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Frequency Response: Stock vs. CleanSweep


msmith

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Hi, guys... I promised you some measurements of the OEM head unit's frequency response before and after CleanSweep, so I took some measurements in my LGT wagon...

 

http://img250.echo.cx/img250/5995/volcomparedefeated8et.th.gif

 

The first graph shows the front-channel factory frequency response of the Subaru head unit with its tone controls set flat, and at 3 different volume settings. The Blue curve is the frequency response at volume 10, the Red curve is the frequency response at Volume 25, the green curve is the frequency response at Volume 35. Needless to say, the behavior is non-linear... Subaru employs a typical loudness compensation curve at low volume (not necessarily a terrible thing) and agressive high-pass filtering at high volumes to protect the factory speakers from failure.

 

The Volume 25 curve shows the correction applied by the Subaru engineer's to compensate for their speakers. Upper bass boost, lower bass rolloff and some mild manipulation of the midrange and upper treble. This is actually pretty tame compared to many of the OEM head units I've tested.

 

http://img250.echo.cx/img250/3127/vol25csactivevsdefeated0cb.th.gif

 

The second graph compares the factory frequency response at Volume 25 (Red) to the frequency response after CleanSweep correction (Blue). As you can see, the CleanSweep effectively corrects the response to within plus or minus 1 dB, which is quite comparable to a good quality aftermarket head unit's frequency response. I picked Volume 25 as the calibration point for my CleanSweep.

 

http://img250.echo.cx/img250/448/volcompareactive4rh.th.gif

 

The third graph shows what results if you apply a CleanSweep (calibrated at Vol 25) but decide to use the factory volume control instead of the totally linear CleanSweep volume knob.

 

EDIT: the curves are mislabeled on the first and last graph: Red is actually volume 25, Blue is Vol. 10, Green is volume 35.

 

These should hopefully answer some of the questions about the need for response correction, volume control linearity, etc. Or it might actually prompt new questions...

 

Best regards,

 

Manville Smith

JL Audio, Inc.

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Wow, great representation! I was already sold, but now you've just made me feel better about it. The one plot I would be interested in seeing would be the frequency response coming from the CS at its own low, med, and high volumes with the factory volume at the calibrated level. (Would this be boring? Does it stay exactly the same as the blue line in your second plot?) I think it would make a nice contrast to your third plot.

 

Thanks again, Manville! Can't wait for the shots of your venting for the amps. I opened up the spare well again today and started dreaming...there's more room in there than I thought. Oh, and just out of curiosity, where did you put your CS?

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Good to see I'm not the only nerd here ;)

 

Is the equalization applied at high volumes linear? i.e. if you have a -40dB sinewave at 60Hz and volume 35, is it still equalized to -8dB?

 

What's your practical expectation of low-end extension without introducing noise? 20Hz? I really had to fight a battle to get my setup to reproduce this, still not as low as I want.

 

Have you tried to see what kind of curve you get when readjusting the stock tone controls? It seems they might be pre-weighted by default. I find -3 on the bass to be close to flat at volume 10, it seems 70-80Hz could be the center frequency by guesstimation, if they are doing this the way I think they are, I bet each one of those lumps corresponds to the right frequency on the 3 tone controls, and < 35Hz unrecoverable without EQ. Oh, and I still find > 12 on the volume control to be very loud, even for non-compressed music.

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What's your practical expectation of low-end extension without introducing noise? 20Hz? I really had to fight a battle to get my setup to reproduce this, still not as low as I want.

 

 

You want lower than 20Hz?

OBAMA......One Big Ass Mistake America!
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Good to see I'm not the only nerd here ;)

 

Is the equalization applied at high volumes linear? i.e. if you have a -40dB sinewave at 60Hz and volume 35, is it still equalized to -8dB?

 

What's your practical expectation of low-end extension without introducing noise? 20Hz? I really had to fight a battle to get my setup to reproduce this, still not as low as I want.

 

Have you tried to see what kind of curve you get when readjusting the stock tone controls? It seems they might be pre-weighted by default. I find -3 on the bass to be close to flat at volume 10, it seems 70-80Hz could be the center frequency by guesstimation, if they are doing this the way I think they are, I bet each one of those lumps corresponds to the right frequency on the 3 tone controls, and < 35Hz unrecoverable without EQ. Oh, and I still find > 12 on the volume control to be very loud, even for non-compressed music.

