# Measuring OEM HU frequency response?



## FordEscape (Nov 23, 2014)

I'm really curious about the frequency range of the high-level signal (not the sound out of the speakers) out of my OEM Ford HU that feeds my MS-8. I have 4 channels of output (front L+R, Rear L+R) feeding the MS-8. In part I'm curious to know if the front and rear HU output signals differ.

Nothing I can do to alter the HU output, so call it 'academic curiosity'.

The car has RCA jack inputs for connecting an external DVD player (L & R audio + video jacks).

Am I correct in understanding that a signal generator to those inputs with an O-scope connected to the high-level outputs I've got pulled to my MS-8 could provide that info?

What would that 'test procedure' be called if shopping for it at local audio shops and what would I expect to pay to get that info? What sort of 'results sheet' should I expect (a table of frequencies and levels, a plot of frequency vs dB, or ??)

Anyone happen to have a recommendation for where to get this done in the Austin, TX area?

Thanks In Advance


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## Sine Swept (Sep 3, 2010)

I do not know about this per se, however I have looked this elegant piece of equipment up and down a few times (not in the flesh however)

Minilyzer ML1 - Audio Analyzer

As for price, I guess if you could afford one it might be worth having.


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## FordEscape (Nov 23, 2014)

Umm, nifty but mine is a 'one-shot' interest so the economics don't work for buying the tools ;-)


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## Jepalan (Jun 27, 2013)

FWIW, per page 9 of the MS-8 user's manual, you only want to connect Front L/R and Subwoofer signals into the inputs of the MS-8. Do not connect rear, side or center channels into the MS-8. 

http://ms8-eu.jbl.com/install.html?file=tl_files/content_resources/jbl-ms8/Owners%20Manual.pdf

You would typically want to use an audio spectrum analyzer, audio real-time analyzer (RTA), or a software tool like Room EQ Wizard (REW) to measure the response of your OEM system, not an O-Scope.


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## gstokes (Apr 20, 2014)

Jepalan said:


> .. You would typically want to use an audio spectrum analyzer, audio real-time analyzer (RTA), or a software tool like Room EQ Wizard (REW) to measure the response of your OEM system, not an O-Scope.


x 2, a software based RTA and a calibrated microphone will serve you well, something like this..

TrueRTA Audio Spectrum Analyzer Download Page

or

http://www.roomeqwizard.com/


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## FordEscape (Nov 23, 2014)

Please read my OP carefully ..... I'm not trying to measure the audible output from speakers/room, I want to know the quality of the high-level signal from the HU alone, not the audible response of the whole system of speakers and amps.

I want to know if it actually delivers a full 20 - 20kHz spectrum to the MS-8 or is it inherently 'limited' in some way. E.g. does Ford filter the signal below a frequency higher than 20Hz because they knew the OEM speakers could not handle those low frequencies (there was no subwoofer in the OEM system)?


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## cajunner (Apr 13, 2007)

FordEscape said:


> Please read my OP carefully ..... I'm not trying to measure the audible output from speakers/room, I want to know the quality of the high-level signal from the HU alone, not the audible response of the whole system of speakers and amps.
> 
> I want to know if it actually delivers a full 20 - 20kHz spectrum to the MS-8 or is it inherently 'limited' in some way. E.g. does Ford filter the signal below a frequency higher than 20Hz because they knew the OEM speakers could not handle those low frequencies (there was no subwoofer in the OEM system)?


that's what everybody wants.

I think there are several threads that have random tests on various OEM systems, I would trust that over having to go through the process of it...

I think ErinH did tests on aftermarket decks, using AudioMark or Audio Precision software/hardware?

I would assume that if there's an external amp to the system, it would be as simple as running an RTA on the electrical signal coming from the deck?

it seems like this should be relatively easy information to find out, Bing probably has to do this sort of testing with each OEM system he's told to keep the factory deck...


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## gstokes (Apr 20, 2014)

FordEscape said:


> ..I want to know the quality of the high-level signal from the HU alone, ..
> 
> I want to know if it actually delivers a full 20 - 20kHz spectrum to the MS-8 or is it inherently 'limited' in some way. E.g. does Ford filter the signal below a frequency higher than 20Hz because they knew the OEM speakers could not handle those low frequencies (there was no subwoofer in the OEM system)?


If you have LF RF LR AND RR speaker wires coming out then chances are excellent they are receiving full-range 20 - 20Khz signal, if you had more than 4 wires coming out there's a better chance that the lows are on another channel but not in your case..
The factory speakers are (usually) passively crossed with a HP filter so they don't receive sub frequencies..
Use the LF and RF to provide full-range signal to the MS-8, that's it..


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## Jepalan (Jun 27, 2013)

You will have to build a voltage divider, or use a high quality LOC (but the LOC could color your measurement). I've always used a LOC or DSP with OEM sources, so I just run the output of the LOC or DSP (set flat) into the line input on the PC and use TrueRTA, REW or similar to measure freq response. This way I am looking at the actual signal with the OEM HU loaded as I will be using it.

There is a bit more info here:
LINK -> http://www.diymobileaudio.com/forum/how-articles-provided-our-members/73776-using-truerta-mobilepre-measure-frequency-response-headunits.html


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## gijoe (Mar 25, 2008)

What Jepalan is saying is that you still need to use an RTA program such as REW, but instead of using a microphone to measure the acoustic response you use the circuit he described to take the electrical output from the source and plug it into the computer.


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## DDfusion (Apr 23, 2015)

I have the non touch screen HU in my fusion. Played with a AC RTA a few days ago. It's all good.


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## Babs (Jul 6, 2007)

I wonder if you could kinda create a feedback loop of sorts for REW.. Get the OEM signal of one channel down to line-level to feed back into the sound-card as a "mic" maybe. Measure a sweep.. Something like the sound-card calibration does it. Basically bypassing the OEM amp and speaker.. Going direct. I dunno. ??


