One speaker or More ?

[C&O Fan]

If the decoder is rated for a 8 Ohms speaker Can you only use one speaker rated at 8 Ohms

Or can you use 2 as long as you wire them in parallel

TIA

 

[C&O Fan]

davidmbedard

 Depends on the decoder......which one are you talking about?

For example, if you have a QSI-R and you wire in 2 speakers in parralel, you will have issues with the decoder (it needs atleast 8).  The issues start with no sounds, to sounds cutting in and out.  But if you wire them in series, then the decoder is happy with 16 ohms.

The Tsunami is indifferent.  The Digitrax SFX needs atleast 16ohms to have any volume.  

 David B

This is the one i ordered

http://www.litchfieldstation.com/xcart/product.php?productid=999003036&cat=0&page=3

[Texas Zepher]

 

C&O Fan

If the decoder is rated for a 8 Ohms speaker Can you only use one speaker rated at 8 Ohms  .... Or can you use 2 as long as you wire them in parallel

Speaker "ohms" are impedance, not resistance.  Two 8 ohm speakers in parallel will look like 4 ohms to the decoder.  It would be better to put them in series and present 16 ohms to the decoder.  OR of course get two 16 ohm speakers and put them in parallel.

 

http://www.prestonelectronics.com/audio/Impedance.htm 

http://www.tape.com/resource/impedance.html

http://www.bcae1.com/spkrmlti.htm 

[rrinker]

 Well you sort of contradicted yourself   Impedence is AC resistence, which is why two parallel 8 ohm speakers look like 4 ohms - they follow the same rules as resistors do in DC circuits. Series resistors add together, parallel is a bit more complicated: 1/(1/r1+1/r2+..+1/rx) but for exactly two identical resistors it simplifies to 1/2 of one's value. 1/(1/8+1/8) = 1/(2/8) = 8/2 = 4. That hols for any number of identical resistors in parallel. 3 x 8 ohm speakers would be 2.67 ohms, 4 of them would be 2 ohms, etc. If the two resistors are different, then you need the actual formula.

                                    --Randy

 

[fwright]

davidmbedard

 Depends on the decoder......which one are you talking about?

For example, if you have a QSI-R and you wire in 2 speakers in parralel, you will have issues with the decoder (it needs atleast 8).  The issues start with no sounds, to sounds cutting in and out.  But if you wire them in series, then the decoder is happy with 16 ohms.

The Tsunami is indifferent.  The Digitrax SFX needs atleast 16ohms to have any volume.  

 David B

To expand on what David B said:  The decoder's sound output is basically the same as a small audio amplifier output.  Output impedance is much higher than most speaker impedances.  For ideal power transmission (sound signal and current) the impedances should match.  When they don't match, the decoder may struggle to produce sufficient output, suffer distorted output, and/or overheat.  The design and rating question for the decoder designer is how low a speaker impedance can be tolerated before bad things start to happen.

Which is why there are decoders that want nothing less than 100 ohm speakers.  And is also why you never want to have speakers with less impedance than the decoder rating.  Greater impedance will not cause any harm.  So 2 identical speakers in parallel will have half the impedance (engineers in the crowd, ignore phase angle and frequency dependencies, they are not significant for this case) of one speaker.  Two speakers in series will have double the impedance.

yours in having fun

Fred W

[ATLANTIC CENTRAL]

Terry,

Everyone has given you great advice here, now to answer your question from an acoustic stand point.

More is better. If you could make room for 3 speakers or 4 or more, as long as the total impedence was suitable for the decoder, sound quality will improve with more drivers or more cone area. This does assume all other factors being equal, such as speaker baffles, enclosures, etc.

Sheldon