[loty]

Hi,

I'm learning a lot about the OB design so please help me out. I'm trying to decide between a 2 way and a 3 way design but can't figure out which way to go. 2 way design with a full range driver and a tweeter on top vs a 3 way design with a big woofer on the bottom, mid range and a tweeter. Right now I'm leaning toward a 3 way design maybe with a U shape for the woofer to extend the low end and open mid and high drivers. What would be the advantage of a 2 way design other than a simpler crossover? And if you do 2 way how do you extend the base without also boxing in the mids?

I'm sorry if I'm asking basic/stupid questions, just trying to learn.

[Early B.]

With OB, you need plenty of bass. That means you're probably gonna build a 3-way with 15" woofers. Build a 2-way if you already have a subwoofer.   

[Scott Joplin]

Hello Loty. Have you looked at the Linkwitz Lab site? I reckon it's the best place to start if you want to learn about OB and dipole speakers.

[opnly bafld]

http://www.quarter-wave.com/OBs/OB_Theory.html

[FullRangeMan]

My suggestion for a hi-end music system is a OB FullRange driver as LiiAudio F15 or F18 if you want more bass. The best baffle shape so far is the Barrel shape as used by Decware.
Lii Audio F15 FR driver $399/pair, not each.
Here Decware OB with the Lii Audio F15 driver:

If one have a woodworker is possible try the Lii Audio F15($399/Pair, pair not each) 97dB/8Ω and benign impedance curve suited to OB or Bass Reflex box or the F18($540/pair), no Crossover, no Tweeter beaming, no Phase rotation, no driver sensitivity loss, no Harmonics loss, no Retail price.
http://www.glowinthedarkaudio.com/lii-audio-f18.html


But if you want less musical fidelity, less soundstage, less musical presence and less harmonics you could use a Two-Way OB with an unfamous cross-over(more  additional parts cost) as this image below:
This is a inexpensive DIY project from an AC member, it have only four(4) parts: Eminence Alpha15A + 4.7mH + Visaton B200 and a MDF baffle.

[jk@home]

If you do get the Lii drivers, I suggest  building test baffles before jumping into a more expensive finished baffle. I have the Lii Fast 15s (Xizi versions), found that a certain driver height and room positioning was preferred. In other words, a baffle on the floor didn't work well in my room (which of course effected the bass). Also play with toe-in, and don't be afraid to add some EQ (how ever done). I'm running mine full range now, later I plan on trying the Liis as mid-bass units in a three way active setup. Do lots of research before jumping in, here and also on the diyaudio "full range" and "multi-way" sites. One last thing, the Lii drivers were pretty hyped up for a while there, but there are a lot of OB driver fish in the ocean.

[Scott Joplin]

Do lots of research before jumping in

That's good advice, I'd also suggest if you haven't heard OB speakers in your room before, that you mock-up something cheap and simple (I used coaxial car speakers and sheets of cardboard) to see if you like the sound and you can place them far enough away from your walls.

[Jon L]

This "ABX open baffle" speaker may be a good option.  Coax driver on top with slot-loaded woofer, and parts list and source all already laid out for the DIY'er.

https://www.youtube.com/watch?v=sgDdjVPODgI&t=1209s

[Jon L]

Just saw this great video and sound demo for a variation of ABX open baffle plus dual GR Research Triple Threat OB subs.  Is this one of the AC guys?
Veeerrry nice, the type of sound I personally prefer, lively, detailed, and dynamic.

https://youtu.be/p7QH6_WKYOk?si=oPRnhlqaZBaC0QaO&t=471

[Poultrygeist]

I like full range speakers to run "full range" with nothing in the signal path between amp and speaker to mar the sound. I bi-amp with a SET amp powering the full range speakers and a more powerful solid state amp driving the bass woofers. I low pass the bass woofers using a plate amp or F-mods and bring them in to fill in what the FR's can't reproduce. I've also used electronic crossovers but only to change the frequency of the bass woofers as they can impart their own sonic signature and ruin the magic of a good SET amp.

I agree with others who recommend the Lii Audio F-15's but with bass augmentation. Once you add bass woofers to OB's the shape and size of the baffles becomes less important. If you have room, H-frames ( open-ended box with woofer in middle ) will produce about the same output as two woofers per side on flat baffles. Flat baffles are much easier to build but once you build a pair of H-frames and since they're modular you can experiment with any number of full range driver tops ( inverted T baffles which rest on the H-frames ).

[Poultrygeist]

[opnly bafld]

The purpose advantage of using an H or U baffle is to a lower the F3 compared to a flat baffle of the same width, but it also lowers SPL, so above a flat baffle's F3 the flat baffle has more output than an H or U baffle. Therefore an H baffle with 1 driver will not have as much output as 2 drivers on a flat baffle.

http://www.quarter-wave.com/OBs/OB_Theory.html

[Poultrygeist]

As pictured below I've tried two Eminence Alphas 15's per side in flat baffle OB's and while the output was more than a single Alpha in H-frames I didn't find it significantly greater. Unlike flat baffles you can get a bit of a megaphone effect with H-frames. 

[Poultrygeist]

I once thought OB cone area had much to do with bass output but I learned that is not necessarily the case. Those two 10" efficient woofers on the left side were designed for open baffles with a high Qts but sounded weak and thin. Once I removed them from the Zeniths and added the 16" Sansui Kabuki woofers recused from the curb I had plentiful bass.

[opnly bafld]

An anecdotal statement that doesn't inform much without the TS parameters. Cone area is indeed pretty important for OB bass to scale.
One 16" driver has more cone area than two 10" drivers (1x16" = 2.5x10").

[Poultrygeist]

Guess I'll need to refresh my math because I was thinking 10 inches + 10 inches = 20 inches. But I don't appreciate your condescending attitude. You can do better my friend.

[BobRex]

Area of a circle = Pi x radius squared.

16" : 8x8 = 64 x 3 (yeah I'm rounding, so what) = 192

(2) 10": 5x5 = 25 x 3 = 75 x 2 =150

Yeah, the sixteen inch driver has more area.

[Poultrygeist]

With the two 8 ohm HE 10" woofers with a Qts above 1.0 wired in parallel for a 4ohm load I expected more usable power with the class D amp but that wasn't the case.

[opnly bafld]

I wired four 6 ohm drivers in parallel to a class AB amplifier and that provided a very substantial increase in output compared to just two in parallel.

Four 10" drivers equals one 20" driver.

And remember not every single ended tube amplifier is a single ended triode (SET) amplifier.

[Poultrygeist]

Don't know who this is directed at but all of my SET amps by definition are single ended. But I have a couple of single ended amps that aren't triodes.