# Thinking Outside The Box, OR: How hard is it find a speaker???



## rdamurphy (Jan 3, 2008)

I went to the LHS today, and bought a second QSI-Aristo for my second K-27, one that I managed to get for a great price: At my LHS! I mean, just above "eBay" prices, but worthwhile to get it "today."

But... No Soundtraxx 3" speakers! I didn't want to downsize, so I went on a little shopping trip, and came across a place that sells auto sound systems. The result? Kenwood 3 1/2 inch KFC-835C speakers.

A before and after photo of the speakers, Kenwood on the left, Soundtraxx on the right:










Nice, huh? 










Then reality set in, sort of. The speaker won't fit between the stacked weights on both sides of the tender, so it was time to take off the tender body, and take apart those weights! Bachmann put some kind of sticky glue stuff on the threads. They weren't easy to get off. But when I did, I found that not only would the speaker fit perfectly, but I could pinch the speaker frame and those mounting tabs between them to hold the speaker FIRMLY in place. On the bottom of the Kenwood speaker, there is a circular lip that matches the one in the bottom of the K-27 tender EXACTLY:



















So, it fits. But, as you can see, it's way too tall for the pc board to go back in, so it ended up double stickied taped to the top of the speaker. The pc board and QSI Aristo decoder does stick up higher, but no where near the bottom of the coal load. 



















A few things:


That speaker is MASSIVE and and I had to disconnect the QSI reed switch reset harnass. Every time I would shut down the power, the decoder would reset. 

In addition, It might not be a bad idea to leave out a few of those weights, to offset the weight of the speaker. I didn't, I don't mind the weight, but I will mention that the tender actually sits down on it's springs slightly. 

I also noticed after I was finished that they are 4 ohm speakers, but that didn't seem to be an issue in testing, no odd sounds, hitches, "motorboating" or any other problems, although I might just add a 4 ohm resistor to the circuit just to be sure. If I can find someone that sells resistors. Might not be a bad idea. 

Sound? Well, um, YEAH! At full volume, the tender vibrates! Seriously... I believe the tender itself acts as a perfectly acceptable "sound box" for a speaker this large. On the dining room table, the locomotive sounds were LOUD! Not only that, the bell sound, which was crystal clear and perfect, was slightly painful from close up. The steam sounds were much better and sounded like STEAM rather than electronic noise designed to sound like steam. Whistle noises echoed. Literally. Off the walls. That's when the wife came downstairs, and further testing was done at a lower volume... 

Any thoughts, suggestions, comments, questions? Robert


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## Totalwrecker (Feb 26, 2009)

Well........................ I asked before I tried a 4 ohm speaker, my sound card wanted 8.... I was advised that 2 - 4ohm in series would be ok.... or to find an 8 ohmer. 

PC sound systems are full of 4 ohm speakers.... 

John


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## Mike Reilley (Jan 2, 2008)

You guys need to hook up with one of our sponsors....Electric Steam Model Works...http://www.rctrains.com/phoenix_sound_system.htm .

He sells good speakers.


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## rdamurphy (Jan 3, 2008)

If I add a 4 ohm speaker, it will cut the current to the speaker in half, meaning less volume. I'm not sure that's a problem, since it's quite loud. I may try that, I really don't want to try to stuff another speaker in there! 

Robert


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## Greg Elmassian (Jan 3, 2008)

Nope, not necessarily true... you may be at max current output now, especially on a system designed for 8 ohms.. 

Most systems when run at a lower impedence, heat more and get more distortion. 

Depending on your "ear", higher distortion is either interpreted as louder, or worse sounding. 

Greg


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## rdamurphy (Jan 3, 2008)

Hmmm, good point. You're right. I think I'll pick up a 4 ohm resister and wire it in, since they're pretty cheap. Better off than taking a chance, and you're right, it may sound even better. Although, I gotta tell ya, that bell couldn't be much better! It definitely sounds better than it did, I compared them before I did the surgery by plugging one, running it, plugging the other one in, went back and forth several times. 

Robert


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## Dan Pierce (Jan 2, 2008)

A speaker is a coil and has impedance ratings, and is not a resistor. You will end up with a RL circuit and the reflected impedance will not be 8 ohms. 

Also note that speakers with large magnets require a larger current to move the cone and the 1 watt amps in sound units could sound softer, not louder with these speakers. 

So my thought is to always stay with 8 ohm speakers to match the sound amp output stage, and add baffles/cones to improve the low frequency sound (sounds cancel from front to rear of open speakers).


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## George Schreyer (Jan 16, 2009)

most speakers, at least lower power ones, have enough parasitic series resistance so that their DC resistance approaches their impedance rating. A resistor in series with one of these will do fine.


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## Greg Elmassian (Jan 3, 2008)

Just to be nit-picky, try to get a non-inductive resistor... 

I don't know the common inductance of 4 ohm 5 watt wirewound resistors, but I suppose it could attenuate/block high frequencies... 

Regards, Greg


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