Sachiko Build for Fostex FE208sigma + T90A

[Toppsy]

Now the Fonkens are finished and playing fine music and out of the way I have made a start on the rather large sized Sachiko cabinet build for Andrew Lehane.

These things are 6'-0" tall x 18" deep and just over 13" wide. More like coffins than speakers Not a size for your average UK room. But then Andrew has a large open space for these that should be ideal.

They will house a Fostex FE208eSigma main driver with a T90A supertweeter helper.

I have yet to cut the holes for the drivers in the front baffles. We are still debating the location of the T90A within the cabinets and here Scott with all his wisdom has been consulted. After all they are his design. Once this has been agreed the holes will be cut.

Hopefully Phil will be machining us some nice aluminium surround rings to the T90A's on his newly purchased lathe. So having now put him in the limelight he can hardly refuse .

Below is a photo of all the cut ply for the build, A total of 68 individual panels to make up a pair of speakers. Here once again PB Plywood came good cutting it on their computer controlled beam saw. Four 8'-0" x 4'-0" sheets in total, though I have lots of spare offcuts. This time around they are from 19mm Cherry veneer birch ply.

[andrew Ivimey]

WOW! all power to your elbow and precision to your eye!

onwards!

[pre65]

Hopefully Phil will be machining us some nice aluminium surround rings to the T90A's on his newly purchased lathe. So having now put him in the limelight he can hardly refuse .

I have accepted this commission.

[Toppsy]

Good on yer Phil.
Andrew will be pleased.
I think he has plans to have then anodised black to match the sigmas.

[Scottmoose]

Nice.

AFAIK, there are only a couple of pairs of Sachikos in the UK; they tend to go down well over in the 'States though. These were the first long-path double horns I did & in size are the closest to Olson's studio horns, which provided the inspiration. Not small, but the general consensus appears to be that it's worth it, if you've got the space. This is one of my favourite pairs, built by Jeff Carder before he got his dedicated range:

[andrew Ivimey]

Totally snazzy - I'm really looking forward

with one caveat ....

There is some magic / 'gotta be cheating' effect with the Sabs. The 4inch drivers are sharp and clear and the bass is fast enough to be realistic - They are very special. Even though they are not the best speakers in the world and yes Lowthers resolve so much more blah blah. But everyone is impressed whether grudgingly or enthusiastically.

[Andrew]

I have a favour to ask chaps.

Where would you put the super tweeter, here's an image of Colin's drawing, to shows the dilemma.

The question is directly above, or off to the side just above (mirror image in the cabs, of course).

Thanks.

-- Andrew

[Nick]

How does your normal listening height map to the position of the drivers?

[iansr]

Below is a photo of all the cut ply for the build, A total of 68 individual panels to make up a pair of speakers. Here once again PB Plywood came good cutting it on their computer controlled beam saw. Four 8'-0" x 4'-0" sheets in total, though I have lots of spare offcuts. This time around they are from 19mm Cherry veneer birch ply.

Colin
I'm intrigued as to what happens when you saw the veneered board - does it leave a nice smooth edge to the veneer or does it splinter at the edge so as to require filling/repairing?

Rgds
Ian

[simon]

I think I'd be inclined to put them above, though it probably doesn't make much difference?

It might be a bit tricky to adequately seal the supertwatters in the cab though perhaps? I've seen them mounted on shelves to the side before, which gets around the airtight seal problem I guess but maybe not an optimal solution.

[Andrew]

Hi Nick, The upper of the two positions is 1160mm. The lower is 1075mm both measure between the centre of the twatter and the 'floor'.

Sitting height is normally considered to roughly 1 meter, isn't it? Does that help?

Hi Simon, good point, the idea is to create a hole a couple of mm bigger than the diameter of the twatter, then we will wrap a rubber strip around the twatter and create a sealed "force fit" into the hole. The unsightly mess will be covered by some nice aluminium plates kindly made by Philip.

thanks,

-- Andrew

[simon]

Ah, the aluminium plates. Hurrah for Philip!

It'll be very interesting to see how you get on sealing the T90s in. I've just used some blutak to seal the EX4s to the cab as a temporary measure and it seems to work okay.

[Toppsy]

Ian,

The cut accross the grain is crisp and clean without any rip-out/tear of the grain. Anoher reason, I find, to use PB Plywood to cut all your veneered ply for you. Just give them a cutting list with an indication of the grain direction and they type this list into a software optimising program they use to cut the sheets, which are 2500mm x 1240mm so oversize your stuff from B&Q etc.

If you are to order some veneered ply from them and require both faces of the wood to be seen then order Grade A-A veneered ply. Otherwise you will get Grade A-B. Similar to Contiboard one gets from DIY stores.

I have a fine toothed 10" saw blade in my radial arm saw and even this does rip/tear the veneer on one side cutting across the grain. I think this is down to the speed of the blade which is a lot higher on commercial gear.

Colin

[Toppsy]

I know the location of the tweeter has been causing Andrew some headache and thought. Both Scott and DaveD prefer the offset location and mirrored for each speaker. Scott has commented these speakers are directional, especially with the curved side variants. However this is not quite so pronounced on the straight cabs that we are building. Offsetting the tweeters helps overcome this issue, though having stated that then said the alternative position would work fine and at the end of the day whichever location one preffered would work (probably) just a good.

So I think Andrew is going to go with the magority vote, guys.

For sealing the T90As I will be using some 25mm wide x 3.5mm thick self adhesive neoprene rubber strip. I bought a full roll of this when I used to build the ESLs. The idea is to drill a 64mm hole. Line this with the tape Struck to the inside of the hole and push fit the 60mm dia. tweeter in for a force fit. As commented previosly the ali rings that Phil will be machining for us cover the unsighty hole.

[Scottmoose]

No no no no no.

A curved front design focuses all radiation output upon a specific point in space, which is the entire point of the exercise as far as it is concerned. A flat-fronted design works in a manner analogous to a very large MTM. Offsetting the tweeter would make no difference in the former case; in the latter, it simply prevents a sharp, deep null in the response due to the location on the baffle & 1/2 wavelength cancellation. However, being a horn tweeter, the T90a is far less affected by such matters, giving much greater positioning flexibility. On the whole, I'd offset it slightly, but in practice, it will be a relatively moot point.