crossover

Just giving you guys a fair warning, this is a very noob question, but it's been a while since I've done a lot with audio (mostly do remote starts / alarms) and I don't think I've ever had to test a crossover in the 10+ years I've been installing. I had a customer come in because their audio system wasn't working at all; the headunit wouldn't even power on. After pulling it apart I found that the previous installer ran the radio ground all the way back to the amp ground. The amp had shorted internally and was showing 6.4 volts on the ground terminal... which was essentially eliminating the radio ground. I re-grounded the radio and it powered on great. Obviously I know that the amp is fried, but I wanted to also test the speakers since I know that a blown amp quite often means blown speakers as well. I was getting 4.1 ohms on the rear speakers (they are good) but I was getting around 11-12 ohms on the front. I pulled the door panels off and found a set of Memphis components. I've never had to test a crossover before. I am pretty sure the crossovers are bad, but I want to make sure before I tell him he needs new components / crossovers. When I pull all of the wires off, I get 4 ohms from the woofer and approx. 3 ohms from the tweeter. When I test the connections on the crossover, I am getting continuity between the + and - of the tweeter. I am assuming this is not correct? I am also assuming that with a properly working crossover, I should still only see 4 ohms (or whatever the set is rated for) on the wiring at the amp... correct? Thanks for the help!Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

If the crossover is blown, is it usually worth it to find a new crossover (if so, anyone know where I can find one) or does it pretty much mean a new set of components? And what is the normal reading for a tweeter? Is it still supposed to be 4 ohms (typically) or do they usually test a little lower?Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

When you use an ohm meter you are reading the DCR (DC resistance) of a speaker. It is almost always different from the nominal impedance and usually for a 4-ohm speaker in the 3 to 5 ohm range. Getting a good DCR reading does not mean the speaker is not blown, however, as the voice coil might still have continuity but be separated from the former or otherwise damaged causing the speaker to short out when used. Also be sure you check continuity to ground (the speaker frame) which should be unreadable high. Reading DCR through a crossover is unpredictable and depends on how the crossover is designed. When you say you read continuity across the tweeter terminals do you mean zero or near zero? If so, then something is not right. Is the tweeter still connected to the crossover or is the output open? Have you read continuity from in to out on the crossover? IMO if a crossover in a component set is fried, which is rare actually, your best bet is to replace it with exactly the same make and model or to replace the component set. If the drivers are still good you *can* find other crossovers that will allow them to work, but the results will never be as good as using the crossover designed to work with those speakers.Support the12volt.com

I stand corrected, the customer thought it was a Memphis but I actually looked at the label (instead of just the terminals) and it's a Diamond audio. Here is what I get on all of the connections of the crossover without anything connected to it (sitting on the bench) My DMM is set on the 200 ohm audible setting.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

Most of those readings look like typical crossover results. Seems like a second order network with the tweeter internally inverted as it should be. I suspect there is nothing wrong with your crossover, but to be sure take out the other one and compare the two. The readings on each should be similar. Have you tried powering the comp set using another amp yet?Support the12volt.com

No I have not tried with another amp yet. Unfortunately since I am only a part time shop, I don't have any inventory and therefore don't have the 'luxury' of just grabbing another amp to test it. I did connect my tone generator to the input and I did get sound through both speakers. I will let him know that the crossovers may be ok and I'll just order an amp for now and go from there.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

I think that's the best way forward. You could just connect the speaker sets to the head unit output to test, by the way.Support the12volt.com

Yea. I had already soldered everything and reinstalled the head unit so we decided to just go with a new amp for now and then if we have to get new components we will, but these will do for now. I will have to keep that in mind for future. I always assumed that you would have to see the 4 ohms even from the crossover in order to get the correct output of the amplifier. Is there a more reliable way to test component speakers directly at the amp; so I know for future?Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205

The crossover will ensure a net 4-ohm impedance is presented to the amplifier at all frequencies, but only with the drivers attached to it and only when dissipating an AC signal. With the DC of an ohm meter you really can't test a system for more than to make sure it's not open circuit, shorted out or shorted to ground. To test any speaker with or without a crossover properly requires using a frequency: a tone generator or simply an audio signal from an amplifier. :)Support the12volt.com

Yea, I picked up the tone generator (this was actually the first time I got to use it... lol). As long as I know that will be an ok tester then that works for me. I just don't want to end up overcharging (or undercharging) my customer for parts they may or may not need. Thanks for the help... it's been a while since I've really done much in audio so I gotta get back into the swing of things.Kenny

Owner / Technician

KKD Garage LLC

Albany, NY 12205