Apollo OB - ?

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Remember the Apollo missions, when they had something go wrong and the guys on earth had to figure out how to fix it with a few parts known to be lying around in the capsule and time was running out ?

Well this isn't at all as dramatic. But I have a small challenge for you :p

My friend came by with some old drivers off fleabay and thought I'd like to borrow them for a couple of weeks to try 'em out with my recently completed tube amp.

Of course, these drivers are no good to man nor beast on their own so I thought about knocking up a pair of OBs so I could at least hear them - and no, I don't have any big cardboard boxes lying around I can use.

I have two 15" Alnico full-range(?) drivers with whizzers good to 5kHz+ and a pair of horn tweeters to augment the top-end. There's a couple of dodgy looking cross-over units covered in grime but I'll worry about 'em later.

Looking in the garage there's a few pieces of old wood I can hack up for this. I've sketched out the shape and size of the wood I have on hand.

So what next - I'm thinking I should take the larger panel of MDF, cut it in half to make two 3' x 3' pieces and mount the big drivers in these ?


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nope, with the big cone working up to 5kHz+ I don't want it sitting so low, I'm going to risk less bass to put it closer to the listening height. Looking at the MDF I have available I can make up two 2' x 4' panels.

not much coming from Houston so I'm going to have to wing it...


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Looking good! Keep us appraised and let us know how the result works for you! Are you going to keep the unfinished look or seal/paint?

Well, I've hooked up just the big full range cones, no horn tweeters connected yet (I'll need to look at the grimy cross over units first).

Playing SADE DVD on my HT system (sony blue ray decoder) through my TGM2 amplifiers along CAT5 speaker cables (just made). Hey, these things don't sound half bad ! In fact they sound very nice. Compared with my Fostex Moon Onkens they have real bass, but are not as crisp sounding. Compared with my PMC FB1's they sound a bit thin on both ends, but they're only just warming up. The cones were quite dusty, don't know where my friend got them from.

Since all these drivers belong to my friend it'll be up to him whether he wants my DIY baffles or not. I enjoyed making them this weekend and it's my first time ever to hear this kind of driver and my first time to hear OB.

There's a bit of work to finish them up. First off, they need to be laminated with some 1/2 Birch ply on both sides of the existing baffle to give them adequate stiffness and they need some proper plinths making up. I won't leave them unsealed, I'll use a combination of black paint and sealed plywood.

I'm going to listen to them for awhile, I may become an OB fan, although I've never heard a BLH. Nice thing about being a newbie in this hobby - so much to explore !

See attached photo of the Apollo OB's in action...


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Much cleaner appearance than mine. Glad to hear you like the OB sound! I finished mine last Fall and haven't found any regrets. They still make me smile every time I listen to them after working an orchestra concert (like today). Balanced sound is so much more natural than the heavy EQ curves coming out of radios these days.


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>>> they have real bass, but are not as crisp sounding.

Excellent! They look really nice in the pics! After you hook up the tweeter and play around with capacitor values maybe the overall sound will get crispier... I use a powered pair of powered Alpha 15's to enhance the bass of my current OB's... you can use a powered sub of your choice.

>>> I may become an OB fan, although I've never heard a BLH. Nice thing about being a newbie in this hobby - so much to explore !

Yup! I did the opposite by building BLH's first then OB's. Currently i am enjoying the OB's but have a pair of BIB BLH's in the room ready for duty when i want to change things around again. You may find, as i did, you really enjoy BOTH types of speaker designs and could live with either. As a DIYer you can also choose to live with both!

I have a handful of sealed and ported speakers sitting in the basement hooked up to nothing and probably won't ever go back to those types of designs for my main listening room. OB and BLH provide a more exciting, open sound IMO.

Enjoy! I like what you did and give you credit for building first and playing with the drivers second. You got to learn and got a taste of OB sound in the process.

gvimhoof, i built an OB with the Alpha 15 and H-frames, the H-frames sound better to me so regardless of the appearance, i think you're getting better sound.

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Well, I like it !

I haven't finished these speakers in terms of adding another layer of plywood and paint etc because the drivers aren't mine.

What I like most about these speakers is that the sound seems to have more 'air' it seems to be in the room and not originating from a speaker. I think this gives more tolerance to where the listener sits which is nice.

I suspect this is just the beginning of the OB journey for me, I'll have to do some more experimenting in the future.

The only doubt I have is that I haven't every built and listened to a BLH and I wonder about it.
I've been thinking about how to combine the attributes of the OB and BLH in a design that has both the 'air' of the OB but also the 'kick' of the BLH. I have some ideas, maybe something will surface in my brain that will make a good summer project when I can work in my garage at tolerable temperatures. I'm watching for more reports and results from the FH3 project too.

How do we find time to build them all ? !
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