Jump to content

Testing speaker impedance


Ianr

Recommended Posts

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

 

Link to comment
Share on other sites

Thank you.

I'm looking forward to reading them.

I'll be looking for some build info on them while I'm at it too as I'm unsure of exactly how old they are.

My father bought them second hand, here in Australia in 1980. I've had them since about 2000 and replaced the crossovers around 10 years ago. All of the drivers are original but if I have to get a new HF speaker I'll replace both.

Link to comment
Share on other sites

First thing to do is disconnect and reconnect all input and output wires at the crossover and at the drivers (unless they're soldered).

Also, it's easy to test if a driver is working or not by putting an empty toilet paper tube or paper towel tube into the horn opening and put your ear on the other end while you're playing something through them.  Or, roll up some paper to make a "funnel" and do the same thing. 

Link to comment
Share on other sites

Thanks for the reply Andy. I'll test the leads I think.

It's taken weeks to convince my self that it is actually faulty. If it tests OK, I'll swap the top sections around and go from there as I guess it could be something else.

 

Link to comment
Share on other sites

22 minutes ago, Ianr said:

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?

 

Ian,

 My K-Horns have the connections on the left, I just assumed that to reduce production variation all K-Horns were built the same, i.e woofer access door and terminals always in the same place.

 

Where in Oz are you ?

Link to comment
Share on other sites

Ian,

Down at Broulee, on the coast between Batemans Bay and Moruya.

I have recently fitted an Eliptrac horn with a coaxial B&C DCX464 to my K-Horns, so have a few spare parts, both original and upgrades from Bob Crites.

What crossover did you get ?

Link to comment
Share on other sites

Wirrunna,

I have the AA crossover which I got from Bob.

I've seen (and saved somewhere) the Eliptrac I think. It's a whole new top section isn't it?

It sounds like a good upgrade but then I'd have to store the old top cabinet somewhere.

I'll check it out again.

I've never seen another pair of Klipschorns anywhere. What era are yours?

Broulee, lovely spot. We love the South Coast but most of our friends moved north so we don't get down there as often as we'd like too. I have an ex work-mate in Bermagui who I ride with (motorbikes). Next time I'm heading down that way I''ll give you a nudge.

Link to comment
Share on other sites

Ian,

Ordered the K-Horns new in 1989, they came with AK3 cross overs. Re-capped with a Bob Crites cap kit, then got Bob Crites DE10 tweeters and A55G mid drivers. Built an ALK Universal crossover at 4,500Hz between mid and hi. Then built an ALK Extreme Slope network 400 / 4,500. Then an Eliptrac mid horn and recently added a B&C DCX 464 co-ax mid/hi driver and almost finished tri-amping with a miniDSP 2X4HD - still tweaking.

The Eliptrac only needs a new motor (front) board in the top hat, not a complete top hat.

I suggest you go for a ride on your bike and have a look and listen. I'm retired so are here most of the time.

 

Serial Klipschorn.JPG

Link to comment
Share on other sites

Wirrunna,

I would not have a clue as to when mine were made or what type of drivers are in them.

There are no labels on them but I believe they are the "Decorator" model due to the finish which remains unchanged since the '70s. As you can see, not attractive at all anymore and something I intend to address in the new year. I've come to think that top-hat treatment interferes with sound dispersion too.

 

I'm also retired so I have the time and have some other speakers to use but it's hard to bring myself to disconnect the K'horns knowing they'd be out of service for some time.

 

That's an old picture and the equipment is different to what I normally use. I'm into digital these days and use Roon via an Antipodes server/streamer and a Denafrips Pontus DAC. A little Miniwatt amp is in play atm and I have a few old valve amps that I rotate through occasionally. Still have my albums and Rega TT so one day........

What's driving yours?

 

Thanks for the invite mate, I'll take you up on that next time. You're welcome to stop in here next time you're up this way too. 5 minutes off the highway.

 

Ian

IMG_1703.JPG

Link to comment
Share on other sites

Speaker impedance is a measure of a speaker's resistance to AC current. The lower the impedance (also called AC resistance), the more current the speakers draw from the amplifier. If the impedance is too high for your amplifier, the volume and dynamic range will suffer. If it's too low, the amplifier could self-destruct in an attempt to generate enough power. If you're simply checking the general bandwidth of your speakers, all you need is a multimeter. If you want to do a more precise test, you'll need special tools.

 

Impendanz3.png.fdf6b20c46ac876369dbd3d15271adde.png

 

 

 

A quick assessment

   

Image title Measure Speaker Impedance Step 1
  
Look at the label for a nominal impedance reading. Most speaker manufacturers list the impedance on the speaker label or packaging. This "nominal" specification (usually 4, 8, or 16 ohms) is an estimate of the minimum impedance for a common audio bandwidth. This is usually the case at a frequency between 250 and 400 Hz. The actual impedance is fairly close to this value in this range and slowly increases as the frequency is increased. Below this range, impedance changes rapidly and peaks at the resonant frequency of the loudspeaker and its enclosure.On some speaker labels, an actual measured impedance is written as specific impedance.To give you an idea of what these frequencies mean: Most bass tracks fall between 90 and 200 Hz, while deep bass you feel in your chest can go as low as 20 Hz. The midrange, including the bulk of non-percussion instruments and voices, covers 250 Hz to 2 kHz.

