Factory 7" DIRTY noise via Oscilloscope & RTA

[JLsport2019]

I finally had my Factory 7" (non-alpine) radio thorough testing if in fact we do need a JL Audio Fix-86 module to "level" the factory built-in amp that is spewing 'dirty' noise through our factory or upgraded speakers.

Can the audio experts weigh in on the graphs down below? I know it's suppse to be flat, and it is not.

RTA & Oscilloscope graphs shown.
Completely mechanical.

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[Steve Cornell]

The 3rd octave RTA graph is not bad at all however that squaring off of the signal in the O-scope is clipping, you need to figure out at what level this happens and never go beyond that level, the wave should be rounded, the proper way to set gains with an O-scope is to start at the head unit and increase the gain \ volume level to where the wave clips (as shown) and then back it down and continue on to the next component in the signal chain and do the same.. I see you are using 1000hz which is the frequency I used back in the day to set gains...

 

[JLsport2019]

The 3rd octave RTA graph is not bad at all however that squaring off of the signal in the O-scope is clipping, you need to figure out at what level this happens and never go beyond that level, the wave should be rounded, the proper way to set gains with an O-scope is to start at the head unit and increase the gain \ volume level to where the wave clips (as shown) and then back it down and continue on to the next component in the signal chain and do the same.. I see you are using 1000hz which is the frequency I used back in the day to set gains...

Thank you Steve for the reply.
Our JL forums here seems slow?

I had my Custom Audio Shop do these RTA & Osscp tests done just to see if the JL Audio Fix-86 is needed per all the posts on other threads concerning my 7" factory radio (non-alpine) spewing out "a lot of noise".

I have a upgraded cheapie Alpine 445-u PowerPack powering 6x JL Audio C2 speakers.

From what I understand, if the 7" factory is not set to "zero"...adding a upgraded AMP just amplifies all that unwanted noise in the first place.

Is there a lesser price alternative to a JL Audio Fix-86 for my Factory 7" radio??

 

[Steve Cornell]

I'll admit I haven't done a lot of factory integration, I have many years of installation experience but most of that is with aftermarket equipment.
I'm sure there are other options but it seems the Fix-86 is regarded as the best solution.

 

[carstereochick]

I showed this to my installer husband John and here are his comments:

• What volume was that test done at? Looks a little low - you want to try at various volumes and see if results change dramatically.
• Looks like the signal is lacking in mid range and the bass is probably boomy since exaggerated at 80 - 125 Hz
  
• Was a microphone used for the test or did they connect directly to the speaker level out of the radio? (Results can vary widely depending on mic placement if mic was used - better off connecting directly to output of radio)

He describes the ideal curve as sort of a lounge chair. I attached a pic of one from a Dodge Challenger Hellcat where we used:

• a PAC Audio pre-amp adapter (The Challanger had come with the stock Harman Kardon system) AP4-CH41
• APA-TOS1 Toslink adapter
• Helix P Six DSP MK2 amp
• Helix SPXL 1000
• Morel ELATE Ti 603 ACTIVE
• Morel TI 122 subwoofer (custom sealed fiberglass enclosure)

Comparing the ideal curve to the stock curve you can see a lot of corrections need to be made. So the Fix-86 alone probably won't achieve that RTA curve, but it helps you get there by smoothing everything out. Then you can use the Twk-88 (or VXi amp with Twk-88 built in) to fine tune and that's what you want the RTA to look like when you're done. He is a former IASCA sound quality judge and one time Top 100 Installer.

The other thing I'll add is the Fix-86 with the DRC-205 has a handy clipping indicator light built in, makes it easy to know your safe volume levels.

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