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Discussion Starter · #41 ·
I went through the procedure with the sine waves (40, 100, 400, 800, & 1000 Hz) and found that the stock head unit puts out distortion at volume level 29 at 100 Hz. Backing it down to 28 means this is the loudest volume without distortion. Has anyone else come up with the same number? Seems kind of low. On the other hand, the 4 channel amp gains can go all the way up without distortion, so there's that. With the sub adjusted, it blended well with the whole setup. My goal was higher quality sound that can get louder to overcome road/wind noise at high speeds. With a 10" sub, it's not supposed to go bump in the night.

In terms of sound deadening, the doors and trunk did provide a very noticeable reduction in noise. As expected, adding sound deadening to the roof didn't result in any miraculous gains in noise reduction, as the metal roof has already gotten sprayed at the factory with some kind of vibration reduction material, but it did however "tighten" up the sound from all the speakers. It's hard to describe. First off, bass localization is gone. And the harsher highs from the rear 2-ways are gone. Everything just "melts" in just right.

In retrospect, I'm expecting this is the first and last time I'll be installing sound deadening in a car. If and when I ever need to do this on another car, I'll gladly pay have an expert do it.

Oh, and that broken passenger visor... I bought a replacement online. It was only $38 shipped.
 

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When I measured just the output from the Head unit, I got near the top of the volume range before I saw any clipping of the signal. Now that I think about it I was using a 1 khz test tone .It was near 7 volts peak to peak before I saw any distortion. I was driving the 20k ohm input impedance of my DSP.
What procedure did you follow? I am happy to duplicate your procedure to see if I can verify your results.
 

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Discussion Starter · #43 ·
When I measured just the output from the Head unit, I got near the top of the volume range before I saw any clipping of the signal. Now that I think about it I was using a 1 khz test tone .It was near 7 volts peak to peak before I saw any distortion. I was driving the 20k ohm input impedance of my DSP.
What procedure did you follow? I am happy to duplicate your procedure to see if I can verify your results.
I basically went plain vanilla and followed Crutchfield's tutorial:


I did the sweep from 40Hz to 1000Hz. I downloaded the wav files from:


I was able to go way high on the volume for the other frequencies. The 100 Hz was the 2nd one I tried (went in order from lowest to highest). I didn't use an o-scope (mine is so old it has tubes in it and hasn't been fired up in at least 2 decades). I just sat in my car and listened for the hum turning into a buzz.

Thanks.
 

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Discussion Starter · #45 ·
My replacement visor has arrived. All done. Just noticed that the replacement doesn鈥檛 have the obnoxious airbag warning on it.




Sent from my iPhone using Tapatalk
 

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I did some measurements based on the Crutchfield tutorial.
I did not see the same distortion at 100hz that you experienced. I measured at all the same frequencies as Crutchfield suggested and the measurements were all pretty similar.
As you can see from the picture, The head unit was putting out 1.6 volts of signal ( the volume bar in the Head unit was at 60. ) at 100hz and the distortion was .02% THD .

IMG_9608.JPG


Heres the same measurement at 40hz.


IMG_9607.JPG


And the same at 5khz

IMG_9613.JPG


Keep in mind these measurements are of the signal path before any
ampifiers/ signal processors or speakers.
Cheers,
Once I get all me equipment installed I will try again.
 

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Discussion Starter · #47 ·
I did some measurements based on the Crutchfield tutorial.
I did not see the same distortion at 100hz that you experienced. I measured at all the same frequencies as Crutchfield suggested and the measurements were all pretty similar.
As you can see from the picture, The head unit was putting out 1.6 volts of signal ( the volume bar in the Head unit was at 60. ) at 100hz and the distortion was .02% THD .

IMG_9608.JPG


Heres the same measurement at 40hz.


IMG_9607.JPG


And the same at 5khz

IMG_9613.JPG


Keep in mind these measurements are of the signal path before any
ampifiers/ signal processors or speakers.
Cheers,
Once I get all me equipment installed I will try again.
That's good to know. I have bought one of those small imported 2.4" LCD Oscilloscopes and will repeat my gain adjustments once I receive it.

Thanks.
 

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also I pulled the inner fenderwells and "painted" the back with rubberized undercoating spray. So far I'm really pleased with those improvements, but always in the back of my mind I wanted to do as you've done with the sound deadening the roof...
Have some more details on this? I'm similar to @MDBolt in that I bought deadening material but haven't gotten around to installing it, partly due to fear of the clips, but what initially motivated me was actually hearing gravel impacts in the rear wheel wells during winter.
 

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Discussion Starter · #49 ·
I pulled out my old RCA Oscilloscope but it won鈥檛 start up. Bad tube(s).

29615


So I ordered and received my cheap 2.4鈥 LCD oscilloscope in the mail and decided to check gain match my amp with my head unit.

First, I disconnected my speakers and pre-amp connectors. Then using 40hz, 100hz, 1khz, and 4khz 0db sine wave tracks on a USB drive, proceeded to measure each pre-out signal with each track. As stated by Nomisnosnibor, the head unit signals are clean.
29617


29618


The little scope surprised me. It correctly showed the frequency and voltage. The sine wave was clean for all channels at max volume 63 and all 4 channels.

With the amp connected and measuring at the speaker outs the sine waves were a less 鈥渃lean鈥 but this is what I settled on.

29620


29621
 

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Discussion Starter · #50 · (Edited)
29624

29622


Bigger JPG files. Zoom in to see the curve and measurements.

The top picture shows the clean signal from the line out at 40hz.

The bottom picture shows a 1khz sine wave measured at one of the speaker outs at my final gain setting.
 

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Discussion Starter · #51 ·
I may have an explanation as to why I initially thought there was a problem previously at volume 29 at 100hz.

When measuring speaker outputs with an oscilloscope, I found that one of my rear speakers was wired incorrectly (polarity switched). So, I'm guessing that at volume 29 is when I perceived a change in the way it sounded.
 

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Yes, doing the tests that Crutchfield recommends, takes the whole signal chain into account. It encompases the head unit / wiring / amplifiers / signal processor / speakers and cabin cabin ( with its associated rattles and buzzes) etc. It isn't the most accurate , but it does take into account the whole listening environment, and that is ultimately what your ears hear. The picture of your old scope made me smile, I haven't seen one like that in a while!! How much did your new one cost?
 

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Discussion Starter · #53 ·
Yes, doing the tests that Crutchfield recommends, takes the whole signal chain into account. It encompases the head unit / wiring / amplifiers / signal processor / speakers and cabin cabin ( with its associated rattles and buzzes) etc. It isn't the most accurate , but it does take into account the whole listening environment, and that is ultimately what your ears hear. The picture of your old scope made me smile, I haven't seen one like that in a while!! How much did your new one cost?
The scope is a clone of the JYETech DSO150, which itself is a kit scope that basically comes unassembled, requiring soldering all components onto the boards.

My clone scope was fully assembled and cost $29 shipped. Surprisingly enough, the eBay seller shipped from the US. The probe that came with it connects via 2 alligator clips. I bought a 1:10 probe from Amazon for $20 but it did not arrive on time. I just used it as it was.

Works great for an uncalibrated scope.
 
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