Tuning amp gains with DMM?
 

So after trying to tune in my Rev410's this weekend I figured out really quick I need another way. hey are so loud I don't feel as if I can accurately tell when they are distorting. I've been doing some research on tuning using different frequency sine waves and reading the voltage of the amp output with a digital multi-meter. I think I understand everything, but have a few questions...

For reference the equation is Voltage = square root of watts * ohms.

1) All the reading and videos I've watched talk about doing this method on 2 ohm loads. The Rev410 runs on a 4 ohm load so I'm assuming I need to multiply the amp RMS by 4 instead of 2.

2) I also read that if the amp has 2 gain controls to treat it as 2 separate amps. EX. If the amp is 100W RMS by 4-channels for a total of 400 watts, divide the total RMS by 2 to get your voltage calculations. 400RMS / 2 = 200RMS * 2ohms = gain voltage.

3) So given these scenarios, the Syn4 running a 4 ohm load should calculate as:
400W RMS * 4 = 1600/2 = 800
Square root of 800 = 28.284 VAC at the amp outputs.

4) Another way to think about it is the Syn4 when bridged only uses one gain knob. So do I calculate it like a 2 channel amp then?
400W RMS * 4 = 1600
Square root of 1600 = 40 VAC at the amp outputs.

Is this correct?

My JL iPhone calc says 14.5, I think your 1st attempt is right but you have 2 channels not 1. Bridged each channel outputs 400 watts. I too tried to set my Rev 10's by ear and realized that was not going to work.

I'm not real sure how you got 14.5? I downloaded the JL app and it gave me 40 VAC with the 400W RMS (like when I calculated on paper) and 56.5685 at 800W RMS.

I think to really maximize this type of method you really need an O-scope to see when the sound is clipping. I think that is the method I am going to try this time when I get the new 410s in

Oops, I forgot to clear it out first, that just assures that your amp won't send a signal that it clips if it is making the stated power, if it underrated then your leaving something on the table or if its overrated you could be doing damage, O-scope is best, but kinda spendy if you don't need it but once every few years.

From what I've read, yes the o-scope is the best method, but they are hard to find and expensive. Using the DMM is the "DIT" way to do things. I think if the math is correct it will work just as well. I also plan on listening to the different tones once I have set the gains with a DMM just to make sure they are safe. Just want to make sure the math is right.

A volt meter won't tell you when your clipping. You need a o-scope for that and they have dropped in price quite a bit lately.
But looking at the electronic signal will never tell you when your pushing the driver to it's mechanical limits.
A volt meter is good if you're running multiple identical amps and have tuned one and are looking at matching the other.
Steve mead makes a device that can tell when the audio being played starts clipping. I personally have never used it but beyond a Real Time analyzer thats the only way you can electronically tell when you are pushing the driver to hard.

I set all my amps with the SMD DD1 meter. Here is link to check it out.

http://youtu.be/SOARCaGU47s

$150? I may buy one and rent it out. Any one interested in that?

A volt meter won't help you when setting gains. Just get a $10 pair of earmuffs and a flat blade screwdriver and you're set. Earplugs work too.

can you go in-depth a little more?

I'm pretty sure the ear plugs are for your neighbors and the screwdriver is for turning the gain up and down...

Well I borrowed Brad's DD-1 and it was very easy (and quiet) to setup the gains. Needless to say I was no where close to the right settings. I did have to call their tech support because I could not get the tower and in-boat amps to clip on the HU. Turns out some HU's will send a good signal all the way to the top volume range at 1kHz. My aux. input was at probably 96-98% before clipping. I feel much better at what the settings are now and hope to get a chance to get on the water to hear it again. I did notice that my subs are not nearly as loud now, but I'm hoping it's just because I didn't want to bother the neighbors.

This did lead me to another question though... When setting up the in-boat and tower speaker amps the instructions on the DD-1 say to set the cross-overs at "full range". The setup on the Syn4 when bridging a pair of Rev410's sets the cross-over at "high range". If the 410 was run on "full range" will that cause damage to the HLCD Is this why WS says to run "high range"?

What is everyone using for test tones? I have 2 o-scopes sitting in the closet so I am going to use it this time for tuning and see how that work.. Going to add a 420 so I can find max HU volume without clipping.. then WS420 gain then the amp gain that should allow for the maximum volume of clean audio.

The DD-1 I was using senses 40Hz for subwoofers and 1kHz for full range speakers. In some of the research I did some people were using tones as high as 8kHz.

The DD-1 tones for finding the HU clipping point were at 0dB, but the CD also had tones at -5dB, -10dB, and -15dB to set the amp gains by depending on weather you wanted sound quality, loudest possible, or a compromise.

I use a function generator app on my iphone but have used test tones in the past.