Mark R. There is a lot of mis-conception that you "have to let the sound out". I have found that you get increased frequency response by having the speaker in a sealed enclosure inside another "almost" sealed enclosure. I recently did a sound install in an older spectrum SD45, and due to the split chassis, the only logical place for the speaker was to mill out the bottom of the fuel tank casting - which I did. Prior to putting everything back together, I always do a test run. As expected, it sounded pretty good with the speaker in a sealed enclosure under the engine. I figured at this point I would then drill a bunch of holes in the plastic fuel tank to "let the sound out". Out of curiosity, I installed the plastic tank without any holes, and the sound was notably improved ! The frequency range was drastically improved and it wasn't as directional - not as obvious that it was actually coming from below the engine .... it got left like that. I think in the case of the speaker being mounted in the tender, if that's where you HAVE to put it, by keeping the speaker / enclosure sealed in the tender, the sound is much less directional taking away from the fact the sound is coming from the tender and not the engine (that's a real pet peeve of mine). As soon as there is an opening to a speaker, it's real obvious where the sound is coming from. With your eyes closed, you can easily orient a speaker box so you are directly in front of it. Put that speaker in another sealed enclosure, you cannot easily tell where the front of the speaker is with your eyes closed - the whole thing sounds the same .... same concept in our sealed engine shells. With holes in the coal load, it becomes real obvious the sound is coming from the coal load. If the tender was sealed, the sound is coming from the whole tender, it's no longer as directional. Just some food for thought based on my own experiences .... Mark.
There is a lot of mis-conception that you "have to let the sound out". I have found that you get increased frequency response by having the speaker in a sealed enclosure inside another "almost" sealed enclosure.
I recently did a sound install in an older spectrum SD45, and due to the split chassis, the only logical place for the speaker was to mill out the bottom of the fuel tank casting - which I did. Prior to putting everything back together, I always do a test run. As expected, it sounded pretty good with the speaker in a sealed enclosure under the engine.
I figured at this point I would then drill a bunch of holes in the plastic fuel tank to "let the sound out". Out of curiosity, I installed the plastic tank without any holes, and the sound was notably improved ! The frequency range was drastically improved and it wasn't as directional - not as obvious that it was actually coming from below the engine .... it got left like that.
I think in the case of the speaker being mounted in the tender, if that's where you HAVE to put it, by keeping the speaker / enclosure sealed in the tender, the sound is much less directional taking away from the fact the sound is coming from the tender and not the engine (that's a real pet peeve of mine). As soon as there is an opening to a speaker, it's real obvious where the sound is coming from.
With your eyes closed, you can easily orient a speaker box so you are directly in front of it. Put that speaker in another sealed enclosure, you cannot easily tell where the front of the speaker is with your eyes closed - the whole thing sounds the same .... same concept in our sealed engine shells. With holes in the coal load, it becomes real obvious the sound is coming from the coal load. If the tender was sealed, the sound is coming from the whole tender, it's no longer as directional.
Just some food for thought based on my own experiences ....
Mark.
Mark,
Isn't it funny how sound works??? I have had similar experiences to what you describe.....Sometimes just experimenting will yield better results...
Interesting idea about trying to make the sound less directional...
On the decoders: I quit using the micro TSU after various wierd problems associated with its ability to recover from shorts. I have taken to retrofitting all of my micros with an inline (auto resetting) fuse from track power to limit amperage through the device to .70 amps...a drastic step but I was desperate. I now try to shoe-horn in the full size TSU as it is far more robust when it come to shorts.
Guy
see stuff at: the Willoughby Line Site
Mark R.I figured at this point I would then drill a bunch of holes in the plastic fuel tank to "let the sound out". Out of curiosity, I installed the plastic tank without any holes, and the sound was notably improved ! The frequency range was drastically improved and it wasn't as directional - not as obvious that it was actually coming from below the engine .... it got left like that.
Not sure this is obvious, but a loudspeaker outside of an enclosure doesn't sound very good because while the front of the diaphram may be compressing the air, the back side is expanding it. The air just gets pushed around from the front to the back of the diaphram.
A loudspeaker is normally placed in an airtight and rigid box so that only one side of the diaphram is exposed to to our ears. (there are exceptions such as bass ports).
If the enclosure is too small (and airtight) it impedes the movement of the diaphram. If the enclosure is not very rigid, it vibrates opposite the exposed diaphram surface, partially cancelling the acoustic pressure, more so at some frequencies than others.
So it is important to mount the loudspeaker with a tight seal in an airtight and rigid enclosure with sufficient volume.
greg - Philadelphia & Reading / Reading
gregc Mark R. I figured at this point I would then drill a bunch of holes in the plastic fuel tank to "let the sound out". Out of curiosity, I installed the plastic tank without any holes, and the sound was notably improved ! The frequency range was drastically improved and it wasn't as directional - not as obvious that it was actually coming from below the engine .... it got left like that. Not sure this is obvious, but a loudspeaker outside of an enclosure doesn't sound very good because while the front of the diaphram may be compressing the air, the back side is expanding it. The air just gets pushed around from the front to the back of the diaphram. A loudspeaker is normally placed in an airtight and rigid box so that only one side of the diaphram is exposed to to our ears. (there are exceptions such as bass ports). If the enclosure is too small (and airtight) it impedes the movement of the diaphram. If the enclosure is not very rigid, it vibrates opposite the exposed diaphram surface, partially cancelling the acoustic pressure, more so at some frequencies than others. So it is important to mount the loudspeaker with a tight seal in an airtight and rigid enclosure with sufficient volume.
Mark R. I figured at this point I would then drill a bunch of holes in the plastic fuel tank to "let the sound out". Out of curiosity, I installed the plastic tank without any holes, and the sound was notably improved ! The frequency range was drastically improved and it wasn't as directional - not as obvious that it was actually coming from below the engine .... it got left like that.
If you read my explanation close enough, you would have caught that the speaker itself was mounted in an enclosure that was sealed air tight. THIS was mounted in the milled out area of the fuel tank. The plastic fuel tank was then installed over this with no holes drilled in the bottom. Obviously the fuel tank casting does not seal air tight over the speaker, so there is no inherent pressure building from the front of the speaker .... just the rear.
I've got no physics explanation other than my own ears, and it sounded really good - much better than without the plastic fuel tank over the face of the speaker ....
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
I understood that you placed the loudspeaker encloser inside another enclosure with the diaphram of the speaker exposed through a milled out area in the bottom. I'm not sure why you would think any additional holes are needed.
Putting the loudspeaker enclosure inside another enclosure increases the acoustic impedance between both sides of the diaphram, improving performance, even if there is not an airtight seal between both enclosures.
I "assumed" the fuel tank needed holes in it because that's how all the manufacturers do their installations. Maybe the manufacturers need to go back to the drawing board ....