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Thread: Erin's 2006 Civic Sedan

  1. Back To Top    #11

    Re: Erin's 2006 Civic Sedan

    I mentioned some of the EQ things I did above and I thought it would be a nice segueway in to discussing some measurement methods I use. This might be helpful to others and hopefully ultimately save you some time when you start doing your own.


    You probably know of the importance of a good spatial average when RTA'ing your system. If not, please read the attached PDF by Geddes which is a study he did for Ford Automotive. It's not too technically heavy which should keep the "I don't like science" excuses to a minimum.

    The cliffs version is simply this: your car (and home) are wrought with reflection inducing panels/walls. When measuring response in the environment, you have two options:
    1. "Gate" the response so you obtain only the response of the speaker you're trying to measure and you essentially ignore everything else.
    2. Measure everything: speaker response and reflections.


    Doing the first in the car?... good luck. How about... don't bother. At least not until you've gotten really good at measuring and understanding what you're measuring. Let's just say for all intents and purposes you won't be doing the first... like... ever (thank you, Taylor Swift, for making that phrase weird now). Really, it's just pretty much trivial unless you have a very specific goal and understanding of how to achieve it this way.

    So, we do the second option. The issue, then, is the fact every measurement you take is a measurement of EVERYTHING occurring at the mic. This is good and it's bad. It's good in the way that there's not a whole lot you can do to the speaker itself so it kind of keeps you from worrying about it. - Although, this is why I really encourage people to study independent tests or do their own to understand the issue(s) with the speakers they've chosen before they use them in the car. - It's bad because, thanks to the nature of the reflective environment, you can't really trust a single point measurement (a measurement taken with the mic in one location). If you move the mic as little as one-half inch you'll get a different result. Most notably in the higher frequencies. This means RTA'ing your car for any desired curve by using one mic measurement is a TOTAL WASTE OF TIME. It's ideal to take multiple measurements in the "head area" and average them together. TrueRTA, OmniMic, and REW allow you to do this pretty easily. Then you have what is known as a good spatial average. It's not an exact method but it's the most realistic and approximates a very realistic response in the seated position.

    For this spatial average I usually just do six measurements total at/near the headrest broken in to (2) sets of (3) measurements. Each set is with the mic pointed forward; one in the center and one to each side of the center a couple inches over. The first set at one level. The second set is simply done by raising the seat height up. If your seat moves forward when raising it, keep in mind your level will rise by just a touch thanks to the mic being closer to the speakers. Not an issue but just wanted to note it.

    Now I've got 6 measurements. What next? Simple: average them all together to get one measurement.

    Here's an example....

    All six measurements taken by the method described above (no smoothing applied):






    Same as above, but with 1/3 Octave smoothing:







    All of the above averaged in to one response:








    Let's talk about the above... at least my personal take on the above. I'm sure others may key on to some other aspects I might otherwise ignore or just overlook.

    Notice how the response varies more the higher you get in frequency? This is exactly why I said using a single point measurement to tune to a curve is a very bad idea.

    I'm going to ignore the shape of the curve, however, for this post... what I really want to focus on is midbass/subbass response, so let's look below 300hz. Anyone notice the one glaringly different thing about the response below this frequency versus the response above it? No matter where the measurement was taken, the response is pretty much the same. This is the critical frequency area (schroeder frequency (Fs)). Linkwitz gives the most simple definition I can think of here:
    The frequency fs is also called the Schroeder frequency and denotes approximately the boundary between reverberant room behavior above and discrete room modes below.
    Which makes sense, right? Look again at the graphs I provided. Reverberation is occurring above about 300hz as evidenced by the diverging responses from the 6 head area measurements. Below this, the response is pretty constant in this area so it is modally (sp?) dominated. What does this mean to us? You can ignore spatial averaging (multiple measurements) when focusing on low(er) frequency response! This saves you time! Of course, every car is different so I suggest you always do a spatial average to determine where this Fs occurs in your car, but you can expect it to occur around the 200-400hz area, depending on car size. The larger the 'room' the lower the Schroeder frequency. This means once you do a spatial average you'll know where this frequency is. From then on, when you only care about working on the low frequency response, you can ignore spatial averaging and just put the mic at the seated position and measure, tune, measure, tune, rinse, wash, repeat until you're satisfied. I will caveat this by saying that tuning low frequency response with graphic EQ's isn't easy because modal peaks and dips are often too narrow and too specific of a frequency to effectively be targeted by graphic EQs. This is where my subsequent posts will sort of pick up.