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## gstokes (Apr 20, 2014)

gijoe said:


> What Jepalan is saying is that you still need to use an RTA program such as REW, but instead of using a microphone to measure the acoustic response you use the circuit he described to take the electrical output from the source and plug it into the computer.


x 2, this Voltage Divider Calculator plus parts labor soldering etc and REW or TrueRTA

or

$43 calibrated microphone, Dayton Audio EMM-6 Electret Measurement Microphone plus cable and REW or TrueRTA

choose your poison..


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## gijoe (Mar 25, 2008)

gstokes said:


> x 2, this Voltage Divider Calculator plus parts labor soldering etc and REW or TrueRTA
> 
> or
> 
> ...


Except in the OP's case, using a mic will not tell him whether or not the OEM setup has a flat response. If it is tuned from the factory, the OEM setup could have some strange response curve built in and the only way to find out would be to check the signal electrically, not acoustically.


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## FordEscape (Nov 23, 2014)

gijoe said:


> Except in the OP's case, using a mic will not tell him whether or not the OEM setup has a flat response. If it is tuned from the factory, the OEM setup could have some strange response curve built in and the only way to find out would be to check the signal electrically, not acoustically.


Bingo, thank you.


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## gijoe (Mar 25, 2008)

FordEscape said:


> Bingo, thank you.


Take a look at Jepalan's post. I don't know much about building this circuit, but this is what you'll want to investigate. I'm not sure if this is the easiest way to go about this (I've never done an install that kept the factory stereo, so it's never been something I've personally took much interest in learning), but it's basically what you'll need to do, unless you can find a forum specific to your car to see if anyone has already tested the OEM frequency response.


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## FordEscape (Nov 23, 2014)

gijoe said:


> Take a look at Jepalan's post. I don't know much about building this circuit, but this is what you'll want to investigate. I'm not sure if this is the easiest way to go about this (I've never done an install that kept the factory stereo, so it's never been something I've personally took much interest in learning), but it's basically what you'll need to do, unless you can find a forum specific to your car to see if anyone has already tested the OEM frequency response.


Yeah, I've not been able to find any OEM specs or test data on the specific HU I have, used on certain Focus & Escape models for '13-'15 (not the unit mentioned by DDfusion). Ford touts it is 'tuned for the application' so it's reasonable to expect the built-in response curve would differ between the Escape and the Focus (the replacement PN's are different for the 'same' component).

It'll take a lot more research to come up with the DIY tools to measure as described in the linked ERIN H post. Somewhat complicated by my Dell laptop's single-jack mic/headphone connector (why I went with the USB UMIK-1 calibrated mic) with no spec found for its acceptable input voltage range to enter into the voltage divider calc. Could be solved with purchase of an external soundcard/pre-in but it starts to add-up and I don't see any other future use for the setup. That's the reason I'd just as soon pay for the one-time measurement by someone already equipped for the job if it isn't cost prohibitive.


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## JohnnyOhh (Feb 19, 2015)

FordEscape said:


> I'm really curious about the frequency range of the high-level signal (not the sound out of the speakers) out of my OEM Ford HU that feeds my MS-8. I have 4 channels of output (front L+R, Rear L+R) feeding the MS-8. In part I'm curious to know if the front and rear HU output signals differ.
> 
> Nothing I can do to alter the HU output, so call it 'academic curiosity'.
> 
> ...


This is an awesome question. I have done this type of testing on my 2011 Ford Mustang GT with Sync. I had a great time doing it & learned a lot. I can share my results with you and the procedure I used. From my experience, Ford does apply equalization to the electrical output on the Sync system.

The testing is pretty straight forward. You just need to disconnect a speaker and insert a resistive load in its place (8 ohm non-inductive resistor would do the trick). You need to hold the load constant so it doesn't vary with output frequency like a speaker does. Then you need to measure the RMS voltage across the resistor while you play sine waves at different frequencies into the resistor. Each time you play a different frequency sine wave, you will record a different RMS voltage and then you can build a simple table with frequency vs. voltage. Then you can plot these in X-Y to see what the frequency response looks like. Ideally you would want to test all the speakers frequency response to see what you have. You can test as many different frequencies as you would like, 15, 30, 60.

A DIY way to do this would be to measure RMS voltage with a o-scope and record the values at each frequency. Another way would be to use a data acquisition tool to do this automatically.

Now, I think a professional way to do this would be using an audio analyzer tool like ones offered by Audio Precision. Unfortunately, these tools cost thousands of dollars if not 10's of thousands of dollars. So DIY method is probably you best bet.

AP High Performance Audio Analyzer & Audio Test Instruments : introtoaudiotest


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## JohnnyOhh (Feb 19, 2015)

I tested about 60 different frequencies (1/6 octave spacing) at each different volume level (32 volume levels total). And that took about 8 hrs once my test system was set up. Although the results are pretty straight forward, collecting the data and setting this up at that level of detail, is time consuming for sure. I wouldn't expect an average shop to be able to handle this type of testing.

It is totally doable though. And a necessity to understand what your OEM system is doing, IMO.


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## JohnnyOhh (Feb 19, 2015)

Here is an example of the frequency response (electrical) from my Mustang with Sync. I recall for this test, I used 20k Ohm load.


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## Spud100 (Mar 30, 2015)

OOH!!, now we can see why factory systems sound funny.

I suspect that other Ford systems have similar responses.

The scary thing is that the response curves become somewhat exaggerated at higher volume settings.

This suggests, with a DeEQ function in a DSP that you need to run the HU in normal use at the volume setting that the system is set up then control the volume through the DSP.

Gerry


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## Phil Indeblanc (May 27, 2015)

Why not just swap the head unit and listen for major or even slight differences?


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## gijoe (Mar 25, 2008)

Phil Indeblanc said:


> Why not just swap the head unit and listen for major or even slight differences?


I'm just speculating here, but the main reason someone would want to know the FR of an OEM system is so they don't have to swap it out. That's the step that is trying to be avoided.

The second thing to note is that you simply do not have the memory capable of comparing slight differences after the time it would take to swap things back and forth, then level match them. Unless there is a direct, nearly immediate, swap then you will not be able to pick up on any slight differences with any degree of accuracy. Sure, you could probably notice the big differences, but for any useful information to be obtained you would need to level match the two sources, then switch them back and forth to compare them immediately.


