How do I test a new crossover with a meter before actually using it?

[JonW]

Well, the inductors for my crossovers are backordered for a while. Which leaves me with time to think about what I’ll do when they arrive. Never having built a crossover before, I thought maybe I should test it out with a digital volt or multi meter before hooking it up to an expensive amp. To prevent anything from smoking and all. You folks convinced me to buy a meter and you recommended this one:

http://www.cs-sales.net/lcm1950.html

$60, no problem. But, umm, what am I supposed to do with it? I’d like to get some guidance on what to check for, to make sure the crossover is AOK. Thanks!

[ThomasW]

The Macgyver way....simply hooking up the different sections to a raw driver (a woofer is fine even for the tweeter section) and running some frequency sweeps using your PC?

[JonW]

Umm, I don't have a PC at home. Well, I have a Mac, but that usually doesn't count. :W Seriously, I don't have a way to hook anything into that computer. It seems that people test their crossovers with meters, to prevent frying the amps..?

[TacoD]

Connect everything and then check if there is no shortcircuit when measuring over the + and - connector.

[JonW]

Connect everything and then check if there is no shortcircuit when measuring over the + and - connector.

Sorry for the ignorance, but here goes...

By connecting everything, you just mean in the speaker (crossover + drivers) and not the amp. Correct?

What do you mean by measuring the + and - connector? Hook up the meter and look for... what?

Thanks.

[ThomasW]

All that will tell you is if you have a circuit. If you test playing using test tones and a speaker you can hear the XO points and check if the frequencies are correct.

John Mulcahy's Room EQ Wizard has a freeware version for the Mac. And if you want a simple tone generator your can download a trial version of the NCH unit here

http://www.nch.com.au/tonegen/index.html

A few more....

http://mac.softpedia.com/get/Audio/Perfect-Tone.shtml

http://www.versiontracker.com/dyn/moreinfo/macosx/22024&vid=129268

[chasw98]

Jon:
You do realize that you are looking at frequency versus voltage, right? This means that if you have your midrange hooked up to the meter and the crossover point is set to 500 hz and the upper limit is 2000 Hz, you should see the AC voltage rise as you go from say 100 to 250 to 500 and as you go from 1800 to 2000 to 2500 and on up you should see the voltage decrease. Hopefully your meter will read with flat or even frequency response up to a good amount. Check the specs that came with the meter to see what it is. Some meters will not read very much above 1000 Hz.

[JonW]

OK gentlemen, let's pretend that you are dealing with someone who doesn't know even the first things about electronics. Has never used a volt meter. You know. Just pretend.

(Actually, part of the appeal of building these speakers is to learn these things.)

if I'm to measure frequency versus voltage... how does that work? Do you use the computer to generate different input signals at different frequencies? And then use the meter to measure the resulting voltage? If so, how do you get the signal from the computer to the crossover? And what range of voltages are you looking for? What values indicate it's good or bad? And how do you look at just part of the crossover?

I think I understand that, say, the woofer part of the crossover should have decreasing output above the crossover frequency. And the tweeter should decrease from below the crossover point. But that's book knowledge. No idea how that translates to the real world. Or how you actually measure that. How would you measure the two parts of the crossover seperately? I'm making the Modula MT's and the circuit diagram looks like it's all blended together (to me, at least).

Looks like that $60 meter has frequency ranges of 4, 40, 400, and 1000 kHz. For AC voltage, it's 50-500 Hz.

All I'm trying to do here is test the crossover so that it doesn't fry the amp when I plug it in for the frist time.

[chasw98]

OK gentlemen, let's pretend that you are dealing with someone who doesn't know even the first things about electronics. Has never used a volt meter. You know. Just pretend.

>>I'm somewhere over the rainbow.

(Actually, part of the appeal of building these speakers is to learn these things.)

if I'm to measure frequency versus voltage... how does that work?

>>A known frequency is generated and the voltage of the frequency is measured. When you measure the AC voltage coming from an outlet, the voltage is 120 volts AC. The frequency is 60 Hz (cycles per second).

Do you use the computer to generate different input signals at different frequencies?

>>That is probably the easiest method for you. An electronics shop would use a signal generator.

And then use the meter to measure the resulting voltage?

>>At this point you will have generated a low voltage (less than a volt) at a specific frequency from the computer. You can measure the voltage and frequency at this point, but you do not need to except for possible troubleshooting purposes. The signal the computer generates will not drive the XO, so it must be amplified.


If so, how do you get the signal from the computer to the crossover?

>>Glad you asked! Now you hook up the output of your computer to a power amplifier or a receiver through the aux or CD line level inputs. Then you hook up the speaker outputs to the input of the crossover.

And what range of voltages are you looking for?

