[ablaze]

I'm using the same pair of cans (unamped) to A/B two sources. whats the best way to match the volumes identically? (I don't trust my ears

)

how's this? play the same test tone out of the two sources, and measure the AC voltage out of each source? does the source's output impedance come into play here?

well, short of an SPL meter, whats the best way to match the loudness/volume?

 

[usc goose]

wouldn't you want to measure the wattage for this? but you'd have to have sensitivity ratings you could trust for the headphones/speakers you were testing.

 

[ablaze]

you mean, measure the current instead of AC voltage amplitude?

 

[usc goose]

if i'm not mistaken, i think it's DC that makes sound. and i think you'd have to measure watts which is volts multiplied by amps. (is there a meter that measures watts?)

then again i was a theatre major so i might have no idea what i'm talking about.

 

[Wilson M.]

You want to measure AC voltage out of the headphone jack. Typically you'll want a volt/multimeter that can measure in the < 2 volt range (almost all do, some are user selected and some are auto-ranging).

I would not recommend sticking the probes directly into the headphone jack. You can get a 1/4 plug and wire it up to the probes and that will be a lot safer to put into the jack.

EDIT: Do this while playing the same single frequency test tone.

 

[Dusty Chalk]

Quote:

Originally posted by ablaze I'm using the same pair of cans (unamped) to A/B two sources. whats the best way to match the volumes identically? (I don't trust my ears ) how's this? play the same test tone out of the two sources, and measure the AC voltage out of each source? does the source's output impedance come into play here? well, short of an SPL meter, whats the best way to match the loudness/volume?

I'm guessing you have a multimeter/voltmeter and don't want to spring for an SPL meter?

 

[ablaze]

exactly Dusty!

 

[eric343]

Goose- yes, you don't have any idea what you're talking about

Wilson - Pretty much. Get a 1/4 (or 1/8) inch jack and connect the multimeter's probes to "tip" and "sleeve" (or left and ground, respectively). Set the meter to as low as it goes (usually the 2 or 5 volt scale if it's not autoranging) and play a test tone, recording the voltage level. (this assumes the test tone is playing in both channels at equal volumes) Now plug your plug into the other source (without disconnecting the probes or causing a short circuit) and play the test tone, adjusting the volume knob until the voltage reads the same as the one you wrote down, or as close as you can get it.

Obviously, if one of the sources (or, more accurately I'm guessing, amps) has a stepped attenuator, you want to use that one for the reference voltage and set the one with the non-stepped attenuator to the voltage you got with the stepped attenuator!

Oh, and do this with all filters or crossfeeds OFF

 

[eric343]

Quote:

Originally posted by Dusty Chalk I'm guessing you have a multimeter/voltmeter and don't want to spring for an SPL meter?

An SPL meter would be less accurate than a multimeter if you want to ensure two amps are putting out the exact same volume, provided you're using one set of headphones to compare the two. If you're using two different pairs of headphones, one per amp, then you'll need an SPL meter due to varying sensitivity.

 

[usc goose]

ok, i think i got it now. so music is an AC current that oscillates in the frequency of the music being produced? i think that makes sense to me. i'm not sure what kind of crack i was smoking earlier.

and i guess voltage determines spl because the resistance of the speakers determines amperage from which you can figure out the wattage which is what sensitivity is measured in?

you don't have to explain it right now if you don't want to, you can tell me if i'm getting warmer or colder. i might figure it out eventually.

 

[eric343]

Quote:

Originally posted by usc goose ok, i think i got it now. so music is an AC current that oscillates in the frequency of the music being produced?

Yep, pretty much. The way I think of it is that the position of the driver is controlled by the voltage (not quite accurate- more later) - the higher the voltage difference across the driver, the farther away from the magnet the voice coil is [or if the voltage is negative, the closer the coil is]. So by oscillating the voltage, you oscillate the driver back and forth at that frequency, causing an acoustic wave at that frequency... Quote:

and i guess voltage determines spl because the resistance of the speakers determines amperage from which you can figure out the wattage which is what sensitivity is measured in?

Ehhh, almost. Voltage is always measured as a difference; as in, the electrical difference in potential between the power rail and ground is +15V (that is, the power rail is 15V higher than ground). In order to create a given voltage difference across a driver, you have to supply enough current that Ohm's Law causes enough of a voltage drop across said driver (voltage drop = current * resistance in ohms). But a driver operates magnetically, so not only does voltage affect how the coil moves, but current does too - more current will also move the driver more. So a power amp might be putting 10V into Speaker A and 20V into speaker B, yet they'll both be putting out the same volume because Speaker A is drawing twice as much current.

However, this assumes that they have the same sensitivity, which is measured in X dB/1W. That is to say, if you put in a 1W signal (1 volt difference across a 1 ohm load, which will draw 1 amp) the speaker will emit an X dB sound (hopefully at the frequency you put into it!). However, a 100dB/1W will get louder with less power than a 75dB/1W speaker will...

Or at least that's as far as I know! I'm sure there's some errors in there somewhere...

 

[usc goose]

the mind boggles. (i'll figure it out eventually)

but thanks

 

[Wilson M.]

Oh goose, you make it all too simple. You seem to like setting yourself up so beautifully for wisecracks.

But I'm practicing restraint and decorum tonight.

 

[ablaze]

ok I don't get it.
alright, I'm comparing two soundcards.
using foobar2k, two instances, each one set to output sound out of a different soundcard (both ASIO)
I've got a 1khz test tone, that I've put to both the players. measured the AC on each channel of card #1, 0.14v. did the same for card #2, adjusted the volume to match 0.14v on both channels.
THEN I listened out of both sources, and one of them is still perceptibly louder than the other! what gives

 

[Chipko]

You must measure them with the load attached, ie your headphones.