GCONS, LC2i Installation & ZX1000.1 Gain Settings

[SnapperKing 6]

I'm in the process of adding a pair of 12" GCONS to the stock Fender stereo system in my 2012 Volkswagen GLI. The subs will be in a sealed enclosure from DC Creations are going to be powered by a Kicker ZX1000.1 (1298w rms according to birth sheet) controlled through the LC2i. I have 2 questions about some adjustments I'm unsure of

1) When setting the gains using the DMM method to obtain the corresponding output voltage for the amp's rated capacity (1000W RMS) - I need the most clean power I can get from this amp. Should I be using 1298w as stated on the birth-sheet to come up with the voltage number I'm looking for? or should I be using 1000W as rated.

2) With the LC2i - can I run this turned all the way up, and simply control the bass through the remote bass control knob? The reason I ask is because I can't really hear any significant bass roll-off at high volumes.

I do NOT want to leave any performance on the table when setting everything up.

Any help is appreciated

Snapper

[95Honda 486]

#1 you cannot set the gain for output level using a DMM and mesuring voltage because you have no idea what the impedance is...

#2 I have an LC2i but haven't installed it yet. What part are you talking about "All the way up"? There are several controls on it... I also know the manul for it is "lacking" to say the least... I would always caution setting devices like this to "maximum" without at least a little experimentation first...

[SnapperKing 6]

#1) "Gain Setting Equation

Voltage of the output = sqrt(RMS Power X impedance of the speaker)

• 
  Example
  Say the amp provides 100WRMS into a 4 ohm speaker:
  Voltage = sqrt(100W X 4 ohms)
  Voltage = sqrt(400W*ohms)
  Voltage = 20V
  Again, that was only an example, use the ratings of your amp to figure that out.
  

Setting the Gain(s)

To set the gain(s), you need two things:

• 
  1. A DMM (digital multi-meter) that is capable of measuring AC voltage (needs to be able to measure up to a range of 200V).
  2. A test tone CD to use to set the gains at the correct setting.
  

Now, to set the gain(s):

4. Take the leads from the DMM and but them on the outputs from the amp.

5. Set the gain so that the outputs of the amplifier equal the voltage you found above. This is a MUST."

#2 - The manual says, "for ground shaking bass" turn the master down, turn the small one almost all the way up, and then bring the master back up." I don't have the product right infront of me at the moment so sorry for not knowing the exact names of the adjustments... But since you have one, you should know exactly what I'm talking about.

SNAPPER

Edited June 29, 2012 by SnapperKing

[AgentTyler 5]

Doesn't impedance change after box rise? So you would really never know what the sub is getting.

[Impious 1,476]

Doesn't impedance change after box rise? So you would really never know what the sub is getting.

Impedance changes based on frequency, enclosure, temperature of the voice coil, etc etc.

But the goal of the DMM method isn't to set the gain based on the impedance of your subwoofer. What you are attempting to accomplish with the DMM method is setting the gain based on the output voltage of the amplifier at a known power output at a known impedance, namely the impedance the amplifier's output power was rated at.

If the amplifier is rated 100 @ 4ohm and you are attempting to set the gain....in theory it doesn't matter if your subwoofer is 4ohm, 3ohm, 2ohm, 1.3ohm, 3.6ohm, etc. What you need to know is what rail voltage the amplifier should be operating at, and adjusting the gain control of the amplifier to achieve that rail voltage. Ideally the output voltage of the amplifier would actually be independent of impedance. If the amplifier is rated at 100w @ 4ohm, that means the amplifier is capable of operating with a 20v rail voltage. In a perfect world, this voltage (20V) would remain the same no matter what impedance load was connected to the other side. The actual power output would depend on the load, as that determines the current output and ultimately the power output, but the rail voltage itself wouldn't change. So, in a perfect world, all we need to know is where the output voltage of the amplifier should be, and we determine this based on the rated power (which is a specific power output into a specific impedance load) and not what the impedance of the load is that is actually being connected.

In practice it does matter as there are some design features and losses that occur within an amplifier that affect it's ability to maintain that rail voltage at higher power/higher current output situations. In many amplifiers the output voltage will decrease as impedance decreases, which decreases it's power output (normally due to current output constraints, power supply constraints, etc etc). But, again, we can use the rated power to approximate where the rail voltage should be for the approximate nominal impedance of the load we are connecting. It won't be perfect, but it doesn't need to be as small differences won't be noticeable in either direction.

