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PostPosted: 14 Jun 2013, 22:47 
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Location: Arizona, USA
UPDATE (11 July 2013) Cobies - Cheap Open Baffle Speakers project page.

Hi Everyone, A new direction for me. I have come up with a really nice sounding, quite inexpensive easy to build open baffle speaker system. I plan to make it a full project write up in the next few days. All parts are stock items at Parts Express and the cost of the speakers, and crossover components is just under $100 for a pair of speakers. All else you need is a sheet of plywood and a little work. Nice sounding, lots of ambiance and rather solid bass down to about 40 HZ. They use a 12 inch woofer and a pair of 4 inch tweeters in each baffle. The parts were selected for low cost and max performance. I used xbaffle.xls to model the speakers before and during the build. Stay tuned for the project.

Good listening
Bruce
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PostPosted: 27 Jun 2013, 08:11 
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Location: Darboy, WI, USA
Nice work! 8-)

I can see how you have the speakers positioned in your room, but what's ideal for open baffle speakers?

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PostPosted: 27 Jun 2013, 09:28 
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Hi, I just yesterday sent off a full write up on this project for posting. I will be a little while before it shows up on the site as Gio has to massage the input. I can PM you a copy I believe it is about 450K.

As for placement... it can be real easy, or more likely take a bit of fiddling to get right. The open baffles are not as sensitive to placement as my Martin Logan electrostatics (very picky) but since OBs have significant rear energy they do interact with the room more than box speakers. My room is rather lively. It is 12 wide, 17 long and 9.5 high. I used some wall treatments (see photo) to tame the wall behind the speakers. In my room the placement worked out to be 10 inches from the side walls, 58 inches from the rear wall (measured at the center of the baffle) and an inward toe in of about 20 degrees. Listening position was approximately 8.5 feet from the center line between the speakers. At that location the sound was really quite nice. Clean, with lots of ambiance. The full write up goes into more details.

Good listening
Bruce


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PostPosted: 11 Jul 2013, 21:41 
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hi folks, I just got around to posting the project online.
Cobies - Cheap Open Baffle Speakers project page.

Cheers

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PostPosted: 15 Jul 2013, 07:32 
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Nice work Bruce.

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PostPosted: 15 Jul 2013, 19:13 
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You remind me of the OBs I built some years back. I probably have posted here sometime back. I and half-a-dozen audio club members really liked the sound on the day. The amp which powered them was a PP valve amp with KT88s about 30W a side. I only made the speakers as a DIY discussion point and knocked them up that morning. At the time I was DIY convener for the club. One club member (Paul) paid me for the parts cost and took them home that day. He still has them and brings them out every now and then. He loves them but has three pairs of speakers in heavy rotation including Quads.

Here is an image of them at Paul's place. Paul later bought the amp which drove them on the day. He still has that too.
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PostPosted: 15 Jul 2013, 20:14 
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hi Mark, it is amazing how easy it is to do a set of OBs. The trick is to get them to sound well. Not quite as simple as sticking a few speakers on a board. With care though, they can be rather nice. It seemed to me that the biggest challenge was finding a suitable low frequency driver. I must have run the modeling program 200 times with various size and placements for the baffle and different woofers. It did get easier toward the end as I began to understand what parameters and other values were important.

Good listening
Bruce

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PostPosted: 15 Jul 2013, 20:46 
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On the day I ran mine I used a simple 3-way Xover. Paul, who took them, spent the next month or so fiddling with Xover before he felt the OB were delivering their best. The 10" diver and mid were in-expensive drivers but the 10" woofer was heavy duty. The tweeter was quite an expensive Seas I think.

By having an over-size baffle board and small "wings" at the back (which also doubled as braces) the woofer was partially (acoustically) isolated from the back wave. I have a layer or two of Dacron (wadding) on the back too. Bass was not heavy but very articulated. For a "roughy" we all were impressed with the sound. Very enjoyable. I would recommend everyone should have a try at OBs. They may be as surprised as I was.

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PostPosted: 16 Jul 2013, 03:27 
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Just took a look at the project entry on the site. Bruce have you tried reversing the rear tweeter polarity? Or what about replacing the rear tweeter with a 4" tweeter\mid. I don't expect you to try the last comment but just tell me what you may expect from such a change.

The rear tweeter polarity swap though may be a good option. In fact depending on how close to the rear wall the speakers are a polarity swap switch could prove an advantage. Easy to do. Also with OBs rear wall placement can make some big changes. Corner positions can be a premium.

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PostPosted: 16 Jul 2013, 10:52 
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Hi Mark, the rear tweeter is reversed from the front one which is reversed from the woofer. The front mounted ones need to be out of phase as the crossover makes one lead by 90 degrees and the other lag by 90. I found that in order to sound right the rear tweeter had to be pushing when the front was pulling. Sort of creating an open back tweeter effect. Swapping the polarity on the rear one to match the front caused the sound stage to get out of whack. Imaging suffered significantly. A second reason for not using a M-T on the rear was cost. The project was a budget affair and there were no decent M-Ts in the sub $4 range. The performance of the systems as shown was quite good and might not have been significantly improved with a M-T.

Since the woofer was going strong up to 3600 I didn't see any real need to put something on the rear to cover that range. It seemed that the reflections from it were sufficient in that range. Most of the spaciousness of the system came from the tweeters, particularly the rear mounted one. The sound was flat without it. The actual effect of the woofer on reflections was greatly dependent on physical location in the room and the type of wall treatments. If there was excessive deadening behind it and on the sides it didn't sound good at all.

They aren't not nearly as particular as my electrostatics, but careful placement is important for good performance.

Good listening
Bruce

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