Another Open Baffle. Advice?


2007-04-21 12:03 am
I’d like to build an open baffle MTM + a woofer, I’m still fairly new to speaker building so would appreciate any advice. I built a big box with Morels in it but preferred the sound of them in open baffles while I was building the box so now I want to do a proper dipole. The main goal is to build an open baffle MTM with good drivers and software crossover and an additional u-frame woofer per side.

For the mid-woofer I’m thinking the Scanspeak 18W Revelators. Baffle will be around 35cm wide and a bit curvy (I don’t know what the curvy bit means either yet but want to experiment with kerf bending timber and also vertically align the drivers). For the u frame woofer I think it will be something like a 12” Peerless, XXLS or just SLS, any recommendations?

For the tweeter I was initially thinking either the Seas Millennium or a Scanspeak ring radiator but I don’t understand how these could work off axis on an open baffle without a rear tweeter which I would like to avoid if possible. I was reading about the Bohlender Graebener Neo3 which seems popular and a good fit for the application with its removable rear cover for dipole use, this would be the main thing I’m after advice on:

- Could the Neo 3 give me sound quality somewhere near a Seas millennium tweeter on an open baffle or is it just a completely different sort of sound and I’ll have to take my chances?
- For the crossover I’m completely flexible as I’ll be going active so can experiment but am thinking the I’d rather cross the W18s up around 2 – 2.5kHz rather than trying to get the Neo 3 down below 2kHz. Can the w18s comfortably go high enough to meet the Neo 3, there seems to be conflicting reports of how high they should go?

The Neo is nice and cheap which is a big plus but if I have to go with something pricey such as the Beyma TPL-150 I can but it’s a huge extra cost and I’m not sure I would see that much difference. I think I’ll start with the Neo 3 and build some practice baffles.

My depth of knowledge is not really up to the task but plan on compensating by getting the best drivers for the job (and budget), a decent test microphone and then software crossover and correction to fix any mess.

When I built my Morel MTMs this forum was great for advice so I just want to run this new one past you and see what you think?
I have been living with a BG Neo3 for the past 3 years. it is a great tweeter.
My OB is a Neo3, a seas MP14RCY, and a pair of Dayton RS270 on a 46" by 18" flat baffle. Current Xo is a DCX with LR4 @ 320 and 3k plus shaping and 3 db of base boost @ 40 hz

I would not go MTM, unless you are in love with H baffles.
The use of a dedicated midrange will give good voice recognition ( I can understand them talking on the "Dark Side of the Moon" for the first time)

you'll probably be satisfied with the neo3. From a measurements point of view, there are things it can do that a millenium or tpl-150 can't.

the choice of drivers for other sections is more forgiving. The more volume displacement you have in the bass, the happier you will be.

Like you said, its a good idea to start simple, as you're biting off a lot already with planning on learning how to do measurements and develop active crossovers.

keep us posted!


2007-04-21 12:03 am
That's good to know about the Neo, I can't wait to give it a try. I'm going with MTM to keep the baffle small. I want to do a proper 3 way with a good mid-range once I learn a bit more - that will be next, this one is to decide whether I want to build it in a box or open baffle.

I'll keep this thread updated as I go, it'll be a drawn out process as I am still in the planinng stages and also just finishing off a couple of other projects. One of them is a tang band boom box for the kids using a 4" tang band subwoofer and the 3" B3S, active cross over and some little class D amps off ebay, I'm at the final box painting stage so this is nearly done.