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## Phil Indeblanc (May 27, 2015)

Yes, ok, 

So either doing a setup to quickly swap, or to play one and measure output, play other and measure. I have been able to tell this difference as I played the same track over and over, and i knew it should sound different. so when I did the swap even a minute later, it was obvious. This is years ago, and it was the reason to get rid of the HUnit.


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## Phil Indeblanc (May 27, 2015)

Its just shocking to me with people doing this as a profession have no idea about the differences...
at the same time it is so oddly understandable.

A person who builds systems professionally is not always going to be the same guy that's gonna be able to tell the difference from one sound to the other. 

If your ear isn't used to hearing sound and then dissecting its character for its nuances, and then measure to test the claims, then its just going to be an unknown.


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## susedan (Aug 11, 2015)

JohnnyOhh said:


> I tested about 60 different frequencies (1/6 octave spacing) at each different volume level (32 volume levels total). And that took about 8 hrs once my test system was set up. Although the results are pretty straight forward, collecting the data and setting this up at that level of detail, is time consuming for sure. I wouldn't expect an average shop to be able to handle this type of testing.
> 
> It is totally doable though. And a necessity to understand what your OEM system is doing, IMO.



Where did you find 1/6 octave tones? Did you make them?


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## gijoe (Mar 25, 2008)

Phil Indeblanc said:


> Its just shocking to me with people doing this as a profession have no idea about the differences...
> at the same time it is so oddly understandable.
> 
> A person who builds systems professionally is not always going to be the same guy that's gonna be able to tell the difference from one sound to the other.
> ...


It's shocking to me how much some people over estimate their echoic memory. Yes, a well trained ear can pick up differences that most people cannot, but I think you have a bit too much confidence in your ability to remember sounds that are generally only stored for a few seconds at a time. Our senses are fallible, and we simply cannot recall auditory information after a short period of time. It's reasonable to hear differences, but being able to specifically identify those difference without an immediate, back to back comparison, is not something I would trust. The sources must be level matched, then compared immediately, and even then, saying one is better than the other is challenging without objective measurements. Swapping a head unit and listening over the course of 20 minutes is completely unreliable, and I would not trust and conclusions made from a "test" of this sort.


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## ndm (Jul 5, 2007)

FordEscape said:


> I'm really curious about the frequency range of the high-level signal (not the sound out of the speakers) out of my OEM Ford HU that feeds my MS-8. I have 4 channels of output (front L+R, Rear L+R) feeding the MS-8. In part I'm curious to know if the front and rear HU output signals differ.
> 
> Nothing I can do to alter the HU output, so call it 'academic curiosity'.
> 
> ...


I inquired about this exact subject a few months back and found what is a great solution. The answer came from Bing at simplicity in sound. See the following thread.

http:// http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/168990-testing-factory-frequency-response-per-channel.html

This solution uses your dsp as the voltage divider and REW is a free program. The only difference between this and using REW as an rta is that instead of measuring with a mic, you are measuring the electronicsignature of your channel at the rca level. This is basically a high resolution spectrum analyser using equipment that many serious enthusiasts have already. (Dsp, rew, laptop) 

Let me know if you have questions. 

This is the factory response of my factory amplified system before I changed to aftermarket.


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## Phil Indeblanc (May 27, 2015)

ndm said:


> I inquired about this exact subject a few months back and found what is a great solution. The answer came from Bing at simplicity in sound. See the following thread.
> 
> http:// http://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/168990-testing-factory-frequency-response-per-channel.html
> 
> ...


(Would be nice to see the before vs after graphs)


Thanks for this...While I mostly agree with GiJoe, maybe most people can't, but I don't think most people spend 25 years of their lives listening to music for the sake of sound vs the sake of pleasure as I have. Granted, many of those were just hearing it vs listening to it. Regardless, I too understand an agree with you ..If you let too many seconds pass you will not have a good comparison. So yes, perhaps unplugging a harness and powering back up with the same track maybe fast using 2 sources of the file and making the swap just by the harness...it maybe too long. But if the difference is large enough, I think I would be able to tell...maybe in a 10sec situation? I don't know...So yes, measured is the way to go.

NDN...I have the RF360.3 DSP, and I do have a mic, which I wont use, and makes sense from what I read to testing electronically, vs acoustically.

So how do I go about this? I have REW on a laptop as well. Maybe a video would be the best way to translate this.

Thanks


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## gijoe (Mar 25, 2008)

Phil Indeblanc said:


> (Would be nice to see the before vs after graphs)
> 
> 
> Thanks for this...While I mostly agree with GiJoe, maybe most people can't, but I don't think most people spend 25 years of their lives listening to music for the sake of sound vs the sake of pleasure as I have. Granted, many of those were just hearing it vs listening to it. Regardless, I too understand an agree with you ..If you let too many seconds pass you will not have a good comparison. So yes, perhaps unplugging a harness and powering back up with the same track maybe fast using 2 sources of the file and making the swap just by the harness...it maybe too long. But if the difference is large enough, I think I would be able to tell...maybe in a 10sec situation? I don't know...So yes, measured is the way to go.
> ...


Echoic memory would say that you've got 3-4 seconds to work with, that's it. So, back to the topic on hand, you really have to measure the frequency response of an OEM HU, you can't swap them back and forth with speakers to hear what kind of EQ might have been applied. The FR could be terrible, and you wouldn't be able to able to accurately show that by swapping HU's, you would have to measure it.


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## ndm (Jul 5, 2007)

Phil Indeblanc said:


> (Would be nice to see the before vs after graphs)
> 
> 
> Thanks for this...While I mostly agree with GiJoe, maybe most people can't, but I don't think most people spend 25 years of their lives listening to music for the sake of sound vs the sake of pleasure as I have. Granted, many of those were just hearing it vs listening to it. Regardless, I too understand an agree with you ..If you let too many seconds pass you will not have a good comparison. So yes, perhaps unplugging a harness and powering back up with the same track maybe fast using 2 sources of the file and making the swap just by the harness...it maybe too long. But if the difference is large enough, I think I would be able to tell...maybe in a 10sec situation? I don't know...So yes, measured is the way to go.
> ...


