about speakers and impedance

[Alvaro Martinez]

Hi All, This is the first time I post here, I apologize if this has been discussed before. I like to tinker with equipment but my knowledge is basic at best, and it advances along with the problems I get to solve :)

To get straight to the point of the problem I need to solve:

I have a Panasonic SC-AK45 system, which is having some issues with random "cuts" in its sound (sub-second interruptions, no distortion, just lack of sound), and I am not experienced enough to figure out if it is because bad cables, speakers, or the system itself.

I have the speakers for an old AIWA stereo system, their tags say their impedance is 6?, which is the same I can read in the Panasonic speakers. However, the Panasonic speakers have two pairs of cables, one for high and another for low frequency, and the manual says the following:

"if you connect speakers with an impedance of 6? each and plug them into the log and high terminals, you will only have a combined impedance of 3?"

I want to connect the AIWA speakers to the Panasonic system, to find out if the speakers are the problem. So the questions for the group are:

1. What would be the safest way to plug these speakers?
2. Any other thing I should check?

Thanks in advance!

[trader_4]

The stereo you apparently had came with speakers and has the crossover network in the unit and it sends separate wires to the speaker elements. Better and more typical stereo gear relies on the crossover being in the sp eakers. You could probably hook one of your other speakers to the high side on the left, the other to the low side on the left. Run the stereo that way, then repeat on the right side.

The comment about 6 ohms becoming 3 ohms isn't clear, but I would expect that they probably mean if you took your one 6 ohm speaker and connected it to both high and low outputs in parallel. I would think they would have just said not to use regular speakers.

Even with the existing speakers, can't you turn the balance one way or the other, see if the problem persists? If it does, it's most likely not that both speakers have failed with the same problem. The stereo failures I've had, when it was intermittent like that, it was never the speakers. More likely a loose cable connection or something shot in the unit.

[mike]

don't sweat the impedance. It's just a test. Don't turn the volume all the way up and you'll be fine.

I don't know anything about how your speakers are connected, but I'll tell you a story. Back in the day, I had a speaker that cut out. The voice coil is wound with very fine, but rather stiff wire that can't stand the flexing. The wires from the terminals are a much bigger extremely flexible braid. There are two holes in the cone where the flexible wires enter from the back. The voice coil wires come out the front and a short distance across the cone where they're soldered to the flexible braid. The whole thing is covered with a glob of insulation. What happened to me was that the connection broke right where the two wires soldered together. It worked until it got hot and the connection broke, then it cooled and started working again. Can also be a function of the cone distention, not heat. Anyhoo, I used an exacto blade to VERY CAREFULLY scrape the insulation gunk off the very thin voice coil wire and resoldered it to the braid. Fixed it. I've also seen the braid break on the back side right where it enters the cone. YMMV

You can test the theory by setting the volume to a very low level and poking gently on the cone to flex the place where the wires join to see if you can make it cut out.

Of course you can get the same symptom from a bad connection on the circuit board or internal to an output IC.

[KLayton888]

Sounds like a question for the sci.electronics.repair newsgroup.

[Tony Hwang]

Hi, Sounds like to me sound is cutting out because Panasonic is over driven (playing too loud) or impedance is too low for the unit. Most often nominal impedance for those kinda device is 4 or higher Ohms. Good high quality amps can take as low as 2 Ohms but I don't think that Panasonic is really high end device. Lower the playing volume and see what happens or use higher impedance speakers. If it keeps happening the amp may burn up. Impedance is one thing but you have to watch Wattage rating too ie. how much power it can take. Low impedance can draw more current from the device destroying the speaker when amp is not designed for that.

[clare]

OK, lets get something straight. Impedence is NOT just a test or a number. Impedence is the AC version of resistance. It is a measure of the load placed on a circuit. Say an amplifier outputs 20 volts and can handle a maximum of 5 amps output. That is 100 watts PP output. If the speaker has a 4 ohm impedence, at 20 volts it will draw 5 amps for 100 watts pp power output If you have an 8 ohm speaker, it will only draw 2.5 amps, which will only ouput 50 watts. If on the other hand you connect a 2 ohm speaker to that amplifier it will draw 10 amps - which will overload the amplifier, and if the amplifier is capable of pumping out the required 10 amps, it will produce 200 watts, and fry the speaker.

Always err on the side of too much impedence rather than too little.

Connecting speakers in series, you add the two impedences together. If you connect them in parallel you reduce the impedence.Rt= 1(1/R2)=

1(1/R2) - so 2 8 ohm speakers in series is 16 ohms, and in parallel is 4 ohms. A 4 ohm and a 8 ohm in series is 12 ohms and in parallel = 2.66 ohms.

So the OP with a speaker with 2 6 ohm drivers would connect the 2 in series to get 12 ohms of impedence to connect to the amplifier designed for 6 ohm speakers and will get reduced output but will not damage either the speakers or the amp.

[Tony Hwang]

Hi, Nit picking? Impedance Z is combination of resistance plus reactance, root of (R+jX)which varies with frequency. So Impedance on speaker is nominal rating at 1000Hz audio frequency. Speaker engineering is quite complex. My old Quad DC amp can load a piece of wire without burning out. Today'S most consumer amps are way over rated. If it is rated at

100W, maybe good for true rms 20W or less. Power is one thing, dirty signal(distortion) can destroy amps more easily than over powering.

