Seeking suggestions for Fostex FE103A

[w_oswald]

Hi, all:
New member here - looks like I've found an enthusiastic DIY group, so here's my questions, if I may:

I recently managed to acquire a pair of old bookshelf speakers with a cool retro look, and a bit of research revealed that these are in fact Admiral Tunnel Reflex systems, "N-2" stlye as shown here: Transmission Line Speakers They do have the speakers as depicted and labelled 5410182, which - presumably - makes them Fostex FE103A drivers. As has been noted, the cabinet design doesn't do justice to the drivers' potential, so - I've retrofitted an old pair of coaxial car speakers into the cabinets, making a nice-looking pair of "utility" speakers.

So, with the cabinets dealt with, I'm really interested in exploring options for the original drivers. Are these still held in high regard, and if so, what application might these fit best: computer monitors, small-room music listening, home theater, or ??? I'm also interested in members' suggestions (whether based on personal experience or not) as to a cabinet design that will bring out the best of these little guys. It has been mentioned that the rear-folded-horn design provided by Fostex is less than ideal. That said, I'd still be eager to try a horn design if suggestions lead me that way.

TIA for any and all comments - as my project list is currently very long, it's hard to say what priority the subject system will take, but right now, I'm just fishing for ideas.

Wilf

[planet10]

Hi Wilf,

There is a warmer part of Manitoba? (well i guess Winterpeg isn't as cold as Churchill )

The FE103A is still a very good driver. Choosing an optimum enclosure can be a bit problematic because due to aging they tend to have a large spread of parameters.

Fonken103, B-Horn II, Frugel-Horn, Aiko would all be cadidates (i should pop one of my sets in Aiko for that matter).

How are your surrounds? Still flexible? And is the surround still attached to the cone (a common thing with these is migration of the glue and the surround at the cone becoming loose.

dave

[w_oswald]

Hi, Dave, thanks for your interest!

He-he- Winterpeg. Well, it was warmer a few weeks ago; now - not so much.

The drivers on hand seem to be uncompromised and sound very good in open-air (might make a great-sounding set of headphones?). I don't find any serial numbers on the cone or basket, but one of the original "Tunnel Reflex" cabinets has a serial number sticker on it: ST 53175. I'm guessing maybe early 1970's vintage? I've heard that Alnico magnets can be weakened by abuse such as mechanical shock or heat, but do they degrade with just age as well? The suspensions seem in good condition too. The half-roll surrounds appear - unlike other pleated cloth surrounds I'm familiar with - completely free of varnish or similar treatment that sometimes becomes brittle. These are just a fine woven cloth, and still appear very supple. They are indeed separated from the cone just at their inner edge, but not detached completely at any point, so the alignment is uncompromised. I was going to glue these down using WeldBond, unless you advise against this or suggest a better adhesive. I'll be sure to measure the parameters for comparison with published values. (Are those for FE103E applicable?)

Thanks for those interesting cabinet design suggestions. The Aiko indeed looks like a nice choice - it bears some similarity to the aforementioned stepped design shown for Fostex FE103E - does the symmetric double-mouth design audibly improve the performance?

Regards,
Wilf

[planet10]

Originally Posted by w_oswald

I'm guessing maybe early 1970's vintage?

... but do they degrade with just age as well?

The half-roll surrounds appear - unlike other pleated cloth surrounds I'm familiar with - completely free of varnish or similar treatment that sometimes becomes brittle. These are just a fine woven cloth, and still appear very supple.

Vintage last 60s to late 70s as best i can determine.

... yes

A good pair looks like the surround has no treatment, but the occasional unit suffering from stiff surround syndrome belies this.

They are indeed separated from the cone just at their inner edge, but not detached completely at any point, so the alignment is uncompromised. I was going to glue these down using WeldBond, unless you advise against this or suggest a better adhesive.

A little paintbrush, something to lift the surround while you work on it and some white (not yellow) glue (or puzzlecoat). Paint both the bottom of the surround and edge of the cone and after letting it sit for a min or two gently press down with a damp finger. Sometimes you'll need some magic tape to hold down a spot that doesn't want to stay.