    Cliffs:
    • Tuning based on one mic measurement is a waste of time. This has a caveat...
    • Take a few measurements in the head area, where you sit. Look at them all overlaid. Where do they really start to diverge? This is your car's Schroeder frequency.
    • Above the Schroeder frequency you must take multiple measurements and average them if you want to tune via RTA.
    • Below the Schroeder frequency, one mic measurement will suffice since the response doesn't change enough to matter.
    • Graphic EQs aren't the best tool for fixing response issues low in frequency. Parametric EQs are MUCH better. But, if all you have is a graphic use it to the best of your potential.


    I'll stop there before people gloss over. Next post...

  2. Back To Top    #12

    Re: Erin's 2006 Civic Sedan

    Taking off from the above, I'm only going to focus on the response below 300hz (graphs are out to 400hz for the sake of resolution).

    The following is with no EQ. Time alignment and levels have been set, however.

    First off, let's take a look at the difference measured from the driver's seat vs the passenger's seat.




    The results show the same response show pretty much the same curves above 70hz. I've seen this numerous times; almost as if the car has varying Schroeder frequencies. One is for the entire cabin; the other is for one location at a time. Of course, I'm not talking about moving the mic to the rear of the car... that's an entirely different can of worms. The point in this measurement, however, is to show that there is actually a sub-band that really needs attention below the seated Schroeder frequency: the midbass band is entirely subject to this. As shown, 70hz is the starting point for different results between seats but 300hz is about the starting point for different results within the same seat. So, 70hz to 300hz is gonna be a total PITA in my car. Through about 5 years of dealing with this same car, my measurements show me what I already know, so it's definitely been vetted.



    Next...

  3. Back To Top    #13

    Re: Erin's 2006 Civic Sedan

    After doing that, it's time to get back to the driver's seat and start measuring response from there.

    One might choose to measure the system response as a whole and use the RTA that way, but it's a bit more conclusive to study each individual side's response (left and right side response). This is easy to do: just pan the balance to one extreme or the other and measure. When you do, you'll have the left side stereo contribution vs the right side stereo contribution.

    So, here we have just that. Panned left is Green. Panned right is Purple. No EQ. 1/12 octave (to show the crappy little modal stuff that 1/3 doesn't get).




    What this really shows me is that both the left and right side stereo contributions have their own problems. Notice that slight dip around 85hz at the driver's seat? Everyone has that problem to some degree because of their proximity to the speaker. Bottom line, that dip is a cancellation mode. There's nothing I can do to fix it, either. I can EQ it up but what will happen is I'll just keep applying more power to the driver's side midbass, causing distortion to ramp up and likely audible issues due to it. And while it may raise the response there, it'll also make resonant modes more problematic. The potential to damage the driver certainly exists. There's just not a whole lot you can do here. Some EQ will help but if you try to flatten it out by adding 4-5dB of EQ you'll alter the response curve in a negative way and create other issues. The only way to really fix a problem like this is to move from the boundary causing the null or move your driver(s). So, I just ignore this. Truth be told, it's not a real big issue when listening. And this is just one more example of why you should not rely entirely on the RTA. You should always use your own ears to accompany what you've measured. If you have a narrow dip it's not as audible as a broad dip; the same goes for a bump in response.

    So, yea... I'm not going to sweat that dip at 85hz measured at the driver's seat. It's a lost cause and serious waste of time to try to flatten it. I just want to smooth it so a bit of EQ here and there will help that.


    Now, look at the rest of the curves. That dip around 85hz on the left side is exacerbated by the rise in response around 125hz. After looking at the decay plot, measured by REW, I see why...




    This is a plot of response over time, laid out in 2-D. The highest levels are closer to the initial response time. As the graphs change color below one another, you're seeing 'slices' of the response in time. Look at the legend. It shows time in milliseconds (ms). Each color corresponds to a time slice/section. Ideally want to see is each slice dying out quickly and contributing less and less to the results. However, what you actually get is modal issues showing up... these are the ones that linger around and don't taper off smoothly. Looking at these plots is pretty subjective and really should be used with some subjective listening as well. But, I'll give some thoughts on how I look at it...

    The 125hz issue showing up in the left side FR plot... now look at the decay plot around that frequency. See how the darker blue looks pretty mountainous here with a dominant spike at about 125hz? Notice how the shade of blue just before this has the same spike? This is an indication of a modal issue. Luckily, I have an EQ band right here... I can cut it some. The problem, however, is cutting here also affects the tonality in other ways. With a parametric EQ, I can set a narrow Q and cut accordingly. But, I don't have that, so I have to cut here with the 31 band EQ. Here is the result when I use the EQ to cut 125hz by 3dB:




    Not surprisingly, there was no miraculous alteration of the issue. It cut the problem by 3dB as it should but it didn't make the ringing issue go away. It did lessen the effect some. This is where subjective listening will tell you if it helped. The drawback here is you also changed the tonality of the system because the Q (bandwidth) of the 1/3 octave equalizer is so wide; it doesn't just change a single frequency.

