 Hello there Bruce here in the shop tonight. We're going to talk a little bit about sound and getting the very best sound you Possibly can out of your locomotives in a little thing. I called how to get the sound out Sounds like a good idea. Okay. Let's get started first. We got to talk about the physics of sound So you don't understand the physics you're gonna have a little bit of a hard time making it work for you Okay, let's start with the concept that sound is pressure waves moving through the air Hit a base drone You can see the diaphragm of the drone move that creates a pressure wave Since we're dealing with electronics and electronically generated signals here We have an item called a speaker that will translate those electronic Impulses into sound pressure waves. How do they do that? Okay? The speaker has a cone and a voice coil that move back and forth based on the electronic Signal that it's receiving when it moves forward it creates a positive pressure here and a negative pressure on this side When it comes back this way this becomes a positive pressure. This becomes a negative pressure So it moves back and forth that creates pressure waves They move off of both sides of the speaker people ask me what does it matter which way you mount speakers? With the magnet up or with the cone up or out or however you want to look at it No, it doesn't not in our hobby if you get into really fine high-end audio There are some people who say yes that the frame that holds the magnet will Distort will reflect the sounds a little bit and may change the image of this way beyond What we're talking about here in our locomotives. Okay? So it pushes the sound It pushes these pressure waves out Well, what happens is as the cone moves this way there's a negative pressure here. There's a positive pressure here nature seeks to Even out Everything in its world So this positive pressure rather than just automatically running away is first going to try and sneak around the speaker And fill in the negative pressure that's on the backside of the speaker What does that do that cancels the sound when it goes this way? It pumps air around here when it goes this way it pumps air around here So it might as well not be moving. It's not making any net effect of sound on the world around it. Fortunately or unfortunately these variations of this cancellation is not complete So therefore it doesn't completely wipe out the sound, but it does significantly diminish it Okay, I've got here a 28 by 40 millimeter speaker. It's a speaker. We're going to use throughout this whole A little session today This is the largest speaker that will fit well Into an HO scale locomotive. It'll fit in the floor or the co-load of a lot of steam or tenders it will fit in the floor of some Cab diesels So a units b units, especially a lot of dummy b units. I use even two of these in a dummy b unit make great sounding models It's about a little over an inch long by about a wide by about an inch and a half long So it's it's a fairly large speaker And so this is going to be kind of our our hallmark of what will really sound good. I'm going to fire this thing up with the sound from a Soundtracks tsunami alco 244 and let you hear it. Okay, there you have the speaker Generating the sound. It's about a third of the way through The throttle range, so it's it's moving along down the road at a pretty good clip And you can hear the sound But what's happening here in free air just to review The sound from this side of the speaker will wrap around and cancel the sound from this side of the speaker and vice versa How do we know that's happening? Well, let's see what happens if we cut down the amount of that sound that's allowed to wrap around Look at that. That isn't even complete. So that leads us to my next point, which is How do we make that happen in our models? if we had a speaker here And we built a big Plane that went up forever and ever and ever and we had a speaker right in the middle of it And you were on that side of the speaker and it was moving air You would hear All of the sound because there'd be absolutely no way that any sound could wrap around the speaker and cancel out No, you wouldn't be hearing all the sound you'd be hearing half the sound because Part of the time the speaker is coming this way and making the same amount of sound on this side of this big plane Okay, it would sound good, but you'd be losing efficiency. You'd be giving away Some of the sound that you've actually paid your money to hear So how can we get the sound off of both sides of the speaker? And still Have good sound. Well, it's my contention that if the sound has to travel About five or six inches Given the wavelengths that we're using For the speaker size that will fit in our models that the Basic cancellation will be avoided and you'll get the best possible sound you can out of your models Okay to show that demonstrate that fact. I have a piece of white plastic here If I mount a speaker in the middle of this piece of plastic Then it's about six inches by about four inches Okay, if the speaker is mounted here Then the sound from this side of the speaker has to travel About two inches over here around and about two inches back about four four and a half inches Uh before it can actually cancel the sound from this from itself Going around this way. It's closer to six inches. Nothing magical about my numbers This is where my number came from. I looked at this and I said this works