Set rew up as you would for measuring as an rta. 
Run the high level wires to the dsp.
Flatten all processing of the signal in the dsp. You want the signal to be unmolested.
Unplug the mic from your preamp and plug the rca output into the input where the mic was plugged. The dsp will convert the high level to safe low level output. 

Then measure your system just as you would if the mic was hooked up.


You will have to do some playing with rew to figure out how to use it but once you can use the rta and impulse measurements in rew, you will know how to do this.


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## JohnnyOhh (Feb 19, 2015)

I created the tones from this website. You can make any frequency & any level sine tones. Worked well for me.

Free Online Audio Tests, Test Tones and Tone Generators

Sine Waveform | Online Sine Tone Wave File Generator



susedan said:


> Where did you find 1/6 octave tones? Did you make them?


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## Phil Indeblanc (May 27, 2015)

I forgot what the "high level wires" were :-/ (I know)

Everything on my system has been done , apart from changing the head unit.

Surprised, that no one with a recent Toyota, the #1 selling car in America, has tested their system to know if the head unit on a basic system puts out a full range across the volume range?


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## susedan (Aug 11, 2015)

JohnnyOhh said:


> I created the tones from this website. You can make any frequency & any level sine tones. Worked well for me.
> 
> 
> 
> ...



Thanks! I've been trying to find some 1/6 pink noise, but no luck yet :/


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## JohnnyOhh (Feb 19, 2015)

I'm not sure exactly what pink noise is. Audio Check has some though. I'm not sure what kind..? Sorry can't help on that one.

High Quality Pink Noise | wav mp3 Audio Files Download



susedan said:


> Thanks! I've been trying to find some 1/6 pink noise, but no luck yet :/


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## ndm (Jul 5, 2007)

JohnnyOhh said:


> I'm not sure exactly what pink noise is. Audio Check has some though. I'm not sure what kind..? Sorry can't help on that one.
> 
> High Quality Pink Noise | wav mp3 Audio Files Download


You will need to start readi g sime of the stickys in this site and get a good understanding of what these terms mean before you will understand this process. I would love to explain but the info is all here and has been covered many times. I am in the middle of some stuff and dont have the time to fully explain.

Sorry bud.start with the first timers guide to measuring your system threàd


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## JohnnyOhh (Feb 19, 2015)

Thanks man. I was just responding to a question from susedan earlier. And the results you have look pretty awesome.

I did have one question for you, once you are all set-up, how long does it take to get those response graphs/results? Are we talking like 10 min, or 1hr, or few hours?



ndm said:


> You will need to start readi g sime of the stickys in this site and get a good understanding of what these terms mean before you will understand this process. I would love to explain but the info is all here and has been covered many times. I am in the middle of some stuff and dont have the time to fully explain.
> 
> Sorry bud.start with the first timers guide to measuring your system threàd


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## motomech (Nov 12, 2014)

Phil Indeblanc said:


> I forgot what the "high level wires" were :-/ (I know)
> 
> Everything on my system has been done , apart from changing the head unit.
> 
> Surprised, that no one with a recent Toyota, the #1 selling car in America, has tested their system to know if the head unit on a basic system puts out a full range across the volume range?


Phil,
I asked Mapletech when he started his Highlander build if there was FR output and as I recall he replied that there was.


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## ndm (Jul 5, 2007)

JohnnyOhh said:


> Thanks man. I was just responding to a question from susedan earlier. And the results you have look pretty awesome.
> 
> I did have one question for you, once you are all set-up, how long does it take to get those response graphs/results? Are we talking like 10 min, or 1hr, or few hours?


As fast as you can measure each channel with rew. I would say less than 30 min start to finish. Depends on how many channels you want to measure and the time it takes to change rcas to the next channel. 

Rew measurements are pretty quick.


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## Phil Indeblanc (May 27, 2015)

motomech said:


> Phil,
> I asked Mapletech when he started his Highlander build if there was FR output and as I recall he replied that there was.


Oh, yes MapleTech. That sweet amp rack build that didn't go in due to the tar spray issue. Bummer on that.
I wonder if he got his sound setup complete? 

I wish he posted some details about it. Did he say so personaly or in a thread you can link/highlight?

Thanks motomech!


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## motomech (Nov 12, 2014)

in response to the FR question mapletech wrote-
"It does...with the caveat that that signal is EQ'd in the HU. When I was doing gain tweaking, I scoped the outputs of the amps, running just sine wave from an ipod app. There is a notable hump around 75Hz, but then a fairly steep rolloff below that. Didn't really look at how flat it was to the lowest frequencies, but those will likely need a decent boost to get 'flat'.
There's some other EQ work done too - I'll put that up once I get to tuning stage - hopefully next week. "

Maybe you can get him out of seclusion to do a followup on his build.



http://www.diymobileaudio.com/forum...-gallery/167133-2014-highlander-sq-build.html


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## Phil Indeblanc (May 27, 2015)

Nice....Yeah, I guess I need a new head unit!
Maybe a 4100nex, or anything better for multi OS (ios&android) compatibility?

I like just about all the tech except for Navigation. Would like camera for not only rear, but another for front....etc


I have a DSP, but it can only do so much when trying to boost certain channels.


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## XR250rdr (Mar 22, 2011)

Phil Indeblanc said:


> I forgot what the "high level wires" were :-/ (I know)
> 
> Everything on my system has been done , apart from changing the head unit.
> 
> Surprised, that no one with a recent Toyota, the #1 selling car in America, has tested their system to know if the head unit on a basic system puts out a full range across the volume range?


I briefly ran a 2014 Sienna factory nav head unit in my 4Runner. Checked frequency response with a similar setup to ndm using REW. The graphs shown are volume levels 20-50 at 10 increments. 60 is maximum.

Ended up taking it out because it had a terrible noise floor.


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## Niick (Jun 3, 2015)

XR250rdr said:


> I briefly ran a 2014 Sienna factory nav head unit in my 4Runner. Checked frequency response with a similar setup to ndm using REW. The graphs shown are volume levels 20-50 at 10 increments. 60 is maximum.
> 
> Ended up taking it out because it had a terrible noise floor.


im pretty sure that the high frequency ripples in those measurements are measurement artifacts. 

