Question about setting gain with O scope

[FML 10+ year member]

So, I just recently acquired an o scope to assist me in tuning my amp to my woofer. Im getting confused on the proper way of doing it. Iv only come across one tutorial that specified where your LPF should be set on your amp when running your test tone (in my case, 50hz) ,while using the o scope. That person said to have it all the way turned up, with the gain obviously all the way down to start.

 

What I noticed was, the signal clipped much sooner with the low pass filter all the way up after only turning the gain about 1/6 turn. But when I restarted the test, i set the LPF at about halfway and was able to turn my gain up about double the amount before I saw clipping. I didn't realize just messing with the filter on a very low gain setting would produce a squared off sine wave.

 

Iv heard to turn the LPF all the way up, set gain, then reduce the filter to desired level. But doing that, I got a reading probably 20 volts lower than where it previously was.

 

Does either way work, as long as my signal isn't clipped? I may be confusing some folks so ill paraphrase:

 

I could turn my gain a bit more than halfway up, with the LPF about a quarter turn and recieve a clean, unclipped signal. But when redoing it with the LPF all the way up at start, (the supposed correct way) I could only get a very small 1/6 turn on my gain knob before noticing clipping.

 

So which way do I want it? Higher filter, less gain, or more gain, less filter? Either knob I turn while running the o scope drastically changes the wave form and im confused. Thanks folks.

 

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[Jeffdachef 5,000+ posts]

have it set where you are normally set at. Usually around 60-80hz depending on your music choice.

 

[FML 10+ year member]

have it set where you are normally set at. Usually around 60-80hz depending on your music choice.

Thats kinda what I assumed. But on a second note, wouldnt you need to run a higher Hz test tone (above 5o to 60) if you have your filter around lets say , 80hz, or does it not work that way? Sorry if these are obvious questions. Im slowly emerging myself into the more technical details of car audio. I don't know everything yet. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[FML 10+ year member]

Or wait, I think my logic is backwards, correct? 80hz setting will play 80 and under, anything *over should be filtered theoretically, no?

 

[Jeffdachef 5,000+ posts]

Or wait, I think my logic is backwards, correct? 80hz setting will play 80 and under, anything *over should be filtered theoretically, no?

It really dependss where your box peaks at. Play some songs, if it hits the hardest at 40hz then use a 40hz tone, 45 or 50hz depending on your music choice also. If you have it set at 80hz you are fine, dont over analyze it man.

 

[FML 10+ year member]

It really depends where your box peaks at. Play some songs, if it hits the hardest at 40hz then use a 40hz tone, 45 or 50hz depending on your music choice also. If you have it set at 80hz you are fine, dont over analyze it man.

Ok thanks. I had previously had issues with my woofer smelling funny, so went on a mission to get a scope to properly set gain. So either way i set things when i tune it, wether it be at 80hz LPF and gain at 1/6, or LPF at 40hz with gain 1/2 the way up regardless of voltage differences, as long as i have a nice clean rounded wave on my scope, i don't run risk of clipping?

Because even after tuned with the scope, my L7 still made weird smells after playing only briefly. Almost smells like a hot tv or computer. But scope says no clipping. This is whats causing all ky concerns.

Thanks for your replies

 

[bgowdy 5,000+ posts]

Ok thanks. I had previously had issues with my woofer smelling funny, so went on a mission to get a scope to properly set gain. So either way i set things when i tune it, wether it be at 80hz LPF and gain at 1/6, or LPF at 40hz with gain 1/2 the way up regardless of voltage differences, as long as i have a nice clean rounded wave on my scope, i don't run risk of clipping?
Because even after tuned with the scope, my L7 still made weird smells after playing only briefly. Almost smells like a hot tv or computer. But scope says no clipping. This is whats causing all ky concerns.

Thanks for your replies

For me it seems L7s are bad about this. They claim to be a 1k rms daily sub. My wife had a L7 15"(the good 2006 series L7 at that) that was paired with a Kicker Zx1000.1 that was clamped at 750 clean(scoped, and turned down some due to her electrical in the car being low) and it still got smelly really quick. alot of ppl have noticed this also.

