The MiniLogans - a design based on the Neo3, Neo8, and an 8" woofer

[fjhuerta]

I can't think of a better name, so this will have to do for a while. Then again, the last speakers I built were the Monoliths - these ones could be the "Miniliths".

OK, so here are the main objectives for this project.

1) Build an (almost) full range bookshelf speaker using an 8" woofer and the B&G Neo drivers.
2) Neo drivers playing in an open-baffle design.
3) 8" driver in a vented enclosure (can this be achieved with size constraints?)
4) The front baffle is supposed to have an "artistic" (yea, coming from an engineer!) shape. No dull square boxes here. I'll try to post some sketches later of what I have in mind - basically, the baffle is designed to minimise tweeter & midrange diffraction, while the woofer will have a standard rectangular enclosure behind it (even if the baffle isn't square).
5) Initial crossover points: 500 ~ 700 Hz to the Neo8, 4,000 ~ 5,600 Hz to the Neo3.

Here are the drivers to be used.

1) Neo3 PDR - baffle-less.
2) Neo8 PDR.
3) Either the SEAS CA21REX or the Audax AP210Z0. I'm still undecided. i think the SEAS will get the nod, because its Xmax is more than twice the Audax. I'll take measurements of both, though.

This will be the basis of the project. I'll begin modeling baffles on Edge and BDS, and find out what works best.

The things I'm worried about, BTW...

1) Taming the low end on the Neos response while open-baffled.
2) Working around the FR of both drivers. They are far from flat.
3) Minimising crossover parts. Since the drivers are relatively benign, I'll try to optimise the design as much as possible.

[JonMarsh]

Sounds like an interesting project, Javier. I'm not sure I'd pursue it the way you plan- but then I'm an old curmudgeon and don't see as much the benefit of open back mids when one has a monopole bass section.

I've got some Neo8's myself, and have wanted to try a system design with them; just haven't figured out what and how... and given that the way I really think I'd like the Neo8 in an array would compete with my RD50's languishing in boxes, too.

The Neo8 is very clean regarding distortion, and with the right size tapered sealed enclosure might not be too difficult to tame.

The woofer side is certainly an open question- if you want small, and ported, you'll have to select your driver carefully for the right T/S parameters for the target enclosure size. "Optimum" setups for an 8" woofer ported can wind up being pretty large- like for the RS225, which thrives in up to 70 liters with LF tuning around 24 - 25 Hz. Have you modelled your proposed choices in Unibox?

In my 8" two way with HiVi M8a, the less than optimum but still sort of OK was a largish 44 liters. It would have to be something of a specialty driver to get below that with bass extension usable to 40 Hz- otherwise, I'd just say go with a small sealed alignment, like MarkK did with his version of an RS225/RS28a two way. But while the RS225 has a great bottom end, combining it with a crossover with minimum component count probably isn't a feasible hope.

Looking at current offerings from Seas, the P21RF/P looks attractive, nice balance of Qts, Xmax, and very smooth response curve that would tolerate a simple crossover. not the Xmax of an RS225, but much easier to work with, and a Qts usable sealed or in ported configuration.

[Paul Ebert]

I seem to recall that John Krutke (Zaph) didn't care for the Neo 3 in dipole configuration.

I've always been intrigued by the Neo 3 and 8.

[fjhuerta]

Jon, thank you so much for your (very thoughtful) post.

Having recently designed a dual 8" woofer speaker, I know what you mean about size requirements. I was thinking about a deep bookshelf, but you are right - a 1 feet long deep speaker isn't exactly "small".

You are really experienced with open baffles, too - if you think there's not much benefit going this route, I'm not really willing to re-discover what most of you have found through your hard work I'll start re-thinking my design (good thing I didn't throw away the little Neo3 baffles!)

Since I won't be going open-baffle anymore, I guess I need to think the following things:

1) How can I calculate a sealed enclosure size for the Neo8? It's not as if it has an Fs, and I assume Vas will be a bit of an issue, too . Can I just build a small sealed compartment, stuff it, and not worry about it?

2) I have the following drivers:
* Seas CA21REX (2)
* Audax AP210ZO (2)
* Dayton Audio RS125-8 (4)

Given my requirements of a small bookshelf, would I be better off with a sealed 8" (which would need to be the Seas, since the Audax doesn't have that much Xmax), or a pair of the RS125 in an W(T-M)W configuration? Is this a matter of taste, or is there a definite advantage in a sealed 8" vs a pair of ported 4.5"'s? I'd assume the 4.5s would allow me to build a smaller box, but I think I saw somewhere (Zaph?) that the RS125 wasn't as good when used too low.

[Gir]

If your going sealed, I wouldn't throw out the possibility of the RS225. Very low distortion and they sound great. I think roll off is about 70 or 80 Hz for my sealed pair, so you'll need to EQ the bass up.