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setting gains?


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fix-8x 
Member - Posts: 18
Member spacespace
Joined: June 22, 2006
Location: Canada
Posted: October 25, 2007 at 7:21 PM / IP Logged  
I was just wondering if, when setting gains, say you use the ear method but just wanted to double check using a DMM, how are you suppose to use a load and disconnect the speaker? The reason I ask this is because I am confused when I hear - use 4 ohms in the formula sq rt of (p * r) but then DMM the amp with the speaker disconnected to find AC. Won't it always measure different depending on the load? What does your meter use as resistance to come up with this measurement if I disconnect the speaker? Do I not have to have my meter simulating a 4 or 2 ohm load or measure a resistor of the same load to set the gain at the true AC I need when i hook the speakers up? Oh and if someone is going to answer that, also if nominal impedance is the average working resistance of a speaker what is the lowest it can ever go? Can it ever hit 0.0 Ohms? Even for a split second? And... if it does is it automatically pooched?
I've finally turned my obsession into my profession
mcdonald2000 
Member - Posts: 10
Member spacespace
Joined: August 09, 2005
Location: United States
Posted: October 26, 2007 at 3:44 AM / IP Logged  

Ha ha! Im not even trying to go there! I have never tried to use my meter for setting gains. All I have ever done is either ask the customer what is the highest volume they think they will go to, and once I have that info, i can find out if the deck is clipping at that level or not, and then adjust the amp according to sound and clarity. I have noticed that some people like distortion, and some don't. If I am installing on a customers car, I just tell them how quickly they will blow their speakers if they like to distort them, and if they don't want to keep buying new speakers to either turn the volume down a little bit, or spend more money and get a bigger amp. Usually (just my rule of thumb) if the gain has to go more than half way, you need to upgrade something. Maybe more preout voltage from the source unit, maybe a bigger amp, maybe better speakers, or a better box, maybe better wire..etc... Never try to get more for less when it comes to sound, usually you end up with a headache. :o)

Now if your meter ever reads o.oo ohm on a speaker, that speaker is DONE!!!!! Or, you have the meter on the wrong setting lol  By the way, I am sorry that I didn't answer that DMM question, truth is, I don't have a clue how to do it, but I have been installing for 14yrs, 11 in a shop, and Im not afraid to say if you find out how to do it with a meter, please tell me! Thanks!

p.s. When I say "do it with a meter" I mean set gains with a meter, I realize some of the folks on here were going to have a field day with that one!

1 ohm
fix-8x 
Member - Posts: 18
Member spacespace
Joined: June 22, 2006
Location: Canada
Posted: October 26, 2007 at 7:32 AM / IP Logged  

I already know how to set the gain by ear with no distortion.  If the gain is more than halfway oh well maybe you're matching up very different components (different companies etc.) it's only to match the level of the head unit .  Of course the speaker would be done at 0 ohms.  No I'm not on the wrong setting, nor did I ever say I was even metering a speaker.  I was asking if you could ever see this during speaker movement?

I've finally turned my obsession into my profession
haemphyst 
Platinum - Posts: 5,054
Platinum spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: January 19, 2003
Location: Michigan, Bouvet Island
Posted: October 26, 2007 at 11:41 AM / IP Logged  
mcdonald2000 wrote:
Ha ha! Im not even trying to go there! I have never tried to use my meter for setting gains. All I have ever done is either ask the customer what is the highest volume they think they will go to, and once I have that info, i can find out if the deck is clipping at that level or not, and then adjust the amp according to sound and clarity. I have noticed that some people like distortion, and some don't. If I am installing on a customers car, I just tell them how quickly they will blow their speakers if they like to distort them, and if they don't want to keep buying new speakers to either turn the volume down a little bit, or spend more money and get a bigger amp. Usually (just my rule of thumb) if the gain has to go more than half way, you need to upgrade something. Maybe more preout voltage from the source unit, maybe a bigger amp, maybe better speakers, or a better box, maybe better wire..etc... Never try to get more for less when it comes to sound, usually you end up with a headache. :o)
First off, I'd like YOU to install my next stereo... (Be sure that you get all off the sarcasm inflected in that statement) I'm really surprised that you haven't had more customers come back... That's the way we used to install at the crap shop I used to work for, then I quit. A respectable installer wouldn't do it that way. There are NO generalizations like "if you have to set it more than half way" or some people like distortion"... Geez, man. I think you need some more book-learnin' time, but that's just me.
mcdonald2000 wrote:
Now if your meter ever reads o.oo ohm on a speaker, that speaker is DONE!!!!! Or, you have the meter on the wrong setting lol  By the way, I am sorry that I didn't answer that DMM question, truth is, I don't have a clue how to do it, but I have been installing for 14yrs, 11 in a shop, and Im not afraid to say if you find out how to do it with a meter, please tell me! Thanks!
You should GET a clue, because it CAN be a helpful skill to have... You set your volt meter to AC volts, and measure the outputs... Wow. Tough.
mcdonald2000 wrote:
p.s. When I say "do it with a meter" I mean set gains with a meter, I realize some of the folks on here were going to have a field day with that one!
Yeah... not really... just you...
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."
DYohn 
Moderator - Posts: 10,741
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: October 26, 2007 at 11:51 AM / IP Logged  

fix-8x wrote:
I was just wondering if, when setting gains, say you use the ear method but just wanted to double check using a DMM, how are you suppose to use a load and disconnect the speaker? The reason I ask this is because I am confused when I hear - use 4 ohms in the formula sq rt of (p * r) but then DMM the amp with the speaker disconnected to find AC. Won't it always measure different depending on the load? What does your meter use as resistance to come up with this measurement if I disconnect the speaker? Do I not have to have my meter simulating a 4 or 2 ohm load or measure a resistor of the same load to set the gain at the true AC I need when i hook the speakers up? Oh and if someone is going to answer that, also if nominal impedance is the average working resistance of a speaker what is the lowest it can ever go? Can it ever hit 0.0 Ohms? Even for a split second? And... if it does is it automatically pooched?

Gain is set with speakers disconnected.

Calculate the voltage output for the speaker load you will use (the nominal rating of the speaker) using Ohm's Law
Amplifier output is AC
A speaker's impedance will fluctuate with input signal frequency but no, it will never drop to zero ohms.  You cannot read impedance with a standard ohm meter.

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DYohn 
Moderator - Posts: 10,741
Moderator spaceThis member has made a donation to the12volt.com. Click here for more info.spaceThis member has been recognized as an authority in Electrical Theory. Click here for more info.spaceThis member has been recognized as an authority in Mobile Audio and Video. Click here for more info.spacespace
Joined: April 22, 2003
Location: Arizona, United States
Posted: October 26, 2007 at 11:53 AM / IP Logged  
mcdonald2000, if you worked for me you'd now be unemployed.
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fix-8x 
Member - Posts: 18
Member spacespace
Joined: June 22, 2006
Location: Canada
Posted: November 02, 2007 at 12:02 PM / IP Logged  

Thank you very much DYohn.

 
I've finally turned my obsession into my profession

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