Any demand for custom sound enclosures?

[daniel_leavitt2000]

One good thing about a fleet, is that I can update the same series of engines much quicker than working one at a time. I have noticed there is a lot of unused room at the top of several Atlas engine like the B23-7, B40-8, C40-8 and the SD50/60/60M series. Creating resin cast enclosures looks pretty straightforward.

Would anyone else be interested in these?

[jdcolombo]

To be really useful, the enclosure needs to be engineered so that a specific-sized speaker can be set into it and sealed.  This means a "hole" that is virtually exactly the size of the speaker (e.g., an 8.1mm x 12.1mm opening for an 8mm x 12mm speaker) with tiny lip around the edge of the opening, recessed down 2mm or so for the speaker. 

John LeMerise has made such an enclosure for the Soberton 8x12mm speaker, using 3D printing, here:

https://www.shapeways.com/product/5L4ZXWA28/8mm-x-12mm-soberton-speaker-enclosure-4pk?optionId=60853776

You can see from the photo how tightly the enclosure wraps around the speaker; I then use a thin bead of gel CA cement around the edge of the speaker (before pressing it into the enclosure) to fully seal it.

If you can get the opening dimensions correct, with a tiny lip so that someone can "drop in" an 8x12mm or 9x16mm speaker, then such an enclosure would certainly be useful (all these engines are outside my time frame, but I'm certain there are thousands of them in use).   Also, note that for best performance, the internal volume of the enclosure needs to be >500 cubic mm.  For example, John L's enclosure for the 8x12mm is 6mm deep; that produces an internal volume of 8x12x6mm, or 576 cubic mm (less a little bit for the thickness of the bottom), which is a good size.  For the 9x16mm, a 9x16x6mm enclosure produces 864 cubic mm, which is a good size for that speaker.  You could probably get away with a 5.5mm deep enclosure for that one.  Or if the enclosure were longer than the speaker, you could use something thinner.  Say, for example, that you've got 20mm of length on the shelf of the engine, but only 4mm of depth.  OK.  9x20x4 = 720, also probably fine.  In general, larger enclosures (more internal volume) are better, until you reach about 1000 cubic mm; after that, the benefits fall off.

John C.

[jridge]

John-
Not to side track this thread, but how does that >500 cu mm volume rule of thumb work for larger speakers (like what I might put in my HO fleet)?  If I used a 28mm round speaker in a cowl unit, this rule of thumb implies that I could theoretically use an enclosure of any depth - i.e 28mmx28mmx1mm = 784 cu mm.  Seems like the rule of thumb should be based on speaker face area, not a fixed value.
Thanks,
Jeff

[tehachapifan]

I got some 3D printed enclosures when I did by first sound install but, lately, I've gotten pretty good (and quick) at making my own styrene enclosures from scratch. This allows me to adjust dimensions and shapes based on the install and whichever speaker I happen to be using at the time. Certainly not a bad idea though.

[jdcolombo]

John-
Not to side track this thread, but how does that >500 cu mm volume rule of thumb work for larger speakers (like what I might put in my HO fleet)?  If I used a 28mm round speaker in a cowl unit, this rule of thumb implies that I could theoretically use an enclosure of any depth - i.e 28mmx28mmx1mm = 784 cu mm.  Seems like the rule of thumb should be based on speaker face area, not a fixed value.
Thanks,
Jeff

Hi Jeff.

You are correct - larger speakers benefit from more internal volume.  I've found that a 13x18 sounds best with an enclosure of 1000 cubic mm or more.  As I noted in my earlier post, the 9x16 benefits from a somewhat larger enclosure - about 750 cubic mm on up.  My 500 cubic mm "rule of thumb" was the bare minimum I think is necessary for an 8x12mm.  In N, we really can't use anything other than an 8x12 or 9x16 in a diesel.

John C.