Hi all,
during my last decoders installation ( see the previous post here : https://forum.mrhmag.com/post/help-to-open-a-brass-tender-12189903 ) I’ve drop down some notes, mainly taken from my past and present experience. Not really a “how-to” article, but a collection of suggestions to achieve the best results from sound decoders in N scale. Hope somebody is interested to hear about or at least agree or not: N scale sound is not so much discussed in Forums, and not all arguments that are valid for bigger scales are still useful in N. Enjoy?
Step-1: Speaker baffle.
First select the biggest speaker that can fit and the one that have best low frequency response. Steam sounds are full of low frequency ( not so much as Diesels ) but also a lot of hi-band “hiss, shish, chuff …) content. A bigger speaker is able to move more air (higher volume) and usually have better “sound-color” at same volume level.
For big steam tenders one of the best 8 Ohm solution I’ve experienced was a rectangular 14x25mm Soundtraxx speaker ( http://www.litchfieldstation.com/xcart/product.php?productid=410096&cat=235&page=1 ).
When the available space was not so much, a good round speaker can be the Soundtraxx ( or equivalent) 14-15 mm.( http://www.litchfieldstation.com/xcart/product.php?productid=410097&cat=235&page=1 )
Low frequency response of both is around 500 Hz and this is one of the best value I was able to find.
When evaluating the speaker space, take in consideration to add a closed box on rear side. Again, bigger is better, but I’ve experienced not big difference from a deep dimension of 2-3 mm to one of 10-12 mm.
In N scale the space is limited, so increasing the speaker deep is always a tricky game. But the physics audio laws stated that the rear sound waves cancel the front pressure, so here some suggestions for N scale.
Cancel the rear audio wave is first rule. Somebody suggest to use the model body to do this job, but I’ve found very difficult to separate the two sides of the audio source and seal one without use a “real box”. I do usually this using 4 styrene square strips and a styrene cover. The rectangular speaker have a plastic chassis so I glue some styrene strips 2x2 mm on back.
The rear of the speaker was also filled with a tiny layer of phono-adsorbent foam that help to reduce the rear waves echo and case vibrations. A styrene cover will then seal the box. See the pictures:
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(click a photo to get a large image)
I shaped the strips with an Xacto cutter and a fine round file around the magnet area and the wires output and use the Faller plastic glue to seal everything. This is a solvent that melt the plastic sides so a very little quantity last long.
To experience how a sealed box can enhance your sound, just connect a speaker in open air to a sound decoder and use a piece of paper tape to cover the back: you will appreciate the increased volume and better sound “color”.
Step-2: How sound leave your model
From top or from bottom? What I can say is that the bottom side is where is simpler to hidden the eventual additional holes needed. Some modelers have do several tiny holes hidden in the coal tank, but, as I model oil tenders only… I’ve no coal around!
You don’t need to make a “strainer” in the tender body, in general a set of 4 or 6 holes ( 1-1,5mm) in-line along the car sill will suffice and are invisible when model is on tracks.
In addition I feel that sound reflecting on the ground result more “colorful” and “rounded” (less hi-frequency) specially in the “chuff” sequence.
How much volume is another common question, but here my answer is “depends”!
In a silent environment as a private train room where several motive power are running, usually I set the sound to a level than don’t disturb operators working in a different area of the layout. Think that a sound you can hear at 2 meters distance is corresponding to a scale 320 meters in 1:1. This is the max level I use and it can be regulated just setting the general volume CV. In some cases (meetings or show, big clubs layouts) where a noisy background is present, just move the same CV to higher value.
If you have the capability to connect a serial communication port to your system, then give a try to JMRI DecoderPro-3 software to program your roster: I’m sure you never come back! And it’s free of charge as MRHMag! ( http://jmri.org/download/ )
Programming all variables that are in the Tsunami is a snap, the user interface is friendly and suggest text description for all intricate bit combinations. Setting and do a real time test of results is simple also for the band equalizer and related functions ( you know you can adjust the equalization to adapt to the speaker diameter ? ).
Step-3: Wiring
In case your loco is not DCC “friendly” …. this the most “creative” part of the job! In old steam engines, as well in brass models, DCC was long way in the future. Given that your model run well in DC, it can only run better in DCC. Other ways, I never hear of a bad running model will be cured installing a decoder. So, first check is related to motor, worms and other mechanical parts to have a good runner (low speed in particular, no wobbling, good “tractive force” , etc. ) The only adjustment you can obtain with a decoder is the limitation of the maximum speed ( without any mechanical change ) and the setting of a “prototypical” speed curve. BEMF technology additionally can help on grades ( but in most cases it will “disturb” in consists ).
Several times you’ve read “isolate the motor” from tracks…. Well, remember this is related to the two Motor Brush (Brush and Cap). No real reason to isolate the motor chassis from the engine.
In N scale Brass steams usually the right side drivers on engine takes one of the two polarity of the DC voltage and the left side wheel in the tender provide the second one. So, in this case ( or also if both polarity are taken in the engine and your decoder is in the tender ) you need to transfer one or two wires from engine body to tender. This is done via the drawbar and some contacts on it. My suggestion is to don’t use this tools! Just use wires and if you find a hidden place that is not disturbing too much the model, use a connector like the mini male-female by Miniatronics or similar show here.
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(click a photo to get a large image)
( for example see here : http://www.litchfieldstation.com/xcart/product.php?productid=999003182&cat=170&page=1 )
Personally in most cases I think the additional mechanical work to fit the connectors give not so big additional value to your installation, and I just use thin and flexible wires ( paint it black with your brush or a fine felt pen) . The limit is that you can’t disconnect engine and tender, but, why you really need to do this? And the additional wires resemble the real connections too. A point of CA where wires leave tender and on the engine and leave it pending with an U curve to permit a good play on curves.
Another “big” invader in N scale is represented by the electrolytic capacitor supplied with the Tsunami or other sound decoders. This help to avoid a decoder reset when running on dirty tracks. An accidental reset with these decoders is “very audible” ! Again the rule is “bigger is better”, but again my suggestion is don’t use the aluminum type supplied as standard ( well, it’s the cheapest model, but not the littlest one).
Try to find SMD Tantalum models as this one: 
(click a photo to get a large image)
Litchfield Station LLC ( http://www.litchfieldstation.com/xcart/home.php?cat=125 ) as well Digikey will delivery it at your door.
Put some (Litchfield sell only 100 uF value, so connect at least 2, but up to 4 or 5 is better ) IN PARALLEL ( means connecting together the same polarity side ) to increase the total value.
That's all for now, friends.... any comment is only welcome.
