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Jacobman
07-10-2007, 04:32 AM
So i know how to set the gain but do you use a test tone for the speakers like you would for a sub. What hz test tone, like 100hz or something?

DejaWiz
07-10-2007, 09:22 AM
When using a test tone and a DMM, all speakers need to be unhooked from the amp(s) first.

For the sub, use about a 50Hz tone, for the mids, about a 200-500Hz tone, for the tweeters, about a 3000Hz tone (or higher, depending on the crossover point). Separate tones if each speaker is being individually powered (biamping or active).

If you are using one pair of channels to run the passive crossovers for the components (or just running coaxials), then a 1000Hz tone can be used to set the gain for those channels.

I'd stick with either a 0 dB or a -3 dB tone.

Jacobman
07-10-2007, 12:54 PM
So when you said separate tones if each speaker is being individually powerd, that means the tweeters would have there own amp? Well in my situation i have 1 set of speakers on a 2 channel amp, so i would then do the formula, Sqrt(rmsXohms), run the 1000hz tone and set to the voltage with a DMM i came up with right?

DejaWiz
07-10-2007, 01:25 PM
That is correct, sir.

Jacobman
07-10-2007, 02:17 PM
Another quick question, if my amp at the time of gain setting isnt getting 14.4v then i would just scale down the voltage for the amount of voltage it is getting? For instance say its 200rms at 14.4v, well if its only getting 12v, then i would be working with 166rms. So then it would be Sqrt(166Xohms) right?

DejaWiz
07-10-2007, 02:35 PM
Another quick question, if my amp at the time of gain setting isnt getting 14.4v then i would just scale down the voltage for the amount of voltage it is getting? For instance say its 200rms at 14.4v, well if its only getting 12v, then i would be working with 166rms. So then it would be Sqrt(166Xohms) right?

Nope, that it incorrect. The actual output of the amp at a given input voltage is going to depend on a few things, efficiency being a major one.

For example, say you have a class a/b amp that's rated at 2x200w rms at 14.4v and a class f-d amp that's rated at 2x150w rms with speakers that are only mechanically capable of dissipating the heat from 140w rms per channel attached to either. You'll want to set the gains for 140w on either amp with the max input voltage your vehicle's electrical system can provide (running).

Now turn the vehicle off and the system voltage drops to 12.5v. The a/b might drop to 2x120w rms while the f-d might only drop to 2x120w rms as well because it's more efficient. Because of these differences, setting both amps to approximately the same gain setting at 12.5v would likely result in the a/b amp to put uneccessary and avoidable strain on the speakers once the ignition is turned on and the input voltage rises to 14.4v.

Now with my example, I used a class a/b as well as a f-d (full range digital) amp. These variances will apply when comparing two different a/b amps against other, not just a/b vs f-d.

Best way to get around trying to figure out how to properly set your gains with a lower input voltage is to measure the outputs and set them while the car is running so you get the max voltage your alt/batt can supply.

As for the formula, don't try to guess and plug numbers in unless you know for certain what your amp is capable of outputting at both 12.5V (engine off) and 14.4V (engine on).