 

Yes, the EQ effect would be linear relative to the recording's signal intensity... it appears to simply be a function of volume control position. By looking at the curve at high volumes you can clearly see that it is a simple 6dB/octave high-pass filter at 20 kHz. It has no way of knowing the level of the recorded signal.

 

I didn't record the tone control effects but I did look at them on the RTA... the bass boost is centered at about 150 Hz (really high) and has a very broad curve... the treble control is broad as well, probably centered at around 5 kHz. The mid is centered around 1 kHz and is very wide as well. Next time I drag the RTA out to the car, I'll store the data and do a graph.

 

As for low frequency extension, the CleanSweep's lowest EQ band is 25 Hz, so it can effectively rescue response down to about 20 Hz. If the OEM system is not rolled off on the low end, you can expect response to extend below 20 Hz, but it if it is rolled off (like the LGT's) then it probably won't extend below 20 Hz. I'll add that to the measurement list if you're curious about it.... I should point out that very few music recordings have significant content below 20 Hz and these are usually either pipe organs, synthesized effects or sound effects (like cannons in the 1812 overture)... for 99.9999% of recorded music, 20 Hz is perfectly fine as a lower frequency limit.

 

Best regards,

 

Manville Smith

JL Audio, Inc.

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i have about $400 to burn, and figured i might as well help ym audio out a bit... i looked up clenasweep on JL's website. so its basically a sound enhancer (i'm sure thats putting it very simply from what i read)? i might be interested. i guess i should ask what benefits it would bring about for a user like me. i have sirius satelite radio going through an fm modulator and i play cds, occasioanlly stereo.
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....but you will FEEL it.

 

you won't hear a heavily amplified 7Hz wave, but it will make you nauseous and vomiting. i had a cool physics professor. :D

 

Actually, they tried that on Mythbusters. They stood in a the center of a semi-circular array of huge woofers with something like 1.21 gigawatts pumping through at frequencies from 2 to 12 hz. No nausea, confusion or pants soiling ensued.

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Actually, they tried that on Mythbusters. They stood in a the center of a semi-circular array of huge woofers with something like 1.21 gigawatts pumping through at frequencies from 2 to 12 hz. No nausea, confusion or pants soiling ensued.

 

 

dang what episode was that? (i hate when I miss good ones)

 

-Nick

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mmanus88.... it would make zero sense to apply a CleanSweep and retain the stock speaker system. The CleanSweep is intended to facilitate aftermarket amplifier and speaker installation by removing the Subaru factory EQ which was put in to address issues with the stock speaker system and setup.

 

Best regards,

 

Manville Smith

JL Audio, Inc.

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That's a cool widget but I'm bummed it has it's own volume knob.

 

I'd prefer a smarter unit that you can calibrate to your factory headunit for it's entire output/power range and then use the volume knob that you already have OR have it regulate the output such that the input volume level has no effect on the output.

 

As to the aux in: nice but again it's a feature I wouldn't use.

 

I guess what I want is the simplicity of a generic LOC combined with the DSP/EQ goodness of the CleanSweep.

 

My application would be Stock HU ->CleanSweep->Empeg Aux In-> Amp, where the Empeg controls the volume and no matter how I twiddel the volume on the stock HU, nothing happens.

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That's a cool widget but I'm bummed it has it's own volume knob.

 

I'd prefer a smarter unit that you can calibrate to your factory headunit for it's entire output/power range and then use the volume knob that you already have OR have it regulate the output such that the input volume level has no effect on the output.

 

As to the aux in: nice but again it's a feature I wouldn't use.

 

I guess what I want is the simplicity of a generic LOC combined with the DSP/EQ goodness of the CleanSweep.

 

My application would be Stock HU ->CleanSweep->Empeg Aux In-> Amp, where the Empeg controls the volume and no matter how I twiddel the volume on the stock HU, nothing happens.

Wow, I'm amazed the volume knob is such a big deal. From an engineering standpoint, it's easy to understand why it's necessary. Just look at the different HU responses across the volume range at the beginning of this post. How would the CleanSweep know the difference between a change in volume, which should be corrected for, and a change in the music, which should not? In designing the CS, there are compromises, as with any design. Regarding convenience vs. sound quality (if you see the volume knob as an inconvenience), I feel like anyone who would even consider buying the CS has already made their decision toward the latter.

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