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Speaker polarity

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Speaker polarity
Posted by 2002p51 on Friday, February 7, 2020 8:04 AM

I tried searching this topic with no success and this may be a dumb question but here goes. 

I'm converting a Stewart/Kato F-unit to DCC according to a video by Larry the DCC Guy. I'm using the same components he is in the video. In it he makes no mention of speaker polarity. Even though the decoder has two tabs for the speaker marked + and -, there are no polarity markings on the sugar cube speaker. 

Does polarity not matter on a speaker?  Can this speaker be connected either way?

 

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Posted by BigDaddy on Friday, February 7, 2020 8:16 AM

Either way works.  Speaker cones vibrate, in and out sounds the same as out and in.

Henry

COB Potomac & Northern

By the Chesapeake Bay

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Posted by mbinsewi on Friday, February 7, 2020 8:22 AM

Thanks OP for the question, and thanks Henry for the answer.

I was wondering the same, as I have a sound decoder with a speaker already attached, and I want to detach it, and hook the decoder up to one of the bass speakers that you got, Henry.  Mine came yesterday.

Mike.

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Posted by rrinker on Friday, February 7, 2020 8:53 AM

 I know some will say it does matter, but when you are feeding a signal that varies between say -1V and +1V, at the middle, 0V, the speaker cone would be at rest. When the swing goes to the - side, it moves one way from center, let's say inward. ANd then when the signal swings to the + side, it would move out. Flip the wires to the speaker, and not it goes in as the signal goes to +, and out as the signal goes to -. No difference at all.

Where it DOES matter is if you install multiple speakers. If you have two speakers, and one is wired opposite the other, one will have its cone moving in, while th other is moving out - the sounds will cancel, and you will get much less volume. If everything including the soudn path was exactly the same, you'd actually get silence.

 SO for one speaker - it's not going to mater. For multiple speakers, it does, unless they are in individual enclosures, say one speaker in a tender and one in the firebox. If the air paths do not connect, one can't cancel out the other.

 WHere this could possibly be different is dependent on the amplifier design. If the signal out goes from say o to +2 instead of -1 to +1, then if the speaker is hooked up one way, the cone will move from center out, or if reversed, center in, never the full travel from in to out. In that case, a speaker may indeed sound better going one way vs the other. As far as I know, all DCC soudn decoders use CLadd D amplifiers. A half bridge design would be this latter stlye, witht he output voltage varying from the common to some positive voltage. A full wave version would be as I described earlier, with the voltage going from some negative rail to some positive rail. Which decoders use which designs, I have no idea.

                                      --Randy

 


Modeling the Reading Railroad in the 1950's

 

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Posted by betamax on Friday, February 7, 2020 9:30 AM

It is all about phasing.  With one speaker, it isn't important.  With two speakers, they must operate in phase, or the sound will suffer.

To maintain the correct phase, the minus terminal from the first speaker is connected to the positive or marked terminal on the second speaker, when they are wired in series.  If in parallel, it is positive to positive.

When this is done correctly, the speaker cones will move in the same direction. If they move 180 degrees out of phase, the low frequency sound suffers as it tends to cancel.

But in your case, with a single speaker cone, it doesn't matter.

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Posted by mbinsewi on Friday, February 7, 2020 9:39 AM

betamax
To maintain the correct phase, the minus terminal from the first speaker is connected to the positive or marked terminal on the second speaker, when they are wired in series.  If in parallel, it is positive to positive.

Not to butt in on the OP here, but not all speakers have the connection tabs with a marking, as to + or -  so, how do you know, which is part of the OP's question.

I get that 1 speaker doesn't matter, but, if you wanted to mount a second speaker, say in a Fb unit, to the sound decoder with a speaker in the Fa unit, how would you tell?  

Mike.

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Posted by RR_Mel on Friday, February 7, 2020 10:15 AM

I’m always looking for good deals on DCC speakers on eBay so I have a pretty good stock on hand.  Just for kicks I just checked them to see if the polarity was marked on them.  Three different batches all have a red dot for +.
 
As mentioned above I don’t watch which is + or- for single speaker installs but as I some times buy 4Ω and 16Ω speakers then I series the 4Ω (red to non red) and parallel the 16Ω (red to red).
 
 
 
Mel
 
 
 
My Model Railroad   
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 
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Posted by 2002p51 on Friday, February 7, 2020 10:36 AM

Thanks for all these answer folks. Good to know I can get this project done easily!

 

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Posted by betamax on Friday, February 7, 2020 12:25 PM

mbinsewi

 

 
betamax
To maintain the correct phase, the minus terminal from the first speaker is connected to the positive or marked terminal on the second speaker, when they are wired in series.  If in parallel, it is positive to positive.

