?? Gain setting question

[thai_creeper 10+ year member]

I finally hooked up the md2 to my 05 L5 12", and I decided to try setting the gains, did the calculations and decided to give it 800 at 2 ohms but I wasn't really liking the output. I took 2 x 800 square rooted and got 40 so I used the DMM and did all of that. I plan on getting a new sub soon, so I thought why not just play with the gains and get the output I want even though I risk blowing the sub. Anyways, when I was satisfied I took out the speaker inputs put the DMM on the amp and I got a reading of 75. I took 75 and squared it and divided by 2 and I got 2812.5, what am I doing wrong? I wanted to work backwards to see how much I was giving the sub at my "satisfied output" setting

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[thai_creeper 10+ year member]

anyone? I'm guessing this is an easy question for the experienced people on here

 

[thai_creeper 10+ year member]

still need help

 

[PollyCranopolis 10+ year member]

The voltage your calculating is for 1 individual channel of the amp. My amp for example: 110w RMS*4@4, used to run 2 comp sets. 4*110=440=sqrt440=20.97 volts. Each seperate channel should be set @ 20.97 volts, providing I'm using the same speaker sets for front and back. If the speaker rms is less than the rms output rating of the amp, you would use the rms rating of the speaker instead of the amp to perform the calculation.

 

[thai_creeper 10+ year member]

The voltage your calculating is for 1 individual channel of the amp. My amp for example: 110w RMS*4@4, used to run 2 comp sets. 4*110=440=sqrt440=20.97 volts. Each seperate channel should be set @ 20.97 volts, providing I'm using the same speaker sets for front and back. If the speaker rms is less than the rms output rating of the amp, you would use the rms rating of the speaker instead of the amp to perform the calculation.

Thanks for the input, but when I play around with the numbers for your example, if I take 20.97 and square it and divide by 4 to go "backwards" I come back to 110 rms, but for the 75 volts I was getting on the DMM I would square and divide by the 2 ohm load and get 2812.5, just wondering why this number is so high when the gain level isn't even at half yet. Yes I know I should set the gains according to the sub rms since it is the lower one in my case but I'm planing on upgrading soon so I just thought I'd play around with the gains. I just wanted to set the gains to the output I wanted and find out how much watts rms I am giving the sub but 2812.5 seems like a rediculously high number..maybe it's my DMM?

 

[helotaxi 5,000+ posts]

Do you have the DMM set for RMS? That sounds like a peak voltage number.

 

[thai_creeper 10+ year member]

Set to ac voltage, is there more than one ac voltage setting? thanks for the help so far

 

[helotaxi 5,000+ posts]

If the DMM isn't a "true RMS" meter, the measurments your are getting are all but worthless. You're getting a peak voltge reading rather than RMS which is what matters. Take your reading and multiply by the inverse of sqrt(2). to get RMS for a sine wave. That gives you 53V. Into a 2 ohm load you get 1400W which is just about right.

 

[thai_creeper 10+ year member]

If the DMM isn't a "true RMS" meter, the measurments your are getting are all but worthless. You're getting a peak voltge reading rather than RMS which is what matters. Take your reading and multiply by the inverse of sqrt(2). to get RMS for a sine wave. That gives you 53V. Into a 2 ohm load you get 1400W which is just about right.

Thanks helotaxi, so if I follow your method I can continue using my DMM right now for gains? Or would it be more accurate using a "true RMS" DMM? If I can just perform a couple extra calculations I won't mind but if buying the other type is more accurate and worth buying I will, what do you think? Also how exactly can I tell if it's a "true RMS" meter, somewhere in the description? I was looking at some online but don't know exactly what to look for

 

[thai_creeper 10+ year member]

bump

 

[thai_creeper 10+ year member]

up for an answer

 

[thai_creeper 10+ year member]

up

 

[helotaxi 5,000+ posts]

It will be labeled as either a "true RMS" meter or will have that listed somewhere in the features list.

 

[thai_creeper 10+ year member]

It will be labeled as either a "true RMS" meter or will have that listed somewhere in the features list.

thanks, i'll try to pick one up

 

[helotaxi 5,000+ posts]

Sears had a pretty good one on sale last time I was there. True RMS on voltage and an AC/DC clamp ammeter as well. That was a month ago so I don't know if it is still on sale or not.