Going Big: 1.5-Way Augmented Full-Range Open Baffles

[techguy0192]

Sharing the details and end results of an OB speaker build I finished recently.


The Build Specs:

3/4" Baltic Birch, painted for a modern look. Nearly every speaker I have purchased or built has had a wood finish, so I wanted to give something new a try.

Mechanical stability was a priority given the large surface area of these baffles and the displacement of the 15-inch woofers. To eliminate unwanted panel resonance, I used large heavy-duty L-brackets (rated for 600 lbs!) to rigidly couple the baffles to the bases. This has proven highly effective; the structure remains inert even at higher volumes. By neutralizing baffle vibration at the source, the Tang Band’s micro-dynamics stay clear and free from the smearing that can be caused by low-frequency energy. At this time, I have no plans for additional bracing.

• Dimensions: 24" W x 48" H, mounted on a 14" base with felt isolation pads.​
• Drivers: Tang Band W8-1808 and Eminence Alpha 15a​
• The Tang Band is offset on the baffle to address diffraction, while the Eminence is mounted near the bottom for boundary reinforcement.​
• No binding posts are used. Each driver is directly connected to its respective amplifier.​

By offsetting the Tang Band, I’ve controlled the diffraction nodes that usually occur when a driver is equidistant from the baffle edges. This help flatten the frequency response in the critical mid-range. With the Alpha 15a near the floor it benefits from boundary reinforcement, countering the natural dipole roll off.



Details:

• Tang Band: No crossover and directly connected to the amp with a 50 Hz high-pass filter between the amp and preamp. I have been trying different amps, some have settings that allow me to further tailor the sound.​
• Eminence: Currently driven by a Bryston 4B SST via an active analog crossover.​
• Harrison Labs FMOD 50 Hz high pass. While the Tang Band W8-1808 is a spectacular full-range driver, asking any 8-inch driver to handle deep bass creates physical challenges. This inline filter between the preamp and amp helps control intermodulation distortion, increase the headroom of the amplifier powering it, and protects the driver from being pushed past its physical limits. It also ensures the two drivers aren't fighting over the same low-frequency air space, allowing for a better mid bass transition.​
• I am utilizing a 24 dB slope for the woofer that’s currently set at 90 Hz.​
• DBX 223 XL analog active crossover, for the woofer only.​
• Cables: I started with Belden 9497 but switched to 14 AWG zip cord for more "meat on the bone". Just recently I swapped in some 13 awg Supra Classic 2.5 cables and plan to try them out this weekend.​

Room:

• Dedicated 12'x14' listening room, dedicated power, and acoustic treatments.​

Results:

The speakers sit 3' off the front wall with a slight toe-in. The result is "artist in the room" realism. I’m getting excellent imaging, which is very important to me, along with depth, speed, and dynamics. Because I have a small listening room, it is easy for the room to be overloaded. The bass quality from these OBs is tight and goes deep. At first I thought about building a couple of H frame OB subs; however, after some adjustments and tweaks there is no need for subs. The active crossover allows me to perfectly match the gain of the different amplifiers and make fine adjusts to get the best performance in my room. So far, so good. Will I make any changes? Maybe, but for now I'm exceedingly happy with how this turned out.

 

[BmWr75]

Nice work!!

 

[macyjrm]

Would appreciate a pic or two of your work from the back sides. I’m a big OB fan and really enjoy the experiments and results from others.

 

[techguy0192]

Would appreciate a pic or two of your work from the back sides. I’m a big OB fab and really enjoy the experiments and results from others.

Here ya go. It doesn't show up in the photo well, but the brackets were painted with a hammertone finish. I did not chamfer the rear of the mounting holes due to proximity of the mounting screws; I wanted to ensure the screws would have plenty of material to bite into.

 

[techguy0192]

Update on the cables being used with the full-range driver. I'm very happy with the Supra Classic 2.5 cables; they will be staying in place. The highs are clear and articulate without any harshness - zero fatigue. Vocals have weight and the meat-on-the-bones I wasn't getting with the Belden. The soundstage and imaging is just as good.

 

[opnly bafld]

Have you ever tried the Belden doubled up?

 

[techguy0192]

Have you ever tried the Belden doubled up?

No, I haven't; however, I do have more than enough Belden cable to try that experiment. When doubled up the Belden would be 13 awg, the same as the Supra.

While both cables are tinned copper, they do have some difference in their geometry. The Belden uses 19 strands while the Supra has 322 stands and much more surface area. Thicker strands are theoretically more susceptible to skin effect. The greater tinned surface of the Supra cable, compared to the Belden, make it a little more resistive - less sharp highs and a more full midrange.

Both cables are good. I've used the Belden 9497 in the past with great results. This is splitting hairs in terms of performance and personal taste. When a speaker has high sensitivity and no crossover, it becomes possible to hear the slightest changes.