So I'm reinstalling a Denon X-3000 that was just repaired, under warranty. It was sent back with a note to "please check all speakers and wiring before reinstalling".
I asked the guy behind the counter and he didn't say much other than " check the speakers".
I'm on site and put my ohm meter on the speakers and get 5.3 ohms on the the l,c,r's (6 ohm spks) and get 7.5 ohms on the rears. I did get quick high readings when slightly pushing in the woofer. It went up then right back down quickly. Is this normal?
What other way is there to test a speaker?

You would want some sort of Impedance meter. An ohm meter merely checks for DC resistance. Impedance is reactive, so you'll measure varying values depending on the frequency applied to the speaker. When you move a speaker while an ohm meter is connected, the magnet on the speaker induces a voltage on the circuit, which affects your reading. Measuring DC resistance gives you a general idea of the state of the speaker but note that it is possible for impedance of a speaker to be lower than it's DC resistance at certain frequencies.

I only have an ohm meter. How much do impedance meters go for? Is there anything I can do on site to check, other than let receiver play for a while?

Check the speaker wires for shorts. Stray wires at the amp or speaker. Stray positive wire touching the chassis of the amp. Staples or cuts in the wire.

An impedance meter won't help unless it plots the impedance curve of the speaker, simple and complex. Your VOM wont help much because it only measures at one frequency with negligible voltage/current probably at 1k.

What are the brand and model number of the speakers? Are they "difficult to drive? It is possible that the "6 ohm" nominal speaker (marketing department spec) really is a 4 ohm speaker over most of the band?

The leads are tinned to prevent stray hairs


Episode ES-700- Point 6 series L,C,R's. 6 ohm's nominal impedance on the specs

So what was wrong with the amp anyway? The check speakers and wiring is a pretty standard service center response when the protection circuit is triggered or the unit had blown outputs. What did they say that they fixed on the unit?

Any burnt or charred parts on the speaker crossover, or any capacitors leaking at the seams, or puffed up?

Maybe nothing wrong with the speaker and the amp was weak?

What "led up" to the receivers demise?

I've had a quite a few Denon receiver go into repair for shutting down and they always suspect bad speaker wiring. Some of them came back still faulty even when speakers were not connected. Now I have hundreds worth of Denon receivers in the shop that I can't do anything with. Screw Denon and switch to Yamaha.

I've been saying that for a dozen years.

How to test a speaker: connect some music to it. This is best done if you have two speakers and you can compare their sound.

Listen for lack of any frequency range in one versus the other. Listen for scratchy sound; parts of the voice coils might be damaged and/or rubbing.

Measuring the resistance only measures the voice coil of the woofer. It says nothing about the tweeter or midrange, nothing about the crossover. A manufacturer I know once made a speaker whose woofer was crossed over so low, using a 12 dB/octave filter, that while the resistance was 6 ohms, the impedance was less than 2 ohms around 100 Hz. This can damage an amp.

Measure the speaker wire for short circuits to one another. Don't forget that something in your system is also probably connected to earth ground or electrical ground, and measure all speaker wire conductors with relation to ground; they should measure infinite. Don't let a + speaker wire that has been shorted to an electrical box miss detection because you did not measure to ground.

There's so much I could write on this.


That is like the first three pages of every manual, where it tells you, for instance, to keep your Blu-ray player more than ten feet from any overhead power lines.


And his thoroughness just confirms that while it's a good idea, it's being ignorantly recommended. Good for you for following up to get some understanding!


The ohmmeter interprets the amount of DC current that flows through the UUT (unit under test) and converts that to ohms.


The voice coil is in a magnetic field. When you push in on the cone, you generate a small amount of electricity. That small amount of electricity feeds into the ohmmeter, which is interpreting the overall current flow, and that changes the apparent resistance. It's normal. It shows that a coil moving in a magnetic field generates electricity.