 

Impendanz2.png.0377ab33ea561f6723e0b162405c25b4.png

 

Set a multimeter to measure the resistance. A multimeter sends out low DC current to measure resistance. Since impedance is a property of AC circuits, this does not directly measure impedance. However, this approach gets you close enough for most home audio systems. (You can easily distinguish between a 4 ohm and 8 ohm speaker this way, for example). Use the lowest setting for resistance. This is 200 ohms on many multimeters, but a multimeter with a lower setting (20 ohms) may give more accurate results. If there is only one setting for resistance, your multimeter will automatically set the range and find it on its own.Too much DC current can damage or destroy a speaker's voice coil.The risk here is low, since most multimeters produce only low current.

 

Impendanz4.png.e1519f7d02511a4c636944d8456fd238.png

 

Take the speaker out of the cabinet or open the back of the cabinet. If you have a loose speaker with no connectors or cabinet, then you don't need to do anything here.

 

Impendanz5.png.06bc6585a6dac06fe72bc331dd4bda79.png

 

 

Disconnect the power to the speaker. If the speaker gets power, it will ruin your measurement and could destroy your multimeter. Turn off the power. If the wires are not soldered to the terminals, disconnect them.Do not disconnect any wires that are directly connected to the voice coil.

 

Impendanz6.png.7926cae6d92e3148c25f70d400ec3432.png

 

 

Connect the probes of the multimeter to the terminals of the speaker. Take a good look at the terminals and determine which is "+" and which is "-". Often this is indicated by a "+" and a "-" sign. Connect the red probe of the multimeter to the positive side and the black probe to the negative side.

 

Impendanz7.png.e4e900c43710cb60d95242f311bbc505.png

 

Estimate the impedance from the resistance. Typically, the reading for the resistance should be about 15% less than the nominal impedance on the label.For example, it is normal for a speaker rated at 8 ohms to have a resistance between 6 and 7 ohms.The majority of speakers have a nominal impedance of 4, 8, or 16 ohms. Unless you're getting a weird result, for connecting to an amplifier you can safely assume that your speaker has one of these impedance values.

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Thanks 1
Link to comment
Share on other sites

19 hours ago, Ianr said:

Thank you.

 but if I have to get a new HF speaker I'll replace both.

they sell the aftermarket diaphragms for peanuts from China ---- and you guys are very close by   you can replace a diaphragm in  15 minutes ---if you got a mate who can solder ,  just bring a couple of beers over  --1/2 an hour  later , you'll be back  listening to music  in no time ---I buy 2  at at time --10$

 

https://www.ebay.com/itm/2x-Diaphragm-for-Klipsch-Tweeter-Horn-K77-89486A-KLP-Electro-Voice-ST350-T35/283187274975?hash=item41ef46e4df:g:NaoAAOSw~ZFbsIOg&shqty=1&isGTR=1#shId

 

 

Link to comment
Share on other sites

A precise measurement

 

Impendanz8.png.9c91419f9ec3f3dffb8e03d77a5e699d.png

Get something that produces a sine wave. The impedance of a speaker varies with frequency, so you need something that can send out a sine wave for any given frequency. An audio frequency oscillator is the most accurate alternative. A signal generator or function generator with a sine or arc function will work, but most models give inaccurate results because of the change in voltage or a poor sine approximation. If audio testing or DIY electronics are new to you, consider test tools that you can plug into a computer. These are often not as accurate, but newbies may appreciate the automatically generated graphs and data

 

Impendanz9.png.8f0054fe5fb9cf37d5235b3968f83d2b.png

Connect the tool to the amplifier input. Look on the label or in the specification of the amplifier for the power in watts. A higher wattage amplifier will give a more accurate measurement in this test

 

Impendanz10.png.5472d0008f9053593b60cf40599e8df5.png

 

Set the amplifier to low voltage. This test is part of a standard series of tests to measure the "Thiele-Small parameters". All of these tests are designed for low voltage.Reduce the gain of the amplifier while a voltmeter set to AC is connected to the output terminals of the amplifier. Ideally, the voltmeter should read between 0.5 and 1 V, but if you don't have a sensitive meter, just set it below 10 volts. Some amplifiers produce inconsistent voltage at low frequencies. This is a common cause of inaccuracy in this test. It's best to test with the voltmeter to make sure the voltage stays the same while you adjust the frequency with the sine wave generator. Use the best multimeter you can afford. The cheap models tend to be less accurate in the later measurements in this test. It may help to buy better probes for the multimeter at the electronics store.

