setting gain with test tone

[WrenchGuy 10+ year member]

The equation is a good reference point. Go by ear from there. Keep listening.

 

[ProgMtl 10+ year member]

or find someone with an oscope and you can visually see when it clips

 

[528hz 10+ year member]

Just wanted to follow up on your ordeal.

I just checked out my gains once more to make sure I wasn't clipping my amp at 54 FVCKING VOLTS!!!!! And it runs strong and clean!

I set my gains using the same 50 hz tone (-3 db) and let the DMM set there and went up on the hz tones 5 hz at at time. Your right that there is huge difference.

Here is a list of the differences AFTER I already set my gains with the 50 hz tones.

35 hz-36.6v

45 hz- 46.7v

50 hz- 54.4v

55 hz- 56.3v

60 hz- 61.7v ( at this point the amp was very mildly starting to clip)

65 hz- 52.1v ( wicked drop in voltage???)

Does anyone know why this is? Would this differ from amp to amp to why the readings would vary? Or does it take more power and make your amp work harder to hit higher frequencies?

 

[liftedcj7on44s 10+ year member]

ive always wondered the same thing mself, logic would make since that the lowr the frequency the more power would be needed but its not ture i guess. also i dont find settings gain with a dmm very good. listen to music something that hits rediculously hard and listen by ear. or get an o-scope

 

[king ranch 5,000+ posts]

Just wanted to follow up on your ordeal.
I just checked out my gains once more to make sure I wasn't clipping my amp at 54 FVCKING VOLTS!!!!! And it runs strong and clean!

I set my gains using the same 50 hz tone (-3 db) and let the DMM set there and went up on the hz tones 5 hz at at time. Your right that there is huge difference.

Here is a list of the differences AFTER I already set my gains with the 50 hz tones.

35 hz-36.6v

45 hz- 46.7v

50 hz- 54.4v

55 hz- 56.3v

60 hz- 61.7v ( at this point the amp was very mildly starting to clip)

65 hz- 52.1v ( wicked drop in voltage???)

Does anyone know why this is? Would this differ from amp to amp to why the readings would vary? Or does it take more power and make your amp work harder to hit higher frequencies?

yea its odd at like 35hz i get like 60 volts then with the same gain setting on a 70hz tone its only like 30volts

thats why i was wondering on the amp sticky for the gains voltage what test tone hz was used

 

[Immacomputer 10+ year member]

You guys are getting different voltages at different frequencies for a few reasons. First, to Colby, if your low pass filter is set on the amp and not disabled when you test, you should see the voltage getting lower and lower as you increase frequency. Crossovers on the amps are not ideal which means that they have slopes that come with them. The "slopes" come from the crossover analysis in the frequency domain (power over frequency). An ideal filter would have peak voltage right up until the cutoff frequency and then have 0 voltage right after the cutoff frequency. This isn't possible in real life so there are slopes associated with the different crossovers. If your low pass filter is set to 80hz as a cutoff point, the voltage will be .707 times the voltage in the pass band. Before that point though, the voltage will have already started to lessen. This is also probably the reason that the OP's sub is louder when he sets the gain at 70hz instead of 40hz. He has to turn the gain up higher to get the same voltage since the crossovers might be affecting it.

Another reason for the difference in voltage could be an EQ setting on the headunit. If the bass on the headunit doesn't give a specific frequency, it's probably centered between 50-65hz. Above and below a small range of frequencies you will see a different voltage because of the boost or cut applied.

It could also be that some DMMs (read cheap DMMs) don't read very accurately for some frequencies far from 60hz. An octave above or below it and you may get crazy numbers. DMMs, especially cheap ones, are not as accurate as people believe. I had one that would tell me that my battery in my car was doing 16.9v!

Colby, your subsonic filter may also be too high and it might be affecting the power in the 30-40hz range.

A good way to set a subsonic filter would involve playing a 20hz test tone (something from 20-24hz would probably do the trick) with the SSF turned as high as it will go. Then slowly turn up the volume and see how the reacts. Make sure that it is not moving too much or over-excurting. Turn the volume to where you would normally have it maxed at if it is safe to do so (it should be if your subsonic filter is all the way up). Then slowly lower the subsonic filter until it appears that the sub is beginning to struggle (your eyes and ears are important tools here, more-so than the DMM) and then turn it up only slightly from there. That should be a nice setting and it shouldn't affect your bass much.

It could be argued that you could even turn it lower because there is not a lot of music that has 20hz content in it. But, that is user and music dependent.