Multimeter for gain adjusting + setting HU without clipping

[kiteman]

i have a 2012 camaro with the boston acoustics upgrade system. i am using my stock HU and replaced the aftermarket amp with a PPI p900.4. plan is a front stage where the amp powers 145w to 2 channels, and bridging the rear channel with 450w for the sub. i haven't exactly decided on speakers/sub yet, but i did at least get started asking advice on the sub in the subwoofer forum.

but before i get there i decided to use a multimeter to set the gains properly on my amp. if you guys are familiar with this you know it requires playing a 50hz test tune through your HU with your amp connected, then using the amps rated watts/ohms to convert to a volt. the voltmeter is hooked up to the speaker terminals instead of the speakers themselves, and then you adjust the gain up or down to get that desired volt level. pretty simple right?

well this method requires that you set your HU at its max level before clipping. my stock HU goes to level 45. i first started this gain setting process with the volume at 20. once i got there i used my audio test tone on my HU and turned up the volume until i heard the unit clip. direction on the test tone explain very vividly what that will sound like when you clip, and i heard it, at volume 32 (of 45).

so then i redid the gains on my amp with the HU at volume 31. i can't honestly say how much they changed from when the level was only 20, BUT after i set them and played the test tune for HU clipping again (obviously i had to hook a speaker back up to do this), the HU didn't audibly distort until volume 36 this time. SO, something is obviously not right...it's like as long as i adjust my gain on the amp at each interval, the HU can go higher or lower in volume and at least according to the test tune, not distort. but that CANNOT be the case, especially with a stock head unit.

does anyone have any suggestions for what i should do/what i'm doing wrong? i have read a lot of times 75% of your max volume on your HU is a good resting place for not exceeding because clipping is possible thereafter, so volume 31 is just under 70% and seems like a reasonable place to remain, not to mention that is currently the volume i used to set the gains on my amp where they should be.

if i'm confused about any of this stuff please feel free to help. thanks!

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[T Reds 19]

It is because the test tone is likely a 0 db test tone when your music it recorded at -5db so reset the gain at the original clipping volume of 31 but with a - 5db tone that matches the music you play.

 

[kiteman]

It is because the test tone is likely a 0 db test tone when your music it recorded at -5db so reset the gain at the original clipping volume of 31 but with a - 5db tone that matches the music you play.

Both test tones I used for the amp gain and the HU were 0db, so I'm not understanding where the - 5 comes into play if I haven't yet introduced that type of tone in my measurements?

 

[T Reds 19]

Set it with the - 5 db and you will essentially be setting your gains a little higher, the db test tone you use depends on the music you listen to. - 0 db is louder than - 5db which is why you can turn your head unit up past 31 without hearing clipping but it it probably there, just trust me

 

[kiteman]

Set it with the - 5 db and you will essentially be setting your gains a little higher, the db test tone you use depends on the music you listen to. - 0 db is louder than - 5db which is why you can turn your head unit up past 31 without hearing clipping but it it probably there, just trust me

OK, so now I will set my amp gain with the - 5 test tone, thanks.

Second question, for some reason my amp won't hit target voltage unless I use band pass filter on both front and rear. Meaning I can't just use hpf or lpf, then the voltages are very low. There is probably and explanation here for why this occurs, but all I really want to understand is if I can use both filters to achieve a hpf and lpf? I would think for the sub I'd turn hpf all the way off, and only adjust lpf. And for front stage I'd turn lpf all the way on and adjust hpf to block out lower tones. Yes?

 

[T Reds 19]

Turn hpf all the way up and set lpf to ~85hz and set your amp to lpf it should work fine for your sub. For the front stage set your hu or amp hpf to ~80.