I've had a similar results when I didn't realize that my "monitor mix" knob on my audio interface wasn't set to full out/computer position. 

Can you post the full IR (s) of that same data? When it happened to me, I had another, smaller copy of the main IR positioned in time exactly where the interface latency (in ms) would be.


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## XR250rdr (Mar 22, 2011)

Niick said:


> im pretty sure that the high frequency ripples in those measurements are measurement artifacts.
> 
> I've had a similar results when I didn't realize that my "monitor mix" knob on my audio interface wasn't set to full out/computer position.
> 
> Can you post the full IR (s) of that same data? When it happened to me, I had another, smaller copy of the main IR positioned in time exactly where the interface latency (in ms) would be.


I think you're right. I'm surprised REW didn't pick it up during calibration.

I found another measurement I did on my laptop and no ripples.


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## 14642 (May 19, 2008)

Here is a way to do it with a volt meter and microsoft Excel. Download the files, put the audio files on a CD, and read the instructions.

https://db.tt/N2kty1TU

https://db.tt/0KPpdvZi


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## Niick (Jun 3, 2015)

One word of caution, every "cheapie" true RMS multimeter (and even a not-so-cheapie one) that I have ever had does NOT measure accurate "true RMS" voltages across the ENTIRE audio bandwidth. 

My experience has been that they are accurate up to about 300Hz to 1kHz......OR SO. 

something like that. 

They (the multimeter marketing/rating/labeling) aren't lying when they say "true RMS", it's just that they also rarely specify a bandwidth across which they remain "true RMS"

EDIT: now that I'm thinking about it, maybe it's like 2kHz..........???


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## FordEscape (Nov 23, 2014)

Andy Wehmeyer said:


> Here is a way to do it with a volt meter and microsoft Excel. Download the files, put the audio files on a CD, and read the instructions.
> 
> https://db.tt/N2kty1TU
> 
> https://db.tt/0KPpdvZi


Downloaded, quickly read the "Demystifying.." Word document and scanned the ppt presentation ...

Sir, I cannot thank you enough for sharing this incredible toolset and 'tutorial', the spot-on answer to my 'academic curiosity' question with the incredible bonus of explanation in terms that even I can understand.

Printing the tutorial, a more considered re-read, burning the CD, warming-up the RMS Fluke and implementing the procedure will follow shortly I assure you. This is going to be a lot of educational fun (the best kind of fun) without a doubt.

And oh boy, not only the frequency response/EQ aspect but a tool to learn with my ears about how the center channel 'works', something I've struggled to comprehend from written explanations.

Un-ending argument may well likely follow, seems to be the nature of this place. But from me you have nothing but un-ending gratitude for your ability to 'understand the customer' and provide tools and products to 'exceed _this_ customer's needs'.

It's hard for a guy like me to hang around here, so much chaff to sift before finding the occasional grains of wheat. Once again, the wheat has your name attached.

*Thank You!*


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## Niick (Jun 3, 2015)

A fluke may well work perfectly. It's NOT what I CONSIDER to be a "cheapie" multimeter. 

When I say cheapie, I'm talkin like under $100 or less usually. 

There are MANY ways to test OEM frequency response. 

If a car audio shop hasn't figured out how to do this by now, I should hope that that same shop isn't carrying high end gear like Audiofrog speakers. 

Unfortunately, the reality of the scenario is often just that.


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## FordEscape (Nov 23, 2014)

Being only a 'curious audio enthusiast', freshman level, not an 'industry professional' in any respect whatsoever, Andy's answer to my OP is most welcome. A Fluke 117 happens to be among the tools in my decidedly 'not audio-oriented' toolkit.

While not a 'super-duper pro instrument' it'll still be fun and likely adequate for my purpose and this exercise, which will undoubtedly be more educational and informative for me than simply paying a 'shop' and leaving with a stack of plots.

For me a huge part of the value in the info Andy posted is the 'tutorial' explanation. That being something that audio shops, in my limited experience, are unable (or unwilling) to concisely and effectively communicate to 'less than experienced' enthusiasts such as myself, even if we're among those likely rare customers willing to pay good money for the time to be educated.

You and your shop may well be the exception to my limited experience; certainly my loss that I'm not closer to you and able to enjoy the benefit of your services.


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## brumledb (Feb 2, 2015)

FordEscape said:


> Downloaded, quickly read the "Demystifying.." Word document and scanned the ppt presentation ...
> 
> Sir, I cannot thank you enough for sharing this incredible toolset and 'tutorial', the spot-on answer to my 'academic curiosity' question with the incredible bonus of explanation in terms that even I can understand.
> 
> ...


Well said, I feel the same way. I have also been looking for a way to measure my OEM system and glad I have been following this thread. Thanks again Andy.


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## Phil Indeblanc (May 27, 2015)

As much as I agree that the time you take out the Stock and swap, it maybe harder to tell...BUT, if you are familiar with a specific song/s and know it very well, as you listened to it over and over and enjoyed each second of a voice, or tune...You will have no problem noticing the difference. As a source unit, it should be uncolored and similar if I put a Pioneer vs a Kenwood, no? These 2 may exhibit slight character differences, but not large gaps in difference.


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## Niick (Jun 3, 2015)

FordEscape said:


> Being only a 'curious audio enthusiast', freshman level, not an 'industry professional' in any respect whatsoever, Andy's answer to my OP is most welcome. A Fluke 117 happens to be among the tools in my decidedly 'not audio-oriented' toolkit.
> 
> While not a 'super-duper pro instrument' it'll still be fun and likely adequate for my purpose and this exercise, which will undoubtedly be more educational and informative for me than simply paying a 'shop' and leaving with a stack of plots.
> 
> ...


There is certainly ALOT of very useful information in there. As is always the case with Andy. 

I REALLY hope you werent thinking that I was somehow dismissing Andy's post. 

I was merely saying:

What's the reason for using a true RMS meter during this exercise?

Accuracy.

If that's the case, then it should be stated that not all meters rated as being "true RMS" are actually true RMS all the way up to 20kHz. 

