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sound decoder speaker ratings Track and electrical/DCC
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Super User 1,071 posts Kirk W kirkifer Super User 1,071 posts
Kirk W kirkifer

Hey Guys,

King of cheap again...

I Found some brand new but "very" old Soundtraxx sound decoders. How old are they? They are so old that they have yellow shrinkwrap around them. The best I can tell, they were made in the late 1990s and are part of the DSD line which got mediocre reviews. For what I paid for them, I am not going to be too picky... If they work at all, I will consider the purchase successful.

Now, here is the real question... If the speaker is the wrong Ohm rating, am I going to blow out the decoder?

How do I know how many Ohms a speaker is rated for? Can I put a multimeter on it and get some sort of a reading? I have a large square one in a package that indicates it is like 100 Ohms... Um... I thought most of these speakers were like 8 Ohms. Is it just not going to work okay, is it going to make any noise at all? What can I expect? One of the round speakers is very clearly marked 4 Ohms... Uh oh.... Do I need to wire another 4 Ohm in series to make an 8 Ohm load?

 

There was a bag of speakers that came with my purchase. There is no theme to the size or type. It almost seems like the previous owner was experimenting with various speakers. Here they are:

[attach:fileid=/sites/model-railroad-hobbyist.com/files/users/kirkifer/IMG_20131216_113813_395.jpg]

 

Here is another question. What lugs do I solder leads to? It seems like there are 4 which is confusing since there is usually only a (+) and a (-) lug. I know in car stereos, the sound will be better if you get the wires oriented correctly.

 

[attach:fileid=/sites/model-railroad-hobbyist.com/files/users/kirkifer/IMG_20131216_114129_808.jpg]

 

Thanks for the help...

 

-Kirk
Kirk Wakefield
Avon, Indiana
 

 
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Prof_Klyzlr Moderator 7,962 posts
Prof_Klyzlr

quicky

Dear Kirk,

I'm away from my main machine, so this'll be quick.

- for a given decoder, you can safely connect a speaker of Equal or Greater impedance (higher Ohm rating).
Just be aware that as the speaker impedance gets greater, the overall volume possible will be less.
Do NOT connect a speaker with LOWER impedance than the decoder is capable of driving. Power Amp Death is a very real possibility.

- IIRC DSD decoders were capable or driving Minimim 8 Ohm loads.

- the 100 Ohm speakers you have are "valid", they were just designed to work with Loksound V3.x decoders which had a minimum 100 Ohm power amp config. (Yes, 4, 8, and 16 Ohms are far more common impedance values. Loksound struggled for sales traction in the US for some time because of this "oddball" design spec)

- yes, getting the PHASE relationship (connecting + and - terminals appropriately in multi-speaker-driver arrays) configured appropriately can make-or-break an install. However, for single speaker installs, just "plug em in and turn em on"...

- the 4 solder tabs on the speaker are most likely configured "2x2". NB that there is a Gap in the Green PCB between the middle 2x solder tabs. These speakers look similar to those shipped with Digitrax SFX/Soundbug decoders. Electrically it's not critical, but for consistency and sanity's sake, I'd make some rule that You can remember, and stick with it thru all installs. EG stick with soldering to the Outside pair.

- It's not strictly accurate, but for "close enough for model RRing" impedance checking, you can use a regular multimeter set on Ohms scale to measure the impedance of a speaker. Just make sure you measure the speaker _standalone_. If it is connected to Any Other Circuitry, the reading will be skewed...

Hope this helps,

Happy Modelling,
Aim to Improve,
Prof Klyzlr
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lexon Prolific poster 1,211 posts
lexon

Decoders

I have had some older SoundTraxx LC decoder in the yellow shrink. SoundTraxx have always been 8 ohms for speakers. I believe the SoundTraxx still has info on the older LC decoders. Some LC were not the shrink wrapped type I believe. The LC type required the bipolar cap.

Rich
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Kirk W kirkifer Super User 1,071 posts
Kirk W kirkifer

speakers wired in series

Okay....

Thanks for the help. I can use an 8 Ohm or larger speaker. I see one of the round ones I have is 4 Ohms, so obviously that one is something I need to sideline or use in a different manner.

Can I wire two 4 Ohms speakers in series and get something that is now capable of 8 Ohms?  If not, where might the 4 Ohm speaker have come from? I have heard that most mfg.'s use 8 Ohm... So, it is just a mystery I am trying to solve...
Kirk Wakefield
Avon, Indiana
 

 
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LKandO Prolific poster 3,839 posts
LKandO

Yes

Quote:

Can I wire two 4 Ohms speakers in series and get something that is now capable of 8 Ohms?

Yes. My Bose 901s have 9 individual drivers in each cabinet. Each driver is 1 ohm. Wired in series the speaker presents 9 ohms of impedance to the amplifier.

bose.PNG   

Alan

All the details:  http://www.LKOrailroad.com        Just the highlights:  MRH blog

When I was a kid... no wait, I still do that. HO, 28x32, double deck, 1969, RailPro
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Prof_Klyzlr Moderator 7,962 posts
Prof_Klyzlr

2x 4Ohm in series = 8Ohm

Dear Kirk,

2x 4Ohm speakers in-series = 8Ohm, so yes, that would be a safe solution.
Just make sure that you are conscious of the "polarity"/phase connections.
(assuming both speakers are facing the same physical direction, when fed a +ve going signal, they should both jump _out_ or both jump _in_ simultaneously...)

Some decoders are Unofficially "rated for 8Ohm minimum, but can handle 4Ohm if not turned-up in overall volume",

but realistically, take the specs as writ, and you should be all OK...

Happy Modelling,
Aim to Improve,
Prof Klyzlr
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