N scale CPR/BCR Royal Hudson build thread

[Cajonpassfan]

Wow Craig, I said "hint hint" and you took it to town! Now I'm really curious!
Of course the real benefit of the forward firing install, if successful, would be behind a moving locomotive, with the sound projecting forward of the tender, where it's supposed to be. Thank you very much for taking on this challenge, and following its great interest. (I still think this sound discussion should be in the DCC forum, or maybe a link there).
Otto K.

[craigolio1]

No problem Otto. In my opinion the greatest asset this forum had is its membership. There are a lot of people who can offer really usefull suggestions that may be obvious immediately to that person, but it completely escaped the initial thought process. I think your idea has merit and I'm interested in seeing the results.

I'll put a link in the DCC forum.

Input and criticism is welcome from all.

Craig.

[jdcolombo]

Hi Craig.

Very intresting experiments with speakers.  Although the physics say that none of this will matter much once you get to a certain enclosure size, experimenting is always worthwhile.

My suggestion: instead of using ONE speaker, why not 2 or 4?  The advantage of multiple speakers is increased acoustic output in the low-midrange region.

None of the speakers we use in N are capable of much acoustic output below 500hz.  Even the 13x18mm speakers are down about 20-30db by 300hz, which means they have very little acoustic output at lower frequencies.  But put 2 or 4 of them together and you double (or quadruple) the acoustic output at the lower frequency ranges.  You also get more output at higher ranges, but the higher the frequency, the more directional the sound.  So the apparent acoustic output of 4 speakers at, say, 1000hz won't be as much as the actual output, because we are always listening to our locomotives off-axis.  As you move off-axis from the speaker, the relative acoustic output from high frequencies that reaches your ears drops dramatically.  This is why when you listen to a stereo system, you need to be fairly precisely seated between the two speakers, with the tweeters more or less at ear level.  If you sit higher or lower (off axis in the vertical plane), the high-frequencies will be attenuated, as they will be if you sit off to the side (off axis in the horizontal plane).   So using multiple speakers in a model has the advantage of significantly increasing APPARENT acoustic output at lower frequencies, which are more non-directional, without overwhelming things at the higher frequencies, which are more directional.

Streamlined Backshop has a number of custom 3D printed enclosures that accommodate multiple speakers.  But you can also simply use two (or four) speakers in individual enclosures, or in one enclosure that has individual sealed chambers for each speaker.  As for wiring, modern sound decoders are good with 4-ohm loads; that's two 8-ohm speakers wired in parallel.  If you want to use 4 speakers, wire two sets of two in parallel, and then wire those two sets in series, which will produce an overall 8-ohm load.  Sound decoders generally can output 1 watt, which is more than enough power to drive two or four sugar-cube-type speakers in a multiple-speaker array. 

Anyway, my thought is that given how far you're going with the speaker experiments, might as well ramp it up a notch, and see how multiple speakers would affect things.

John C.

[craigolio1]

Great idea John.

They don't need to be in their own individual sealed enclosures. They can all share the same enclosure so long as the rear waves are isolated from the front waves, and the two speakers are wired in phase.

In the set up I have here it's very easy to add a second speaker at the back end of the enclosure with out modifying the set up at all. I'll give that a go and see what happens.

Craig

[jdcolombo]

Great idea John.

They don't need to be in their own individual sealed enclosures. They can all share the same enclosure so long as the rear waves are isolated from the front waves, and the two speakers are wired in phase.

Craig

Yeah, that's right.  You should be able to add a speaker to your sealed box and reap the benefits, as long as the two speakers aren't so far apart from each other that the FRONT waves end up bouncing off the tender shell and getting out-of-phase, resulting in cancellation at some frequency.  I've never done a multiple-speaker install, so I'll be following this closely - going to be fascinating!

John

[peteski]

Here is a good primer on enclosures (in addition to what Craig mentioned): https://en.wikipedia.org/wiki/Loudspeaker_enclosure https://www.diyaudioandvideo.com/Tutorial/DesignBuildSpeakerBox/

Of course those are for full-size speakers (not our tiny sound emitters).

