostex drivers (and there were a few there) driven by the same amps and associated gear.

Relieved of deep Bass duties the FR125s do sound much better. Using the SDX7, or perhaps Exodus Audio's EX-6.5 woofer, would probably make for a much better sounding solution regardless of ones choice of amplifier.

Best Regards,
TerryO

[rajacat]

These Omega (upgraded to Hemp drivers) Bipoles image very well. I have them placed about 5 feet from the front wall, 3' from the side wall, about 6-1/2' apart, toed in moderately (about 15 degrees) and they are tilted slightly upwards.  They image really well in the wide sweet spot but the odd thing is I can walk around the room and it seems like I'm at a concert and the instruments retain their appropriate placements and when I walk between and behind them it feels like I'm walking among the band and the instruments are quite localized. This is almost counter intuitive. I would've never thought that bipoles could image this well. I'm even happy with their playback of classical orchestral music.

Despite the small (4-1/2") drivers these bipoles pump out quite respectable bass. Sometimes I think my sub is on when it isn't. They're currently being powered with modded Heathkit W5m monoblocks @ ~30w/channel.

-Roy