GM MLTL fine tuning

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Tools

Didn't know if I should start a separate thread on this.

I found out that even working with 'pretend tools' like Roto tools to do router work there's a big difference.

After smoking up the place with a 1/4 in straight bit from one outfit, I finished off with a fresh set I got from Tool Shop -- the Menards brand for those in the Great Lakes region of the US. The set of 6 was still only $6.00.

What a difference. I was hogging out the waste with just a 3/8 in
and it went with no smoke and like butter.

For this kind of work (like making square flush mounts) if I had to get a router I'd likely go with one of the new Tridents. The body is narrow and allows for good detail work.

Previously I shied away from doing this sort of thing, but with some good bits the job was easy. Still not CNC perfection but it's getting better.
 
Update

Today I went to the Home Depot. Down in the insulation department they have small bags of fiberglass insulation (they asy its 2 in thick once unrolled) in small quantities. It's sold to fill in around utility boxes in wall for lights and other hard to get at places.

Price is $4.00 for a 16 in x 2 x 48 in piece wrapped in a plastic bage like cotton candy.

The idea of playing with that stuff still gives me the willys.

Other thing I did was make a version of the Lon MLTL with the
fat port. i recut the box and installed a port length of 2 x 6 with an elbow on the side. The goal is to get the terminus closer to driver height and make the build more conventional.

Other technique I've mentioned since frugality is the goal is assemble with clear tub caulk. This is a very sturdy seal and prob'ly doesn't resonate at all. However the boxes look like they are constructed of snot.

Not ready for anyone's formal entertaining area.

:cool:
 
Having a listening test starting today witht eh GM MLTLs. One is the original design with the port out the bottom.

I put a bonnet on the magnet (described elsewhere) and
put some rope caulk on the legs and did the flush mount as described above.

The other one has the same sort of port on the inside of the box and side mounted.

Still didn't fly for the fiberglass insulation but they are stuffed top above the driver, one side, and the back to about 3/4 down to the port.


I have made some homebrew phase plugs which I'm testing on old cheap drivers for a bit. Still not wanting to cut into the Fostex.

Everything done is reversible.

I had some gaskets made at a gasket manufacturing place for a line array. The line array was not successful and so I've reused the gasketing for the Fostex. Those were round and what I'd like is for them to die cut some gaskets to the shape of the driver. The gasketing supplied by Fostex is pretty flimsy. I was surprised that the gasket shop was so amenable to doing a small job like that and only for about 50 cents each. Die cutting would be another matter.
 
Gaskets:

Look how the flange on a Foxtex FE is made. If you drop an FE into a baffle hole without a gasket, the outer edge of the basket will not touch the baffle. Adding a gasket exacerbates the situation. The old gasket that was supplied with FE drivers is very thin and performs the intended task: It maakes an air seal. (The last FE206E's I got has an 1/8"x1/8" foam strip supplied.) Even with the Fostex gasket, if you tighten down on the mounting screws you will bend the frame.

If you use foam weather strip or other thick gasket material, you cannot bend the frame enough to bring the frame edge down to the baffle surface. What you wind up going is floating the driver on the gasket. If this is what you want to do, have at it.

Several experts here suggest bracing the driver against the back wall of the cabinet. I don't see this working well if the driver is floating on the baffle.

What I do is place washers on the underside of the driver frame so that the frame is firmly mounted to the the baffle without bending the frame yet the gasket is compressed enough to seal.

YMMV

Bob
 
I've noticed the bending problem. Also prob'ly misunderstood the
nature of the driver to the mounting surface and that 'suspension' was a good idea.

It seems like a long time since this has been discussed in any detail. All I recall is a few pictures in Speakerbuilder.

The washers can bring the inside of the stamped frame up to 'level'
but then the cavity still needs a treatment. Lately they've been talking about caulk or modeling clay to do that.

But the thin styrofoam or whatevs sealing gasket with the Fostex gets worn after time. And wrinkled as I recall.
 
The unheralded return of ShimBoy

I'm rechecking all this stuff today.

My cutout for the BIB (which is up on the operating table for a flush mount job) is a snug fit. I have to push it in and extract it with
bit of leverage. This indicates a good fit in thh BIB box and I would not want to tinker with it.

In the GM MLTL box I have to see if the fit is that snug-- but I doubt it.

I was thinking of shimming in and snugging that one up with some
oak banding of the iron-on variety. It's flexible and can be fitted around a circular cutout. It can be handled like marquetry and cut with a knife.

I also had my Speakerbuilding 201 book out (by Alden.) He only shows one example of gasketing and that one is a custome job designed for the unit.

I pulled off the exess foam gasketing and what remains is a compacted layer inside the stamped cavity of the frame.
 
more test tones

I was using the test tones on the MLTL today.

A question for GM if he is lurking about:

Greg, you said that Lon has his MLTL tuned lower than normal.

My test tones comparing the Harvey BVR with the GM MLTL both running FE127e gives more volume in the MLTL and a distinctly different sound at certain frequencies.

Since this is a Mp3 download of some tones, I'd have to
look up the exact frequency but it's in the just audible range.


I've been wanting to use that online test tone thingie that Zilla
linked to but that machine (I have a couple computers on a home net)
is never on when I'm running these tests it seems.)

I still have the old smaller port which I can , in effect, reattach as the bottom plate of the speaker and see if that drastically changes that volume difference.

I am curious about all these things, but have no test gear.
 
Re: more test tones

loninappleton said:

Greg, you said that Lon has his MLTL tuned lower than normal.

My test tones comparing the Harvey BVR with the GM MLTL both running FE127e gives more volume in the MLTL and a distinctly different sound at certain frequencies.

Hmm, you talking about yourself in the third person reads a little strange......... ;)

I haven't reverse engineered any of Scott's designs, so don't know what's up, though I'm surprised a dinky little MLTL would output more than a BVR designed for the same driver. WRT a distinctly different tone at some frequencies I imagine the BVR isn't working the driver as hard due to vent loading over a wider BW, or at least that's what a BVR is supposed to do.

GM
 
Holey brace fro MLTL

I would like an opinion on installing a holey brace on my GM MLTL
build.

The MLTL is similar to the Mileva if I recall correctly.

With the port flush at the bottom what would a holey brace look like?

Is it even a good idea?

The build has the driver flush mounted and stuffed above the
driver. No other internal treatments.
 
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