Setting gains w/ a multimeter

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Thuan

Copper - Posts: 88

Joined: May 20, 2004

Location: United States

Posted: November 13, 2004 at 5:07 AM / IP Logged

I'm having some problems setting my gains with my multimeter. I've already played around with my gain setting by ear but I wanted something of better accuracy so I purchased a multimeter.

I disconnected my speaker wires for my subwoofer from the terminal...popped in a test cd for 50hz...turned the HU's volume to 3/4 of max...hooked up the multimeter to the speaker output and got a reading of 44.8v on the multimeter. 44.8 didn't seem right because my amp should only put out 400rms@2ohms (28.28v). When I change the track to an 80hz track I recorded the reading on the multimeter drops to 14v...at a 100hz track the reading on my multimeter is at like 6 or 7v...is there a certain frequency I MUST use to set gains with a multimeter? If yes, then what would the recommended frequency be? (If I turn my gain down to match 28.28v with the 50hz track I recorded I can barely even hear my subwoofer...even though the HU is at 3/4 of its max).

My amp (Soundstream VGA800.5) is "suppose" to put out 400x1@2ohms..I'm running my JL12w6v2 in parallel which would give me a 2ohm load. So what I did was take my amps rms which is 400 and multiplied it by my subwoofers impedance which is 2ohms...that would give me 800, I then took the square root of 800 to determine the voltage I would try to dial everything in at (which is 28.28v).

I felt that my subwoofer was underpowered so I went out and purchased the multimeter hoping it would help me diagnose my problem. Originally I thought my low power problem was due to a bad voice coil within my subwoofer..but I already tested the resistance for both voice coils and they both read a steady 1.9ohms. It's weird because when I play a 100hz track I have to turn the gain all the way to the max and the reading on the multimeter is only 24v. What am I doing wrong here? Please help...this is getting crazy.

Thuan

stevdart

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Joined: January 24, 2004

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Posted: November 13, 2004 at 7:38 AM / IP Logged

You should have only a slight variation between the different frequencies. I suspect your recorded tracks aren't at an equal level. 50 Hz should be about the highest voltage, but just slightly. Did you record the frequencies using the same source and all set at 0 db reference? Does one sound louder than any of the others when you play the tones?

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Thuan

Copper - Posts: 88

Joined: May 20, 2004

Location: United States

Posted: November 13, 2004 at 3:52 PM / IP Logged

I recorded the tracks at 0db like you recommended me to do using frequency generator 2.6. The 50hz track definitely sounds louder...but I figured that's because it's a lower frequency.

Thuan

stevdart

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Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: November 13, 2004 at 4:24 PM / IP Logged

You should run off another CD if you still have the program available. The db level shouldn't be noticeable, although there is a slight difference in output voltage with the 50 Hz. You recorded sine waves into .wav files, right?

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

chevyman26

Copper - Posts: 227

Joined: April 14, 2004

Location: United States

Posted: November 13, 2004 at 7:02 PM / IP Logged

Just a shot in the dark, maybe it doesn't even work like this, but is there still a crossover on that's cutting off those frequencies?

You'd better get me out of this lord... or else you'll have me to deal with. -- Hunter S. Thompson "F.A.L.I.L.V."

Lizardking

Copper - Posts: 184

Joined: August 23, 2004

Posted: November 13, 2004 at 7:07 PM / IP Logged

I did mine this way and you have to set the crossovers to full range so you don't cut the frequency by accident. If you recorded the 50hz tone that's all that will play and the same using a 1000hz tone for the highs.

Thuan

Copper - Posts: 88

Joined: May 20, 2004

Location: United States

Posted: November 14, 2004 at 5:15 PM / IP Logged

Yes, I recorded and saved the files as .wav.

I turned off the xover on my HU and just used the one on my amp.

I don't think the frequencies are being cut off....I still hear it but the voltage readings on my multimeter isn't stable with different frequencies.

Thanks.

Thuan

haemphyst

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: November 14, 2004 at 6:09 PM / IP Logged

AND, unless you purchased a "TRUE RMS" volt meter, you WILL read different voltages at different frequencies, evn though your RMS voltage might be the same frequency after frequency...

Also, how do you know all of the levels were recorded to the CD at the same amplitude? For a GOOD reference and test CD, with known good calibrations, and absolute zero recording levels, check out the Stereophile Test CDs here...

PCs are NOT good sources to record from unless you have a software that you KNOW can be held reliable. As for the software you were using to record your test tones, is it saving them as true uncompressed WAV/PCM, or is it saving them as MP3, and then those files get converted back to WAV in the burning process?

All of these can have an effect on your absolute accuracy. One last thought... are your tone controls set to flat, with the loudness contour (button) OFF?

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Thuan

Copper - Posts: 88

Joined: May 20, 2004

Location: United States

Posted: November 14, 2004 at 6:41 PM / IP Logged

The different voltages I'm getting is any from 6v @ 100hz and 44v @ 50hz....what's a true RMS meter?

Well I don't know for sure but I just used Frequency Generator 2.6 to make my frequency test cd....so this isn't a good program?

It's saving them in wav format and burning them as a wav file

Yes, I set everything on my HU to flat and I dont use the loudness button.

I'm not looking for dead on accuracy....I'm just looking to get close.

How should I set these settings with this program (frequency generator 2.6):

Carrier - 1 to 1000

Fine tune - 950 to 1050

Amplitude - 0 to 16384

AM/FM/PM?

11./22./44.1 khz?

I set the program to record a 50hz track and it shows -6.56db....how do I change it to 0db? Do I need to change it to 0db?

Thuan

stevdart

Platinum - Posts: 5,816

Joined: January 24, 2004

Location: Pennsylvania, United States

Posted: November 14, 2004 at 9:25 PM / IP Logged

Haemphyst, check out the Frequency Generator 2.6 Demo trial version, good free for 14 days.......it's pretty good for the average person. After the 2 weeks, your computer won't open it anymore, so you have to get your fill or pay 49 bucks.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

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