advanced questions on gains/clipping

[skittlesRgood 10+ year member]

i want this to be a very helpful topic. if you have knowledge of what im talking about please give as much detail as possible.

i got a tone generator for xmas and ive setup a little testing station in my room. i quickly found out that if i set the gains with a 1000hz tone i would get very bad clipping when i droped the frequency to 250~hz. i thought this was pretty interesting seeing as how this is how everyone is told to set the gains for the mids and highs. i didnt use the dmm at all in this so its not exactly how everyone sets gains but it gives me an idea of a potential problem. i made a couple little videos to help explain.





so here you can see that even though the volume was not changed, when the frequency was lowered it started to clip. but when i raise the frequency i didnt get it to clip. of corse i didnt try anything over 5khz so who knows whats going on up there. it got too annoying hearing something so high pitch lol. anyways, perhaps some of you could help me test this out. set your gains for your mids/highs with a 80hz tone instead and tell me if you get better low end responce from your mids. also report how your highs are effected if they are on the same channel.

this is very early testing, i may have been doing something wrong but it seems pretty straight forward so far. if anyone sees any flaws in how i did this please go ahead and comment.

Click to read more...

 

[gunz4me2 10+ year member]

Interesting results. I will say that an amplifier doesn't work as hard at 1,000 Hz as it will at 50 Hz. Now you have me wanting to try this test with my oscilloscope and dummy loads.

 

[skittlesRgood 10+ year member]

it gets you thinking doesnt it? ill try more testing tomorrow but if you test this out please report your results here. maybe even make a video if there is anything to show.

 

[MakeshiftAudio 10+ year member]

Increasing frequency increases impedance which decreases power throughput.

 

[skittlesRgood 10+ year member]

that doesnt end the thread, that confirms that this is a problem. thread blown open. why set gains at 1khz if more power is presented at 100hz and clips the signal? why isnt everyone told to use an 80hz tone instead?

 

[MakeshiftAudio 10+ year member]

I don't know many people that tune their subs etc at 1khz. It is an issue, and most tuning should be done around the lowest frequency you expect to play, or your box tuning, then have your high pass filter remove the stuff below that to a safe level.

If you still have an issue with this, I will explain later today after I get some sleep.

 

[skittlesRgood 10+ year member]

ya but im not talking about subs here. im talking mids and highs. so it sounds like we have some very bad common knowledge around here because everyone ive talked to says to use a 1khz tone for mids/highs. that makes this testing pretty important dont you think?

yes, sleep is good. im going to go get some as well.

 

[murilo 10+ year member]

set that trigger! haha

 

[skittlesRgood 10+ year member]

what trigger?

 

[Canaan 10+ year member]

I did a few similar videos like this one about 2yrs ago.

I set the gain on a PG RSd600.1 w/ a DMM at 60hz and showed a clean waveform on the O-scope, kept everything the same and ran a 30hz tone to the amp...amp produced a clipped wave.

It all has to do w/ impedance rise.

 

[skittlesRgood 10+ year member]

hmmm... never thought about imp rise with mids... more stuff for me to test. thanks.

 

[Johnny Law.Lulz 5,000+ posts]

I set my gains with actual music. I sit there and listen and set it where it sounds good, then turn it up for a few and see how hot my shit gets. But im not looking for amazing sound either so, it sounds fine to me. But on my Aq2200 i do notice that the lower my hz drops in songs, the more intense or the quicker the clipping light comes on. but my sub was made to handle a little bit so i just back the volume down a tad.

 

[skittlesRgood 10+ year member]

again, we are not talking about subs here. with subs you set the gains at 50hz and you dont go much beyond +/-25hz so i dont see it being as big of a deal, and we all pay very close attention to our subs and most people will catch if something is wrong. now with the mids, going from 1000hz to 300hz and it starts to clip and your mids are crossed over at 65hz, thats a lot of clipping. so if anyone has been wondering why they dont have much mid range, this could be the problem.

 

[gunz4me2 10+ year member]

With non-inductive dummy loads, I didn't notice much of a difference between 50 and 1000 hz on an old school Orion 250 SX Digital Reference. In other words the amp clipped at the same volume level which approximated to 75 watts RMS per channel with both channels loaded. At 30 Hz, it started to clip a little sooner, at 65 watts RMS, but I wouldn't call this a major difference.

Question, did you adjust your oscilloscope for the proper timing when doing the sine sweeps? That is why I test with a single tone per frequency because if you shift too much, you MUST change your timing to capture the entire waveform on the oscilloscope. Then again, I am also using pure resistive loads versus reactive loads (i.e. speakers).

 

[skittlesRgood 10+ year member]

With non-inductive dummy loads, I didn't notice much of a difference between 50 and 1000 hz on an old school Orion 250 SX Digital Reference. In other words the amp clipped at the same volume level which approximated to 75 watts RMS per channel with both channels loaded. At 30 Hz, it started to clip a little sooner, at 65 watts RMS, but I wouldn't call this a major difference.
Question, did you adjust your oscilloscope for the proper timing when doing the sine sweeps? That is why I test with a single tone per frequency because if you shift too much, you MUST change your timing to capture the entire waveform on the oscilloscope. Then again, I am also using pure resistive loads versus reactive loads (i.e. speakers).

ya the reactive load acts much differently. as mentioned above, imp rise is a factor and a non reactive load isnt subject to imp rise so you would get a very flat power responce as your testing showed.

did you watch either video? even if i didnt adjust the scope correctly you can CLEARLY hear the speaker distort.