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Ianr

Testing speaker impedance

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On 12/29/2020 at 8:32 PM, Ianr said:

Hi all,

I have a pair of '70s era Klipschorns and as difficult as it can be to determine for sure, I suspect the tweeter in one is blown.

 

To test I intend to remove the speaker connections at the crossover and test there. Or should I disconnect at the speaker and test there?

 

On another note, my speaker terminals are both on the left hand side of the speakers. I thought one should be on the right side so both cables ran from the sides closest to the amp. Do I have 2 right hand speakers which would mean that there is someone out there with 2 lefts?

 

Thanks for any assistance.

 

Ian

 

The simplest way to see if tweeter is working is just put your ear right next to the tweeter with music playing. Do the working one first then do the problem one. Testing with a ohmmeter at the speaker is preferred way then at the wire going from the crossover to the speaker. Bad connection possible is the reason why. Getting to the tweeter buried in the cabinet can be a witch if you have short or big arms. I have tested many a speaker over the years with a AA battery. Just momentary touch the battery to the wires and see if you get a sound. Some may not want to do it with a battery fearing burning out the speaker but if you just touch it quickly it has never been a problem for me. 

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I believe this thread has drifted off course.  Let me use small chunks of information.  Sorry if it simplistic.  Ya gotta understand the basics though.  Sorry if the following is too simple and complicated at the same time.

 

It is very possible that the tweeter is burned out.  This is to say the wire windings have melted in a small section.  The wire in the coil is finer than a human hair. The tweeter is capable of absorbing only about 2 to 5 watts continuous power despite specs that the system as a whole will take 100 watts.  The mid driver might take 40 and the woofer 100 watts. Know that you don't have to have done anything very naughty to blow a tweeter.

 

The tweeter wire is wound around a tube which is mechanically connected to the diaphragm.  This is perhaps why people say the diaphragem is damaged.  Essentially this is true of all drivers.  This is winding is called the "voice coil."  Voice coils sit in a magnetic field caused b the permanet  magnet of the speaker.  Current through the voice coil makes a magnetic field which pushes and pulls with force to move the diaphragm.  The moving diaphragm makes the audible music. It is a bit more complicate than grade school of winding wire around a nail and picking up paper clips but that is the general idea.

 

We want to test whether the coil has melted in a section and thus causing an open circuit.  If no complete circuit, no current flow, no magnetic force, no movement of the diapragm and no music.  But there could be a loose electrical connecton.  About which more later.  We are though trying to determine what is going on deep within the tweeter  at a microscopic level by using a multimeter (ohm meter) connected to feed wires.  

 

Testing or listening for acoustic output is well done with a listening tube.  However.  You should know that these tweeters as filtered by the crossover or not really sound tinny and that is because  music above 3000 Hz sound like that. 

 

Testing electrically is the most classic and reliable when a burned out voice coil is suspected.  Use an ohm meter. which is part of a multimeter.  This is really sending a direct current or zero Hertz signal to whatever is connected to the ohm meter probes.    This may seem strange.  We are testing a speaker by feeding a 0 Hz signal to determine whether it works at 3000 Hz and above.  

 

Actually the ohm meter is just detecting whether there is an electical path free of gap(s) in the wire.  We actually detect the d.c. (direct current (zero Hz) resistance of the coil.  This is usually about 5 ohms, 8 or 10 ohms is good too.  A burned out winding measures "infinite ohms" which is what is shown on the diplay when the probes are not touched together.  Maybe OL on the digital display.  Older and newer meters will show 'infinite in their own way.

 

Actual electrical testing.  You should go to the crossover screw down teminals.  Turn the amp off of course. The two wires connected to the tweeter should be seen and please note which wire (red stipe and another not). goes where.  Take a picture or make a drawing.  Disconnet both (not technically necessary but lets keep things simple).  It is a matter of backing off the screws about a half turn.  Righty tighty, lefty loosy. The "spade lug" (U shaped) should come free from under the screw head. I see no reason to mess aound with the tweeter driver end and that end is usually soldered.

 

Now, connect or hold the ohmmeter probes to those two wires / spade lugs. 

 

If the voice coil is good, you will see on the meter a reading of 5 to 10 ohms or like that. Also you will hear a mild scratching sound from the tweeter.  This sound is because the meter, through the probes, is sending a little current into the tweeter.  The tweeter is trying to make a bit of music.  A good sign that is can make music.

 

OTOH: You may well find that the meter is showing OL still and there is no scratching sound.  That is just about proof positive thatthe voice coil is blown, ie melted. 

 

Note: Sometimes over age the screw down connection at the crossover has corroded or loosened.  Just snugging up the screw will cure that. Do it for all the screws while you're in there.

 

There is some traffic above which is showing the measurement of the overall speaker "impedance" at the input terminal to a driver or box by the constant current technique.  While intersting it is certainly not necessary to determine whether you've got a blown tweeter.

 

Sorry if I've said too much or too litle.

 

WMcD

 

 

 

 

How to test acoustically?  Yes, the improvised stethoscope with a paper towel roller works.  

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27 minutes ago, WMcD said:

I believe this thread has drifted off course.  Let me use small chunks of information.  Sorry if it simplistic.  Ya gotta understand the basics though.  Sorry if the following is too simple and complicated at the same time.

 

It is very possible that the tweeter is burned out.  This is to say the wire windings have melted in a small section.  The wire in the coil is finer than a human hair. The tweeter is capable of absorbing only about 2 to 5 watts continuous power despite specs that the system as a whole will take 100 watts.  The mid driver might take 40 and the woofer 100 watts. Know that you don't have to have done anything very naughty to blow a tweeter.