So four to six inches is the minimum number It works. Okay, let's let's show. Let's take a look. Okay back to our speaker With the tsunami generating alco sounds in it And sitting here in free air Sounds like it did before now. Watch what happens when I put this white piece of plastic In front of the speaker now. It's not sealed or glued down or anything else I'm just going to hold it in place and you can hear what happens Notice how the sound gets louder as well as there is more Bass there's just more definition of the individual sounds you can hear the individual Almost almost hear the individual explosions from the prime movers that locomotive was running along Listen again. Isn't that neat? Okay, let's go back and look at this piece of plastic that I was talking about Six inches long four inches wide About an inch out of the middle of it for the speaker If I were to fold this side down And I were to fold this side down So there was just the speaker left here You'd have about two inches about an inch and about two inches. Yeah, I know that doesn't add up to four But it's close. Okay Gee doesn't that sound like the shape of the shell Of an ho locomotive a couple inches up an inch across a couple inches down And about six inches long So if I were to mount the speaker in say the fans of a locomotive You'd get the same effect the sound would have to go down Through the mechanism inside which will slow it down Come around say through the trucks Back up the side of the locomotive before it can cancel the sound coming out the top. That's the basis. I'm talking about Now there are folks who say that you absolutely must have an enclosure in order to get good sound out of your speakers I seriously disagree I don't disagree that you have to limit the Bleed around the speaker the cancellation But there's more than one way to do that Yes, an enclosure will do it and yes, there are times where that's the best way to do it Given the locomotive that you're trying to do the installation into but it isn't the only answer And so a good craftsman has many tools in his toolbox. Let's look at some different tools here Now we're going to take the same speaker and use it With an enclosure and compare it to a speaker similar to the one in the white card I made up this little test board many years ago and I've used it for a lot of different things But what's important about it is here on the end There's a 28 by 40 millimeter speaker That is in an enclosure Commercially available enclosure that about doubles the price of the speaker it costs about the same as the speaker So the speaker plus enclosure costs about twice as much money and it takes up a lot of room But it gives you some fairly good sound And over here we have the same speaker Same style of speaker at least mounted just in the middle of the board. Okay It just sticks through the board. That's all so you have the distance around the board To prevent the cancellation. So let's compare the two And first we're going to look at the box The speaker in the box Okay, that sounds pretty good. It's got a nice volume. It's got fairly good sound to it and just By itself with no subjective comparison. It sounds really good So now let's listen to the speaker outside the box the one over here in the middle of the panel I don't know if you can hear a difference between those two Unless they're right up against each other. So let's start off I'll turn on the speaker in the box and then I'll switch to the one outside of the box and give you a side-by-side comparison Here's a hint. I don't think you're going to see a difference Particularly in the level of the sound But in the subtle nuances of the sound And the timber of the sound and the depth of the sound the fact that it doesn't sound like it's flat and just Right there next to you. I think you'll hear a difference Hopefully on this video, you'll be able to hear the difference between the two So we'll start off with the box and then we'll switch to the speaker out of the box Okay, I throw out a locomotive back down to an idle and Turned on the horn. So listen to the horn And the prime mover idling in the background With the box and out of the box and see the difference on the higher end of the register I don't know about you, but most people that I've made that demonstration to have said wow There's a big difference between those How can I have my locomotives sound like the speaker out of the box? So let's work on how to think outside the box That will be the topic that's covered in my august of 2012 column in model railroad hobbyist Go to the website and look at the column download the magazine and join in the discussion on the model railroad hobbyist website by clicking on the Box at the end of the column for reader comments And you can vote for the column which includes this video And you can share comments And I'm sure that there's going to be a whole bunch of people That are going to say a whole bunch of things that they've been kind of programmed to think And I've heard a bunch of them as I've given this clinic at various nmra events Over the years And I've had a lot of people I finally in one clinic had one guy say When one fellow was saying but you got to put it in enclosure and this other fellow finally said look listen to the difference Yes, there is a difference. Let's think outside the box and have some more fun with our locomotives This is bruce Thanks for watching. See you on the model railroad hobbyist website