Adding a second speaker

Why not series parallel the speakers so the impedance remains the same?  I've never seen anyone suggest putting a capacitor across the speaker.  I can't imagine this won't affect the sound and the volume.

Interesting. I am under the impression that such an arrangement would filter out the low frequencies and would be used with tweeters--not full range speakers. 

Actually, the capacitor is going to affect the sound a lot more than the series/parallel connection.

If you connect two speakers in series, the volume of each will be less than for a single speaker.  Turning up the volume control may result in clipping distortion in the driver amplifier.'

If you connect two speakers in parallel, each will have the original volume IF the driver amplifier can drive twice as much current without distorting. 

You can also try using two speakers of twice the desired impedance in parallel, or two speakers of half the desired impedance in series, but there is no guarantee that the speakers will have the same sound output efficiency as the original speaker, and since they will each run at half the power of the original single unit.

For the marginal audio drive circuits in our trains, the best bet is to try each way and see if there is a compromise with the volume control adjustment that gives good results with no distortion.

I did this to my set of Weaver E-8 that were upgraded to EOB.  Eventually I disconnected one of the speakers that was hooked in parallel.   While I never did damage to the Lionel power board or Sound board there always seems to be more heat than neccessary where the electronics were installed.  Mike Reagan, TAS at the time, agreed that it would work before I installed it. I Believe two 16 ohm speaker hooked in parallel would be equivalent to an 8 ohm speaker. I hooked two 8 ohm speaker in parallel which would be equivalent to a 4 ohm speaker. If I did my resistance calculation in parallel correctly.  

Who knew I would be posting picture of all this obsolete electronics.

Speaker in the fuel tank

Speaker in the rear of an A unit.

He was talking about replacing two speakers with four speakers.  That's why I suggested the serial-parallel arrangement, the impedance would remain the same.  I agree, it will obviously take more power, and I'm not sure I'd advise it, but that's the desired way if you want four speakers.

John, I believe his original comment about 2 and 4 speakers was in reference to an 8-track STEREO player - one speaker enhanced to 2 speakers per channel.

Was your 8-track stereo -  so was it 1 extra speaker per channel but two separate channels?  But to the matter at hand, how many speakers are you trying to add?

Considering the effort required to install speakers in the dummies, another option to complicate your life is to add an amplifier. This eliminates the parallel vs. series dilemma. Here are two stereo amplifier modules I just found on eBay (search on "audio amplifier module") that are $3 and $8 (w/volume control) with free shipping.  Or I occasionally see "amplified speaker" sets for PCs and MP3 players on sale retail in the US for about $10-15 and the included speakers might even fit.

Obviously if you have 2 slaves you can drive one per channel and feed both Left and Right inputs with the master sound.  Yes, there are issues such as providing DC power to the amplifier.  Just my opinion but there's an appeal to having that prime mover rumble step up when a slave is attached and again with another.

But if a capacitor does the trick then case closed. You can always add an amplifier later.

That puts a different slant on it.

I've had good luck using 8-ohm speakers with an 8-ohm, 1 watt resistor connected to one of the leads on each speaker.  Each speaker/resistor combination has a total resistance of 16 ohms, so when they are connected in parallel I am back to 8 ohms total resistance.  I've done this in 4 multiple unit diesel consists and in one large steam engine tender.  They've been running fine for several months with no distortion or sound volume problems noted.  The 8-ohm resistors are available at Radio Shack or almost any electronics supplier.

Bob Bartizek

Just wiring the two speakers in series would accomplish the same thing-and cause less loading and heating in the driver amp.

Many years ago it was important to hook up the correct impedance loudspeaker to an audio amplifier that had an output transformer.  The output circuits would produce the rated output power only with the correctly connected loudspeaker.  The impedance of the speaker was reflected back to the output tubes and multiplied by the square of the turns ratio in the transformer to create the proper load on the tubes.

Today's solid state amplifiers don't have an output transformer.  They act as a good voltage source unless the output/speaker is such a low impedance that it draws too much current.  The impedance doesn't need to be "matched" to the output.

Connecting two speakers in series would draw less current than the original single speaker, and the volume will be reduced.  If you can get enough volume without any clipping on the peaks, then that is the best way to go.  Using the resistors in series with each speaker causes the same volume loss, but doesn't reduce the heat in the output amplifier.

BTW, the impedance of a loudspeaker is only a nominal specification.  If you look at the actual impedance at various frequencies, levels and acoustical coupling arrangements, the impedance graph vs. frequency is in no way a straight line!

Not anymore, they bit the dust in December!

Madison sound has some excellent 2 inch 8 ohm ones.

Dale H

Sorry I've been away from the forum for awhile. Let me better explain the setup with the 8 track player. Back in the late60's early 70's my brother was in a band. They had a Kustom PA system with 4 speaker columns. Each column had 4 12 inch speakers with a total impedance of 8 ohms per column. The 8 track was a kraco car 8 track stereo player. I made a 12v power supply and connected the 8 track to 2 of the columns. A classmate in my electronics class suggested to hook up the other 2 columns with a capacitor across the extra columns. The columns were connected in parallel with the capacitor across the input of the extra columns. All I remember about the capacitors were they were bigger then a m-80 firecracker. The capacitors were supposed to keep the total impedance at 8 ohms. Does this make any sense to anyone?

No.  You were loading the audio outputs with 2 8-ohm arrays in parallel, or 4 ohms, plus you were adding an additional load at high frequencies with the capacitor.  I feel sorry for the 8-track player!

Did you friend pass that electronics course?

I'd be guessing no.

Who knows what happened to my classmate (not my friend). He was a real screwball. As for the 8-track player, for being an off brand cheapo it was bullet proof. I would blast that thing through all four columns and you could hear it a block away. And it was in the basement.

Maybe the capacitor was in series with the second speaker. That was a long time ago