    This site is a great reference for what frequencies influence what you hear and can help you understand the tradeoffs you deal with when changing EQ bands to fix problem areas:
    Interactive Frequency Chart - Independent Recording Network



    There are other frequencies that do the same thing. 100hz definitely lingers. 83hz lingers as well. Remember earlier my bit about bumping up 80hz to fill in that hole caused by the left side response? What do you think happens when you do that regarding the modal issues? It's a nasty problem. What you really need is a way to target specific modes without negatively affecting the other areas you want to fix with standard EQ methods. This would be a really good intro in to why parametric EQs are so good. So, I'll stop here and pick up there when I have the chance.

    Keep in mind I've only really discussed one component of the system response here. The right side response has it's own problems as well.


    Cliffs:
    • Room modes suck. They muddy up system response as a whole.
    • When the midbass is muddy it overshadows everything good about the rest of the system.
    • All cars have modal issues smack in the midbass area.
    • Standard EQ can only go so far. But when properly used, EQ can help tame some of the modes which results in a much more tonally pleasing car stereo and much better blending with sub on the low end and midrange on the high end.


    /



    Hope this stuff helps you guys out!


    - Erin

  4. Back To Top    #14

    Re: Erin's 2006 Civic Sedan

    As mentioned above, I use REW for my testing. It's free and pretty easy to use once you figure out how to use it. :blush:
    I've used every bit of software under the sun. At this point, I've just grown to like REW more than I used to so I've gone back to it for my tuning measurements. For those wanting to see how I'm using REW, here's some info.

    RTA vs Impulse Response Measurement Method:
    One thing to note is there are different meanings of the term, at least how we use it:
    1. RTA - Real Time Analyzer:
      • This is simply a real time measurement of what the mic hears. Birds chirping, subs playing... whatever. It records it.
      • RTAs are typically used to record pink noise.

    2. Impulse Response:*
      • This can be a form of RTA, depending on how you look at it. An impulse is used typically to measure something before a reflection because you can gate the response. In other words, let's say I want to measure Speaker A. I know that the walls and floors create reflections occurring after 3 milliseconds (ms) that will 'tarnish' the speaker's response as measured by the mic if I let it. To keep this from happening, I look at the impulse response, tell the software to ignore everything after 3ms. Bammo... no more reflections in the measurement. Just Speaker A.
      • The impulse response is measured by sweeping a sine wave and capturing the response.


    * I have severely watered down my explanations here and there are caveats; especially when you get in to different window type methods. But for the sake of this post, it's fine.

    The bottom line: In a car, you don't care about impulse gating. You can't really achieve a reflection free zone so there's not much point in trying. -- If you care to disagree please see discussion and reply here (link) so I don't get this one junked up). -- Therefore, we just disregard the whole gating process. That leaves us with a very long impulse response that matches what an RTA would show you, if the signal were the same (ie: pink noise). IOW, using a very long impulse window (100's of milliseconds) in the car will yield an RTA measurement.

    Why use this impulse method if it essentially nets you the same thing as an RTA measurement? Because RTA measurement only gives you RTA data; SPL vs frequency. You can't get Decay or some of the other things I am looking to get. More data. That's all. I get in to it more below.



    Cliffs:
    • When measuring a car, there are a couple ways to do it.
    • RTA and Impulse are not the same. They each have their own use. However, when the impulse is used without filtering or gating it, it nets you the same result as an RTA.
    • The benefit of using impulse measurements are you get more data such as decay, group delay, etc.
    • Like a standard RTA measurement, multiple impulse responses should be taken and averaged together if you want to tune to a car.

  5. Back To Top    #15

    Re: Erin's 2006 Civic Sedan

    I'll discuss how to use either of the two methods listed above. But first off, let's discuss the equipment you need and why you need it.


    • If doing RTA only measurements all you really need is:
      1. A CD with pink noise
      2. A mic to capture the sound.

    • If doing impulse measurements you need two things:
      1. A way to use the software's signal generator and send that signal to your audio system. This can be done by using a soundcard output and run it in to your audio system auxiliary input.
      2. A mic is used to capture the sound.


    If you are looking to achieve a target curve of any sort you MUST USE A CALIBRATION FILE with the mic.



    -------------------------------------


    For impulse measurements, this is the gear I'm using. It's pretty simple:
    1. M-Audio Transit. This sends the signal from REW software via a 3.5mm male/female cable to my P99's auxiliary input.
    2. Dayton Omnimic USB microphone. It comes with a cal file.



