Rob's OBLA-33 (Open Baffle Line Array) project.

[Rob41]

Thank you, Rob, for posting all the pictures and detailed information regarding your speakers build! I also got the inspiration from you to build my own open baffle speakers. This was my first attempt to build speakers and the results are beyond my highest expectations. The pictures in my theater room are the best I can do with all the black velvet absorbing light from the camera flash. They are 75 inches tall. No fancy wood work, since they will be covered with black grill cloth. Each speaker has a center column of 9 PT2C-8 tweeters and two columns of the 6 1/2 inch woofers, total of 18 woofers in each speaker. I am using an Ashly XR-1001 electronic crossover. The crossover frequency I have settled on is just slightly higher than 2000 K , with a Linkowitz-Riley steep 24 dB per octave filter. The woofers are crossed over to SVS powered subs at 80 Hz. The speakers sound just fantastic with no lobbing or any other objectionable issues.

Some background. I am a recently retired psychotherapist and needed a winter project to get into. I have had many interests throughout the years, pilot, traveling etc., but always came back to and enjoyed an interest and passion for electronics, audio and recently home theater. I collected a large amount of McIntosh stereo equipment over the years and owned countless great speakers. Some of the speakers were the Infinity Kappa 9, McIntosh, Ohm Walsh, VMPS, GoldenEar, Carver Amazing Platinum Mark IV, etc.

I am considering having custom made passive crossovers, 4th order Linkwitz-Riley, 2100 Hertz. I would like to be able to eliminate the electronic crossover, and all the additional in-wall wiring that I will have to do with bi-amping the speakers in the theater room. I am thinking the passive crossovers may degrade the sound of the speakers. Comments would be appreciated.

These speakers that I have constructed have impressed both me and my wife. They are absolutely incredible! Thank you again Rob.

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Wow Empire, this is great! It looks like you did a really great job too. It's really nice to hear you and your wife are impressed with them. I do feel somewhat validated considering the speakers you've had.

It's pretty cool that you needed a winter project and I need a psychotherapist! Lol, I couldn't resist.

I have not built passive crossovers before so you'll need some expert advice elsewhere but I'd be very interested in the outcome. At some point I'd like to try that as well. With active, the driver control is better and steep slopes,phase, timing are all easier with active. You also get to use all of the power the amps supply without a passive diminishing some of the power. However, the power issue is likely a non issue for either of us as our amps surely provide considerably more than either of us really need. BTW, what amps are you using right now?

You mentioned no lobbing or other issues and this brings up something I see over and over. When people start doing the math and calculations combing is always brought up. In the case of our 6 1/2" drivers, the formulas demonstrate that combing will be an issue. But, in the real world listening to these line arrays, there is no audible combing whatsoever. Perhaps, using 4" mid-woofers instead would yield further improvements. I really don't know, but I can't complain about what I'm hearing with the current drivers.

I'm flattered that you and Hans found this concept interesting enough to try and I couldn't be happier at how well they turned out for both of you!

To quote Bob Carver "Enjoy the music!"

 

[StimpyWan]

You mentioned no lobbing or other issues and this brings up something I see over and over. When people start doing the math and calculations combing is always brought up. In the case of our 6 1/2" drivers, the formulas demonstrate that combing will be an issue. But, in the real world listening to these line arrays, there is no audible combing whatsoever. Perhaps, using 4" mid-woofers instead would yield further improvements. I really don't know, but I can't complain about what I'm hearing with the current drivers.

Like you Rob, I've spent many hours reading papers and posts, regarding line array construction. And like you, avoiding combing and lobing issues if often discussed. From what I've studied, you, and Hans, and Empire all avoided introducing combing problems, by all following the same layout design (yours). With your original design using symmetrical WTW driver placement, you pretty much defeated combing from the start, since a symmetrical array has a much better radiation pattern. Most arrays use a single stack of woofers, and another stack of tweeters, side by side, which while more affordable, isn't the best design, as a WT array has greater combing issues.

Also, your design uses tight spacing placement on both the tweeters and woofers, and in their relation to one another. I believe this also helps to negate combing issues, as there is less chance of sound fluctuations, as you stand up and move around the speaker. since the drivers are laid out so tightly to one another. So, congratulations on a winning, well thought out design, and on inspiring others to try their hand at speaker building too! Nice work!