 

Not to butt in on the OP here, but not all speakers have the connection tabs with a marking, as to + or -  so, how do you know, which is part of the OP's question.

I get that 1 speaker doesn't matter, but, if you wanted to mount a second speaker, say in a Fb unit, to the sound decoder with a speaker in the Fa unit, how would you tell?  

Mike.

 

 
That is why I used the term "marked terminal".  It may or may not have a "+" on one terminal.  Any decent speaker will have a mark, be it a dot of paint or a "+" indicating which one is the "marked" terminal.  
 
In parallel, it is marked to marked, in series unmarked to marked. This is important for maintaining the correct phasing.
 
 
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Posted by mbinsewi on Friday, February 7, 2020 1:04 PM

Thanks.  I notice the Soundtrax speaker I have, has a red slash (like a small felt pen) very near (not on) one of the terminals, so I'm thinking that terminal is the + side.

Thanks again.

Mike.

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Posted by rrinker on Friday, February 7, 2020 3:41 PM

 If not marked and you really must know, convention is that the cone moves out when the positive terminal is positive. You can use a 9V battery and a devent resistor, 1K should work, and briefly touch the speaker terminals. If the cone moves out, the one with the battery + side is the positive speaker terminal. If the cone moves in, the battery + is on the speaker -. Don't leave it connected and do NOT attempt this without a resistor, a 9V battery will fry one of these little speakers. 1K should allow some movement to be seen. If not, try a slightly smaller resistor. 

                               --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by hon30critter on Friday, February 7, 2020 7:24 PM

Hi 2002p51,

Streamlined Backshop offers some really good information on working with sugar cube speakers. The second link explains how to wire multiple speakers should you decide to do so. Scroll down past the sales pitches:

http://www.sbs4dcc.com/tutorialstipstricks/sugarcubespeakernotes.html

This tutorial specifically addresses multiple speaker installations including a discussion of 'phase' (polarity):

http://www.sbs4dcc.com/tutorialstipstricks/wiringmultispeakers.html

Dave

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Posted by wjstix on Tuesday, February 11, 2020 12:01 PM

Doesn't this get into an issue re ohms too? Like if a sound decoder is designed to use an 8-ohm speaker and you decide to use two, you have to use two 4-ohm speakers (total of 8-ohms)...??

Stix
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Posted by mbinsewi on Tuesday, February 11, 2020 1:27 PM

I think Dave's 2nd link goes over that.  I'll have to read that again when I get that far.

Mike.

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Posted by rrinker on Tuesday, February 11, 2020 1:46 PM

 There are several ways to go about it.

You can use 2 at 8 ohms, for 16 ohms, which just won't be as loud.

You could use two 16 ohm speakers in parallel for 8 ohms.

Many decoders now support a range of speaker impedence, the minimum being something you don't ever want to go under, that could damage the amplifier. It's like using too small a resistor on an LED - too much current flows, burning out the LED (or amplifier final drive in this case).

Then it gets creative using arrays of the small speakers where you can fit more than one or two in the loco - 2x 8 ohm in series, both of those in parallel with another pair of 8 ohm in series, and you end up with 8 ohms. (each pair is 16, 16 parallel with 16 is 8) 

                                                   --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by gmpullman on Tuesday, February 11, 2020 2:21 PM

RR_Mel
I’m always looking for good deals on DCC speakers on eBay so I have a pretty good stock on hand.

I also like to have a decent stock on hand because I never really know which locomotive I mught want to choose for a sound upgrade and whatever its internal configuration may be I want to have a variety of speaker styles to choose the best fit.

One thing I strongly suggest is to "audition" your speaker choices before installation and making the final connections into the locomotive.

I use one of the several old MP3 players I have on hand. Their output seems to be close to the wattage of some decoders.

 SPKR_test by Edmund, on Flickr

In the example above I'm also using a small audio amp and I'm keeping the outpuit level well below the clipping limit. This allows me to see what wiring arrangement gives me the best sound output as well as making sure the speaker I'm installing is in good condition. I play music that I'm familiar with so I can get an idea of the frequency range of the speakers I'm planning to install.

Many of the "second-tier" dealers are selling off old stock or speakers that don't meet OEM specs so it is good insurance to test them first. I've come across a few duds now-and-then.

Good Luck, Ed

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Posted by wvg_ca on Tuesday, February 11, 2020 8:12 PM

There is no difference with polarity on only one speaker ... where it matters is two or more as phasing should be the same to avoid cancellation ... how ever convention is to make the speaker move out on the rising edge of the sine wave ..if all speakers are mounted this way, phasing is not an issue ..

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