RailPro > RailPro Specific Help & Discussion

Dual Speakers

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Josephunh:
There in lies the problem as not sure anyone makes one that small.

Alan:
Crossovers are for dividing the frequencies of a signal into various ranges, typically low (woofer), mid (midrange or squawker), and high (tweeter). You are not trying to separate the frequencies with your dual speaker installation. You want both speakers to reproduce the entire frequency range.

Two speakers can be wired to one output with either series or parallel hookup. Each wiring arrangement presents a different load on the amplifier output. Series wiring sums the impedance of both speakers and so reduces the output of the amplifier. Parallel wiring cuts the impedance in half so it doubles the output of the amplifier. Unfortunately, the amplifier has only so much to give. If the impedance of the load is too low then excessive current flow will damage the amplifier. Therefore, parallel wiring of speakers can be dangerous for the amp.

Series wiring speakers will decrease the overall volume even though there are more speakers because of the higher net impedance. Parallel wiring speakers will increase the volume providing the resulting impedance is above the amplifier minimum. I suspect this is where you are running into trouble. The two iPhone speakers in parallel are quite likely presenting insufficient impedance to the amplifier resulting in excessive current in the output transistors which causes distortion which is the crackling you hear.

KPack:
Thanks Alan for the explanation.  The Railpro amp is capable of outputting 2 watts of power (if I remember Tim Ring correctly), which is possible if you hook up two 8 ohm speakers in parallel.  The speakers I use are normally only rated for 1 watt max power, so when using multiple speakers (which I always do) I wire in series so the amp is only putting out 0.5 watts of power.  With this arrangement I am minimizing damage to both the amplifier and speakers.  Plus it is PLENTY loud.  Model railroad sound should be pleasant to listen to and add to the experience, not give you a migraine.

-Kevin

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