 

[Jeffdachef 5,000+ posts]

Ok thanks. I had previously had issues with my woofer smelling funny, so went on a mission to get a scope to properly set gain. So either way i set things when i tune it, wether it be at 80hz LPF and gain at 1/6, or LPF at 40hz with gain 1/2 the way up regardless of voltage differences, as long as i have a nice clean rounded wave on my scope, i don't run risk of clipping?
Because even after tuned with the scope, my L7 still made weird smells after playing only briefly. Almost smells like a hot tv or computer. But scope says no clipping. This is whats causing all ky concerns.

Thanks for your replies

Might be because the sub's voice coils cannot handle the power. Use your ears also, if your subs are not getting any louder then lower the gain a bit more. How is your head unit setup? Your pre-out voltage signal might be strong from the head unit. Have loudness off, EQ on flat, LPF 80hz, bass boost off

Also see if you can get a close up of the wave, there might be signs of distortion. Clipping and distortion are related but not actually the same thing on the scope. Even if the wave is round, a closer look might show you jagged ends on the waves.

 

[gckless 5,000+ posts]

Might be because the sub's voice coils cannot handle the power. Use your ears also, if your subs are not getting any louder then lower the gain a bit more. How is your head unit setup? Your pre-out voltage signal might be strong from the head unit. Have loudness off, EQ on flat, LPF 80hz, bass boost off
Also see if you can get a close up of the wave, there might be signs of distortion. Clipping and distortion are related but not actually the same thing on the scope. Even if the wave is round, a closer look might show you jagged ends on the waves.

Clipping is distortion.

 

[FML 10+ year member]

Might be because the sub's voice coils cannot handle the power. Use your ears also, if your subs are not getting any louder then lower the gain a bit more. How is your head unit setup? Your pre-out voltage signal might be strong from the head unit. Have loudness off, EQ on flat, LPF 80hz, bass boost off
Also see if you can get a close up of the wave, there might be signs of distortion. Clipping and distortion are related but not actually the same thing on the scope. Even if the wave is round, a closer look might show you jagged ends on the waves.

Yeah i made sure all my settings were flat, other than the subwoofer level (0-15)since its a Kenwood. I leave that all the way up. When the RCAs were tested, they put out about 2 volts each.

The l7 15 is 1000rms, 2000 watt peak. Im running probably right at 1000, maybe a tad bit more since im using an older RF power elite b.d amplifier.

I bought the scope because ever since i wired the woofer to 1ohm to this amp, iv gotten odd smells. Most Everyone on here told me i was most likely clipping.

Could you explain the deal about matching head unit voltage? My understanding is that'd you just subtract those volts (in my case 4v) from your amps output when setting gain. I skipped that and just set it where its at since the wave was perfect. Also, im just 7using standard test leads, but iv heard about o scope "probes" that are used?

 

[Jeffdachef 5,000+ posts]

Clipping is distortion.

a clipped wave has a maximum limit of how high of a signal can pass through cleanly; when the level of signal going through exceeds that maximum, the tops of the waves get clipped off (flattened out). Afterwards it becomes a square wave

Distortion means any change in the wave-shape of a signal from the input of a device to the output. So even a simple change in tone, without clipping, can be accurately called distortion.

http://elpaso.apogee.net/md/graphics/dadind02.gif

Thats why when dirty power like Audiopipe Has a seemingly round and unclipped wave, however, you zoom in closer and you see there's distortion that you cannot get rid of unless you lower the gain close to minimum levels.

 

[gckless 5,000+ posts]

a clipped wave has a maximum limit of how high of a signal can pass through cleanly; when the level of signal going through exceeds that maximum, the tops of the waves get clipped off (flattened out). Afterwards it becomes a square wave

Distortion means any change in the wave-shape of a signal from the input of a device to the output. So even a simple change in tone, without clipping, can be accurately called distortion.

http://elpaso.apogee.net/md/graphics/dadind02.gif

Thats why when dirty power like Audiopipe Has a seemingly round and unclipped wave, however, you zoom in closer and you see there's distortion that you cannot get rid of unless you lower the gain close to minimum levels.