[clare]

Which is still the AC equivalent of resistance. DC doesn't have reactance. So yes, nit-picking

Todays consumer amps are generally rated "peak power" or "peak music power" which really doesn't mean a lot. The better ones also have their RMS output listed - which is REAL power. Good amps also give you percentage total harmonic distortion at rated power.

American consumers (and generally Canadian as well) buy numbers and price, not performance and value. The marketing people know this and take advantage of it,

[gregz]

It was explained recently on Rec.audio.tech. You might specify 1000 hz, but you must consider the minimum Z and it can't be less than 50% of specified Z. Most common modern amplifiers can't drive low Z. The lowest Z of a speaker is usually on the low end.

Greg

[gregz]

It's sounds to me like the source is supplying biamp or some fashion as you say. I can't give advice not knowing what is going on. I would suggest using other speakers Greg

[Alvaro Martinez]

Thanks for all your replies, I will read them carefully and try what you are suggesting.

Just wanted to add two comments: First, the problem occurs even when the volume is low (maybe at 20% of the maximum). Second, these are old systems, I don't know exactly because I got them both from relatives, but they are probably 15 years old or so, and mid-tier at best. I don't want to get them working as if they were new, just want to avoid having to throw it away, or spending $200+ in a new one.

Regards

[makolber]

If you have a left and right speaker connected to two different sides of the amplifier... And both sides are cutting out at the same time Then the problem is probably NOT the speakers.

If only one side is cutting out, SWAP the left and right side See if the problem"follows" the amp or the speakers. Having two of wverything helps a lot when troubleshooting. Happy hokidays

Mark

[Fred McKenzie]

Alvaro-

For the purpose of troubleshooting, just plug one AIWA speaker into the low frequency connection of each side. That should work well enough to determine if the speakers are your problem.

You did not say, but if it affects both left and right channels at the same time, replacing the speakers would not help that. You may have dirty volume and/or balance controls. Rotate the controls in both directions several times and see if that helps. If it gets worse or results in scratchy sound, it may be necessary to spray some contact cleaner inside the controls.

Fred

[clare]

How are the volume and balance controls? perhaps cleaning them up with some Nu-Trol will solve the problem??? Wouldn't be the first time.

[Jerry.Tan]

This thread brings up something I've wondered for a long time. Back around the 1950s and 60s, they used 70 volt (primary) transformers at EACH speaker in a large building, such as an auditorium, or when speakers sent a signal to rooms all over a school or factory. These smallish transformers had a 70volt primary and the secondary usually had a ground, with 4, 8, and 16 ohms, which went to usually just one speaker. All those 70volt lines went back to the source amplifier, which had a 70 volt output, coming from the amplifier's outpit transformer, (and there was usually also at least an 8 ohm output as well on the amp.

Anyhow, these amplifiers were high power vacuum tube amps, and had some massive output transformers.

Back then, I played around with a lot of electronics, and got my hands on several of those old tube amps, and a coffee can full of those (at the speaker) 70v transformers. I learned at that time, that the reason they did the system that way, was because there would be too much loss running an 8 ohm line for hundreds of feet, as well as serious impedence problems, if there were 10 or 20 speakers around the building (which makes sense).

What I never did fully understand is whether the number of transformers placed onto the amplifier's output could overload the amp, if too many were used?????

My other question is whether they still use those 70volt transformers on modern semi-conductor amplifiers, and if so, how would they derive 70v from a bank of output power transistors, since they dont have audio output transformers anymore?

[Pico Rico]

yes. see, for example:

[trader_4]

Sure, there is no free lunch. The amp that's driving it has to be sized to the total load and if the load exceeds that, then it's overloaded.

The concept here appears to be the same as with power distribution. Instead of sending 120V from the plant to your house, they step up the voltage, the step it back down. You can send the same amount of power long distances two ways:

A - higher voltage and lower current B - lower voltage and higher current

Choice A gives you less loss due to resistance in the lines, ability to use smaller conductors, etc.

IDK, Pico says yes and provided a link, but the link appears broken. I don't see why they can't still be using audio output transformers for special applications like you're talking about. They are just a transformer, still available, etc.

---

It's an interesting question. That's as extreme an example as I've ever heard. Most of the consumer audio companies have been playing spec games for a long time. Too many customers thing that 1000W automatically means that the system is way better than one with 50W, that they really could use all that power with their speakers, even if it were available, etc.

[Mike Hartigan]

If my feeble understanding of electricity is correct (never a safe bet),

1,000 watts at 12 volts is 83.3 amps! I'm wondering how much copper was in that box?

[Pico Rico]

I give up. I don't know why friggin google gives "..." when trying to copy and paste a link. Search for "138905-1_10-05_constant_voltage.pdf" and you will find it.

friggin google!

[trader_4]

Not sure what's going on by you. I just copied and pasted the link from internet explorer to google groups and it worked.

Anyway, it does address what the poster was asking about.