I'll be sure to measure the parameters for comparison with published values. (Are those for FE103E applicable?)

on average

The Aiko indeed looks like a nice choice - it bears some similarity to the aforementioned stepped design shown for Fostex FE103E - does the symmetric double-mouth design audibly improve the performance?

The 2 are broadly similar in design phikosophy, both using the stepped format 1st used by Harry Olson. We've not tried Aiko with FE103A or FE103, but it is really good with FE108eS (and not at all good with the Lyeco 4" originally designed for). I will try it with FE103A. The Fostex factory horn is not at all good.

dave

[mor2bz]

MJK open baffle was designed for these, using alpha 15" and fe103, 2nd order xover on both drivers, xovered very low.

you would need about $200 and 30 watts to do this. very good.

[planet10]

I mounted up a set of FE103A into Aiko today. Getting some hours on them in the shop, will haul them upstairs tomorrow or on the WE and see how they do.

dave

[gvimhoof]

Originally Posted by mor2bz

MJK open baffle was designed for these, using alpha 15" and fe103, 2nd order xover on both drivers, xovered very low.

you would need about $200 and 30 watts to do this. very good.

I built a pair of speakers w/ the Alpha 15" in H-frame and the FE103E in open baffle on top (based on MJK's articles). Putting the 15" in an H-frame allowed narrowing the speaker to a footprint of only 16"X17". If you have the room to place these out from a back wall (3~5ft out), then this is a pretty do-able approach that wouldn't require a lot of time to execute. I have been VERY happy with the results. Great little driver!

[planet10]

Originally Posted by planet10

will haul them upstairs tomorrow or on the WE and see how they do.

It is done. They seem to be pretty good. More after i get a chance to listen when i can turn them up. Pictures too.

dave

[planet10]

Chris came over and we had a short listening session. Even with the jerry-rigged installation, i think Aiko is the best box we have tried these in.

Because of the magnet brace, and the depth of the drivers, they are literally sitting on their magnets and about an 1/8 (or more) of an inch proud of the baffle, with some fat whetherstrip sealing them. The tunnel effect from this mounting can be heard, and i get the feeling that the fix (shimming the supraBaffle a further out from the box) will have benefits in terms of the volume of the air cavity.

As mounted they strain a bit on the upper harmonics of vocals (early reflection from the tunnel caused by the mounting) & a tiny bit of cupped hands (should go away with slightly larger air cavity). They image pretty good, but aren't quite up to a set of Fonken (but then not much anything is )

Recommended.

Pictures still not taken.... they will come.

dave

[w_oswald]

Thanks to all for the suggestions! The endorsement of using these drivers in a 2-way open baffle design is valued; although for my own reasons I will stick with a single-driver full-range system for starters. However, the Aiko BLH cabinets under consideration will fit nicely beside my TV, so I would definitely try them out for Front L/R in a 5.1 setting, where they can be actively crossed over and helped out at the bottom end.

Dave, you are sure a busy guy - your personal attention here is very much appreciated!!! Well, Aiko it shall be then. I will resist the temptation to mess with the design (much), and here's why: Despite the great benefits offered by the online community, one thing we can't do is listen to each other's work (unless one's lucky enough to have nearby fellow hobbyists or can travel to audio fairs). My alternative is to build something known and acknowledged as good by our peers; then I will have a basis for comparison of any alternatives I may wish to experiment with.

Regarding the Aiko design:
1) For the FE103A, what size of rear cavity did you find optimal, and how critical is the tuning of that volume?
2) Is that 10-3/4" diameter baffle important to voicing, or it is more of a visual thing?
3) Your very nice drawing doesn't give any indication of mechanical assembly means. Would I be correct in assuming that these are typically just glued-up?
4) Any other tweaks recommended? (I'm thinking in particular that phase plugs may be worthwhile for these drivers.)

I am of course very interested in seeing some pictures of your speakers - waiting patiently for your post!

Cheers,
Wilf