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Gain Setting With DMM

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pofke13lt 
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Posted: January 29, 2007 at 5:58 PM / IP Logged  
I have two Kenwoo 9102d mono amps and two Kicker L7 15" subs that will each be running at 2ohms for 850watts rms a piece.
According to the gain formula my voltage should be at about 41 volts.. But when I plug in my AC Voltmeter to my speaker terminals the voltage is reading very low.. like I have to put the gain all the way to max for it to read somewhere around 20sum volts.. Only if I raise up the bass boost [to nearly full] does it change the voltage to around 41 volts..
What am I doing wrong? I really need to finish this install tonight! And i dont think i can set the gains by ear because the subs are not in seperate chambers in my ported box, so i think that would interfere..
aznboi3644 
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Posted: January 29, 2007 at 6:31 PM / IP Logged  
What is your deck volume and sub level set at???
pofke13lt 
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Posted: January 31, 2007 at 11:09 AM / IP Logged  
aznboi3644 wrote:
What is your deck volume and sub level set at???
Volume was set at 18 on my Alpine 9813.. Thats a few clicks before distortion.. The sub level was set to max, but the numbers on the DMM didnt get higher than 23v until I turned on MX [media expander] which is like the decks Bass boost.. Then I was able to adjust the gain and bass boost on the amp to reach 41volts, but the gain had to be on Max and the bass boot past 3/4 way up... So i was like hell no im not plugging in my new speakers with those settings.. So i turned down the gain and boost till I was at 25v [assuming that I was misusing my DMM so i used a lower number] and left it like that.. Its ridiculously loud and sound good, but i would still like to know what i was doing wrong.
lamikela1 
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Posted: January 31, 2007 at 11:49 AM / IP Logged  
What are you using as a source signal?  50hz 0db?  1000hz 0db?  Also, the volume should be 3/4 of full volume to set this up.  Everything else should be flat, no boost or cut.  Where is 18 on your volume scale?
stevdart 
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Posted: January 31, 2007 at 12:10 PM / IP Logged  

3/4 volume is not a hard and fast rule...but pofke13lt, you will need to be a lot more precise in where you set the deck level in order to get highest signal strength.  If you're not using test tones, do so and get the deck level just bare-ly below the advent of clipping.  Those "few clicks" you have it set below the perceived distortion range could very well be a difference of 2 or 3 times as much output voltage.

I still like using the hearing methods for finding gain settings, for the very reasons you are experiencing here.  If you find those levels by listening to the sine wave test tones, and then double-check with the DMM, you will no doubt achieve more accuracy.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
pofke13lt 
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Posted: January 31, 2007 at 8:39 PM / IP Logged  
lamikela1 wrote:
What are you using as a source signal? 50hz 0db? 1000hz 0db? Also, the volume should be 3/4 of full volume to set this up. Everything else should be flat, no boost or cut. Where is 18 on your volume scale?
50hz tone.. I read that you need the eq flat, but bass all the way up on some tutorials. Anyways, I think i have the DMM on the wrong setting or somethin..
lamikela1 
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Posted: February 01, 2007 at 3:06 PM / IP Logged  
50 hz is good for setting up the subs.  You should start with the volume about 3/4 up, the input sens on the amp should be all the way down to start.  Connect your test leads and increase the input sens until you get the proper voltage.  Be sure that the filtering on your amp is not attenuating the signal.  To be sure you should just defeat all filtering while setting up the amp.  The DMM only needs to be properly calibrated and set to the proper range.  If it will read 120vac properly then it's good.
lamikela1 
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Posted: February 01, 2007 at 3:27 PM / IP Logged  

I should have also mentioned that not all test tones are set to 0db.  The ones that are posted on this site are set at -12db.  If you use that one you may not be able to get the voltage set high enough.  If you do use a 0db tone, setting your HU gain at 3/4 will limit you to not going any higher than 3/4 volume.  If you use a test tone that's lower than 0db then you will need to turn the volume up higher to get the same  voltage setting but when you play any material that is recorded at a higher level you may damage your speakers or amps if you are not careful.

I personally think it's better to set up at 0db as that's the safest method.  There is not much if any material that will be recorded above that level as it will cause distortion in most cases.

That's just my opinion.  Please don't anyone jump on me for that!  I am open to other's opinions as well.

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pofke13lt 
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Posted: February 02, 2007 at 4:59 PM / IP Logged  
I looked at what my max volume is on the radio and its 36.. I never listen to it past 18 or 20 because it sounds like its distored.. But if i did the 3/4 thing shouldnt my volume be set at 27? Wouldnt it totally mess up my door speakers and stuff having it this loud?? or do i disconnect them?
aznboi3644 
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Posted: February 02, 2007 at 6:43 PM / IP Logged  
do you have any high pass filters for your speakers??? if not than you should.

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