Sound speaker in Con Cor - Kato designed S-2 4-8-4

[Tom Todd]

I am adding a sound decoder to this loco.  Before I begin I have a question about speaker placement.  The tender has no holes in it for the sound to "get out."  I'm thinking of drilling some holes and placing the speaker and enclosure there.  But where do I make the holes?  I read somewhere that drilling small (#80 drill bit) holes in under the coal  in the tender.  But this one is oil fired.  My 2-10-2 by Con Cor has holes in the bottom of the tender, but the S2 tender is a Vandy and curved at the bottom, more likely to show.

Thoughts?

Tom

[jdcolombo]

You don't need any holes.

When I first started sound installs, I drilled holes in the coal load of my tenders.  Then I decided to try it without.  Without sounds fine - in fact, it may sound a bit better, because it gives a bit more reverb effect to the sounds.  Do your sound install and don't worry about holes.  If possible, do the install so that the speaker fires upward into the empty tender shell cavity.

DO worry about the speaker: use an 11x15 or 13x18 cell-phone type ("sugar cube") speaker in an enclosure that is at least 8mm deep.  Do this, and your sound will be excellent.

John C.

[Tom Todd]

Thanks,

Tom

[reinhardtjh]

And make sure your enclosure is sealed to the speaker.  Any air leak will lessen the effect and reduce the sound quality.

[Cajonpassfan]

John C., that’s an interesting solution, I’ve got to try it. Nothing is simpler than that, and I do like simple. I assume that a plastic tender with no holes still has enough cracks and crevices where the sound is forced to “leak” out?
For what it’s worth, there is room to drill holes in the Concor tender floor ahead of the front truck and also below the foot plate facing the locomotive, see below. The speaker is located inside the oil tank, firing down. I don’t have a way of measuring the effectiveness of this approach, but whenever possible, I like to push the sound forward. It sounds right to me...
Otto K.

[jdcolombo]

Tender shells are hardly air-tight.  It's why they work so poorly as baffles (enclosures) even though some manufacturers continue to try to use them that way (why they do this is truly baffling - pun intended).  The biggest "hole" in the shell tends to be at the front where the wires enter from the engine.  You wouldn't WANT to seal this off, even if you could, because later getting the tender shell off would be a nightmare.  Then there are the holes for the trucks - either a hole for the "fingers" from the pickup wipers, or holes for wires.  And of course the where the shell fits to the tender underbody isn't sealed tight, either.  The shell is like a sieve - air escapes everywhere.

Actually, my first "no holes" install was a mistake.  I just forgot to drill holes in the coal load.  Nothing bad happened, and in fact, I sort of liked the result better than my "hole-y" (as opposed to "holy," which I'm certainly not ) installs.  And then that led me to not drilling holes for my diesel installations, and that worked out just dandy, too.

John C.

[peteski]

This is an interesting discussion. I'm not audio engineer but just like everybody else, have my opinions.  I also think that I'm  capable of some logical thinking, and have some life experience to base my opinions on. 

First, I like to add my 5 cents about enclosed speaker.  Except for some esoteric designs, best sound quality is obtained by totally isolating the front and back of the speaker cone (or in our case flat "piston" which moves the air to generate sound).  Sealed enclosure is one way of doing this. That prevents the positive/negative air waves produced by the front and back surface of the speaker cone from canceling each other out.  While a small volume sealed enclosure has its own set of problems, it is the best solution in our miniature world.

If the speaker (already mounted in an airtight enclosure (for best sound quality) is then hidden inside a plastic tender shell, like John said, some of the sound waves will escape through small gaps in the tender, but the sound vibrations will also vibrate the shell itself, which in turn will transfer the vibrations to the ambient air outside of the shell.  But the plastic tender shell transfers mid frequencies better than the higher ones.

While that works, IMO, it is not ideal (especially for steam locos).  Steam hiss (noise)  has quite a bit of high frequency component in it and those (to my ears) get muffled by installs where there are no holes drilled in the tender directly over the speaker cone, allowing the speaker cone vibrations to vent out.  Well, the amount of muffling depends on how many openings are in the tender and how loarge they are, but I feel that the crispest sound of steam hiss can be achieved by having the speaker cone vented directly to the ambient air outside of the tender shell.

A simple experiment. Cup both your hands to create as tight as possible air chamber, and cover your mouth with them, again sealing any gaps as much as possible.  Your mouth is the "speaker", while your cupped hands are the tender shell.  Make a high pitched sound (as high as you can), or even just speak.  The sound is muffled and lacks crispiness. Then make a small hole in the cupped hands (move your thumb slightly to make a small opening). Make that sound again. Now it is crisper, but still somewhat dull. This simulates the small gaps in the tender shell.  Now remove your cupped hands from your mouth and make that same sound again.. It is much crisper sounding, not muffled at all.    That's "peteski logic" for you.

[jdcolombo]

Hi Pete.

While your analysis of the potential muffling of highest-frequency tones is correct, what I've observed is that this muffling actually brings the high-end of the small speakers we use in these applications into better balance with the midrange and lower midrange.  I don't really notice a problem with the sound of steam hiss in my non-hole-y installs.  It sounds pretty hissy to me.  It might sound MORE hissy with holes in the tender somewhere, but I don't observe a noticeable lack of crispness in the sound in this situation.

Of course, everyone's hearing and sound preferences vary.  My reference headphones are Sennheiser HD650's, which are noticeably "mellow" in the high end.  Other folks really enjoy something like the Focal Utopia or Stax electrostats, both of which receive rave reviews and which I couldn't listen to for more than 15 minutes before the elevated (to my ears) treble drove me nuts.  So what I find perfectly fine, others may not.

I was actually pretty surprised that the BLI Mikado has no holes for speaker sound exit; instead, the speaker sits in the top of the tender shell, firing down toward the decoder.  There is no lack of high-end in this layout; rather, the problem is a lack of "body" to the sound, which is why I ended up replacing this speaker with an 11x15 in a sealed enclosure (still firing down at the decoder from the top of the shell).  It IS true that my replacement has a bit less "ring" to the bell than the stock speaker.  I think that's just dandy, but YMMV.

In any event, I'd recommend that the OP try a non-hole install.  It may be pretty much the only option for an oil-burner, unless you were going to mount the speaker to fire out the bottom of the tender, which then has the disadvantage of the sound focusing down at the track, and some of the same muffling issues from such an arrangement.

John C.