Designing Locomotive Acoustics for On-Board Sound Systems

As I re-read this PDF document several times I became aware of a possible speaker installation that was not covered in this document....excerpt:

"Separate back wave from front wave: It is important for sound quality that the inside cab area be sealed as much as possible to prevent the back wave from escaping through grills, vents, fans or other openings in the diesel or electric locomotive cab or through the openings in the chassis where the motors connect to the trucks. If there is any leakage of the back-wave to the outside, it will mix with the speaker front-wave and cause destructive inference in some base tones and perhaps constructive interference for some of the higher frequency tones. The respective path lengths for the front-wave and the escaping back-wave and the position of the listener will determine which frequency components are degraded or changed. Usually, since the acoustic chamber and path lengths are short, any back wave escaping from the locomotive causes degradation of the sound. If the back wave is allowed to escape close to the front-wave, the degradation is more severe. As the scale of the model decreases, this becomes more of a problem since the distances between front and back waves become smaller.

Vent the front-wave sound under the locomotive: Propagating sound upward into the open air seems to produce lower quality sound unless you are directly over the speaker. The sound has no opportunity to reflect against different parts of the layout such as buildings, mountains, etc. that add both volume and presence. Our experience is that the best design choice is to propagate the sound under the locomotive. The next best choice is out the sides of the locomotive through vents and grills. If sound is vented under the locomotive, always be aware of the affect of trucks and other obstacles and other factors that can either improve or degrade sound quality. Do not vent sound straight down too close to the track where it can be reflected back and decrease volume and sound quality. Venting the sound directly under the fuel tank usually does not produce good sound in smaller gauges (HO and N) since there is little space between the bottom of the fuel tank where the sound is vented, and the top of the track. Sound usually reflects back from the track resulting in poor volume and presence. Venting through the gear tower and chassis over the open truck areas seems to produce the best sound."

What I find interesting here is no mention of venting the 'front-wave' from the front of the tender, verses out the bottom, or out the coal load?? Why does this interest me? I have at least 4 locos with vandy tenders (C&O) that I wish to install sound into. He covers vandy tenders to some considerable degree, but does not mention this possibility.

I happen to have a friend who has a relatively cheap little IHC steamer that has its sound vented out the front bulkhead of the tender right into the cab area of the loco....the sound is GREAT. On the other hand I have a 2-8-8-2 with the sound vented out the coal load that I consider substandard. So I am giving real serious consideration to experimenting with one of my Spectrum C&O Heavy Mountains with their vandy tenders and venting the sound forward out of the tender.

Has anyone else seen such an installation? Does anyone have a photo and/or illustration of the 'factory sound' installation in these Spectrum models??

Bruce at www.litchfieldstation.com speaks about this issue in his excellent presentation which can be followed at this link  http://litchfieldstation.com/DCC-University/HowDoIGetTheSoundOut/HowDoIGetTheSoundOut_files/frame.htm

well worth a read IMO.

Interesting website there, but as I looked thru it pretty throughly I still did not see a reference to venting the primary sound pressure wave 'out the front of the tender'. I did see a lot of 'out the coal load'.

 The problem I see with "out the front" of the tender is that it would be quite close to the cab, ith similar issues to the fuel tank venting. A large chunk of the sound would be reflected off the backhead rigth into the speaker, and out ahead of the loco there would be very little sound.

                                       --Randy

I was just listening to your 'sound samples', and had a question about the EMD 567 Sound of the F7 locos. (BTW, great presentation !! )
http://www.ulrichmodels.com/Sound_Samples/SoundSamples.htm

I assume the speaker is installed similar to the factory MRC installation on the rear of the metal chassis. But I believe I have been exposed to two different speaker orientations:
1) the front wave of the speaker faces downward and the rear face of the speaker is cover by a round plastic back-wave cavity enclosure.
2) the front wave of the speaker faces into the round plastic back-wave cavity enclosure while its rear face faces downward in the loco.

I would think the second orientation would be less effective than the first ?? Doesn't the already small front face of these small speakers produce a much more positive sound than the back face that is greatly cover by the metal frame of the speaker itself ?? Why would one install these small speakers 'backwards' ??

I've run into a similar situation for the P2K PA/PB locos where the speaker has been installed in a relatively shallow box up in top of the shell. First off in one case its installed with the front wave of the speaker projecting down into the shell. In the second case the speaker's front face projects into the small cavity box.....Strange??
And in both cases I would question the size of the 'back-wave' cavity enclosure box. It seems so shallow as to not really allow for full speaker excursions. Shouldn't these back-wave cavities be 'allowably large' so as to not impend full speaker excursions??

  I feel that you are reading into this sound installation stuff too deep.  As long as the sound force is not confined, it radiates out quite well.   Face it, the sound of Sound/DCC decoder wlil not be 'stereo' no mattter what you do - that is 'life'.  I have 'factory' sound engines and I have installed 'aftermarket' sound into several engines.  A good speaker enclosure is a key issue - and some way to get the sound out of the engine.  If it sounds 'OK' - it is a good installation!    At least I am not trying to install sound in an 'N' scale engine!

