Awesome write-up, your experience will come in handy when I upgrade my base stereo in the future.

 

Thanks if you have questions feel free to ask. I have a one hour video Video it's long but hopefully helpful It is boring in parts but I think it would be helpful in providing some answers to various install questions. Most of the video covers everything but I did not get into the Fakra adapter details that I posted on other posts but the Fakra adaptor and wire codes are verified and I had no warning lights using the Audio Control LOC units (highly recommend these)

 

Also as mentioned in other posts I can verify the factory head unit clips at level 29. I used a pocket oscilloscope and a 0 db 1khz test tone.

Mine clipped at 22. The correct test tone frequency to use is 650Hz, this is the peak output frequency with the factory EQ not bypassed. You will also get an artificially higher number if the engine is running and the alternator is charging (higher voltage in to the head unit is higher unclipped output from the internal amplifier).

It'll also depend a little on what source you're using on the head unit. Aux input is a big variable because how much voltage you're shoving into the 3.5mm jack in the car will vary what point the head unit clips at.

 

There is no EQ unless your talking about the bass/treble controls. I'm referring to the base audio system (non-HK) sound system. I had the tone controls flat and the car was not running during the test so it was just off an input voltage of 12 volts running off the battery. I'm not sure where you came up with the 650Hz figure but I doubt it would would give much different results but maybe it would. Mayber a level or two but not the difference you're stating. That being said I have previously ran the stereo prior to this test pretty high around level 34 and did not hear any audiable distortion but that was listening to music not test tones. In the final analysis I can confidently say that for the base system you can go up to 28 and use that to set your gains. Its all relative we're in the real world listening to music not test tones. Again only speaking for the base audio system not HK sound system which may be much different, not sure. As already stated this is only rated and set using the USB input and FLAC files which is what I always listen to. I'm not sure how much this really matters I know I probably I left headroom on the table.

Since installing the system I don't think I ever set the volume higher than 23 or 24. My amp gains are real low maybe at 25 percent as the LOC has a strong line driver built in providing good voltage. I did not max out my gains on the amps to the brink no need as I am getting great results with lower settings. My main concern was getting the LOC set properly at level 28 once that was established using my pocket O scope. After that I set the other levels manually. My results are clean and distortion free and probably better than those who max out their gain settings. Just because you can go higher doesn't mean you should or that it's better. That's an opinion and I'm sure others will disagree, but hey I've only been building systems for 20 years so what do I know.

 

Well, I'm skeptical about your measurements. So far my system as is sounds great to me but I will admit I have not listened to other sources other than USB input. I do have a professional RTA measurement microphone so maybe I will crack out my laptop and RTA with some pink noise and see if there are any real peak output issues with EQ manipulation. I certainly won't be measuring it at anywhere near 100db levels.

I would expect EQ manipulation on the HK system as HK is in general is known for such tweeks and they are also using active crossovers in their system as well as other methods. Still I wouldn't think they would boost the lower midrange area as this would create a drone like sound.

The base system doesn't seem to be a good motivation or reason to drastically EQ the car as your graph suggests since the OEM base speakers actually perform well both in and out of the car. I have bench tested the OEM speakers with decent results so it seems there would be no need for the factory to initiate such a drastic EQ correction. Especially at the 650hz range which makes no sense to me.

Most manufactures that do mess with eq apply an active filter on the lower frequencies to improve performance. This would be expected at frequencies 150 hz and below. I'm not sure why the graph you linked to showes that the factory would create a peak at the 650 hz range. I did notice the measurements were taken at way over 100 db level which seems to make me wonder if that had something to do with the results. Almost all speakers, even cheap ones, can play the the midrange frequencies with little effort so that whole scenario of the factory boosting the 650hz midrange makes no logical sense to me. Why would they do it? Speakers don't need help in that region. It doesnt make any speaker sound better regardless of quality. The graph is showing an 8 db boost there and I certainly can't hear that when listening to my system. At the same time looking at that graph there is significant peak at the 50-60hz range though not as pronounced as the 650hz peak it still seems about 4db up at that level. Why would they eq that? This would be harder on their factory speakers to perfom bass which would defy logic. Seems like they would just not eq it at all which is what I think they actually did. I edit audio as part of my work as a professional so I would think my ear would be able to discern such a large boost in that 650hz range. That midrange area is very droning when boosted so I'm sure if it were actually there I would notice it so I'm currently doubting the methodology in how this measurement was taken and what equipment was used to acheive these results.

In any case, I have no access to the ETM to change byte settings as I don't have the software or special cables required. I could enable the accubase correction on my Audio control LOC unit if I felt the lower frequencies where being attenuated or something so I suppose I could look into that after cracking out my RTA and RTA mic. Currently Accubase correction is completely off as during my original research, and my ear it seemed to indicate that the base audio system had no eq correction to it. Certainly listening to my system there is good bass response in the 50 to 60hz range so any lack of base through OEM EQ settings I'm guessing would have been in the lower 40hz range which is pretty low but maybe the accubase could correct that not sure if it's needed.

 

First off, another user replied with essentially identical measurements. Doubt my measurement all you want, but it was confirmed by somebody else.
Secondly, those measurements were made electrically. The absolute SPL level is not relevant. I am obviously not measuring this output acoustically, that would be irrelevant.

A lot has changed in car audio over 20 years. Base systems from everyone have substantial amounts of EQ now. The head units have the processing power for it, gone are the days of needing hardware based filters. Some of the factory EQ is just correcting for the response environment of the car, but not all of it. A lot of the best high end car audio shops have turned their stage 1 audio upgrade into just adding a DSP and amplifier to the stock speakers because fixing the factory processing is their first order of business.

 

Okay so it’s the base audio system without external amplification under HU power.

When you took the measurement did you use pink noise? You said you did this electronically what exactly does that mean? For example are you saying you played a pink noise track and measured the speaker or line level signal outputs to get your results? I understand you did not use a n RTA mic just wondering exactly how the measurement was achieved.

 

Okay so it’s the base audio system without external amplification under HU power.

When you took the measurement did you use pink noise? You said you did this electronically what exactly does that mean? For example are you saying you played a pink noise track and measured the speaker or line level signal outputs to get your results? I understand you did not use a n RTA mic just wondering exactly how the measurement was achieved.

I would assume he used the line level output into an input on a laptop. Pure electrical signal measurement.