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how loud should loco sound level be?

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    April, 2015
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Posted by Enzoamps on Friday, September 08, 2017 12:16 AM

I am concerned at the lack of implied frame of reference.  That is to say where are we listening from in a model sense.  If I put my face by trackside and a train whooshes by, I can expect sound like I was standing by a real track.  The loco starts quietly a half mile away and builds until next to me it is loud, then fades as it passes.  A large range in decibels.  (I am a pro audio professional myself)

But standing in an aisle looking down on a train, it is more like I am three blocks away from the tracks, so the changes in level from the half mile points down the track to the closest point are mush less.   Not only that, the closer you are the more high frequency information is in the sound.   At my country home I can hear tracks a couple miles away, and the low rumble of the engines comes to my ear, but not treble-y things like a bell or hiss of air exhaust.

So which tonal structure am I looking to hear on my layout?  Right by my face?  or two miles away?  If I had specific listening posts around the layout, I could say "put your face here as #8 rumbles by."   On the other hand, if the train is across the layout, I really ought not expect to hear every clink and clank and cycle of the air compressor.

If I could have a by my face listening post, then i could put a dedicated speaker at that spot instead of a tiny tinny speaker in the little train.  The sound could be awesome, and I could even have the doppler shift as it went by, something that is sorely lacking in the model sound we have now.  The lack of doppler tells my ears I am listening from inside the train itself, not trackside.  But that turns my layout into a series of dioramas, at least sonically.

  • Member since
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  • From: somerset, nj
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Posted by gregc on Friday, September 08, 2017 6:11 AM

Robert Frey
Greg, I also had a problem with the answer of only a 3 dB change in my sound meter readings, because I have  added enclosures on some of my speakers when putting them in a DCC locomotive.   And the most you can get is a full 3.0 dB increase in the sound pressure reading.

you can't assume that an enclosure is going to double the sound level output.

Robert Frey
This can easily change the Voltage on a 8 ohm speaker from 1 volt ac to 2 volts ac which is a + 6 dB change.

you can't assume doubling of electrical power to a loudpseaker will double the sound level.

Robert Frey
The problem is the dB calibration point, which can be moved by plus or minus 10 dB.  You will need access to someone who has a true dB sound pressure level (SPL) meter, with an A scale for your calibration setting.

we used a sound level calibrator which produces a constant level output at a specific level to calibrate our measurement equipment for the type of measurement we're making.  And we made our measurements in anechoic (non-reflective) space.

 

re: sound level drops 6 dB w/ a doubling of distance

why don't you just make a measurement some distance away (1ft) from the thing you're measuring and make another measurement twice as far away (2ft)?  put the sound source on the edge of a table to minimize reflections.

 

 

greg - Philadelphia & Reading / Reading

  • Member since
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  • From: somerset, nj
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Posted by gregc on Friday, September 08, 2017 6:20 AM

Enzoamps
So which tonal structure am I looking to hear on my layout?  Right by my face?  or two miles away?  If I had specific listening posts around the layout, I could say "put your face here as #8 rumbles by."   On the other hand, if the train is across the layout, I really ought not expect to hear every clink and clank and cycle of the air compressor.

propagation of sound with distance depends on frequency.   Lower frequencies travel further with less suppression.   And that distance doesn't scale.   You can't expect the same effect 1 scale mile away as you do when you hear the rumble of a train a true mile away.

And our model sound doesn't reproduce the low frequencies of a prototype locomotive.

Bose house systems just put a woofer anywhere in a room because low frequencies are less directional than high frequencies, you may feel them more than hear them.

it might be "neat" (cool) to put a woofer under a layout that produces the rumble of a train on that part of the layout.

greg - Philadelphia & Reading / Reading

  • Member since
    August, 2006
  • From: Greendale, WI
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Posted by Robert Frey on Friday, September 08, 2017 7:46 PM

Hi Greg, your comments are correct. Very interesting information on your low frequencies information. Yes, I have head the Bose house system with a woofer at a NMRA Train show. It has really cool low frequencies sound.

Now my story. I got into sound when trying to replace 32 ohm speakers with 8 ohm speakers. I got a True rms Volt meter, and a Sound level meter or sound pressure level (SPL) meter. I become very interested in getting much more information on the (SPL) meter, understanding it, and using the dB measurements. I had my new engineering problem of:

 

How much sound pressure level can I get for just 1 Watt?

 

This interest also came with some sound meter experiments with enclosures, and with many internet searches. This is where most all of my information came from. (Not a sound Engineer.) I was using the sound meter to adjust my horns to a sound level that I liked, and that number turned out to be 66 dB(A)@3’ on a (SPL) meter. (Locomotive with horn on the layout, yard stick to my head, sound meter reading is below 66 Avg.)

Now, with my old 164 decoder, came up with an answer of two 8 ohm speakers in series for 1 Watt will work. Got two 4 inch dia. 8 ohm speakers, made an sealed enclosure for each, and connected my old 164 decoder, turned ALL the Volume CV,s to max. Way, way too loud the noise, but was under 1 Watt. (No burn out!)

Have a 44 ton Diesel which stays in a city. I stand at the city, put one speaker 4’ left, under the layout, it is also directed to reflect sound off the floor back to my center. Done the same on the right side, and they are in series. Put on a Diesel I liked, in the city. Horn on, walk by city with the Decibel 10 App. Print the “I like my horn” record of 50 seconds. Put 44 ton Diesel back, the old 164 decoder and the Diesel with same DCC address. Horn on, walk by the city again with the Decibel 10 App of 50 seconds. Change the horn CV volume, until it produce similar dB highs near two places, on a 50 second record. I like my 6’ left and my right 6’, but another 6’ the sound level drops at the 6 dB, doubling the distance rate.

 

Bob Frey

 

PS: My problem now is that I have had a stroke. Can’t get under my UP&W anymore, but have more time for the internet.

Website: http://bobfrey.auclair.com

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Posted by Enzoamps on Friday, September 08, 2017 11:54 PM

greg

I don't expect sounds to scale, but perspective matters.  WHen my train is across the room, it ought not sound the same as when it is in front of my belt buckle.  And for the reasons you expressed: the sounds vary in carrying distance by freq. That was the whole point of my query as to what the implied frame of reference is for the layout sound.

  • Member since
    July, 2009
  • From: somerset, nj
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Posted by gregc on Saturday, September 09, 2017 4:37 AM

Enzoamps
I don't expect sounds to scale, but perspective matters.  WHen my train is across the room, it ought not sound the same as when it is in front of my belt buckle

i think you bring up a different perspective that needs to be considered

i provided some numbers based on scale distance and an annoyance level.   I believe these are one criteria that sets some bounds.

but i think your point is because sound doesn't scale, perhaps these levels should be even lower so that locomotive aren't as loud across the room which because of modeling compression, is intended to be many more than scale miles away (60 ft > 1 scale mile).

so, as you said, some compromise seems appropriate to reduce the level when near the loco and tolerate a higher than desirable level when across the room.

greg - Philadelphia & Reading / Reading

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