>>Now you want to measure voltage at the output of the amplifier. I.e. the speaker terminals. 2 to 5 volts AC will be good for now. Depending on the power of the amplifier the voltage could go up over 40 volts AC.

What values indicate it's good or bad?

>>There is no good or bad. If the output of the amplifier is at 5 volts and it is hooked up to the input of the crossover, then with a 250 Hz signal, you should probably read approx. 3 - 5 volts coming out of the lo frequency section of the crossover. It can depend upon how much loss is in the crossover or whether a load needs to be hooked up to the crossover outputs to simulate a speaker being attached to it. Right now you are looking for output in the desired frequency range.

And how do you look at just part of the crossover?

>>By changing the frequency being generated from the computer and then amplified by the amp, you should see the voltage rise and fall as it moves through the various ranges (hi, mid, lo) of the crossover output. A 1000 HZ signal will probably come out of the mid output of the crossover and so forth.

I think I understand that, say, the woofer part of the crossover should have decreasing output above the crossover frequency. And the tweeter should decrease from below the crossover point. But that's book knowledge. No idea how that translates to the real world. Or how you actually measure that. How would you measure the two parts of the crossover seperately? I'm making the Modula MT's and the circuit diagram looks like it's all blended together (to me, at least).

>>You are quite correct in that statement.

Looks like that $60 meter has frequency ranges of 4, 40, 400, and 1000 kHz. For AC voltage, it's 50-500 Hz.

>>Adjust the setting on the meter to match what you are looking for from the system. A 2500 Khz signal should be in the 1000 Hz range on your meter. A 5 volt AC signal would be in the 40 volt range.

All I'm trying to do here is test the crossover so that it doesn't fry the amp when I plug it in for the frist time.

>>You're doing fine. If you ask these questions early in the morning I can answer them easier. At the end of the day and having to type this much, sheesh! You owe me a cold one!

Chuck :T

[JonW]

Chuck-

Thanks for the long reply. Let’s see if I can figure this out…

Do you use the computer to generate different input signals at different frequencies?

>>That is probably the easiest method for you. An electronics shop would use a signal generator.

Actually, I burned a CD of test tones. I'd think it would be easier to just play those rather than hook the computer into the preamp/processor. Good idea or bad?

And then use the meter to measure the resulting voltage?

>>At this point you will have generated a low voltage (less than a volt) at a specific frequency from the computer. You can measure the voltage and frequency at this point, but you do not need to except for possible troubleshooting purposes. The signal the computer generates will not drive the XO, so it must be amplified.

If so, how do you get the signal from the computer to the crossover?

>>Glad you asked! Now you hook up the output of your computer to a power amplifier or a receiver through the aux or CD line level inputs. Then you hook up the speaker outputs to the input of the crossover.

I’ve got separates, so I go from Computer -> Preamp/processor -> Amp -> Speaker

But I thought the whole point of doing this was to prevent hooking up the amp? So I don’t fry the amp if I did something horribly wrong with the crossover.

And what range of voltages are you looking for?

>>Now you want to measure voltage at the output of the amplifier. I.e. the speaker terminals. 2 to 5 volts AC will be good for now. Depending on the power of the amplifier the voltage could go up over 40 volts AC.

What values indicate it's good or bad?

>>There is no good or bad. If the output of the amplifier is at 5 volts and it is hooked up to the input of the crossover, then with a 250 Hz signal, you should probably read approx. 3 - 5 volts coming out of the lo frequency section of the crossover. It can depend upon how much loss is in the crossover or whether a load needs to be hooked up to the crossover outputs to simulate a speaker being attached to it. Right now you are looking for output in the desired frequency range.

So, basically, am I just looking for anything in the 3-5 volt range. And then that says I’m OK?

And how do you look at just part of the crossover?

>>By changing the frequency being generated from the computer and then amplified by the amp, you should see the voltage rise and fall as it moves through the various ranges (hi, mid, lo) of the crossover output. A 1000 HZ signal will probably come out of the mid output of the crossover and so forth.

Looks like the crossover point of the Modula MT is around 1800 Hz. So for the tweeter section, I’m looking for increasing voltage from about 750-3000 Hz and a flat voltage above that? And for the woofer, I want to see flat voltage from 100-750 and then decreasing voltage at higher frequencies? So maybe the 3-5 volt range is the top, flat part. And I’m looking for values at there or lower.

But I still don’t see how I’ll test the woofer part of the crossover separate from the tweeter.

>>You're doing fine. If you ask these questions early in the morning I can answer them easier. At the end of the day and having to type this much, sheesh! You owe me a cold one!

Absolutely! Next time you’re in the Midwest or I’m in Florida, you can collect a cold one (or a few) for all your help.