Jim

jrbernier

I feel that you are reading into this sound installation stuff too deep.   

If it sounds 'OK' - it is a good installation!    At least I am not trying to install sound in an 'N' scale engine!

Jim

If you are satisfied with 'OK', then I'm sure there are a lot of installers that are very happy with you.

I'm not looking for 'stereo', I'm just looking for good base response out of small speakers....tough to do and get that real low rumble sound. If a little research iinto optimizing the speaker installation will enhance this, then I'm willing to spent some time optimizing the situation....at least if I'm going to spend this extra money putting sound in my fleet, I want it well spent.

I once walked into a train show up in PA quite some number of years ago, and there was a fellow there with a CD recording/player (I believe these were new tech at the time) and some good home speakers. WOW, it was like the locomotive was right there in the room with us !!!

And I couldn't agree more...thank goodness its not N scale I'm fooling around with.

 With the Revolution I installed the QSI HB106R extended bass speaker and the QSI baffle for it in a P2k E8, pointed down at the opening behind the front truck.  Although I was pleased with the frequency response over all, I thought it was a little too "plastic" sounding.  I covered the back (top) and 1/2 of the sides of the baffle with museum putty.  It helped the over all tone quite a bit.  If there is a reduction in bass response, it's hard for me to tell, cause of the improvement over that plastic sound.  Someday I want to try a baffle made out of a tube of cardboard, fiberglass or G10.   I can't "seal" up my shell, cause I need those top vents and rear door open for cooling the RC board that runs the motors and the Revolution.

 DC
 

 ....interesting reply from Steve at Ulrich Models

There are rules in the speaker game but there also is a large abstract area where rules do not seem to apply.  I have been playing around with speaker combinations for two years and I still find trial and error the best method.  This is what I do know about the MRC speaker and baffle.  It is an outstanding combination and out performs almost any other round 28 mm speaker and baffle I have used, except for the QSI large base speaker. It has more base and more volume than the other baffle combination I have tried.  I think there are two reasons. (1) the speaker is sealed into the baffle with a sticky gasket. (2) I think the rounded corners also help.  To tell you the truth, it works so well, I have not flipped the speaker to try it. Also, it comes as a sealed unit.  The seal is really important as any leakage can destroy the base response. The exception is a well designed port. It also nice that the wire terminals are exposed in the face-down orientation.

In the case of the Loksound decoder that uses a 100 ohm speaker, I removed the MRC speaker and installed a 28 mm Loksound round speaker with a new gasket into the baffle.  The combination out performed the LokSound speaker in its factory baffle significantly. I then tried flipping the Loksound speaker in its factory baffle to be like the MRC, but there was no improvement or degradation. So far I have not seen much difference based on the speaker orientation in the baffle. I wish I could take credit for finding this speaker but it was suggested by one of my customers.

The other thing I have found is that placement of speakers inside shell is important.  I have some oval enhanced base speakers that I put into SD70Ms and such.  In the Athearn, I thought they would sound best with the speaker surface pointed out the radiator fan openings.  However, I later flipped the speaker over and pointed it down at the trucks.  There was a significant improvement.  I believe it is due to the shell acoustics and the sound resonance from the shell itself. When the speaker was open to the air, I did not get any of those effects.

I am afraid that I cannot explain the physics behind the results.  I only know what seems to work.  Too bad for MRC. Nice speaker and lousy decoder. I hope they keep making the enclosures.

As a rule, the decoders will sound even better when you have the locomotive in front of you and on the track than in my presentation.  I did everything I could think of to obtain real sound.  I use a professional mike and a preamp but there is nothing like being there.

http://www.ulrichmodels.com/Sound_Samples/SoundSamples.htm
On this page, note this reference, "An Enhanced Base Speaker, 40 mm x 18.5 mm, was mounted in the shell for these samples. This speaker and enclosure produces better sound than the tank mounted speaker and eliminates the problem of metal debris being picked up by the speaker. Click here to see a typical install "

railandsail

I'm investigating this whole subject of optimum sound installations in HO model trains. I ran across this PDF document with good explanations and nice illustrations. Thought this forum might find it interesting, if it hasn't already been posterd

REMOVED BAD LINK

 

 

Apparently the link to this PDF has gone bad, and/or changed?

Does someone with more computer knowledge than me know how to retrieve it??

I just got a "RED" security threat from ESET and the site was blocked, when I tried to open it.

I suggest your research it yourself, and not post any links.  

A thread from 2009, which hasn't drawn any intetest.

Mike.

That link tries to install something on my computer.  Why are you posting links like that?  

Any link that requires you to install something else to see the page is malware until proven otherwise.

That makes three of us. I should have known better than to click on that link. Thanks a lot Brian. 

Rich

Look at the date folks .... this thread is 11 years old. That original link has probably been broken or hacked by now.

Mark.

Mark R.