Sound cancellation is a problem for lower frequencies in the home acoustics, but due to the tiny size of our sound transducers and the enclosure sizes, that is not much of a factor. But I suspect in the N scale world, with multiple drivers on opposite sides of an enclosure we might encounter sound cancellation of higher frequencies.

[Greg Elmassian]

Although this is in the ceiling of a G scale rail truck, the idea is the same (put it in the ceiling since the interior is all open)

[peteski]

I've done couple of sound installs (N scale steam) where the sound was directed upwards through dozens of tiny holes through the molded coal load (or the coal load was replaced by a piece of black foam rubber which looked very convincing as N scale coal.

[craigolio1]

I've seen it mentioned in a few install threads that the modeller felt drilling holes in fan grills or what have you didn't help much.

Trapping the sound in side could cause some of the high frequencies to be absorbed and make the volume quieter. The listener would then turn it up. They would perceive the lack of highs as the lows being louder. That said, based on the frequency response, our speakers only produce highs and so the outcome will likely not change the "bass response". I'm testing it both ways.

I didn't get around to testing tonight but the various enclosures are prepped and wired and all ready for testing hopefully Sunday.

I added the extra speaker to the one sealed enclosure. It'll be tested like the others; both through the floor holes only and also through a larger opening in the front of the tender into the back of a cab.

Craig

[peteski]

I think the people who do not bother to drill holes in the shell believe that the sound will still escape to the outside through the air gaps in the loosely fitting shell.

Craig, I agree that creating openings (holes) to allow the air moved by the speaker cone to propagate to the ambient air should improve the sound quality of certain (higher) frequencies.  Whether the frequencies emitted by a sound decoder are high enough to be within that range the question (which should be determined by your testing).  Personally I like to create open paths for the air to travel from the inside of the shell to the outside.   After all, every device containing an acoustic transducer I have ever encountered (HiFi speaker systems, small transistor radio or any small audio device which has a loudspeaker, or even an earphone) had the cone behind some open grille or opening.

[craigolio1]

Peteski,

You bring up valid points. Something I have learned over time, is that people's perception of sound quality and what that means varies both in personal taste and what their experience with sound includes. I'll give you an example. When I set up a surround sound system I use (when I say I, I mean that I push buttons that make some kind of computer do this) an SPL meter and EQs of some form or another to balance the sound from every speaker in the room using white noise and various test tones. Then I sit down and use the "Lobby Attack" and "Dodge This" scenes from The Matrix to have a listen. I then make changes to the balance by ear. I have heard this movie hundreds of times on the best and the worst systems and I know exactly how I want it sound. Finally, I sit down with the owner and we have a listen together. We make final changes based on what they think sounds good. By the time I leave, four people's versions of what sounds good has changed the way the system sounds, the audio engineer that mixed the sound track, the person that created the software / hardware that measured/EQd the set up, me, and finally the owner.

Now, I have never heard what it sounds like when helicopter crashes into the side of a glass skyscraper, nor what it sounds like when you unload a mini gun at a range of 2m, but anyone CAN tell you whether it sounds good or bad. Everyone's taste is different but one thing that is common between every audio system is that the user prefers it when one part of the system is not over powering another. Loud bass sounds awesome when crap is blowing up all over the place but if there isn't enough mid and top end to balance it out then it's just annoying.

 I suspect this is why some people perceive the sound of a speaker enclosed in a loco as "sounding better". Our micro sound systems are so anemic when it comes to bass and mid bass response that the reduction in highs creates a perceived improved balance for that listener.

I think you are absolutely correct in that opening up a way for sound to escape preserves the highest frequencies that can be absorbed by any surface. As you pointed out, no one covers the tweeters in speakers system and people claim to even be able to hear the difference with the grills off and there for play their music with them removed.

Does this science (if you can call it that since there is sooo much personal opinion involved)  translate all the way down to our little micro systems?  Physics says yes. But can we hear it? Well there in lies the question.

Consider also that sound transmits through everything. Since it's a physical wave of energy that's in motion, it will pass that energy into anything it contacts. How much is lost depends on the material. To preserve the reproduction of the sound, the best quality speakers are made from very thick and dense materials, braced, and filled with dampening matetials all to prevent, amoung other things, the enclosure it self from generating its own sound. When a rigid panel vibrates it generates its own sound.

