How do you test your AMP's output with a Volt Meter ???

[metaverse]

EDITED POST [3.29.2012]

While running my subs (channel 1) and tops (channel 2) via speakons with my crown xti4000 and setting the built-in limiter at -3db on both channels ... Can I then put my volt meter into A/C mode and attach the red and black meter pens to the red and black binding post outputs on channel 1 or 2 while the amp is power the drivers via the speakon cables ??

Is that the proper way to test my amp's output voltage ??



Original Post:

Hello BFM,

In the past few months I teamed up with a friend of mine who has experience , tools and a woodshop to build some BFM fdesigned cabs... specifically Otop12's and T60 slims. We've got to the point where the only thing thats really left is "testing the speaker with a volt meter". As far as his knowledge goes this means just testing to see if the connection is solid and when he used the volt meter the other day it read " 0 " which in his mind equals a perfect connection ... But from reading these forums I know that we're missing something ...

I'm very much confused on what exactly we're looking for here ... I read others posting things like "i'm using a crown xti-1000 for my T60 , running it at -6db and getting 50v" ... ... ... I dont understand this ... I get the -6db part from a beginners perspective as being a measure of volume but thats about it.

Could you guys possibly help me out and explain what this means as if you were explaining it to a 10 year old ??

I dont want to blow my T60's or my two Otop12's (3012HO) running my Xti-4000 through them ...

many thanks
~ meta

[Tom Smit]

Read this thread to test volts out of the amp.

[metaverse]

Big thanks for the first step in the process but i'm still in the dark ...

[Dan30]

What amp are you going to be running tests on?

[Rune Bivrin]

Using the voltmeter to test the speakers is pretty pointless. You may use a resistancemeter, a.k.a ohm meter to test if the connection to the driver is OK. You should read somewhere between 5 and 6 ohms for an 8 ohm driver.

The voltmeter comes into play when setting the limiter that should be a part of the signal path to make sure the voltage to the speakers doesn't exceed a speaker specific voltage. 50V sounds like a T60 voltage even if I don't have those plans.

Voltmeter and Ohmmeter are usually part of the functions of a multimeter.

[petegt]

I dont think he understands what people are using the multimeter for.

We are using the volt meter on the AC setting to measure the power that the amplifier is outputting and therefore what the speaker is getting.

To measure output to a sub woofer I normally play a sine wave of about 50hz from my laptop through my crossover, limiter etc to the amp then put the 2 prongs of the meter on the binding posts of the amp.

From the AC voltage you can then use ohms law to calculate how many watts.

Watts = Voltage (Squared) / Resistance

[Dave Non-Zero]

Simply as possible- Volts is a measure of the 'pushing force' that the amplifier delivers to the speaker.

The impedance of the speaker is how much force it takes to push it. So the higher the impedance of the speaker, the more 'push' is required by the amplifier to move it.

You use the multimeter in 'A/C' setting to measure the voltage that the amp is putting out. then you look at the plans to see what the maximum voltage level that the speaker can safely handle, and you turn your limiter up or down the amp doesnt put out more than that level.

You don't need to calculate power or watts or even measure the impedance of the speaker or anything. Purely the voltage that the amp is putting out.

[metaverse]

I dont think he understands what people are using the multimeter for.

Bingo

You use the multimeter in 'A/C' setting to measure the voltage that the amp is putting out. then you look at the plans to see what the maximum voltage level that the speaker can safely handle, and you turn your limiter up or down the amp doesnt put out more than that level.

You don't need to calculate power or watts or even measure the impedance of the speaker or anything. Purely the voltage that the amp is putting out.

ahh haa !!!

ok , I get it now ... well , for the most part ...


I know that a limiter keeps the volume from peaking into the red and clipping ... but what happens when the voltage gets too high ?? Does it stress the limiter itself or just the speaker or ... ???

[Rune Bivrin]

The limiter sits before the amp, and it's purpose is to limit the voltage going into the amp, thus protecting the speakers. The limiter operates at low voltage levels, and is designed to withstand anything you throw at it gracefully.

[metaverse]

Ahhh ... Ok ...

so when I "turn the limiter up or down" that is increasing or decreasing the amount of voltage it lets through ???

Is it good to run a speaker closest to its voltage limit as long as its not clipping ???

Any other general advice / examples of how the CROWN xti-4000's built-in limiter (or limiters in general) should or should not be run ???


thanks again guys

[Rune Bivrin]

Ahhh ... Ok ...

so when I "turn the limiter up or down" that is increasing or decreasing the amount of voltage it lets through ???

Correct.

Is it good to run a speaker closest to its voltage limit as long as its not clipping ???

Speakers don't clip. They break...

But other than that, as long as the voltage limit is observed you should be good. However, if you find that the limiter is limiting a lot, chances are you need more speakers.

[subharmonic]

Image the limiter like a govenor on a car. It doesn't slow down the engine mechanically. It keeps the speed from goong too high. If your car can go 100mph but will break, you would put a govenor on it capping the mph to 90 so you have a magrin of error. Then you can try to go faster all you want but you will be limited to the setting. Same for limiting voltagyes.

[metaverse]

Speakers don't clip. They break...

However, if you find that the limiter is limiting a lot, chances are you need more speakers.

I'm assuming that is another way of saying "... in that case you should be using a smaller amp." ??

@ SH - thanks

[Scott Brochu]

Can you test the volts to a speaker on a particular channel from the wire terminals on the back of the amp while that channel is being used via speakon cable to the subs/main?

[Tom Smit]

Can you test the volts to a speaker on a particular channel from the wire terminals on the back of the amp while that channel is being used via speakon cable to the subs/main?

Yes you can.

An amp is an amplifier, which means it amplifies...makes bigger. Or, you could call it a "multiplier" in that it multiplies the voltage it receives. The limiter therefore, limits the "small" voltage which in turn is preventing the amp from doing too much multiplying of that voltage. And that is, thus, less voltage to the speaker.

Speakers don't clip. They break...

However, if you find that the limiter is limiting a lot, chances are you need more speakers.

I'm assuming that is another way of saying "... in that case you should be using a smaller amp." ??

@ SH - thanks

No. If the volume is turned up because one thinks it's not loud enough, and the limiter is starting to engage, then there are not enough speaker cabs to make it louder. Also, when adding more speakers to the pile there is:
-less risk of the speakers adding their own "colour" to the sound
-more voltage being used to make sound rather than voice coil heat (power compression).