Cell Phone speaker questions.


tootnkumin

tootnkumin

Well-Known Member
Staff member
As these speakers are becoming more frequently used as alternatives to the ones fitted by Locomotive manufacturers and possibly in multiple figurations, some info might be helpful, 2 things in particular. How to find out what the Ohms Impedance is, and is there a way of determining their polarity. And is either an issue.

With single applications, niether seems to be of great importance, but in multiples, both could be. I'll tackle the polarity issue first because of the way the wiring of multiples is affected by it, or can just the way the contacts on the speakers are arranged be used as the guide and it doesn't matter which wires are attached to the decoder, as in a single application, even though most decoder take off tabs are marked + or - ( I do note that wired instead of tabbed decoders usually use the same colored wires for both, so maybe, not a real issue).

The Ohms Impedance though could be much more important, as that can be vital in not overloading the amplifier in the decoder, if too low an Impedance is used. Is there a relatively simple, even if, near enough, rule of thumb method using an Ohm meter to get an indication. Reading about this seems to say, that is not very accurate.
 
I did some online research today. The cellphone speakers I found were all listed as 8 Ohms, where the impedance was mentioned at all. For many of them the impedance was NOT stated.

- Jeff
 
jdetray said:
I did some online research today. The cellphone speakers I found were all listed as 8 Ohms, where the impedance was mentioned at all. For many of them the impedance was NOT stated.

- Jeff
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I must have missed those Jeff, information is very scant, but I guess as the ones being sold on ebay are for specific Phone models, that's not an issue for the seller. Hopefully it's a common impedance.
 
tootnkumin said:
How to find out what the Ohms Impedance is, and is there a way of determining their polarity. And is either an issue.
Click to expand...
Finding the impedance of a speaker is not straight forward but it is not really hard just cumbersome. It also varies with the frequency AND it varies with the enclosure. For each different enclosure a speaker is placed the resonance frequency or frequencies will be different (this is why I like enclosures that have a cubic volume of n to the x, where n is the area of the speaker cone). Fortunately these i-phone speakers sort of have their own enclosure so it removes one variable. To get the impedance, the speaker must be put in series with a resistor of known value. A audio signal needs to be applied and voltage measurements taken on both sides of the resistor. The resistor needs to be a 5% tolerance or lower.

Put the measured values into the formula to calculate current I = (V1 - V2) / R where V1 is the source side, and V2 is the speaker side.
Once I is calculated the speaker ohms impedance Z is given by Z = V2 / I

So having said all that... For the non-precise work we are doing one can get an approximation with a normal DC ohm meter. A well behaved 4 ohm speaker will register at about 3.6 ohms and an 8 ohm speaker will show 7.2 ohms. As soon as one gets into building crossovers and multi-speaker configurations this approximation will NOT work, and one must do the whole smear above at many frequencies of input in order to graph out a speaker's inductance behavior.

My personal rule of thumb is that if I don't know I hook that much real resistance into the line (4 ohms or 8 ohms) and just deal with the decreased volume. Another thing I do from time to time is simply hook two identical speakers in series. In 1979 I purchased a set of Advent Series 1 speakers. Advertised as 4 ohms. I found out they really averaged closer to 3. My Marantz (1440 specifically) was rated at 4, so I just hooked two of them in series on each channel.

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The only difference with the polarity is that when power is applied positive to positive and negative to negative the speakers cone will move out (push). Reversed polarity and the speaker cone will move in (pulled).
 
Thanks I.H. I was hoping there might be a rule of thumb process. I guess the polarity thing boils down to placing them side by side and apportioning the polarities to the contacts the same on each one and wire accordingly. Then test the free ends either way on the decoders pads or wires to see if there is difference in sound quality. Most applications will only involve 2 speakers anyway, although I've heard of as many as 4 being used in a steamer and of different sizes. One of the guys at the club who uses Loksound V4 decoders exclusively, paired the speaker in the tender with a small one in the smokebox. The improvement in how the loco sounded, particularly regarding chuff and steam hiss was marked. Really made a huge improvement.
 
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I've used the Zimo sugar cube in intermountain ES 44 and they sound great.They have singles and double depending on room.
 
CambriaArea51 said:
I've used the Zimo sugar cube in intermountain ES 44 and they sound great.They have singles and double depending on room.
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The factory double sugar cube speakers in mine were--horrible. I ended up using a single iPhone 4 speaker assembly, which sounded a lot better than the pair of sugar cubes.
 
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