 

Impendanz11.png.8df981b262fab0b00d5463f349c74082.png

 

 

Choose a high quality resistor. In the list below, find the power rating (in watts) that is closest to that of your amplifier. Choose an electrical resistor with the recommended resistance value and the power rating listed or higher. The resistor does not have to be exact, but if it is too high, you may be limiting the amplifier and interfering with the test. If it is too low, your results will be less accurate.

    100 W amplifier: 2.7 kΩ electrical resistance with a minimum of 0.50 W
    90 W amplifier: 2.4 kΩ, 0.50 W
    65 W amplifier: 2.2 kΩ, 0.50 W
    50 W amplifier: 1.8 kΩ, 0.50 W
    40 W Amplifier: 1.6 kΩ, 0.25 W
    30 W Amplifier: 1.5 kΩ, 0.25 W
    20 W Amplifier: 1.2 kΩ, 0.25 W

 

Impendanz12.png.9ba00ee231ac29b6b01c5c2bb9acfc4a.png

 

 

Measure the exact electrical resistance, which may differ slightly from the printed resistance. Write down the measured value.

 

Impendanz13.png.c0d1d844df025b2a6653afe5b847cba3.png

 

Connect the electrical resistor and the speaker in series. Connect the speaker to the amplifier with the electrical resistor in between. This creates a constant current source that powers the speaker.

 

Impendanz14.jpg.af27341b01ed3d3aa874a7f8288065cb.jpg

 

Keep the speaker away from obstacles. Wind or reflected sound waves could interfere with this sensitive test. Keep at least the magnet side of the speaker in a wind-free area at the bottom (cone facing up). If high accuracy is required, mount the speaker on an open frame where there are no solid objects within 60 cm in any direction

 

Impendanz15.jpg.82f9619da4ab5cc05e7b49d92982076a.jpg

 

Calculate the current. Using Ohm's law (I = V / R or current = voltage / resistance), calculate the current and write it down. Use the measured resistance of the electrical resistor for R.

For example, if the electrical resistor has a measured resistance of 1,230 ohms and the voltage is 10 V, the current is I = 10/1,230 = 1/123 A. You can leave this as a fraction to avoid rounding errors.

 

Impendanz16.jpg.2ac14812c8ed6019c597ea02016cc59c.jpg

 

Adjust the frequency to find the resonance peak. Set the sine wave generator to a frequency in the middle or upper range of the speaker's intended use. (100 Hz is a good start for bass units.) Place an AC voltmeter on the speaker. Adjust the frequency downward by 5 Hz at a time until you see the voltage rise sharply. Turn this frequency back and forth until you find the frequency where the voltage is highest. This is the resonant frequency of the speaker in "air" (an enclosure and surrounding objects will change this).You can use an oscilloscope instead of a voltmeter. In this case, find the voltage associated with the highest amplitude.

 

Impendanz17.jpg.3ce65c475ce91c3ad6064bfb50ebf2c4.jpg

Calculate the impedance at resonance. You can substitute the impedance Z for the resistance in Ohm's law. Calculate Z = V / I to find the impedance at resonance frequency. This should be the maximum impedance of your speaker in the intended audio range.For example, if I = 1/123 A and the voltmeter measures 0.05 V (or 50 mV), then Z = (0.05) / (1/123) = 6.15 ohms.

 

Impendanz18.jpg.dca3ff7c0bedcfd09849fc14a7197bc5.jpg

 

Calculate the impedance for other frequencies. To find the impedance in the intended frequency range of the speaker, fit the sine in small increments. Document the voltage at each frequency and use the same calculation (Z = V / I) to find the impedance of the speaker at each frequency. You may find a second peak or the impedance may be quite stable as you move away from the resonant frequency.

 

 

 

 

 

 

 

 

 

 

 

  • Like 1
  • Thanks 1
Link to comment
Share on other sites

Wirrunna,

what I had saved was for a Volti VTrac horn replacement.

It appears that the Eliptrac might be hard to come by these days. The company shut the doors and a guy still makes them to order, as of Dec. 2019.

How long have you had yours?

Randyhoo, I've seen them on ebay. They do the job OK?

Link to comment
Share on other sites

babadono,

that's true but the bass connections from the crossover are on the main cabinet on the left, below the crossover. I have toyed with the idea of moving the crossover and may well do so when/if I have to replace the tweeter.

Thanks for the reply.

Link to comment
Share on other sites

Ian,

I ordered my Eliptrac horns in April -Dave Harris at fastlaneaudio@aol.com, $299US for the kit, $233 shipping for 35lbs of machined mdf. A recent thread - https://community.klipsch.com/index.php?/topic/196538-eliptracs-in-the-house/

 

I like your knotted pine finish on the K-Horns.

 

Amp I use is a NAD C725BEE receiver pre-out into miniDSP 2X4HD then back to the NAD for bass and to an Audiophonics MPA-S125NC Hypex Ncore NC122MP for mid and hi. With this setup the NAD remote operates the tri-amp system as if it was still just a stereo as the NAD has a 12vDC signal to turn on/off associated equipment that connects to the extra amps via a 3.5mm stereo plug and cable. The miniDSP stays on all the time.

 

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...