Tried something today dealin with gain and lowpass crossover

[luvinthebass 5,000+ posts]

so i tried somethin new with gain setting, and first off i wanna know why can't you set your low pass crossover to 60 hz and use a 60 hz -3 tone THEN set your gain?, despite that question i tried that and the output rules, i don't think the amp was clipping either, i tried it the other way settin the gain with the lowpass off and then put the low pass on at 60 hz and the output just sucked for music.

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[pwnt by pat 10+ year member]

because the crossover point is already 3db down. By using a -3db tone on a slope that's already 3db down, the passband is 6db higher than the crossover point. Thats probably why output was better, cause the amp was being driven into clipping.

 

[luvinthebass 5,000+ posts]

because the crossover point is already 3db down. By using a -3db tone on a slope that's already 3db down, the passband is 6db higher than the crossover point. Thats probably why output was better, cause the amp was being driven into clipping.

what if i set it with a 0 db tone at 60 hz, same thing would happen?

 

[pwnt by pat 10+ year member]

with a 0db tone at 60hz crossover, you're still 3db down. set it without the crossover, then add the x-over in

 

[Immacomputer 10+ year member]

Setting with your ear and 0dB tones are the way to go. This -3 and -6 with DMM garbage is a terrible fad and almost always comes out sounding like shit.

 

[jacka 10+ year member]

Setting with your ear and 0dB tones are the way to go. This -3 and -6 with DMM garbage is a terrible fad and almost always comes out sounding like shit.

I agree, I set mine by ear at first and left it for a while. Then decided to try with a DMM. Problem with that is you never know how it's gonna sound like with music, at least I didn't. I reset mine by ear and left them ever since. Though you still have to be careful when you have headroom.

 

[JimJ 5,000+ posts]

This -3 and -6 with DMM garbage is a terrible fad and almost always comes out sounding like shit.

It's a terrible fad that both Richard Clark and David Navone happen to endorse //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

I'm not supporting it one way or the other, I'm just saying there are some good ears out there that it works for...

 

[aaron7114 10+ year member]

wait a minute. I might be reading this wrong but you are supposed to have the low pass crossover off when settings the gains?

 

[thch 10+ year member]

the lowpass filter affects some of the higher "lows" thus, testing at 40hz might give 14.1V out of the amp, while 60hz might give 10V out of the amp. if you test at 60hz, and 40hz is +3dB (compared to 60hz), then you have increased chances of clipping.

I'm still of the opinion that the DMM stuff is just a tool to aid in setting gains, with the final autority resting on the ear.

 

[pwnt by pat 10+ year member]

I've always adjusted to max output with a dmm, then adjust by ear turning down the gain only - never up to level match

 

[luvinthebass 5,000+ posts]

i think i'll try it by ear tomorrow with a 60 hz 0 db tone, thanks for the replies guys.

 

[aaron7114 10+ year member]

i think i'll try it by ear tomorrow with a 60 hz 0 db tone, thanks for the replies guys.

I think I might try the same....but I will probably use 50 hz tone. Is there any advantage over each one?

 

[xluben 10+ year member]

setting by ear just means you did it the right way, and it wasn't loud enough, so you turned it up //content.invisioncic.com/y282845/emoticons/satan.gif.9c6a335ed7aeeed3ee273e573f1fcaac.gif

everything pwnt by pat has mentioned is pretty good info. gains should be set with a DMM as reference level and then only turned down to level match, never up.

a DMM can't verify that an amp isn't clipping, but if you turn it up past what the DMM is telling you, it's almost certain it will be clipping (unless music is recorded well below reference).

to the OP, you shouldn't be setting the gains with the same frequency as the filter if you want to get 'full' power within the passband.

if you're filters are fairly steep (12db/octave or steeper) you should be fine using a 40 or 45Hz tone to set the gains with. that should be out of the top and bottom end roll off.

also, your 'backwards' method of gain will work, but not as you are currently doing it.

as mentioned in the sticky, if you play your desired -3dB frequency, the voltage output should be 0.707 times that of you reference level.

ex:

you want 800W into 2 ohms, LPF at 60Hz, SSF at 20Hz

that should be 40V output within the passband (40 or 45Hz or whatever you choose)

and 40*0.707 = 28.28V at the cutoff points (60Hz and 20Hz)

so you start by turning off the filters and setting the gain using the 45Hz tone.

then you set each filter individually to match the 0.707*V value.

now go back and check the 45Hz tone, if your crossover slopes aren't steep enough it will have gone down a bit.

you should be alright turning the gains back up a little to get the desired voltage output at the gain setting frequency.

ideally you would want to choose the gain setting frequency halfway between the SSF and LPF on a log scale!

(i use 40Hz when my SSF is 20Hz and my LPF is 80Hz).

hope that helps!

 

[Immacomputer 10+ year member]

a DMM can't verify that an amp isn't clipping, but if you turn it up past what the DMM is telling you, it's almost certain it will be clipping (unless music is recorded well below reference).

People put too much trust in what their DMMs say. I know many people out there have very trusty true RMS multimeters but the average 16-20 year old kid is probably not going to want to spend over $60 on a DMM and will buy some ghetto walmart DMM.

My multimeter is no where near accurate on AC when the frequency is below 50hz compared to a really nice fluke I used from my work. It will also give me different readings every time I power cycle it.

 

[xluben 10+ year member]

People put too much trust in what their DMMs say. I know many people out there have very trusty true RMS multimeters but the average 16-20 year old kid is probably not going to want to spend over $60 on a DMM and will buy some ghetto walmart DMM.
My multimeter is no where near accurate on AC when the frequency is below 50hz compared to a really nice fluke I used from my work. It will also give me different readings every time I power cycle it.

i agree, those walmart ones ****.