Another issue is where rated power falls in relation to actual power output. The amp might be capable of more or less power than it's actually rated for into the specific impedance it was rated at. In all but the most extreme circumstances they will be different but not by an excessively large amount. That means the voltage setting could be a little high or a little low....but again, small differences won't matter.

The larger issue for me is the level of the test tone. If you use a 0db test tone (which most people use/recommend), 90% of people will end up unhappy with the result and think the need to buy a more powerful amplifier. Since music hardly spends any time at 0db, you will have a very low average power output from the amplifier. With a -6db or -10db test tone (depending on circumstances), the DMM method is good enough to get the gain set to a level that is relatively safe and leave most people happy.

The problem is, you could probably do just as well by setting it by ear....so why bother? There are other issues as well that overall just make setting the gain by ear the easiest and best solution a majority of the time.

[95Honda 486]

#1) "Gain Setting Equation

Voltage of the output = sqrt(RMS Power X impedance of the speaker)

Example
Say the amp provides 100WRMS into a 4 ohm speaker:
Voltage = sqrt(100W X 4 ohms)
Voltage = sqrt(400W*ohms)
Voltage = 20V
Again, that was only an example, use the ratings of your amp to figure that out.

Setting the Gain(s)

To set the gain(s), you need two things:

1. A DMM (digital multi-meter) that is capable of measuring AC voltage (needs to be able to measure up to a range of 200V).
2. A test tone CD to use to set the gains at the correct setting.

Now, to set the gain(s):

4. Take the leads from the DMM and but them on the outputs from the amp.

5. Set the gain so that the outputs of the amplifier equal the voltage you found above. This is a MUST."

#2 - The manual says, "for ground shaking bass" turn the master down, turn the small one almost all the way up, and then bring the master back up." I don't have the product right infront of me at the moment so sorry for not knowing the exact names of the adjustments... But since you have one, you should know exactly what I'm talking about.

SNAPPER

This doesn't work. At all.

[SnapperKing 6]

I understand that the voltage method is dependent on the rated wattage output @ final impedance of the subwoofer(s) (e.g. I will be running the ZX1000.1 to 2) Dual 2 ohm subwoofers wired for a final impedance of 2ohms. the amp puts out 1000W @ 2 ohms so thats the wattage number I will use.)

I took those steps from the pinned thread below which everyone seemed to think was a great "how-to-set-your-amplifier-gain".

If "this doesn't work. At all." Maybe the other thread needs to be unpinned.

[///M5 2,833]

Unpinned. Originally was posted due to a huge amount of misinformation explaining how to do it poorly. While its a bad idea, it's even worse if you do it wrong.

Seriously need to think about your goals before setting gains. It is related.

[95Honda 486]

Look at this impedance plot. It is actully a pretty flat one, and is probably smoother than what you have. If you look carefully, you only see 2 ohms at roughly 20Hz and 35Hz. Everywhere else it isn't even close to 2 ohms... This is why it is impossible to set a gain threshold with a voltmeter into a reactive load. Anyone who says otherwise is full of crap...

[SnapperKing 6]

Wow, I've never seen that before. Good info thanks

Hypothetically speaking here... If your lowest total impedance is 2ohms at 20Hz and 35Hz, and is greater than 2 ohms at all other frequencies within the range of the graph. Setting your amp output voltage for the lowest subwoofer impedance (~2 Ohms in this case) would actually be conservative assuming that the output of the amplifier decreases with increasing resistance. Wouldn't I expect to see less distortion/clipping at the higher resistances (as a result of the decreased power output)?

I could see a problem if you set your amplifier using a voltmeter at one of the higher resistances and then you hit 20HZ or 35HZ, impedance drops down to 2 ohms and the power output/distortion spikes. Not the other way around.

Just thinking out-loud.. my logic is probably incorrect.

[95Honda 486]

Clipping will happen when you reach the voltage threshold of the amp, not the power threshold (assuming it can supply the needed current to keep the voltage up). What this means is, you could run a 500 watt amplifier into hard clipping while producing less than 500 watts if the impedance is relitively higher than the power rating load impednace. This happens all the time...

The whole point here is, what is the reason to set something very precisely when the results are meaningless?... You spend all day with a voltmeter measuring down to a mv, but as soon as the impednace changes (additionally, you have no idea what it is) everything you have done is for nothing...

Also, clipping doesn't hurt a thing. Too much power does. I wouldn't worry about clipping at all, I would worry about potentially sending too much power to my subwoofers and causing thermal failure...