    You don't have to use what I have. In fact, you can save a good deal of money by simply using:
    1. Your laptop's built-in headphone output
    2. This Dayton mic (click link here). There are numerous other mic alternatives. This is just an easy one with one USB cable. Plug and chug. And it comes with cal files.



    ------------------------------------------


    You know what you have to have. Why do you have to have it?
    1. The soundcard output is used to send the signal to your auxiliary source. Every headunit should now have one of these. This is how I do my testing most of the time. If it doesn't, you may be limited to using the pure RTA method only.
    2. The mic records the system output. Simple as that.




    -----------------------------------------


    Here's some pictures of my gear:


    M-Audio Transit, using the output via a 3.5mm headphone extension cable.








    Dayton Omnimic USB mic (it has electrical tape because I broke the tip; these things are pretty fragile and I made a goof):







    Mic in the headrest:









    3.5mm aux cable plugged in to my headunit's aux input on the face panel:


  6. Back To Top    #16

    Re: Erin's 2006 Civic Sedan

    Woke up early before the little one did to make this video so forgive me if I sound half dead and my video has the shakes.

    This covers only the RTA aspect of using REW. I'll post another video soon showing how to use the impulse measurement method since I feel it's a bit more complete depending on what you want to do and given I'll be posting results from that kind of measurement.

    Let me know if you have questions.



    [youtube]bds759UuWiU[/youtube]



    - Erin

  7. Back To Top    #17

    Re: Erin's 2006 Civic Sedan

    AE IB15's are now out of the car. I'm considering ways of implementing the JL 13tw5's now. Got a few ideas. The good news is that the space savings is going to be about 4" in depth if I go the route I'm most likely going to go. I'll let it sit tonight and think about it a bit. I hope by this weekend to have the JL's in the car and playing music.









  8. Back To Top    #18

    Re: Erin's 2006 Civic Sedan

    sub enclosure progress....




    for what it's worth, what I've decided to do is a bit off the mark of my initial intentions. but for a couple reasons which are somewhat scatterbrained.

    One thing I learned from experimentation is the trunk causes problems. It did IB and it does with a sealed enclosure. With any enclosure in the trunk, what you get in to is a cancellation from the sound hitting the rear of the trunk and bouncing back forward in to the cabin. That's just the nature of the beast. In addition, the trunk is one more area that can be excited. As I found through some playing around with over the past few months, this is a problem for me. So, I wanted to eliminate the trunk. I had planned to make a modular setup. One that attached to the existing IB wall and removed. But, I found doing this really was more trouble than it was worth. Instead, I picked up some void free birch in 1/2" size and attached it to the existing wall. Weight added is less than 5lbs which is minimal considering the space savings. Using the existing IB wall as a basis for the enclosure allowed me to only consume about 4" of the trunk as is. A savings of nearly 4 inches itself.

    What I'll be doing to finish out the enclosure is placing a piece of wood behind the baffle wall. Picture in your head taking a standard IB setup and just putting a piece of wood behind the woofers. Now you have a sealed setup. Doing this, with the trunk dimensions I have, provides me over 1 cube per driver at 4" depth consumption. This means I have wiggle room. If I want to decrease the enclosure size per driver, I simply move the rear wall forward. If I move it up an inch I can lower the Qtc and save space. I plan to do some testing once the baffle wall glue dries and I get some pieces of wood cut to play with enclosure size.

  9. Back To Top    #19

    Re: Erin's 2006 Civic Sedan

    rear wall test fit went well. I had to break out the baby sledge to get the wall in place. It ain't going anywhere without significant effort... and that's without screws.


    I'm going to finish it all with carpet. Right now I'm just trying to make sure everything goes where it needs to. I'll be doing some sweeps with the dayton DATS soon.








    13tw5v2's are in. I did an impedance sweep on woofer in its own chamber and the difference in Qts is only 0.01 (0.629 vs 0.619).

    Initial impressions: I made the right decision to switch. I'll give it a bit more time to sit and discuss my impressions after the new factor has worn off. But for now I'll say that my reasons for going with the wall/enclosure design paid off.

    I need to lay some carpet over the baffle but had to put the car together to drive to work tomorrow so that'll come this week.





  10. Back To Top    #20

    Re: Erin's 2006 Civic Sedan

    I did some very minor work on the kicks last night and tonight. I had some serious gaps thanks to the grilles I used to protect the speakers. So, I used some great stuff foam to fill in the transition from floor to kick cover and then sanded it down a bit. Nothing special... and carpet will go over it. But at least now I won't have a large hump from the floor to the speaker.





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