Impedance load

Can someone help me make sure I got this correct? I am trying to determine where I should set my gain at on my amp and Ill be using a cd with a sine wave 0 db and 50hz. What im trying to figure out is my impedance load per channel. On my kicker spec sheet it says the input impedance is 22k ohm. Input sensitivity is 150mV-3V- RMS. Now if I bridge the amp dont I have to drop the impedance load down 1/2? So this would mean I want to match 11ohm right? I think I might hve this all wrong. The kicker guy I talked to said I should get the volt out on my deck and match the amp to it. However the JL audio tutorial is telling me something a tad different. Someone please help. If you need any more info let me know and Ill get what I can.

As always Thanks

Ok i think I might have somewhat of a understanding.

 E=(P*R)^.5

I have my subs hooked up at 4 ohm bridged mono to the amp. this means Im producing 360 watts RMS. Roughly.

so (360*2)^.5= 26.8  (each channel seeing a 2 ohm load)          or is it                      (360*4)^.5=37.9     <--- (this is all info i got from a previous post.)

And if this is the correct way to do it then why'd the dude from kicker tell me to check the voltage on my rca's and then match the amp to it. (ex rca's from deck produce 3 volts, so measure what the voltage is from the amp to the speakers and match it to 3 volts. given the head unit is at 3/4 and all filters etc are off.)

Just have fun with it, and when your finally all done, you'll adjust that gain by ear, I promise you that.  I tried the same thing, got some advise that because the speaker has a different ohm resistance to each and every frequency, you would have to know what that resistance is.  I found that 50 Hz came up to the limit of volts really fast, meaning 50 hz plays louder than most of the other freqs.  After setting the volts to the limit at 50 Hz, then testing the voltage while playing regular music, I found it to be quite low.  So I put the DMM away and set it by ear.

stevdart, do you know which one of the three ways i gave is correct? if all three are correct which is the best other than your ear.

look into getting a Fluke Scopemeter... then you can easily check when it begins to clip... use a test disc with a 400 cycle or 1 k test tone and you can actually watch what is happening while you are turning it up..... you'll certainly SEE when it begins to square wave on you....

you can also use Sencore's Power Amplifier Analyzer PA81... although they are kinda pricey as well... ( last one i bought ran me around $3000 CDN )

OK, that amp is rated at 360 watts RMS X 1 into 4-ohms.  So, disconnect your speakers from the amp, set your amplifier gain to minimum, turn up yout head unit to it's maximum output volume before clipping (which you should have already determioned before you begin, and if not try about 75%), play your 50 Hz tone, connect your multimeter set to AC volts (RMS if it has such a setting) to the amplifier output terminals and slowly turn up the gain control until you see no greater than 37.94 volts.  This will be equivalent to 360 watts output into 4-ohms.  Be sure to turn the head unit off before you re-connect your speaker leads.

To check the voltage output on yout RCAs, connect one meter lead to the outer ring of one RCA (red or white it doesn't matter) and the other lead to the inner socket or pin.  Read it on AC volts scale.

The Kicker guy was right in saying that.  He was referring to setting the amp gain to match the deck output.  But here is where it gets a little confusing:  look at the gain control.  Most amps it is a screw that turns clockwise.  All the way to the left, or counterclockwise is thought of as off, or at its lowest point.  You are starting there to begin matching gain to the deck output.

Now here is what is tricky.  The gain at far left is actually for high voltage input.  And the more you turn it clockwise, the gain is matching lower voltage.  So far left is maybe 10 volts, and far right is 1 volt.  If you are matching 2.7 volts, the amp gain screw will be turned clockwise about 3/4 of its travel.  As a contrast, my HU is factory, and I get about a 9 volt signal from it to the amp, so I find that my amp gain is barely moved to under the 1/4 area to match the input.

This BCAE page  explains it really well.

I read the voltage with the speakers hooked up.  Because I thought  the amp won't make voltage without a resistance load.  Read on AC volts at the 200 level.  With a test sine wave,  I got an unwavering reading.

I also read the input voltage of the deck  at the amp speaker terminals, with the amp gain off.  I don't know if this was correct, because the reading was lower than I thought it should be, but I got a volt reading.  Like I said earlier, it was interesting, but then I set it by ear.  Actually, I set the gain more clockwise.