That's all. 

I wasn't "arguing"........or.....saying "no that won't work"...... 

Nothing like that.


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## brumledb (Feb 2, 2015)

Niick said:


> What's the reason for using a true RMS meter during this exercise?
> 
> Accuracy.
> 
> If that's the case, then it should be stated that not all meters rated as being "true RMS" are actually true RMS all the way up to 20kHz.


Do you know any specific dmm's that are accurate up to 20khz?


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## FordEscape (Nov 23, 2014)

Niick said:


> ...
> I wasn't "arguing"........or.....saying "no that won't work"......
> 
> Nothing like that.


No, no, I didn't take it that way at all and do appreciate your comment of warning about meter factors. Wasn't in the least intending to suggest your post was in that 'chaff' category 

Looking at the AC volts True RMS Accuracy Specs for my Fluke 117 I find .... 
accuracy 45 to 500 Hz =1.0% +3
accuracy 500 Hz to 1 kHz = 2.0% +3

So that's definitely interesting, would not have thought to look absent your comment, and will still have fun measuring and plugging the data into the spreadsheet to see what it shows, accepting that there may be some instrument-limited factors in-play beyond those ranges.


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## JohnnyOhh (Feb 19, 2015)

You can look into these PC based o-scopes to measure voltages. Even better you can see the voltages too with them. I've been playing with this one for last few months. It is decent for the price. Bandwidth should be sufficient. The display is on your laptop screen. Connected via USB cable.

Part:
SainSmart DDS120 Silver PC-Based USB Oscilloscope Digital Storage 20MHz Bandwidth 50MS/s

Link:
SainSmart DDS120 Portable Handheld PC-Based USB Digital Storage Oscilloscope 20MHz Bandwidth 50M/S 3D Printing, Arduino, Robotics | Sainsmart



brumledb said:


> Do you know any specific dmm's that are accurate up to 20khz?


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## Niick (Jun 3, 2015)

brumledb said:


> Do you know any specific dmm's that are accurate up to 20khz?


That's a very good question. I do know that the Fluke 289 (my personal favorite DMM of all time) definitely is true RMS well past the audio bandwidth. 

But it's also quite expensive.


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## brumledb (Feb 2, 2015)

I actually just purchased one of these:

Amazon.com: SainSmart Upgraded Mini Pocket-Sized Handheld Digital Storage Oscilloscope ARM DSO Nano DSO201: Industrial & Scientific

I haven't played around it with it yet but I have upgraded the firmware. I know this would show the voltage, just wasn't sure about the accuracy aspect. I may pick up a Fluke 115 to complement it.



JohnnyOhh said:


> You can look into these PC based o-scopes to measure voltages. Even better you can see the voltages too with them. I've been playing with this one for last few months. It is decent for the price. Bandwidth should be sufficient. The display is on your laptop screen. Connected via USB cable.
> 
> Part:
> SainSmart DDS120 Silver PC-Based USB Oscilloscope Digital Storage 20MHz Bandwidth 50MS/s
> ...


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## XR250rdr (Mar 22, 2011)

brumledb said:


> Do you know any specific dmm's that are accurate up to 20khz?


Fluke 87V will, runs about $400

http://media.fluke.com/documents/80v_____umeng0200.pdf

See page 44 (PDF page 52)

287 will as well, runs ~$450

27 II and 28 II will, both run ~$450.

Benchtop DMMs 8808A and 8845A/8846A will also, but they're more than a little overkill.


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## XR250rdr (Mar 22, 2011)

brumledb said:


> I actually just purchased one of these:
> 
> Amazon.com: SainSmart Upgraded Mini Pocket-Sized Handheld Digital Storage Oscilloscope ARM DSO Nano DSO201: Industrial & Scientific
> 
> I haven't played around it with it yet but I have upgraded the firmware. I know this would show the voltage, just wasn't sure about the accuracy aspect. I may pick up a Fluke 115 to complement it.


That looks pretty sweet, I should pick one up. Definitely easier than lugging out the old Tektronix oscope I have now.


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## brumledb (Feb 2, 2015)

Thanks for the recommendations. Yeah these are kind of expensive to only use occasionally. Maybe I can find a good deal on a used one. I'll compare the specs of these to some others and see if I can find anything more budget friendly.




XR250rdr said:


> Fluke 87V will, runs about $400
> 
> http://media.fluke.com/documents/80v_____umeng0200.pdf
> 
> ...





Niick said:


> That's a very good question. I do know that the Fluke 289 (my personal favorite DMM of all time) definitely is true RMS well past the audio bandwidth.
> 
> But it's also quite expensive.


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## brumledb (Feb 2, 2015)

XR250rdr said:


> That looks pretty sweet, I should pick one up. Definitely easier than lugging out the old Tektronix oscope I have now.


The only problem is the firmware it comes with pretty much sucks so you have to update to BenF. If you get one let me know and I can give you the files and procedure for upgrading. Save you some time from having to scour the internet.


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## Niick (Jun 3, 2015)

Check this out, here is one of my cheapie meters against a 100Mhz scope

(Now, it should be noted that if ABSOLUTE accuracy is what someone is after, scopes don't read absolute voltage levels as well as a good meter. A good scope can be off by a couple percent when it comes to absolute voltage)

Hang on, let me make that pic bigger.......


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## brumledb (Feb 2, 2015)

Niick said:


> Check this out, here is one of my cheapie meters against a 100Mhz scope
> 
> (Now, it should be noted that if ABSOLUTE accuracy is what someone is after, scopes don't read absolute voltage levels as well as a good meter. A good scope can be off by a couple percent when it comes to absolute voltage)
> 
> Hang on, let me make that pic bigger.......


What do you mean by absolute voltage?


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## XR250rdr (Mar 22, 2011)

brumledb said:


> The only problem is the firmware it comes with pretty much sucks so you have to update to BenF. If you get one let me know and I can give you the files and procedure for upgrading. Save you some time from having to scour the internet.


Cool, I'll let you know. Probably going to wait a bit since I just bought a Helix DSP and still need to buy a measurement mic.


