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trying to understand VU meters...

soulsurfing

soulsurfing

Spinning Barry Manilow records backwards
...in that thought...
I have two carver tfm-45 amps with stereo VU meters. I am presently running them in 'mono/bridged' mode. In this way the amp is putting out 1000 watts.

They have VU meters that have two scales. One that reads wattage and one that reads db. 0db = 375watts with 3db overhead that = 750 watts. While in stereo mode the meters read wattage as expected.
But now that I have only one channel of the pre amp running into both channels of the amp (with a weird speaker connection on the amp) how should I read the meters now?
they both bounce...
Do I add them together to 'read' wattage?

Should I just throw the 'wattage' reading out the door and just read the db part of the meter? (0db = max output= 1000w)

Halpz!
 
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I always wondered about the accuracy because depending on speaker efficiency db's will be different. Also they don't change even if no speaker is hooked up. I just like the meters in my amp for the cool factor and not a practical measurement of power.
 
ya' it ends up being 'relative' more than accurate. I was just wondering how an amp that is running in bridged mode/mono changes the two meters. 0 is about max (relative) output.
I have one amp running the right channel but both meters are bouncing away. Do I ignore one meter...add them...?

Just wondering.
 
They are really only eye candy. They are not an accurate reflection of how much power you're using.
 
Tim64 wrote: "I always wondered about the accuracy because depending on speaker efficiency db's will be different."

They're not dB SPL, so speaker efficiency doesn't enter into the equation.
https://en.wikipedia.org/wiki/VU_meter
https://en.wikipedia.org/wiki/Decibel see Acoustics and Audio Electronics sections.

If I had to guess, I would guess they're reading db relative to rated power output into rated impedance... in stereo.
In bridged mono, see the manual?

Chip
 
Depends where in the pre/amp circuit they are connected.
They are probably D'Arsonval movements shunted to calibrate for voltage.
 
I think digital watt meters are probably accurate aren't they? I mean how hard is it to measure how many watts is going out?
 
If one really wants to know about VU meters, Crown has written about them in the manual for the OC-150a, Output Control center, a 3-amp metering device that will switch speakers and headphones and such, too.

http://www.crownaudio.com/media/pdf/legacy/OC150AManual.pdf is the link to download the manual and the metering discussion starts on page 16 of the pdf, page 12 of the manual (if it is the same manual I dl'ed a while ago). It is a technical discussion as it is a technical topic but it gives the answers to questions folks haven't even asked about the VU meters that Joe calls eye candy. Most are, some are not. It is up to the user to determine the value of the information from a metering system. Knowledge of the intent by the manufacturer, eye candy or a visual tool is necessary for this evaluation. Crown made their unit as a tool for those that are informed enough to use it.
 
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Thanks Blue Shadow for the link. a little over my head...tho' I did catch the gist of it.

Carver's manual doesn't state what, if any, changes are made to the meters nor how to read them in bridged mode. (or if it does I'm missing it)
Carver's meters have two scales as mentioned above. One in db and one in watts - assumes 8 ohm load. I understand that it is relative average output and not actual based on the meter's ballistics.

I may never know (it doesn't really matter to be honest), just how to read them in mono state.
Thank everyone! I'll chase this down trying a different avenue. Maybe I can take it in to my tech and see if he can tell what's happening.
 
They're also just a simple voltage meter circuit. One that is properly calibrated is typically done to get a specific output voltage on the speaker terminals at a single frequency, with the assumption of a specific speaker impedance. Since speakers are rarely that precise impedance, and the impedance swings with frequency, basically they aren't accurate except under particular conditions on the workbench. My Phase Linear 700 does the setup to be accurate at 350 watts into an 8 ohm load at I think 1 khz. Outside of that, its just blinky lights. I do seem to remember testing it at various other output voltages and it tracks pretty well, but I never bothered to check frequency response on the meter.
 
soulsurfing said:
One that reads wattage and one that reads db.
Click to expand...
This is generally the most accurate scale as it indicates db below full power output.

Unless your speakers present exactly the load(nearly impossible) that the meters were calibrated with, the "watts" scale is as others have suggested, just eye candy.
 
VU meters are easy to understand. They have little lights in them and bounce around when the music's on.

Any other questions?
 
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