RF-25 Resistance Question

[cornwall123]

Anyone know the resistance/ohms of the RF-25? I believe the two tweeters in my pair of RF-25's are dead. I took them out today, and checked the resistance/ohms. Not sure of the terminology. I came up with a reading of .4 on both sides. I was wondering if that sounds right, and what exactly does that .4 mean.

I'm pretty confident that crossovers are good with that reading, but wanting to check and make sure what it's all about.

[WMcD]

That seems very odd. I'd expect a good driver to have resistance of 4.0 to 8.0 ohms or so. Your figure of 0.4 is not expected.

In almost all cases a blown tweeter will read infinite. It is difficult to say what a display on a digital multimeter will say but it will be whatever it says with the meter set to ohms and the probes are not connected together.

In a very unusual failure the internal windings could fuse together to give a low reading. However, I'd be a bit surprised that both failed into this condition.

Let me ask. Did you disconnect the feed wires from the crossover when making the readings? Are you measuring at the back cup? Also, did these units fail recently, were they fed with loud music before the failure?

Are these new to you? These units are made for biwiring. There is a cup in the back where you connect the speaker wire. There are four terminals. There should be pair of shorting bars connecting the pairs in parallel. Maybe you know this.

Please tell us more.

The "ohms" is actually a measure, roughly,of whether the unit is conducting current when a voltage is applied. In the case of the test with the meter, it is direct current or zero Hertz of alternating frequency. The meter has a battery which applies a zero Hertz (cycles per second).

Resistance (in Ohms) = Potential (in voltage) / current Intensity (in Amperes). Or Ohms = V / I.

The implication of that ratio is:

If you have high "ohms" (say 1000 ohms,or greater-- to pick a number) there is high resistance to current flow,and current is very low (no sound). In a burned out driver this shows the wires inside the driver have been melted out to an open circuit..

If you have 4 - 8 or so ohms,this indicates a normal set of windings. This is just because there is a long lenght of thin wire in the coil of the "voice coil".

If you have 0.4 ohms,this would show that the windings have fused from heat, but by accident, fused together (very unusual).

Wm McD

[cornwall123]

I don't think I made myself clear. I tested the wires coming from the crossover to make sure the crossover wasn't fried. I have done any test on the tweeter. I got the .4 from the crossover.

I recently traded for these speakers, and have a feeling the guy knew they were bad. I haven't played any sort of loud music through them. I was using them as front surrounds, so only listened to them at regular volumes. I know have some wf-35's, and was going to use the RF's as surrounds. Once I got them away from the center I noticed they were very muddy sounding. I then took a book to cover the top woofer and noticed no sound from the tweeter.

I removed the tweeter from the lead wires when I tested the crossover. I then took the red, and black post of the meters, and touched to the green wire, and then the black wire. I did this with both speakers and both of them read .4 on all four wires.

I didn't know I could test the tweeter, and not real sure how. I'm guessing I touch the post to the place where the wires clip on. I'm new to using this meter, and to any of this voltage/meter/resistor stuff. I had these hooked up through the bottom post of each speaker, with the Z looking clamps on the speaker post. Even then I had no sound.

I'm not real sure what the feed cup is. If the feed wires are the wires that come from the crossover and hook onto the tweeter I did disconnect those.

When testing the wires that come from the cross over to the tweeter should those read .4? How exactly am I suppose to connect the multimeter to the speaker, and the wires leading to the cross over?

[cornwall123]

Quick update. When I put the two multimeter post to each tweeter speaker terminal I get 3.0 on one, which would be 3 ohms and correct if I understand this. The second one I couldn't get anything from. Either way neither of them made any noice when hooked up in the speaker. Now I have no idea if it's the speaker or the crossover. I can't seem to get any reading from the cross over, but then again I don't have but barely a clue on how to use this meter.

[cornwall123]

Anyone know how to remove the crossover from the RF-25?

[WMcD]

Let's give this one more try. Excuse if I'm going back to basics.

1) I tend to doubt there is a problem with the crossover unless the previous owner has fooled with it. Crossover components are usually the most robust part of the electrical components.

2) The woofer is fairly robust. The mids (in a three way system) are less robust. But the tweeter on any system is relatively fragile and is almost always the first thing to fail when the system is cranked.

3) I understand that you're not very experienced with the meter and what you're trying to measure. That's okay, everyone has to learn.

4) One of the most telling tests of a speaker driver (tweeters included) is to measure the resistance at its electrical terminals. To do this the driver must be diconnected from the crossover. Depending on the crossover design, this might not be necessary. However, not having actual knowledge of the crossover design, we must disconnect the driver from it.

5) In theory and fact, it is really only necessary to disconnect one feed wire from the tweeter. This is because we want to avoid any of the test current from the meter from going into the crossover and one wire will prevent the electrical circuit back to the crossover being formed . But, you might as well disconnect both wires.

5.1) Make marks and notes on which wire goes to which terminal, One terminal of the tweeter may have a + in the plastic casting or a red mark. I'm belaboring this point but experienced or not, we think we'll remember what goes where the next hour, day, or week. But it ain't necesarily so.

6) I'm not sure what you're doing with the multimeter or what type you have. Something is going on with you wanting to convert 0.4 ohm to 4.0 ohms. The old ones have R, Rx10, Rx100 scales. And you must use the "zeroing" adjustment. The new digital ones have may have other settings. You can send us all a picture if you have doubts. And of course, read the instructions.

7) Set the meter to the lowest ohms setting. When you touch to probes together you should read something down near zero, maybe 0.1. With the probes not connected to anything, there will be some indication. Hard to say what yours will show as a read out (is it digital or analog?)

8) Touch the probes to the two terminals of the tweeter at the brass or silvery colored solder. The probes have a point and these should penetrate any oxidation. Look at the reading on the meter. A good driver will indicate about 4 - 10 ohms. An open voice coil will show little change.

9) Another very reliable test, perhaps moreso, is to connect a 1.5 battery across the tweeter terminals. As you connect and disconnect there should be a scratching sound from a good driver. (Sometimes you get this when connecting the ohm meter, too.) If no sound, you have burned out voice coils.

10) I'm fairly confident you will find that the tweeters in both are burned out.

11) What to do? If you look at the structure of the horn and driver, you will see, probably that the voice coil assembly is held in place with a few small nuts and bolts. Klipsch will probably sell you replacement parts for about $40 apiece. I expect that since you've done this much exploratory surgery that you can do this relacement yourself.

12) If you do replace, please take some digital photos and post them to this site. You will be the expert to people following in your footsteps.

Best,

Wm McD