You asked earlier about hearing distortion, or clipping.  When your testing the limit of the HU, listen to the front speakers.  There will be a strong and steady increase of volume as you turn up the dial, but at a certain point you will notice the sound gets fuzzy and the volume doesn't increase at the same rate.  That is the distortion point.  Keep the sub off while you do this.

Then, when your listening at the sub for distortion, unplug the front speakers.  Adjusting the amp gain, you will again get to that point where the sound is dulled, not crisp, somewhat fuzzy.  That's that point again.

1.  Are your front speakers running off the head or off an amp?  If off your haed and you can only go to half and you get "mad distortion" it's bacause you have a crappy head unit.  If off an amp, then ITS gain is set wrong too.

2.  Does the sub amp work?  You should be able to read the voltage output with speakers connected or not.  (The amp will make voltas with no load, just no current.)  Is the amp turning on?  Is it getting a signal from your head?

3.  Set your meter to AC volts and stick the leads into an outlet in your house.  If it doesn't read 115 to 120 volts, then your meter is broken or you are not using it correctly.

1. My front speakers are hooked to another amp. That amp is not tuned correctly. However I turned the hi/low pass back on and I could reach 3/4 easily.

2. I will double check all of these but yesterday everything was working fine.

3. I checked the meter on my battery and got 12.5 constant.

1.  Start with this amp and set the gain correctly, or disconnect it until you do unless you want to blow your main speakers.  What is the highpass setting you are using for your mains?

2.  OK

3.  Make sure you are not trying to read the voltage output from your amp in the DC volts scale (which is what is required to read the battery.)  Audio is AC voltage.

1. The amp powering my mids highs is behind my 200 pound box, I was going to wait and tune this one after I got in the brown bread.

2. OK

3. Poo, I was trying to read off DCV. I thought since I was getting the power from the battery It would be direct current? Something inside the amp makes it switch?

Hey Dyohn.

I went out and gave it a shot, and whatya know I can read the voltage. I set my meter to 200 on the acv, and my reading would go to about 5.0. Now 200 is my lowest setting. I am guessing that because I am showing single digits is b/c I am seeting the meter at 200. If I were to have and set it at 20 would it say 50.0 or what Im reaching for.. 37.94?

Ok, here it is guys. After talking with a tech guy from kicker for a good 15 minutes I decided this. I will set the gains by ear!!!! YAH!!! What I learned from all this was simple. Screw that damn DVM. Heres what I did. I put in a CD that I know pretty well and set my gain like I have been doing for the last 6 years. After I set amp A to where I like it I put in the test cd, checked the voltage, and then unplugged A and plugged in B. With the test CD still rollin, I ckecked the voltage on amp B and set thatto the same voltage as amp A. turned everything off, made sure both amps were plugged in and off she went booming like an elephant giving birth to quadruplets. (thats sposed to signify loudness :) The delima I had during this today was the fact that without me noticing UNTIL today one of the subs wasnt even hooked up. This in itself was for one stupid on my part and for two a great help in gaining more SPL. DUH!!! In any case I will never try and set an amp with a meter again. Possibly with an Ossiliscope, that is if im lucky enough to find someone who has one who wouldnt mind me playing with it. Another thing I learned behind all of this is that if i were to tune the amp to the frequency of 50hz blah blah blah then my amp would only be tuned to that specific freq. Apparently amps produce differant voltage when they play different tunes or freq's. Now I dont know a whole lot about this, but if you want to know more call kickers tech line and ask for... well I better not say his name.

Stevdart, you were correct that I would resort back to my ears.

DYohn, perhaps there is a way to set the gain correctly the way you explained it, but for my purpose and lack of patience I didnt. In fact Im sure there is a way to do it that way, why else would JL say to do it that way, and many others... ya know. In any case it isnt the way for me. I am glad I went through the trials and triulations.... I got to learn a lil bit which is what makes it all worth it. I dont know what I would do if I didnt have this forum and you guys to help me out.

haemphyst, thanks man. I would like to know what you mean about the input impedance on my amp will never change. You mean the input I am getting from the deck?

As long as you're hapy and your amps aren't clipping, then cool.  Enjoy your system.

What haemphyst means about input impedence is it is determined by the electrical characteristics of the input stage on your amplifier and it is fixed.  You can't adjust it.  It is also not somethng you need to worry about in most consumer equipment.  When you mentioned this in an earlier post, it was a red herring and really has nothing to do with the process of setting the gain on an amp.