I am installing a QSI Revolution into an Atlas Silver Trainmaster (HO). The model has the A frame suitable for dual speakers. A simple question, but one that I am unsure of the answer. When installing dual speakers, should they be wired in parallel or series? I am thinking parallel is the way to go, but wanted to seek clarification.
What does the decoder instructions recommend? Wired in series will double the impedance; in parallel will divide the impedance. If you get the speaker polarity reversed in parallel, they will cancel each other out and produce weak sound. Either way, the sound could become distorted if the decoder does not support dual speakers.
It does not say anything, other than a reference to installing “speaker(s)”, which implies more than one, hence the question. QSI has an example installation on their web site that shows the exact same model with 2 speakers installed and discusses the fact that twin speakers were installed, but no specifics about the way they were wired.
There’s LOTS of information on the American Hobby Distributors web site about Quantum Revolution decoders and speakers, including the following:
http://qsisolutions.com/news/09/best-sound-parallel-wiring-073109.html
How funny is that, I was on the same site and found this document
http://www.qsisolutions.com/pdf/loco_acoustics_design.pdf which aside from being a really interesting read specifically states using series connection for the speakers.
Since the reference you found is more recent and specifically says use parallel, it looks like that is the way I will go. Evidently does not really matter with this decoder and I can try both and see which works the best for me.
Out of curiosity, which speakers are you going to use? And what diameter are they? I have a B23-7 that I’d like to do the same thing to.
Thanks
The critical point that determines how to wire the speakers is matching the output impedance of the amplifier. As previously stated, wiring in series increases impedance while wiring in parallel reduces impedance. Whichever way you wire the speakers, you don’t want the resulting impedance to drop below that of the amplifier rating or you could burn out the amplifier. For instance, if the amplifier has an output impedance of 8 ohms, you would not want to wire two 8 ohm speakers in parallel as that would put a 4 ohm load on the amplifier. If you wire the same two speakers in series, you get a load of 16 ohms which produces a little less volume but is safer for the amplifier. If you want to match the output impedance exactly, you have to choose speakers with the correct impedance. Two 16 ohm speakers in parallel would put you close to the 8 ohm impedance. Likewise, two 4 ohm speakers in series would also put you close to the 8 ohm impedance.
Also previously stated is the need to keep the speakers in phase. For a parallel circuit, this means that all of the positive speaker posts are connected to the positive lead from the amplifier and all of the negative posts are connected to the negative lead. For a series circuit, the positive lead of the amplifier is connected to the positive post of the first speaker. The negative post of the first speaker is then connected to the positive post of the second speaker. Finally, the negative post of the second speaker is connected to the negative lead of the amplifier. When speakers are out of phase with each other, one speaker will produce a positive cone throw while the other produces a negative cone throw. With speakers separated by some distance, the out of phase condition can be subtle. However, with both speakers close together inside a loco shell, especially when facing each other, the out of phase condition will create rather obvious c
Had I planned this a bit better I would be using a pair of these speakers http://www.litchfieldstation.com/xcart/product.php?productid=999003042&cat=235&page=3
but a forgot to order them from Litchfield when I ordered the QSI sound decoder. The decoder was supplied with a 1" round speaker and I happened to have an identical speaker in the spares box, so I am using the two of them. It has meant fabricating a styrene mount for the A frame as the speakers are just a bit too small for the available opening. I will be testing it shortly, and if I am not happy with the result, may well order the 1.2" speakers from Litchfield anyway.
I hooked 2 8ohm in parallel per the recommendation of the QSI site identified by Cacole and the thing sounds wonderful. If I can get the lighting to work to my satisfaction I will be a really happy camper.
Thanks for the information. I see from your link that they say those speakers have to be connected in series. I wonder what the ramifications would be, if any, if they are connected in parallel as per QSI’s suggestion?