Look at the date folks .... this thread is 11 years old. That original link has probably been broken or hacked by now.

Mark. 

Rich

The date is the first thing I looked at, knowing who the OP is.  I had forgotten Brian has been on here that long.

Pretty obvious the site is BAD.  I use ESET, and it blocked it the second I clicked on the link.

And just to get a back a little on topic,  I've never considered what the thread is about.  I know a speaker enclosure is important, just as it is for your home stereo system.

YES, I still have one! with a big speaker in each corner of the room, for the surround sound!  

I'm thinking of enclosing the speaker for my next sound install in cherry wood. 

Mike.

I have this file downloaded some 10 years ago, it is still on my PC. I have uploaded it here, link will expire in 29 days. I hope it will work.

I think this document is very useful for anyone trying to install sound in locomotives. 

Hrvoje

OK Hrvoje, I was very skeptical, but I took a chance,  and it worked, and it is full of great info.

It is about how the speakers are mounted, and contained.  

I'll take some of my comments back. 

Mike.

Okay guys, sorry for that bad link, I removed it.

But I ask how does someone corrupt a PDF file that they didn't create?? And if I long ago downloaded that PDF file to my own computer why can't I find it now?? (that is where I searched when I could not open that link,...again sorry about that bad link, I was unaware that it could create a problem)

The reason I reopened this discussion is I have been corresponding with this gentleman who produces some very fine sounds,...

There is another reason I have reopened this subject thread,...to include a link to this gentleman's knowledge on this subject.
https://www.scalesoundsystems.com/

https://www.scalesoundsystems.com/design
and his white paper
Concepts and Considerations in Speaker System Design for Small Scale Model Trains: a Technical White Paper

railandsail

Okay guys, sorry for that bad link, I removed it.

Rich

OKAY, I removed that one also.

I just found out why I didn't find that PDF file on my external hard drive,...because when I did a search for it, the file name title was joined together "AcousticDesign' rather than 2 separate words. I guess thats how it got filed automatically when I originally saved it, ....as I would not have selected that 'together wording' I don't think? Ahhh...this wonderful world of computers

Link to the white paper:

https://f5479436-5972-4fe2-a17a-b4fbd2ea046e.filesusr.com/ugd/7e84c8_7c6fc668d6334d309188adff97535673.pdf

Paper opens correctly as downloaded; I see no malware warnings and get no alert from Ghostery.

That second white paper link was NOT the problem,...it was the older white paper link I had posted previously.

railandsail

That second white paper link was NOT the problem,...it was the older white paper link I had posted previously. 

That said, you nearly brought down three computers.

So, what happened when you clicked on the bad link and found out that it had a problem? Did you not get a warning?

Rich

 QS Solutions is long gone, so someone else has hijacked or else registered the domain name for obviously nefarious purposes. QSI is still around, but they only sell direct - at one time, QS Solutions was part of Tony's. It seems their only support is from the Yahoo Group, now on Groups.io.

 Ulrich is closed as well, so I wouldn't click on that link either.

                                                --Randy

Randy, that advice would normally be quite appropriate. But in this case when a long time forum member posts a link, especially one from a well known source, you would think that it would be safe to click on it, and usually that would be true. Unfortunately, that did not occur in this case. Blame Brian, not the forum members who clicked on it, trying to be helpful.

Rich

richhotrain

Randy, that advice would normally be quite appropriate. But in this case when a long time forum member posts a link, especially one from a well known source, you would think that it would be safe to click on it, and usually that would be true. Unfortunately, that did not occur in this case. Blame Brian, not the forum members who clicked on it, trying to be helpful.

Rich

 

Rich - Also keep in mind the links were probably active and problem free when this thread was created back in 2009. Would have been a non-issue had this thread not been resurrected from the dead ....

Mark.

Totally agree with you on that issue, Mark.

I have long argued that threads should be locked after a year of inactivity.

Rich

 Therein lies the rub. Options are:

1. Lock old threads. Now over the long haul (and I've been ehre for the long haul), you have multiple threads, all rehashing the same thing, just a few years apart because the old one got locked on time, so a new one is started askign the same thign that's already been answer in 5 previous old threads.

2. Let them be acted on - in general, this is a fairly slow moving hobby, so it's more rare that the previous information is no longer valid. But at least there aren't 5 threads on the exact same subject.

Now, on things with links, that's going to be a tough call. Are they still valid? Does the company still exist? I wasn't 100% sure but being fairly invovled in DCC I was pretty sure I herd that QS Solutions was dead and buried a while ago, so I wasn't about to click. Not everyone will know that, but that's why good protecton on your computer is important, so it does no harm. In this SPECIFIC case, since it was the OP resurrecting the thread - yeah, he probably should have validated what was being posted first. If someone ELSE reopened it by posting a link to a different document on designing speaker systems for models, it's hard to blame them if  a link in a message 10 posts back is no longer any good. 

I suppose a majority of the old thread resurrection could be solved with a good working search. But then people would have to actually use it. 

                        --Randy