 

[Rob41]

Thanks for posting what I was unable to put into words. I think you are correct. I/we ended up with something that works extremely well not because I did such a good job with the design, but because I listened to those far more talented than my self. I had several exchanges with a couple icons in the industry who convinced me to make a couple fundamental changes from my original plan. Jim Griffin who is a renowned speaker designer and PHD who has written many white papers including those on line arrays gave me some great advice. And so did Dave Smith, (former designer who has worked for JBL, KEF, Meridian, McIntosh, Snell and PSB etc).

I had what I'd like to think was a good idea, but the contributions made by Jim Griffin and Dave Smith are likely what allowed the final design to be catapult into another league altogether. These are the finest speakers I've heard so I am, of course, sold on the concept. I will likely build more speakers but they will include the lessons learned from the masters as well as my own bumbling efforts.

I'd like to thank Hans and Empire for sharing their beautiful creations here as well. They both did a fine job and added their own ideas making each of their builds unique.

Just thought I'd throw in another clip even though it's low resolution. I'm playing some Creed unplugged through a Burr=Brown dac and tube buffer. The track was recorded on some 40 year old tape which is playing through a Pioneer reel to reel to keep things analog.

 

[Xtinc]

You OB Line Array guys are crazy...in a good way. Thanks for sharing. Maybe one day I'll have the opportunity to hear awesome builds like the ones in this thread.

 

[Donkey Karma]

I bet the Bur Brown is a great match for your arrays. I have always found them very detailed and not overly colored. I bet it makes them shine!

 

[GuyK]

Your end results are superb! Thanks for sharing!

 

[Rob41]

You OB Line Array guys are crazy...in a good way. Thanks for sharing. Maybe one day I'll have the opportunity to hear awesome builds like the ones in this thread.

Thank you, I tend to jump in with both feet when I decide to do a project. Why not do a build yourself so you can live it?

I bet the Bur Brown is a great match for your arrays. I have always found them very detailed and not overly colored. I bet it makes them shine!

I don't have a lot of insight regarding dac's but it sounds good to my ears.

Your end results are superb! Thanks for sharing!

Thanks Guy! I've got to apologize, I missed your question on the very first page of this thread where you asked about why I decided to go two way rather than a line of full range drivers. Might be a long time coming, but I went this direction for two reasons. I wanted to go open baffle and there aren't a lot of drivers suitable to a line array with a high Qts (above about 0.70). Also, I wanted to enjoy the delicate and scary accurate highs that ribbon type tweeters can provide.

I am completely sold on a few things after doing this build. YMMV but these are my beliefs.

1. Full length (i.e. nearly floor to ceiling) line array's are superior to, and easier to build that shorter CBT type line array's. Varying driver output levels and arching is not necessary with full length and when built full length, many issues with a space are eliminated or reduced. First order reflections on the ceiling and floor are gone, and instead, those surfaces actually have the affect of lengthening the speakers.

2. Distributed bass, or at the very least, properly located bass, is the only way to go. Many top speaker designers have known this for decades, but they also know they couldn't get the concept past the marketing departments. We have all been happy with our speakers having the woofers located in the same enclosures as the rest of the drivers, but once you hear what a properly implemented DB brings to the table, you just can't go back. The way bass behaves is very different than the higher wave lengths. Room modes, nodes and standing waves do exist and negatively affect any space without DB.

3. That brings me to number three and likely the biggest part of any system. The listening space itself. Admittedly, I have a terrible space. My space is in my partially finished basement which still has a concrete floor and painted walls of drywall. It is a very "live" space that promotes awful reflections. However.......the full length LA speakers help to diminish some of the issues. As I mentioned above, the ceiling and floor are an asset by audibly adding to the length of the speakers rather than creating first order reflections. My placement along the long wall helps reduce immediate first order reflections with the side walls. There is a lot of room for improvement in my space to say the least. Aside from the ceiling and floor, all the regular rules still apply. The listening space has the single biggest impact on overall results and room treatments can bring huge gains. Room treatments are nothing new but it's something often overlooked.

 

[Xtinc]

Thank you, I tend to jump in with both feet when I decide to do a project. Why not do a build yourself so you can live it?

I have built smaller projects, but have very limited wood working skills / tools and space for large OBs arrays as these.

 

[Rob41]

Yeah, you've got to have a place for them to fit. I got lucky with the wood work but messed up the finish. I'll be building new baffles and leaving a natural finish. If you were closer I'd have you over for a listen.

 

[damacman]

Holy mother of line arrays! And that big Nikko Alpha 650 kickin' it out!

Love it!