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Giant Open Baffle WAW
I have a set of the SB 8" fullrange drivers that a friend of mine bought for us to experiment with. I have built them into a large ported enclosure and also added a filter to smooth out the response. I also tried them open baffle just for the fun of it, but of course there was no bass to speak of. I have always wondered what could be done with open baffle bass, so I ordered a set of GRS 18PT-8 woofers to try. They model well in Basta, and with a 24" baffle, sub 50hz should be easily achieved. I may even be able to get into the 30's. So, I am starting a very large woofer assisted wide range build. I just started one side with removeable separate baffles that will allow me to experiment if needed.
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Oops, first pic did not attach.
I will be cutting out the holes and attaching drivers soon.
If you've never messed with OB, you'll probably be pleased. I'd also try the woofer in an H frame as it gets even better, in my opinion.
I made this design bolt together to make sure I can try a bunch of different baffles and wings to see what it does to the response. This will be a big learning experience, and should be fun.
In the distant past I heard a pair of very large OB speakers built by John Busch when he (and I) were still living out in CA. They were called the "Widowmakers" and sounded great. Pic attached below. He used two 18" Goldwood high Qts (but low Xmax) woofers, an offset 7" midwoofer with nice open basket, and a conventional dome tweeter. He knew how to build these systems and make them sound pretty good. So there is precident for good sound. Make sure to NOT put the midwoofer in the exact center of the baffle. Better would be over at the edge, but unfortunately you have a wing there that will not be helpful to the rear output (it will diffract it). You could put it half-in, half-out of the baffle at the top (e.g. the top of the driver is actually above the top edge of the baffle) and get away with having it centered, and then the tweeter can be put just below the driver. Or just remove the part of the wing that is close to the driver if you use the John Busch configuration. Both of these will help to preserve a relatively good off axis pattern for the mid.
To see an example of how to NOT do it, see other attached picture below of me behind an early OB system like the one you are designing that I built way back in 2006... I mounted the mid and tweeter in the exact middle and this was a big mistake.
BUILT IT LIKE JOHN BUSCH:
NOT LIKE CHARLIE:
Not sure if it is just me, but your pics are not showing up.
I got the drivers installed. I planned on trying both a center mounted fullrange and an offset zmd see how they measure. I willl take the advice and start with offset. I will get measurements this weekend. Hopefully I can cobble together a passive filter for the fullrange and use my mini dsp on the woofer to see how they sound. Running test tones, I already know I need a much heavier and stiffer baffle to contain this 18. It walks across the floor right now.
Cinder blocks in the back on the base . . . ?
For now, that may be a good idea.
Plan B if this works well, will be to us a 6.5" mid and the GRS (or similar)planar open back tweeter.
I have a rough crossover designed for this. It should be a good starting point, but I am not happy with the electrical phase. At 2 points I have a 90 degree phase shift. It shouldn't be a problem with my amplifier, but not great practice. The goal of this project is to see if I like open baffle bass. I measured these on a 7 foot ladder out in my yard. I think I should get a bit of a boost in bass in room. Again, if I like these, I will probably shift to a 3-way setup. I also ordered a bunch of components from Meniscus on sale to start experimenting with these. Hate to see them go.
I basically added about 9 db of baffle step too tilt the upper response down and to gain enough low end and get a flat response to 50 hz. I think in room, I should see strong bass into the low 40's.
I also kept the upper response a bit on the hot side, to keep the power response of the 8" fullrange in check. When I filtered these flat, they sounded super dull. We will see if this response will be better.
Nice! Who doesn't like an 18 or two
I'd like to suggest taking your measurements on the ground, you aren't going to be listening to it on a 7' ladder, so you might as well capture the response that it will have on the ground. Just my two cents.
I totally agree. I did that to get my initial crossover. I will be taking many more measurement to tweak these. I was worried about measuring on the ground with such a low crossover point. Much more to come.
I got the pair ready for initial crossovers. Just waiting for a few components I didn't have.
They look so small lol
I bought four 15" drivers from Charlie to do a big OB 3 way project. Probably won't get to that project until next Spring.
Craig I bet you've heard that before.
For how cheap these drivers are, you could easily do 4 18s. Could be fun.
Oh snap!
Eyes bigger than your ears in this case?
So I got the initial crossover up and running. First impressions. The bass is still a little on the lean side. I used DSP and need about 4db of boost on the low end. I tilted the response down on the 18 10db, but should be about 13-14db to get better response to the low 40hz range. That would put the entire speaker efficiency to 79db. I also need to pad the full range down just a bit.
Take aways:
The soundstage on these is unreal. Super wide and deep, but the imaging is a bit fuzzy. This is the best I have heard these SB 8” full rangers sound, but I don’t think I am into full range drivers. I prefer a dedicated tweeter. Bass is awesome, but so inefficient. This is the first time I have ever drove my 200wpc amplifier into clipping. I think there is some merit to open baffle, but for bass I think the “juice is not worth the squeeze”. It takes a giant speaker and lots of power. I am going to enjoy these for a few weeks, but I do not think I will continue tweaking them much or keep them. This was a super fun way to play with open baffle, but if I do anything else with it, I will have a sealed woofer for the bass.
I found it best to use a bit smaller of a ‘broad’ ranger in a two-way for their higher end extension, but in any event there is the draw (imo, I was weened on Maggies) to DIY open backs.
I really like the open baffle sound. These are just way too big for my space. I think I may do the grs open back tweeter, a nice larger midrange, and then do a sealed woofer. I am hoping if I cross to the woofer below 200hz, I can have most of the benefit.
I think the best thing about OB speakers is the bass. My .02
Like I said, goto H frame on the woofer. 6-8" front and back.
Does that work Ok crossing on the high end at 200hz? If so, I could shrink the width and do the H frame. I also have a bunch of 3" fullrange drivers that I could use for the high end. I am up for any kind of experiments either these.
I've always liked my hybrid OB designs where the woofers were 200 - 300 Hz or so and were sealed or ported boxes. The mids were pure OB on as narrow as possible baffles and the tweeters were not dipole.