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## Niick (Jun 3, 2015)

brumledb said:


> What do you mean by absolute voltage?


Like a metrologist would measure. Liek when you get a peice of test gear calibrated. the value that the meter SAYS is 1 volt, is it really 1 volt. maybe it's 1.23 but your meter is out of calibration. 
Thats what i mean by absolute


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## XR250rdr (Mar 22, 2011)

brumledb said:


> Thanks for the recommendations. Yeah these are kind of expensive to only use occasionally. Maybe I can find a good deal on a used one. I'll compare the specs of these to some others and see if I can find anything more budget friendly.


Looks like there are a bunch of used 87Vs on ebay.

Should be able to get one calibrated for ~$60.


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## Niick (Jun 3, 2015)

im uplaoding a video showing exactly what i mean.


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## Niick (Jun 3, 2015)

All right everybody........

http://youtu.be/ow2NS408j9o


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## Niick (Jun 3, 2015)

Ok everybody, keep checking back at this post, I'm going to edit it and upload 3 more videos, this one, and 2 more. I have a winner. I'll show a meter that I bought NEW for 200$ that is accurate up to 20k

This post will have a total of 3 videos: 

1- http://youtu.be/uJ_RHoLkmtw

2- https://youtu.be/ASfVLjRdXAo

.....and we have a winner!!

3- http://youtu.be/vNVRHAyBvps

All right, there ya go, a few meters tested, only one of them will work for testing even kinda accurately voltages above 6kHz or so.


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## FordEscape (Nov 23, 2014)

Niick - I've appreciated your feedback / info on this thread, hoping you are still following this and can continue my education now that I've got some suitable 'instrumentation' lined-up. BTW "you are overthinking" is a most appreciated response when appropriate
 ....

*Test Scenario* - My first interest is measuring characteristics of the speaker-level outputs of my OEM *HU*, which is currently connected to an MS-8 with external amps 'downstream' of that as shown in my sig-block diagram. Obviously, I don't want to damage any of my components, instruments, nor my ears.

*Question 1* - My understanding is that I can leave my MS-8 connected to my HU for while measuring the HU output voltage with a DMM (which has appropriate 'voltage @ frequency' specs as you previously explained).

I further understand that the MS-8 presents a 'load' to the HU independent of the downstream amps, so I can turn-down my MS-Axxxx amp outputs to zero, saving my drivers and ears when measuring high HU volume settings, and that should not affect the measurements at the HU outputs. The voltage readings should therefore be representative of what my MS-8 gets from the HU without worrying about the varying impedance of the system speakers at various HU volume/frequency settings (the MS-8 'isolates' that varying 'load' from the HU).

Then, using the Excel spreadsheet tool provided by Andy, I 'convert' those voltage measurements to convenient frequency/EQ plots to demonstrate the EQ curve imposed by the HU at various output levels.

Your correction of any mistakes in this 'logic' would be most appreciated.

*Question 2* - I _may_ have access to a PicoScope 2004A USB oscilloscope. Never having used an O-Scope I've been doing some reading about that. At this point my question is about connecting the O-scope probe ground for car audio measurements. The scope has passive 1x/10x selectable probes. Should the probe ground be connected to the (-) HU speaker lead of interest when measuring, or should it be connected to the HU chassis ground? I know I'll need to be very careful to not exceed the scope's limited allowed AC input voltage range.

Thanks in advance for any 'continuing education' you can provide.


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## 14642 (May 19, 2008)

I wouldn't go ape **** over the difference between true RMS accuracy and not exactly accurate. The difference between RMS and Peak voltage is only 3dB. Measuring within 3dB at high frequencies is surely sufficient for measuring the output of a head unit or a factory amplifier. 

I developed that tool for a presentation I did at the SEMA show. The audience was retailers who were thinking about getting into 12V--tint guys and guys who do bolt-on performance and vinyl wraps.


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## 14642 (May 19, 2008)

5.57 to 4.8V is 1.3dB.


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## 14642 (May 19, 2008)

Here are the measurements i made of my wife's Fiat with the same Craftsman meter as in your video and the left and right midrange outputs measured with REW and a soundcard.


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## brumledb (Feb 2, 2015)

Andy Wehmeyer said:


> I wouldn't go ape **** over the difference between true RMS accuracy and not exactly accurate.


It's funny because I just bought a Fluke 87, not even 1 hour ago, because of this thread. Oh well, at least it was a good deal on a used one.


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## 14642 (May 19, 2008)

brumledb said:


> It's funny because I just bought a Fluke 87, not even 1 hour ago, because of this thread. Oh well, at least it was a good deal on a used one.


Of course, it's better to buy the better one, but my caution was intended to be applied to the question, "Are slightly inaccurate measurements worse than no measurements at all?"

Certainly not.


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## Niick (Jun 3, 2015)

Andy Wehmeyer said:


> 5.57 to 4.8V is 1.3dB.


What about 5.7 to 0.4?? See this video again....

https://m.youtube.com/watch?v=uJ_RHoLkmtw

Now that is CERTAINLY not remotely going to net you useable results. 

By the way, this is a cheapie craftsman meter. Meaning ANY 'ol cheap meter WILL NOT work.........

See what I'm sayin? The meter has to be at least somewhat decent.


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## Niick (Jun 3, 2015)

Andy Wehmeyer said:


> Of course, it's better to buy the better one, but my caution was intended to be applied to the question, "Are slightly inaccurate measurements worse than no measurements at all?"
> 
> Certainly not.


for sure, SLIGHTLY inaccurate, no problem.

Extremely inaccurate........ PROBLEM

I was hoping to show that not just ANY ol meter will do.


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## Niick (Jun 3, 2015)

FordEscape said:


> Niick - I've appreciated your feedback / info on this thread, hoping you are still following this and can continue my education now that I've got some suitable 'instrumentation' lined-up. BTW "you are overthinking" is a most appreciated response when appropriate
> ....
> 
> *Test Scenario* - My first interest is measuring characteristics of the speaker-level outputs of my OEM *HU*, which is currently connected to an MS-8 with external amps 'downstream' of that as shown in my sig-block diagram. Obviously, I don't want to damage any of my components, instruments, nor my ears.
> ...


yes, your logic is spot on. As far as taking audio measurements with single-ended (almost all) oscilloscopes, there is these wonderful devices called differential probes. Here is a pic of my favorite one.