The simplest, as I said, is to play it. Your ear is connected to a GREAT and sensitive analog computer and you'll be able to detect most of what you need to know just by listening.

EXACTLY what mrtristan said.


Let's just be ridiculously clear: your ohmmeter checks a ZERO Hertz, which is to say, DC. There is ZERO signal at any other frequency.


Always a good question in case these are some rare speakers that gave problems to the two people who have bought them in the last five years!


That's usually an engineering department spec and in fact its correctness may be controlled by FTC regulations.

What was the reason you sent it for service- blown amp? Inspect the speaker wires, make sure there are no splices and that no stray wires are on the ends- if it's dark where the wires are inserted, use glasses and bright light.

I was told by Electronic Express, who services most brands, that most brands that are rated for 6 Ohms really don't like it very much, so 8 Ohm speakers will work best.

If you let the receiver play, you risk launching the amp all over again. Put a big non-inductive 2 Ohm resistor (or, two 1 Ohm in series) in-line for the LCR speakers. If it doesn't run hot or blow up, the speakers may be too difficult for the receiver. Contact Denon CI and ask about the real limits for these receivers.

What brand and model of speakers are these?

If you build speakers, Parts Express sells a woofer tester (WT-3) and it will do impedance sweeps for individual drivers or a complete speaker system. It's not terribly expensive, either.

If you want to test the resistance at different frequencies, download a frequency generator app for your phone, use an 1/8"- stereo RCA cable to connect to a receiver/amp, measure the voltage drop across the speaker and use Ohm's Law to calculate the resistance at that frequency. Excel would be a great way to plug in the numbers and get the results.

Actually, that's a better way to test an amp. If the speaker makes noise when a battery is connected to the wires and it doesn't show an extremely low DC resistance, a lot of amps will still puke.

I'm not following this:


it = the resistor or resistors? or the amp? or the speaker?


This seems backwards. If the speakers were too difficult because they had too low of an impedance, the resistors would run hot. (You do have to add "turn it up" to get things hot; music at 70 dB won't help here.)

If the speaker impedances are too low and you add a resistor, then the receiver would get less hot than without the resistor. I can't imagine the speakers getting hot under any circumstances except really high power and an amp that can put out more current than a Denon.

Contact Denon CI and ask about the real limits for these receivers.

Think about it- what was sent in for service- a receiver, a resistor or a speaker?

If the resistor runs hot, it's doing its job. I meant to do this for testing, but if you're familiar with Bob Carver's offer to customers for his modification of any solid state amp to make it sound more like a tube amp for the low, low price of $400, it involved inserting a 1 Ohm resistor in series with the output, inside of the amp. It lowers the damping factor, adds a bit of compression and lined his pockets.

Difficult loads make the outputs run hotter and yes, the resistor will become hot, but only when a lot of current passes through. I doubt one of these receivers will really cause this and it's the whole reason we're having this discussion- they aren't designed for high current operation.

The resistor causing the amp to run cooler is the main point of this test. The other point has to do with people who should have test equipment, but don't. It's not rocket surgery- we should all have this stuff, in one form or another. I use the WT-3 woofer tester because I build speakers and it tests Z, Inductance/capacitance, produces a phase plot, performs rub and buzz test and a lot more. It's also good for locating speaker problems- I have seen speakers that looked normal, but were wired incorrectly.

It should be fine. Impedences tend to vary slightly. If you dont hear the woofer's voice coil rubbing, and by using your ohmeter you get a in the ball park reading, the voice coil is not shorted.

BTW a lot of amps today shut down when faced with 4 ohm loads! Just saying. Not like the good old days when a cheap assed Japanese receiver could handle 2 ohms all day.

Name a few- all of the Pioneer, Sony and other mainstream stuff had a warning to use 4-8 Ohm speakers, but when Speakers A+B was selected, they were in series. I think Harmon Kardon was the major exception WRT running well with 4 Ohms, but the 330C existed only because the 330A and 330B blew up a lot.