Micro Speaker Enclosures for Model Locomotives

[BeeMac]

Hello Audiophiles,

I am seeking your advice on designing some enclosures for small full-range speakers to be mounted in model railroad steam locomotives. The two speakers I am looking at are here:

http://www.tb-speaker.com/uploads/files/29b9280a3b093e13e9494ebd3092b41a.pdf

and here:

http://www.tb-speaker.com/uploads/files/d3c15338f8d87344d99cea4a37b04b02.pdf

The scale is HO (87.1:1) and attached is a photo of some typical tender shells, of injection molded plastic. Another photo is of a complete tender, with the trucks (wheel & brake assemblies) attached. The normal options for mounting the speaker are either centered in the frame, facing downward or under the coal or wood load, facing upward. In the latter case, a large number of small holes are drilled in the coal load, between the chunks, or small bits of wood are loosely arranged on a mesh.

I believe that most commercially available sound-equipped locomotives have the speaker in the base, as shown in the attached parts diagram. The high frequencies would strike metal rails and wooden or plastic ties and hopefully mostly reflect, but I believe there is little effort given to enhancing bass, which is the goal here.

The internal volumes available in the tenders shown in the photo would, I believe, be in the range of .014 - .034 liters. I expect that the standard base would be replaced by a 3D printed version with whatever ports, baffles, horns, labyrinths or other structures you might suggest. I have tried some of the online calculators, but I'm not sure they scale this far down in size. I expect to eventually construct a small anechoic box with a turntable for the models and a swing arm for the microphone to control vertical angle (azimuth?) to evaluate designs. Suggestions on that can wait for now.

One last crazy idea, probably too easy to work. Can the natural frequency of the driver be lowered by adding weight to the cone? The Mechanical Engineer in me says that it should, but there surely must be trade offs.

Sorry to be so long-winded. If anyone here can point me in the right direction or make suggestions on design approaches or better speakers, it would be greatly appreciated.

Thanks.

Bill MacIndoe
Rhode Island, USA

 

[Bigun]

My guess is - best to put the bass driver under the baseboard not in the engine or train because you’ll never have enough space to do it right. Low frequences need big drivers but it won’t be critical to isolate these low frequencies to the train. On a large layout maybe install several bass drivers underneath the baseboard and arrange for the sound to follow the engine.

 

[xrk971]

The problem is that these DCC locomotives have their sound generators on board as a hard wired chip. Unless you make it a wireless transmit the sound can’t be on the baseboard. Additionally there are multiple trains with different sounds and their spatial location would be off if not on the train.

I think look for aftermarket replacement iPhone speakers - they are tiny have good output and have quite a bit of bass given tiny volume.

Amazon.com: Earpiece Ear Speaker Replacement for iPhone 7 Plus,iPhone 8 Plus with Earpiece Metal Bracket and Tools and Screen Adhesive: Cell Phones & Accessories

 

[BeeMac]

My guess is - best to put the bass driver under the baseboard not in the engine or train because you’ll never have enough space to do it right. Low frequences need big drivers but it won’t be critical to isolate these low frequencies to the train. On a large layout maybe install several bass drivers underneath the baseboard and arrange for the sound to follow the engine.

Bigun,

That system already exists:

SoundTraxx

 

[chris661]

I'd go for a subwoofer + satellite option. Tactile transducer on the base of the entire model, and a small speaker on the train.

Chris

 

[picowallspeaker]

Bee Mac, why don't you use the boxed speakers with passive radiators?
Sound Module - TB SPEAKER CO., LTD.

 

[BeeMac]

Bee Mac, why don't you use the boxed speakers with passive radiators?
Sound Module - TB SPEAKER CO., LTD.

Picowallspeaker,


Thank you. I already had looked at those modules. Only two would fit even the larger two tender shells and the bass performance of those is worse than my original two choices. Those two modules have -3dB points of around 420 Hz. The two round ones have F0s of 220 and 170 Hz.


Bill MacIndoe

 

[xrk971]

You should try the iPhone speaker. It’s tiny and powerful.

 

[Bigun]

Bigun,

That system already exists:

SoundTraxx

That's cool - that is what I'd use if I had the time to build a layout. I remember standing on the platform near Lydney whilst a pannier tank ran around the train. The rumble I felt through my feet as that huge weight moved around was really neat. I don't think a small speaker would give me enough to be happy without some big honkin' sub. Even a Deltic needs big lungs to be interesting.