Now, you can find these for about 400 on eBay. 

They are labeled as either Panoma Electronics OR Fluke. Same thing. The Panoma is the 6731, I'll have to look up the fluke model #. 

If you don't want to spend that much, there is a AWESOME differential probe made by a company called Quant Asylum, the QA190. It's less than $100 brand new. AND it does voltage AND current simultaneously. (It's 2 ch.) 

That's what I would highly recommend. Using ground referenced oscilloscopes (single-ended) is NOT like using a multimeter. You cannot just probe "will-nilly" across any ol two points in a circuit. 

Now, I SUPPOSE as long as the ONLY thing connected to the car was the oscilloscope (because as soon as you connect the ground clip whatever you've connected it to is now at the same electrical potential as earth ground) then you'd be ok. But that bothers me. 

Maybe someone else will chime in here.

Anyways, yeah, I use differential probes.


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## Phil Indeblanc (May 27, 2015)

FORGET IT....GET RID OF THE OEM head unit!

"It will be hard to compare"

My A$$$$$$ it will be....
Its a day and NIGHT difference....DSP or no DSP...this thing now sopunds like a FULL and deep and dynamic sounding system! Geeezzz....all this time I have been wondering if its the speakers, or tuning, or what??? HEAD UNIT!!!!


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## FordEscape (Nov 23, 2014)

Phil Indeblanc said:


> FORGET IT....GET RID OF THE OEM head unit!
> 
> "It will be hard to compare"
> 
> ...


Lol, congrats and good for you !

But for some (lots?) of us it just isn't a preferred option.....I'm among the thousands (millions?) of owners of vehicles where the "head unit" integrates so many functions other than audio (climate controls, for just one example) that the compromises associated with currently available replacements outweigh the audio benefits for us. Not saying it can't be done, and not denying the audio benefits, but there's other compromises inherent. So, we're rockin' on with the OEM HU, doing what we can to get the most enjoyment from it.

While enjoying my newfound hobby of higher quality car audio, I'm content with the reality that my least compromised and most enjoyable listening environment is my home and never the two shall meet.

As dad (may he RIP) used to say .... "that's why there's 31 flavors".

Again, congrats on finding what works best for you!


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## Phil Indeblanc (May 27, 2015)

LOL....Sorry I came off this way. Its been months and I was just over the stage of getting a chunk better sound, but I knew something is missing and not right.
Spent months and COUNTLESS HOURS researching different things. And all the while its the HU!!!

Now instead of the LOC, I will want to run the RCA's as that too might make a difference I'll regret later/?


Its funny...I'm the opposite. I would LOVE to listen to my music at home. But a family environment makes it hard and very few. So the alone time I have in the car is where I can try and do best to appreciate the nuances of sound and great music.

There is only 1 RockyRoad...yet can't argue with pops on the 31 flavors!


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## FordEscape (Nov 23, 2014)

Hey man, no apology needed for sharing the joy !

My goodness, if you've now got an HU with RCA-out, I wouldn't hesitate one moment to toss that LOC as far as I could.


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## j4gates (Jan 1, 2016)

Great info in here...


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## FordEscape (Nov 23, 2014)

Just to 'wrap' this thread ... means, methods and results (pics of plots) of my quest to measure my OEM HU frequency response are here http://www.diymobileaudio.com/forum/3661137-post117.html

(tons-o-fun with the USB PicoScope 2204A)


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## Phil Indeblanc (May 27, 2015)

Well, I am using a RF 360.3, so I don't think I'll be tossing it anywhere soon...But will use it with the 4100nex and bipass whatever EQ/xover the HU does(use them flat or off), and try and tame the 30+bands.

Great stuff, and this will be great info for many Ford owners as often parts are overlap across different models.


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## Amgclk65 (Dec 8, 2015)

Hello,,
Would anyone happen to have the files Andy Wehmeyer put out on page 2. I want to measure my factory HU.


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## FordEscape (Nov 23, 2014)

Amgclk65 said:


> Hello,,
> Would anyone happen to have the files Andy Wehmeyer put out on page 2. I want to measure my factory HU.


Many months later I just saw this post .... see this reply I posted on another thread for a suggestion (Andy's contact info on the last page of the pdf document found there)


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## brumledb (Feb 2, 2015)

Amgclk65 said:


> Hello,,
> 
> Would anyone happen to have the files Andy Wehmeyer put out on page 2. I want to measure my factory HU.




I have them. Send me your email and I’ll send them to you. 


Sent from my iPhone using Tapatalk


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## MikeyB (Apr 16, 2021)

Jepalan said:


> FWIW, per page 9 of the MS-8 user's manual, you only want to connect Front L/R and Subwoofer signals into the inputs of the MS-8. Do not connect rear, side or center channels into the MS-8.
> 
> http://ms8-eu.jbl.com/install.html?file=tl_files/content_resources/jbl-ms8/Owners Manual.pdf
> 
> You would typically want to use an audio spectrum analyzer, audio real-time analyzer (RTA), or a software tool like Room EQ Wizard (REW) to measure the response of your OEM system, not an O-Scope.


Yeh - not strictly true - most modern digital oscilloscopes (which can be picked up pretty cheaply) will do a fast Fourier transform on a time domain signal and you'll get a nice free response curve if you play some pink noise source.


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## drop1 (Jul 26, 2015)

FordEscape said:


> Please read my OP carefully ..... I'm not trying to measure the audible output from speakers/room, I want to know the quality of the high-level signal from the HU alone, not the audible response of the whole system of speakers and amps.
> 
> I want to know if it actually delivers a full 20 - 20kHz spectrum to the MS-8 or is it inherently 'limited' in some way. E.g. does Ford filter the signal below a frequency higher than 20Hz because they knew the OEM speakers could not handle those low frequencies (there was no subwoofer in the OEM system)?


Plug your speaker outputs straight into a computer and use rew to see the built in eq curve. Keep the volume low. That's what I did.


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