FredT... WOW! I was amazed at the speakers in those pics. You are very fortunate to have heard so many of these designs. From inexpensive wide range Foster drivers to Jordan's and everything in between. Even the humble Pioneer B20 was in there... Pi... Klipsch! Very cool!
Hope you enjoy the TB 8"... it looks really great to me on paper and in the pics.
Godzilla
Hope you enjoy the TB 8"... it looks really great to me on paper and in the pics.
Godzilla
I finished the enclosure construction this morning, installed Bob's proprietary compensation network, installed the drivers, and placed them in the system. My first impression is very positive except for a lack of high frequencies. This afternoon I substituted a different value for one of the inductors in the filter and that problem was solved. Now I need to listen for a few days with several different type amps to decide whether I can rekindle my love affair with single drivers.
Speakers - FredT300B's Photos
Speakers - FredT300B's Photos
Yes, I installed bi-wire speaker terminals with the network connected between the lower and upper positive terminals, so the network is in the circuit through the lower terminals and bypassed through the upper ones. This way, if I decide to use dsp equalization I won't have to rewire the speakers.
With the network in place I found the bass is more prominent (inductor and resistor in parallel), but the upper treble is too attenuated (the network includes another small inductor in series with the bsc filter). Reducing the value of the second inductor brought the treble back, but I need to give them some breakin time and then experiment with different values. Bob also suggested I might want to substitute a zobel instead of the second inductor.
To answer your question directly, without the network they have that familiar single driver characteristic - relatively weak bass and prominent highs.
I'm driving them with class D monoblocks, and I expect that without the network the bass will be more pronounced and the treble less bright with my SET monoblocks, which I'll try later.
Yes, but that's not what's needed in this application. The series resistor attenuates the signal by about 3-4dB across the sound spectrum. The inductor provides a short circuit for only the lows below 500hz or so. A bypass cap would "undo" the attenuation of the highs, but the typical full range driver's output increases with frequency above 1khz, so adding top end would be counterproductive.
Bob told me it's ok to let the cat out of the bag about his compensation network, so here it is: A 4mH inductor in parallel with a 12 ohm resistor (I used a 10 ohm), with those components followed by a series 0.5mH inductor to roll off the highs. Bob modeled this combination but hasn't heard it since he uses DSP compensation in his speakers. I found the 0.5mH inductor's value was waaaaay to high and tried a 0.33, then a 0.24, followed by a 0.15mH. The 0.15 seems to be about right, but even that value shaves off some brush-on-ride-cymbal sounds. For example, that sound in the first few measures of Patricia Barber's "Let it Rain" from "Modern Cool" is better with no series inductor at all. I'm now listening to the speakers with a zobel consisting of a 6.8uf and a 10 ohm, which Bob suggested I try instead. That seems to be the best solution.
I hope in all this discussion I'm not biasing anybody in either direction about these TB drivers. Don't forget these are FR drivers, and they are about four hours out of the shipping box - much too early to form an opinion! I also haven't experimented yet with different amps and with speaker placement and toe-in. I'm providing this info only because others have asked about my first impressions, and also because I find this kind of ongoing discussion interesting when somebody else is first hearing a new design.
Forgot to mention, if anybody will be in the Houston area next Saturday, I'm hosting the Houston Audio Society's monthly meeting at my house. The meeting topic is a comparison of several different types of speakers, and all are invited to join us. I'll post directions here: houstonaudio : Houston Audio Society
We'll listen to the same tracks on each of these speakers: 1) Maggie MMG's, 2) a Jim Griffin design bipole MLTL using CSS drivers, 3) my Art Array line arrays, 4) The Brines Acoustics TT-2000's which are the topic of this thread, and 5) a typical "high end" design, the Selah Audio Texas Revelator Towers, a 2.5-way using Scan Speak Revelator 7" woofers with the Revelator Air Circ tweeter. Each of the above, with the exception of the Selah design, cost about $400 to $600 including the cost of the enclosures. The Selah's were about $1,800 with veneered enclosures.
The purpose isn't to impress any of our members whose systems are typically in the $25K to $250K price range, but to hear the HUGE differences in the sonic characteristics of these similarly priced, but very different designs.
