I noticed this in a pop-up and curiosity made me look. I have not been converting DC locos to DCC/sound lately but notice this might be interesting in some cases.
http://www.bowserorders.com/.sc/ms/dd/ee/14466934/Bowser%20Speaker%20-%202%20sugar%20cube%20speakers%2C%20wire%2C%20plug
One reason for my interest is based on some articles I read on another forum a few years ago (by L. Hanlon IIRC) that showed frequency test curves for a variety of micro and other speakers As I recall, some of the classic HO size ovals did not compare so well to other options. So this might be an interesting option in narrow hood diesels such as GPs. I was using micros from Knowles, then CUI primarily based on those articles, with custom styrene enclosures.
It looks like twin micro speakers in a rectangular enclosure that might fit the space where an oval would typically be installed. There is nil description, such as ohm rating of the setup, etc. I presume the speaker inner faces are flush against the inside wall of the enclosure as the micros almost demand the enclosure being sealed for decent performance. Of course this enclosure volume is pretty small, so lower frequencies likely will not make the items on your shelf rattle. But they may be pretty good for close spaces.
I haven't kept up, so perhaps other vendors (e.g., TCS) have narrow hood micro enclosures meant as an option for the narrow hoods, etc.
Paul
Modeling HO with a transition era UP bent
Larry Puckett shows off a couple versions of dual enclosures at 13:06
Henry
COB Potomac & Northern
Shenandoah Valley
I bought a couple of the Bowser enclosures, both the bare-bones enclosure (add your own speaker(s) and the ones including the wired speakers.
There is room in the depth of the enclosure for air space behind the speaker.
Bowser uses a little strip of PC board that contacts the little springs on the cube speaker and this makes wiring easier but they do not include this PC board if you buy the enclosure alone, too bad.
I have used the twin enclosure but blanked off the second opening and only used one speaker. They sound great.
There is a wide variation between sound quality of seemingly identical speakers. I found that some I bought in bulk were next to worthless, yet others that look the same, even down to numbers printed on them, sounded excellent.
I always test my enclousure and speaker using a cheap MP3 player before installing in an engine.
One of MY favorite go-to cube speakers is this model from ESU 50321:
https://www.modeltrainstuff.com/esu-50321-loksound-speaker-11mm-x-15mm-square-8-ohms-0-5w-with-sound-chamber-set/
The enclosure is versatile. You can stack extenders to make several sized enclosures. Using the whole kit makes for a nearly perfect sound chamber and the results are very good for the price.
SD_9-decoder-sp1 by Edmund, on Flickr
This pair was used in a Proto2000 SD-9. When soldering to the cube speakers I always tack them down with double stick tape otherwise the magnet will jump to the soldering tip
SD_9-decoder-sp by Edmund, on Flickr
S1 being speaker 1, a smaller enclosure (the Bowser is way too deep to fit here) and S2 is a larger ESU enclosure mounted in the cab space.
My test setup:
SPKR_test2 by Edmund, on Flickr
I can also check to see if parallel or series wiring will work and also check speaker phase by reversing wires and checking sound output.
I thought I had some photos of the Bowser speaker. If I find them I'll post them. I can give you dimensions if you'd like.
good luck, Ed