Problem Setting Gain "properly" Using DMM

[boogiem0nst3r]

Setup:

Jl 500/1 (crossed at 80hz 12db, eq off, bass boost off)

w/ Phoenix GOLD RSD12D (wired at 2ohm)


Phoenix GOld RSD 300.4

Crossed at "approximately" 60-70hz
Boost off.
HP Selected.

w/ Phoenix Gold RSD65c's (amp is bridged)

HU: Alpine CDA 9856 (all eq off, bass 0, trebble 0, volume at 25/35)

Test Tones used: 50hz, 1KHz.

So I tried setting the gain using the DMM method, only once the gains are "properly" set using my DMM, the output is VERY "low"

By low, I mean with the subwoofer I can barely hear it inside the car, and with the components they aren't even "louder" then stock.

and before with my stock speakers i was running it off headunit power only.

By "low" output, I mean if I were to turn it up to a level where its audible (and without distortion) it is much more drastic then how much its set to.

THe proper gain for both amps (assuming I did it right) is the gain is almost down to 0. WIth it set using my ears, its more up to like 2/3 ways up.

What am I doing wrong?

-Vinh

[stipud]

First and foremost... in North America, unless you have a True RMS voltmeter, you absolutely must use a 60Hz test tone, otherwise you will not get a proper voltage reading.

JL Amp... since it makes the same power from 1.5-4 ohms, you have to calculate it as if it was a 4 ohm load. So... sqrt(500*4) = 44.72v. You could probably go a bit higher as well. You might want to increase your crossover to ensure you are not cutting 60Hz down at all.

RSD300.4... aim for about sqrt(75*4) = 17.3v out of one channel. Since you have it crossed over above 60Hz, you will have to lower the crossover in order for the 60Hz test tone to register properly. Once the gains are set you can raise it back up to where it was before.

[boogiem0nst3r]

First and foremost... in North America, unless you have a True RMS voltmeter, you absolutely must use a 60Hz test tone, otherwise you will not get a proper voltage reading.

JL Amp... since it makes the same power from 1.5-4 ohms, you have to calculate it as if it was a 4 ohm load. So... sqrt(500*4) = 44.72v. You could probably go a bit higher as well. You might want to increase your crossover to ensure you are not cutting 60Hz down at all.

RSD300.4... aim for about sqrt(75*4) = 17.3v out of one channel. Since you have it crossed over above 60Hz, you will have to lower the crossover in order for the 60Hz test tone to register properly. Once the gains are set you can raise it back up to where it was before.

you're right, at 4ohms it would be 44.7 volts, which is what it says on JL's website to set it at, if the load is 4ohms. However it also specifically states that if the load is 2ohms, i should set it at 31.6volts

But I digress, setting it at these "proper" voltages, using my digital MM, the output is very low...and no im not a basshead...but turning on or off the sub barely shows a difference (i can't hear it over the speakers).

and is there any reason why I should use "60" hz, versus 50 or 1k for mid?

[fuzzysnuggleduck]

and is there any reason why I should use "60" hz, versus 50 or 1k for mid?

Yes!

In North America our (A/C) power runs at 60Hz. Any DMM bought here which is not a "True RMS" meter can only accurately measure A/C voltage if it's oscillating at 60Hz.

[stipud]

you're right, at 4ohms it would be 44.7 volts, which is what it says on JL's website to set it at, if the load is 4ohms. However it also specifically states that if the load is 2ohms, i should set it at 31.6volts

But I digress, setting it at these "proper" voltages, using my digital MM, the output is very low...and no im not a basshead...but turning on or off the sub barely shows a difference (i can't hear it over the speakers).

and is there any reason why I should use "60" hz, versus 50 or 1k for mid?

As I said above... unless you have a True RMS multimeter (very expensive usually), then it will only register an accurate voltage reading at 60Hz in north america. That is because this is the same frequency as our power outlets. A True RMS meter is accurate in a much wider frequency range, rather than being tuned to one specific frequency like cheaper multimeters are.

I would like to see where JL tells you to use 31.6v, because this does not make sense considering how the slash amps work. The gain should be the same regardless of the impedance, and it will scale back power accordingly, when it senses the subwoofer load. I would recommend setting the gains as if it was a 4 ohm load... at 31.6v you are probably only getting 250w on test tones, but on music that will be substantially lower.

You are right though... a gain matched subwoofer is very quiet... it was only a few dB over flat in my car. I only use the DMM gain method for adjusting my components. On the subwoofer, I use an LPL (PG low pass level remote sensitivity knob) and set my gains much higher, so I can remotely control the sensitivity for different music. When done with care and maturity, this works very well. Obviously leaving it cranked at max sensitivity, and then putting in a very bassy album will cause clipping and damage the amp and speakers. So you must turn it down before putting in anything loud, and only turn it up until you reach a suitable volume, well before you start hearing distortion.

I am not sure if JL offers anything like the LPL.

[dwnrodeo]

I agree, the DMM method is great for components. I usually adjust my gains by ear using a dynamic track (on CD not mp3) then check with my DMM and a 60 hz test tone. This will ensure that my L and R channels are set to the exact same voltage and not clipping. With the subwoofer, I set my LPL to just under halfway and adjust using a dynamic track. That way I can increase the LPL for quiet songs and decrease for louder songs. Checking my sub level with the DMM, it was much higher than it should be if I were calculating it using the DMM method, but still not clipping on music. Like Stipud says, just be smart about using the LPL.

[ttocs]

eh, I will keep quiet on this one. Promise.

JL is giving specs to tune them to?

[Eric D]

eh, I will keep quiet on this one. Promise.

JL is giving specs to tune them to?

The JL manual give you a chart of the voltages for your woofer load, and has directions on how to use the DMM to adjust the gain.

[boogiem0nst3r]

i actually followed this tutorial right here,

http://mobile.jlaudio.com/support_pages.php?page_id=143

which gives voltages for the amps at different loads, an what test tones to use.

i've heard numerous poeple tell me about 50hz and using 1khz as well, and it was only right now did i learn anything about using a 60hz, very interesting!

[ttocs]

what kind of meter are you using? One thing that tutorial fails to tell you is that any time you use a meter in a situation where you are fine tuning it that you need to check the meter on a known load to verify that it is working and reading correctly. In this case you could try checking your wall voltage to verify that it shows 120v. It would be better and safer to do it on a smaller load but there is nothing wrong with this method.

Meters(especially cheap ones) readings can drift after time from changes in temp/humidity as well as with the internal battery voltage goes down or when corrosion developes on the leeds. I worked at a high-end semiconductor manf facility for a while as a calibration tech and was responsible for taking meters in 2x a year to have them calibrated. It was suprising to see how much then needed to be adjusted and these were not cheap meters........

Its funny as that tutorial is almost exactly the way I would tell you tune the system by ear with the exception of disconnecting the speaker. That is the way I have been tuning my systems and my customers systems for 10+ yrs.