Fostex fe167e bookshelf design

[nacho]

Hi folks,
I need your help in choosing a speaker design. I've looked at the fonkens, the zigmahornets and the Brines' FB-16s. I'm thinking that for my purposes the fe167e drivers will fit the bill. In terms of size I'm looking at a bookshelf and at the same time, I think the fe167e would offer some more bottom end. I've looked at the Fostex recommended designs for the fe167e and I like the idea of the "standard recommended bass reflex type " enclosure located at the bottom of the page:

http://www.solen.ca/pics/fostex/fe167e_enc.pdf


My concern is that it's a 15 litre box and may not give me the lower end punch that a bigger box may be able to. I then looked at Godzilla's measurement table and found a 25 litre box that's based on the simple fostex design but just expanded to 25 litres.

http://www.zillaspeak.com/FostexReflexCabsFE.asp

Can you share your thoughts as to this design and what I can expect. Has anyone used the design measurements on godzilla's site and if so, what did you think of it.
Thanks

[Scottmoose]

Ah. You need to be a bit careful here. Those dimensions are actually for the discontinued FE167, not the current FE167E, which has different parameters. They're copied directly over from the Fostex site -being an all-round good bloke, Jeff (Godzilla) loaded them onto his site for reference purposes in case Fostex remove them from their own, which, being legacy units, they might do at some point.

If you want a good standmount / bookshelf for the 167, then I'd build this. It has a bit more volume than the FB-16 (similar to the Fostex box) but the alignment will probably be similar to Bob's. I don't know what the internals of his FB-16 are, but we often have a similar take on BR design. Internal dimensions 19in x 6.75in x 12in (HxWxD). Driver-centre 9.5in down from the internal top (i.e. at the half-way point). Port centre is 3in up from the internal bottom. Port is 2in in diameter and 2in long. Line the cabinet with carpet underlay or similar, top, bottom, rear and one side-wall.

As you can see from the attached FR graph, this gives an EBS alignment, which should give decent extension without boom (which you'd get from a reflex box if you used a QB3 max-flat alignment. Impedance is steeper than an MLTL floorstander, but nothing to get worked up about. Driver excursion is fairly mild too. Should make a nice little standmount.

[andrew ivimey]

Scott, Hi, can I ask a general question that is sort of relevant to this thread?

I have seen odd looking designs with FR single drivers where the bulk of the cabinet is a type of a horn, but the cabinet is actually narrower than the driver. The driver mounted on the front has a baffle, which, of course extends a few inches (or why not further!?) out from the sides of the cabinet.

Is this silly, necessary, adds to or detracts from the functioning of the speaker etc?

[Scottmoose]

Depends on the design really. Are you thinking of the Nagaoka D-101 Swan, or something like it?

[andrew ivimey]

No, not really. I didn't explain myself well. I'll try again. Think of e.g. a Fsotex sigma 108 mounted in a very thin tube vertically about four feet long. The 108is forward firing, mounted at the top of the tube and will recess into the tall tube so the back firing sound is damped and becomes useful bass by the time it comes out of the bottom of the tube. If the 108 were mounted just on the tube (at the top), the flanges would actaully stick out a little wider than the width of the tube. Actually the 108 also has a circular 6inch radius baffle, extra to the tube,so it looks like a musical flower!

That's an example. Getting bigger it could be 167, 206 or 208.

Does this extra baffle work? what could be the pros and cons, the baffle could be bigger, a different shape and so on?

[Scottmoose]

In general terms, they'll always do something to the sound, affecting the step-point, but the shape itself should really be taken into consideration as part of the design too. Very few people, me included, bother as muc as we probably should when it comes to box speakers, but for horns and OBs it's a whole new ball game. The attached page is taken from Olson's Acoustical Engineering (I really should buy a new copy -my old one fell to bits) and shows the diffraction effect different baffle shapes have. As you can see, a sphere is ~ideal, with a trunkated pyramid following.

However, we need to remember that the response of the cabinet, and the surface-wave travelling across the baffle isn't linear, so the theoretically ideal baffle shape, even if possible / practical, in reality might not be the optimum choice. We can use different baffle shapes to re-shape the sound to our own requirements. A baffle should really be regarded as a separate transducor in its own right you see, with primary and secondary radiation that needs to be acounted for. Complicated in a way, but great fun, and can be amazingly effective.

[Scottmoose]

It might have helped if I'd attached that page...

[planet10]

Originally Posted by Scottmoose

Olson's Acoustical Engineering (I really should buy a new copy -my old one fell to bits)

My 1st copy was a pile of bits. It was long out of print, and not available so i photocopied all "10,000" pages of one borrowed from the library (i did buy a copy of the Old Coloby reprint when it cam out, but i still use the loose-leaf one)

dave