Setting gains

[TX-Foilhead]

Just wanted to get a confirmation that I'm on the right track. I've got a pair of Rev10's powered with a JL750/1. Even though there are seperate connections for each speaker on the amp since it it mono it sees the 2 speakers paralleled which is a 2ohm load, correct? I tried set them by ear, but it's too loud and hard to run back and forth as well so I'm doing it with the DMM and have them set for 2ohms now which is a lower output voltage, but need to recheck everything now that I have a fresh battery in it.

[EarmarkMarine]

This isn't the only way but the easiest way is the following.
Disconnect the speakers.
Measure just one of the speaker terminals (they are paralleled internally).
Use a 1 kHz sine wave test tone.
Turn up the input sensitivity until you measure 38.7 AC volts (full power for a 2-ohm load) at the output (without speakers connected).
You're done.

David
Earmark Marine

[AirTool]

This isn't the only way but the easiest way is the following.

David,

I read the above....but I thought one had to place a load/resister across the empty speaker connections and then measure the voltage. So are you using the internal impedance of the amp as the load?

I've always wanted to do this but I thought I needed a dummy fixed resister.

If I remember my Norton and Thevenin equivalent circuits correctly (maybe now you are impressed), power is max'ed when the external impedence matches the internal impedence. I'd have to play around with it to figure the voltage. I wouldn't have guessed 38.7. I do remember it is RMS and your sine wave input makes it where you don't have to have a "true rms" dmm.

Man, I love boating.

My 70-year old Dad is a retired electrical/power engineer. I should test him on this one.

[TX-Foilhead]

Thanks David, that's what I did.

Air Tool, I don't know if that works with every amp, but it's the way JL suggests and they have tables to give you the voltages for the various loads, they may have done that to come up with the results.

[EarmarkMarine]

It does depend on the particular amplifier topology.
You can also use "AC voltage squared divided by impedance equals power" (using the manufacturers specs) with the speakers still in the circuit. But be careful as some amplifiers cannot meet spec. So if doing this with other products beyond JL Audio it's best to have a handheld scope to see when the amplifier is going into compression.
The above might apply to an isolated tower zone. But when considering the in-boat zone with different bow and cockpit areas plus fullrange to sub level matching, a basic voltage reading is not enough to properly tune a system.
We use a far more sophisticated method for total system set-up based on a number of electrical, audible and visual cues.


David
Earmark Marine

[TX-Foilhead]

I've always used that as a max and then balanced things downward if needed, the Rev 10's are about as loud as anyone in the boat wants long before max volume. One of these days I may give the driver some earplugs just to see what happens at the end of the . but For now it sounds fine at both ends of the rope and my bank account has tapped out.