We'll listen to the same tracks on each of these speakers: 1) Maggie MMG's, 2) a Jim Griffin design bipole MLTL using CSS drivers, 3) my Art Array line arrays, 4) The Brines Acoustics TT-2000's which are the topic of this thread, and 5) a typical "high end" design, the Selah Audio Texas Revelator Towers, a 2.5-way using Scan Speak Revelator 7" woofers with the Revelator Air Circ tweeter. Each of the above, with the exception of the Selah design, cost about $400 to $600 including the cost of the enclosures. The Selah's were about $1,800 with veneered enclosures.
The purpose isn't to impress any of our members whose systems are typically in the $25K to $250K price range, but to hear the HUGE differences in the sonic characteristics of these similarly priced, but very different designs.
Sorry to be dense, and I'm not nearly as knowledgeable as I can tell you are about these things, but but wouldn't the bypass cap (of a sufficiently high value) put the brush-on-ride-cymbal sounds back in? I'm a fumbler and a noob at these things, but I had the same issue with FE207E and FE208-Sigma in Bob's cabinets and the bypass cap was a lifesaver.
Yes, you are correct. I have used a by-pass cap many times and it brings back the very top end.
That wasn't a "dense" post at all. Yes the cap would let the highs back in, but the current filter design uses an inductor to take it out. I'm finding the best solution with these drivers seems to be either no series inductor, which might be a touch bright with poorly recorded music, or the zobel, which shaves just a touch of brightness off. For now I plan to stay with the bsc filter plus the zobel, and re-evaluate it after these speakers have about 100 hours playing time.
Yes, but as these drivers accumulate some playing time I'm finding the zobel isn't necessary. Even with less than 24 hours' playing time these drivers are amazingly smooth compared to Fostex and Lowther drivers I've heard. The treble "edge" I heard early-on has disappeared, and I'm hearing better upper treble resolution with no zobel in the circuit, so I'm using only the BSC filter, which consists of a 4mH inductor and a 10 ohm resistor in parallel.
All my listening so far has been with a prototype pair of D-Sonic 250 watt class D IcePower monoblocks with Lundahl input transformers, and also with a Krell KAV-400xi integrated. Over the next few days I'll be experimenting with a pair of SET tube monoblocks, and the speakers positioned closer to the corners in a smaller room, with and without the BSC filtler in the circuit. I'll report on that later.
The TT-2000's sound very good with corner placement, toed out 45 degrees, no BSC, driven by a 3 watt 2A3 SET amp. The corner placement gives adequate bass reinforcement with zero BSC, and this provides a direct connection to the amps, enabling them to take full advantage of the drivers' high sensitivity. The speakers sound more "alive" in this configuration, and as several speaker designers including Earl Geddes and Duke LeJeune have demonstrated with their speakers, the 45 degree toe-in provides a very realistic soundstage due to the lack of sidewall reflection. I would prefer just a bit of BSC, even with this placement, and will add a second switchable 7 ohm parallel resistor to the filter to provide the option of 10 ohms or 4 ohms resistance. I'm really beginning to like these speakers. 
This is the link to a picture of the econon-system, which includes an Oppo source, a modded Audio Experience MK-III preamp, Bottlehead Paramours, and the TT-2000's. Speakers - FredT300B's Photos
This is the link to a picture of the econon-system, which includes an Oppo source, a modded Audio Experience MK-III preamp, Bottlehead Paramours, and the TT-2000's. Speakers - FredT300B's Photos
oops, isn't that a proprietary secret? lol.
yes, i'm very curious to know if they'll become acceptable without a BSC circuit.
The answer to that question is an umambiguous "yes" and "no".
Some of my single driver friends listen to speakers with small Fostex drivers that make my ears bleed with their brightness, yet they remark about how good the sound is. For these folks a bsc circuit is completely unnecessary.
My ears are tuned to the sound of the typical "high end" multi way speaker with crossovers that incorporate any filtering needed to remove distracting peaks, highly resolving but not overly bright treble, and warm full-sounding midbass. These ears would still like to hear some bsc, but with the speakers positioned near the corners of the room I could get by with about half the bsc provided by the stock filter.
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