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[Drew Tronvig]

Actually, shopping around I see that there are pretty cheap analog meters. I was picturing a huge old tube-based volt meter. That's how long it's been since I shopped for purely analog meters. (Of course I'd still like to have the computer-based meter for when I'm looking at digital audio.) So long as an analog meter responds about like the temperature of the voice coil does then that tells me pretty much what I want to know.

Well, if we aren't talking about the absolute maximum amplitude during some ten-thousandth of a second cycle slamming the tweeter against something, then we're pretty much concerned about power that'll significantly raise the temperature of the tweeter coil.

The coil and whatever it's directly attached to have some amount of "thermal mass", so it isn't going to get significantly hotter in a ten-thousandth of a second. It's kind of hard to imagine that the coil temperature will significantly change in less than about a second. So I think that in practical terms we're talking about the waste heat generated at the coil on a time scale of seconds. (It occurs to me that the power of a signal at too high a frequency for the driver to respond to would be the worst, because it'll all translate to waste heat. Hence tweeter coils frying from the very-high-frequency signals generated by a hard-clipping amp.)   

So it seems to me that what we want is a pretty good measure of the power delivered to, say, the tweeter coil on a scale of seconds, which would be about what an analog meter would show. The digital meter would probably miss a lot of the high-frequency AC, while on the other hand reporting a "peak" integrated over too short a time period to be useful The digital info from a good A-to-D converter should be able to catch all the detail, but the typical computer-based meter will just report the maximum sample amplitude and hold that for two-seconds or so. What would be really sweet would be software that would take those samples and integrate the power on the same sort of time scale as an analog meter. Anybody know of software like that? You'd think that in the whole world of digital sound processing there should be some VST plug-in like that.

[Ivan Beaver]

Actually, shopping around I see that there are pretty cheap analog meters. I was picturing a huge old tube-based volt meter. That's how long it's been since I shopped for purely analog meters. (Of course I'd still like to have the computer-based meter for when I'm looking at digital audio.) So long as an analog meter responds about like the temperature of the voice coil does then that tells me pretty much what I want to know.

Not all analog meters are the same-most are accurate around 50-60Hz.  It takes special meters to be accurate at higher freq.

That is why I recommend the HP 400.  It is accurate to well  well above audio freq.

[Tim Perry]

I have never seen a "el cheapo" AC meter that reads peak voltage.  They all have the readout in RMS.  Your standard wall outlet is 120V-but the peak is 170V.  Never seen one read that.

HOWEVER the term "peak" means different things to different people.

You have but you just were not aware.  Most AC meters use a simple rectifier / filter arrangement that do not indicate much difference between  sine waves or any other kind of wave form.

If for example I need to measure accurately the RMS voltage of a tube filament that is being regulated by a triac supply a true RMS meter is called for. I use a Fluke model 177 for this.
These tubes may cost several thousand $  and correct filament voltage is important in extending tube life.

Explanation of true RMS conversion is here http://en.wikipedia.org/wiki/True_RMS_converter

[Drew Tronvig]

So we are talking about huge old tube-based meters, or in the case of the Fluke a fairly pricy precision meter. It would be kind of cool but cumbersome to haul around an HP 400. Is there something more like a compact $50 meter that will catch high audio frequencies, without needing to be quite so precise as the Fluke?

Not all analog meters are the same-most are accurate around 50-60Hz.  It takes special meters to be accurate at higher freq.

That is why I recommend the HP 400.  It is accurate to well  well above audio freq.

[Mac Kerr]

Actually, shopping around I see that there are pretty cheap analog meters. I was picturing a huge old tube-based volt meter. That's how long it's been since I shopped for purely analog meters. (Of course I'd still like to have the computer-based meter for when I'm looking at digital audio.) So long as an analog meter responds about like the temperature of the voice coil does then that tells me pretty much what I want to know.

If you convert the voltages to dBm there is an excellent meter being sold by Pete Erskine on eBay.

Mac

ps I paid $100 for mine.

[Ivan Beaver]

So we are talking about huge old tube-based meters, or in the case of the Fluke a fairly pricy precision meter. It would be kind of cool but cumbersome to haul around an HP 400. Is there something more like a compact $50 meter that will catch high audio frequencies, without needing to be quite so precise as the Fluke?

It is one thing to read a sine wave on a digital meter.  Quite another to read a music type signal.  The meter will not "average to anything close to reality.

That is why I recommend an analog movement meter.  It is MUCH easier to "average by eye" with an analog meter.

The HP 400 is not a tube meter.  Yes it is a good bit larger than an handheld multipmeter- but it reads a lot lower voltages-that can also be helpful-not in loudspeakers-but in signal levels.

[Drew Tronvig]

Looks good, and I'll probably bid on it. And certainly I'd end up converting Volts to dB, so this saves some math.

If you convert the voltages to dBm there is an excellent meter being sold by Pete Erskine on eBay.

Mac

ps I paid $100 for mine.

[Drew Tronvig]

The HP 400 is not a tube meter.  Yes it is a good bit larger than an handheld multipmeter- but it reads a lot lower voltages-that can also be helpful-not in loudspeakers-but in signal levels.

Yeah, I'm lookin' at those. Still a little cumbersome to cart around, but with a reasonable case...

[Tim Perry]

Yeah, I'm lookin' at those. Still a little cumbersome to cart around, but with a reasonable case...

Here's one of mine. used for many years in broadcast and PA repairs / service. the oscillator went flaky so its been shelved for some time. i just checked the voltmeter. been setting a long time but the ni-cad battery's still worked. Had them custom rebuilt in the 90's at a battery place.

The PI set was an ebay purchase.

[Charlie Zureki]

I get Ohm's law when it comes to DC, but I'm a little hazy on exactly what AC voltage means. I understand that the same voltage amplitude at higher frequency would mean a higher AC voltage,

Thanks,
Drew

   Hello,

   The same voltage amplitude at a higher frequency is EQUAL to the same voltage amplitude... changing the frequency does not add voltage...

   Hammer