 

The tweeter wire is wound around a tube which is mechanically connected to the diaphragm.  This is perhaps why people say the diaphragem is damaged.  Essentially this is true of all drivers.  This is winding is called the "voice coil."  Voice coils sit in a magnetic field caused b the permanet  magnet of the speaker.  Current through the voice coil makes a magnetic field which pushes and pulls with force to move the diaphragm.  The moving diaphragm makes the audible music. It is a bit more complicate than grade school of winding wire around a nail and picking up paper clips but that is the general idea.

 

We want to test whether the coil has melted in a section and thus causing an open circuit.  If no complete circuit, no current flow, no magnetic force, no movement of the diapragm and no music.  But there could be a loose electrical connecton.  About which more later.  We are though trying to determine what is going on deep within the tweeter  at a microscopic level by using a multimeter (ohm meter) connected to feed wires.  

 

Testing or listening for acoustic output is well done with a listening tube.  However.  You should know that these tweeters as filtered by the crossover or not really sound tinny and that is because  music above 3000 Hz sound like that. 

 

Testing electrically is the most classic and reliable when a burned out voice coil is suspected.  Use an ohm meter. which is part of a multimeter.  This is really sending a direct current or zero Hertz signal to whatever is connected to the ohm meter probes.    This may seem strange.  We are testing a speaker by feeding a 0 Hz signal to determine whether it works at 3000 Hz and above.  

 

Actually the ohm meter is just detecting whether there is an electical path free of gap(s) in the wire.  We actually detect the d.c. (direct current (zero Hz) resistance of the coil.  This is usually about 5 ohms, 8 or 10 ohms is good too.  A burned out winding measures "infinite ohms" which is what is shown on the diplay when the probes are not touched together.  Maybe OL on the digital display.  Older and newer meters will show 'infinite in their own way.

 

Actual electrical testing.  You should go to the crossover screw down teminals.  Turn the amp off of course. The two wires connected to the tweeter should be seen and please note which wire (red stipe and another not). goes where.  Take a picture or make a drawing.  Disconnet both (not technically necessary but lets keep things simple).  It is a matter of backing off the screws about a half turn.  Righty tighty, lefty loosy. The "spade lug" (U shaped) should come free from under the screw head. I see no reason to mess aound with the tweeter driver end and that end is usually soldered.

 

Now, connect or hold the ohmmeter probes to those two wires / spade lugs. 

 

If the voice coil is good, you will see on the meter a reading of 5 to 10 ohms or like that. Also you will hear a mild scratching sound from the tweeter.  This sound is because the meter, through the probes, is sending a little current into the tweeter.  The tweeter is trying to make a bit of music.  A good sign that is can make music.

 

OTOH: You may well find that the meter is showing OL still and there is no scratching sound.  That is just about proof positive thatthe voice coil is blown, ie melted. 

 

Note: Sometimes over age the screw down connection at the crossover has corroded or loosened.  Just snugging up the screw will cure that. Do it for all the screws while you're in there.

 

There is some traffic above which is showing the measurement of the overall speaker "impedance" at the input terminal to a driver or box by the constant current technique.  While intersting it is certainly not necessary to determine whether you've got a blown tweeter.

 

Sorry if I've said too much or too litle.

 

WMcD

 

 

 

 

How to test acoustically?  Yes, the improvised stethoscope with a paper towel roller works.  

Man that was brilliant!

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Ah that's interesting. Wirrunna.

There seems to be a lot of DIY involved in both the driver construction and crossover mods, is that right? I don't have the space or equipment to do much - no garage, just a small shed full of motorbikes and a carport unfortunately.

I think I saw in a post that you can also get them delivered already assembled. If so that would be the best option for sure.

I can't find a full description of the kit anywhere to see exactly what you get.

Frustrating.

 

Ian

 

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WMcD, thanks for the input. Rest assured, you didn't say too much at all.

I have confirmed, via the stethoscope improv that there is no sound at all from that speaker in question and later today (when I finally stop searching for some meaningful Eliptrac info, why is it so hard?) will do some electrical testing as you described.

 

Ian

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Ian,

Quick fix, send me a PM with your address details and I will put a square magnet K77 with optional Z brackets in a padded bag and post it from the Broulee post office on Monday morning.

This will get the K-Horn going, and meanwhile we can explore options for other horns, upgrades etc. and maybe give you an excuse for a ride down the coast.

 

https://community.klipsch.com/index.php?/topic/144700-eliptrac-400-kit-finishing-update/&ct=1557489906

 

Longer fix, replace the K55 mid horn driver with an A55G and and the K77 with a DE110 and try an Extreme Slope 400/4500 crossover, all parts sitting in a box under the house.

Eliptrac assembly instructions.pdf

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Wirrunna,

 

PM sent. Thank you.

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Hi again,

Just as a matter of interest, your parts box has 4 drivers and 2 crossovers that you are no longer using?

If so, would you be interested in selling them? It might be a good, easy upgrade path for me. After all, my drivers are all about 50 years old.

Dave is not doing pre-assembled kits any more so that avenue looks like a dead end.

 

Thanks, Ian

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Wirrunnna,

just looking through some old stuff for another members question, in this case the Klipsch Heritage Owners Manual and found this -

 

"There is a left and a right low frequency cabinet with respect to the input panel. This allows the speaker’s binding posts to be oriented toward the electronics to minimize the length of speaker wire."

 

There ya go! Maybe we both have right hand speakers.

 

Ian

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Ian,

How did the replacement K77 go ? I measured it with a multimeter and got 6.8 ohms and a scratchy noise out of it so I assumed it was good to go.

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@Ianr Did you try my suggestion regarding the screws in the crossover yet?  I found a lot of corrosion around a few screws in my 1980 Heresys. 

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yes, I did thanks wuzzzer.

I try to do that annually so they're pretty good.

Ian

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