Physics Project, setting gain with Oscope, info please.

[Driv3]

Talked to my physics teacher about using this so called oscilloscope that I continuously see mentioned on here, due to the fact that our class is embarking on Periodic Motion. This has little to do in common with car audio besides the shared unit of Hz. To my joy, he said i can make a project of setting my gain using his o-scope!//content.invisioncic.com/y282845/emoticons/inlove.gif.6846f78f06b405429ef3a00129788a2a.gif Now, my system is all in boxes right now and will be assembled by the weekend.

Can an expert or moderately intelligent person tell me what i need to do? Does my system have to be fully installed (subs/amp) in my car for the scope to work? can I just bring the amp in class or would i have to bring the o-scope out to my car? also can you give me a sort of step by step or a good quality link i can use about setting gain with the oscope?

This is much appreciated from my system sound quality to my grade, thanks a lot gang!

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[Gawdzila]

Hey //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Having a physics degree, I feel qualified to say that periodic motion is one of the most important subjects in all of physics. Indeed, periodic motion has a lot more to do with car audio than you think. Both electrical signals and sound waves behave very similarly, and they are both modeled almost completely with periodic motion -- which is why the electromagnets in speakers can so directly translate an electrical signal into music, or why you can hear a "60Hz hum" sometimes if you have a speaker next to a wire carrying wall current.

That oscilloscope you'll be using measures electrical signals for things like frequency and amplitude. As you know, sound signals also have a frequency and amplitude. The only differences are that with sound you can hear the frequency as the pitch, and the amplitude represents voltage in an electrical signal, but volume in a sound signal. There is a very tight relationship between what you will see on that scope and what you hear coming out of your speakers.

Unfortunately I'm just a very beginner in the ways of car audio, so I can't give you a good procedure myself.

With just a little digging, however, I did come across a couple of good instructions:

This article has a write-up with some explanation about the underlying principles.

should also give you some pointers about how to actually, physically go about using the equipment.
Study hard, and dig beneath the surface -- this fun and useful little car audio project has the potential to teach you some very deep things about how the universe works. Good luck!

 

[TaylorFade 10+ year member]

You won't need much power to do a demonstration in class, so just drag a small 12v batt in with you and the amp. Just put the remote on a toggle from the + terminal. Use a headphone jack to RCA and use your phone or iPod as your source, speaker wire to the scope and bingo bango.

 

[keep_hope_alive Premium Member]

the point of using an oscilloscope to set gains is to match the output voltage of the head unit with the input sensitivity of the amplifier's pre-amp section. To do this you will need both the head unit and the amplifier, and obviously cables to connect everything. You will need a source signal, such as a CD with sine waves - 50Hz and 1000Hz are common for subwoofers and speakers, respectively.

You play the CD, and measure the outputs of the amplifier. You choose a head unit volume to set the gains with, this is never the max output of the HU, we commonly use 70% or so if the speakers are also amplified externally. If you have speakers powered off your head unit, then you may set gains a lot lower since the head unit will have audible distortion around 50% volume. Once you have chosen the HU volume to use and the test tone track to use (put on repeat) , you adjust amplifier gains until you see clipping then turn back down. Note that you do not connect both scope leads, just the red one. you ground the black lead to chassis/amp ground. if the amp is bridgable you will see that there is a signal on left (+) and right (-) but the right (-) is 180deg out of phase. you can discuss how the concept of bridging works for extra credit. Be prepared to do an Ohm's law calc to discuss what power output this will be at the expected impedance load. Note that once you connect the load, some voltage sag will happen and the actual power output may decrease.

The supply voltage used will determine where the amplifier's voltage rails are, and thus where you will start to clip. To do this in class you will need a power supply capable of 5A or so between 12VDC-13.8VDC

 

[Vincer77 10+ year member]

You have a great teacher!