So, you can copy and paste, congrats. I see right where you c&p the text in red from here, but then you added the blue, which isn't accurate. Clipping and a square wave are different. For the rest of it, um, ok?

As I said before, clipping is distortion.

Edit: Actually, in reference to my third sentence, here is a direct copy and paste from the same page you were looking at: "a clipped sine wave can look kind of like a square wave. Because of this, many people get the idea that clipping their amp results in square waves--but this is almost always false"

 

[FML 10+ year member]

Umm anyways....?

 

[T3mpest 10+ year member]

Just to add, clipping is distortion. Clipping an amp produces higher order harmonics which is also what causes the wave wave to square off. It's not very audible, since it's even order harmonics and most of the time, the subs inducatance will filter most of it out. However, the increased overall volume from the higher gain even with that harmonic filtered out, still cooks the coils pretty easily, although it's VERY easy on tweeters for this reason, no higher order filtering due to smaller voiceoils. Main thing is, don't get too technical or overthink it..

Use the O scope/DMM to get in the ballpark, then see what kind of output you have. Then turn the knob up and down a bit on some loud music and make sure you don't need a bit less or more gain depending on the sitation. Ears should always have the final say, just check the sub once in a while for heat/over excursion until you know things are ok.

Anyways a perfectly square wave is literally impossible to reproduce as it would have to have a harmonic that is infinitely high in frequency to produce a 0 rise time.. Since we can't do that, no matter how clipped your signal is, you can't make a square wave. People get far too caught up on the details here. The main issue with clipping is your pushing your amp at its' limits, which often does the same to the sub. If the sub isn't getting hot or moving too far, dont' worry about it lol.

 

[FML 10+ year member]

Just to add, clipping is distortion. Clipping an amp produces higher order harmonics which is also what causes the wave wave to square off. It's not very audible, since it's even order harmonics and most of the time, the subs inducatance will filter most of it out. However, the increased overall volume from the higher gain even with that harmonic filtered out, still cooks the coils pretty easily, although it's VERY easy on tweeters for this reason, no higher order filtering due to smaller voiceoils. Main thing is, don't get too technical or overthink it..
Use the O scope/DMM to get in the ballpark, then see what kind of output you have. Then turn the knob up and down a bit on some loud music and make sure you don't need a bit less or more gain depending on the sitation. Ears should always have the final say, just check the sub once in a while for heat/over excursion until you know things are ok.

Anyways a perfectly square wave is literally impossible to reproduce as it would have to have a harmonic that is infinitely high in frequency to produce a 0 rise time.. Since we can't do that, no matter how clipped your signal is, you can't make a square wave. People get far too caught up on the details here. The main issue with clipping is your pushing your amp at its' limits, which often does the same to the sub. If the sub isn't getting hot or moving too far, dont' worry about it lol.

Yeah, i get all that. I have just found it extremely difficult to hear audible distortion coming from my woofer,that being its a 15 L7 in a ported box. Hearing it on mid and front end speakers is no problem, but i cant tell by ear if the sub is receiving distortion, therefore the just "listen to it " method is worthless to me.

Whole point in learning the technical stuff in car audio for me is because my woofer smells like it's burning plastic only after a minute or two of moderate play. Just trying to get it dialed in. Thats when i noticed that changing the crossover had as much effect on the waveform as did adjusting the gain, which left me confused. I realize the gain is not a volume knob, just boggles me that in one crossover setting the gain is fine, and in another it's too much.

I mean, if I blow my L7 (highly unlikely, seen vids of them taking 2 to 3x peak power and be fine, only a wall socket seems to be the way) , ill just get something better. Im just trying to soak up all the info I can. Grew up in my teenage years to just plug it in, turn it up, to finally getting down to the science. I like it better that way, knowing what makes things go and how to properly adjust your components.