How does this affect our micro system? When we put a speaker inside a loco some sound is lost due to every surface the sound contacts absorbing energy at specific frequencies before it can escape and find its way to our ears. Sound escapes in two ways. As you pointed out, it finds its way out through every tiny unsealed hole and crack either by accident, or through holes created for this purpose (your preference). Also, it escapes by vibrating the exterior surfaces of the loco, in a sense turning the loco into a giant speaker it self.

All of that nonsense I just typed explains why I've chosen the different designs we have here. There is uniformity in that all of the speakers have the same size of enclosure, the same signal source and the same power being applied to them.

We have sound passed directly out the bottom, trapped inside relying on small holes and body vibration, sound trapped inside but also directed out one large hole into a cavity (kind of a combination of both previous, thanks Otto!), and the increased output of two paired drivers (thanks John!). I even considered trying to use a tuned port to boost lower frequency response at 300hz but at 1/4" wide it would need to be 9" long.

We will be able to scientifically, mathematically and subjectively figure out exactly and without any doubt what the BEST combination is for a tender mounted speaker. Period. No further testing will ever be required.....

....well for me and Fredrick anyway. Naturally everyone else here has a completely different impression of what good quality sound is and should of course perform their own testing to ensure that I'm not full of crap.

Haha. I love this stuff. Hopefully I can get time tomorrow to post some cool looking graphs of the results.

Craig.

[craigolio1]

Sheesh apparently I haven't used all of my words for the day.

This has nothing to do with our N Scale project but in the interest of an HO modelers who may be following, in researching speakers we could use I happened upon some YouTube videos where modelers had used replacement iPhone speakers in the tenders of some smaller steam locos. In one video he posted an A/B comparison of a larger Soundtraxx(?) speaker an even on YouTube you could hear a remarkable difference. The phone speaker is way smaller but is enclosed in a custom enclosure designed to do amazing things, that no doubt took a long time and cost $$$$ to produce. It proves that enclosures play a noticeable part (even in our micro systems) , and for HO diesel and steam modelers where space it more available I think it's worth experimenting with.

Craig

[peteski]

Yes, perception os sound quality is a very individual subject - everybody has different standard.

As far as getting good sound out of small package, Bose seems to have some magical solutions. Even their tiny Bluetooth Sound Link Mini speaker system , about a size of a brick, sounds amazingly good for its size.  Their Wave music system IV desktop radio/CD player also sounds incredibly well for its size. I think that one uses some type of transmission-line enclosure.  Similar type of enclosure.  I suspect that one of their "secrets" is extra-long-throw transducer (speaker) which even when the cone has a small area moves  a lot of air.

The sugar-cube speakers we use in out model also have much softer suspension and longer throw than the standard miniature speakers which have been used since the infancy of DCC sound decoders. That is why sugar-cube speakers (in a good enclosure) sound so good.  But the miniature sizes we are dealing with, and limited space for enclosures also have physical limitations which I suspect cannot be overcome.

You are correct, every material exposed to sound waves will vibrate and cary the wawes, some materials better than others. The plastic model's will do that quite well, but it sill still attenuate some frequencies.

[craigolio1]

There is no replacement for displacement.

Craig

[Cajonpassfan]

There is no replacement for displacement.

Craig

Lol, fascinating thread
But the last comment brings up the question of just how much "displacement" we really need for our little trains, and what the "scaled down" sound should be like. (Just what is the "displacement" of an N scale steam locomotive?)
Clearly, the lack of bass frequencies is a challenge, but I'm not sure I want my N scale trains to sound like the real thing. I do want some scaled down rumble, especially with diesels, but steam is an entirely different animal where bass is much less important. I want crispness, and subtle layers of effects, I want it nicely synchronized to motion, and I don't want it so obviously coming out of the tender; hence my efforts to project sound forward. But ultimately, the locomotive with its sound effects is still an integral part of its scaled down operating environment, and I'm looking for something credible on my home layout where the sound doesn't have to compete with other noise as is often the case at public shows or large clubs (or even layouts where crews continuously communicate via radio chatter). This is obviously a very personal, subjective matter, and others may see it differently.
Thanks for the heavy lifting Craig, following your testing with great interest.
Otto K.