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Discussion Starter #1
Long time lurker (almost 2 years with only 4 posts... 5 counting the post pad I needed...)

I recently broke down and bought a new truck. It is a 2014 RAM 1500 with a "Premium" (cough, cough) Alpine sound system that really has the bottom end over-emphasized. Configuration of the system is 3 dash speakers, 2 front door, 2 rear door, 2 rear headliner, and an 8 inch sub in a sealed plastic enclosure.

I figured this was the perfect excuse I needed to buy a mic with a calibration file and play with REW to see what the is going on. I think I have gotten $100 worth of entertainment already characterizing the listening space. There are some "interesting" choices made by the Alpine engineers if I am interpreting REW plots correctly. Too much happens through the head unit for me to consider gutting everything. After reading a bunch at other forums, it looks like a DSP (e.g. Rockford Fosgate 3Sixty.3) is in my future.

This is the overall response in the environment with tone controls set to flat. (Sorry about being a bit off from preferred scales).

overall response  - all controls flat.jpg

Quite an emphasis to the bottom end. I hear it as being muddy or boomy on most songs.

The waterfall with default settings looks like this:
waterfall - default.jpg

Extending the Time Range to 600ms, everything from 100Hz down is still alive.

waterfall - 600ms.jpg

Am I understanding the concept of the waterfall graph information correctly? This is a visual representation of the "Mud" I hear?

Rather than repeating a bunch of information, here is a link to another forum if someone wants to look at more data than what I have posted in this forum. In the link, I detail the range of impact the tone controls have and close mic the speakers.

Link to many measurements
(Mods - I did not see anything discouraging this, but I will edit it out if you prefer)
 

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I don't know anything about any particular issues associated with automotive audio, but...

I don't see any big concern with the waterfall as the drop is rapid and relatively consistent. I would assume the Topt is in a reasonable range for a small space. It looks worse that it is as the bass freqs are greatly boosted. Once they are brought down to a more reasonable level the waterfall will look more normal. See the waterfall info posted by brucek here . It may have been brucek, or possibly Wayne Pflughaupt, or maybe it was someone else who pointed out that the waterfall is a room decay characteristic that will only be influenced by changing the room acoustics not the signal characteristics. The peaks or dips in the SPL can make the waterfall decay seem to look better or worse however if they are not taken into consideration. I didn't find the relevant post with quick look however.

It is probably not possible to significantly change the acoustics significantly in the cab so the waterfall plot is not particularly helpful?

As I said, I have not read up on auto sound practices so take these comments accordingly.
 

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Discussion Starter #3
Thanks for the reply. I did read through that thread before I posted. Not sure I followed it all. Perhaps a reread is in order. I saw the argument about amplitude having an effect. I am hoping that is the case. your right, there is not much I can do with the "room". The DSP will let me remove all of the EQ and get a flat starting point.

I tried it with the doors open to change the acoustics and did not see a significant difference to my untrained eye. There were a couple of nulls by 600ms.


waterfall doors open.jpg
 

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Discussion Starter #4
This is the total range of the bass adjustment with the factory head unit. I went a bit beyond 200Hz to give it a frame of reference.

bass - adjustment range.jpg
 

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I would not be too concerned about waterfall chart just the SPL chart, however...

The freqs where the decay stops (the SPL levels off) may just be getting at or near the noise floor. You may want to run a sweep without the amp on to see what the measuring system + external noise level is. At these low freqs there is often noise from other sources that influences the charts.

You may also want to look the spectrogram for another perspective. The influence of noise will show up there as well.

There isn't a "loudness compensation" control turned on in the head amp that would account for the boosted bass is there? It just seems the bass SPL is too hot even with the bass adjustment set to minimum - strange. I presume there is no level control on the bass amp itself.

Just random thoughts.
 

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A simplification of the waterfall plot:
Since the frequency plot at the top isn't flat. Look at the drop in SPL for a given frequency. You'll see a pretty decent 35db drop at the low frequencies that "don't look great". The higher frequencies "look good" and are dropping 40-45db over the same time period.

Because the starting level is so much lower you see less big solid red, but it's about the drop.
 

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Discussion Starter #7
This morning I made a new set of measurements at peak levels that closer match what you guys are used to seeing in the home theater world.

bass response peak ~100db.jpg

waterfall peak ~100db 300ms.jpg

waterfall peak ~100db 600ms.jpg

spectrogram peak ~100db.jpg

I get the concept that the Spectrograph is sort of like looking at the waterfall from above, but I don't really get the longer tendrils that curve left and right (changing frequency). I do see that by 400ms the level is down about 40dB for pretty much every frequency.

So, can I make the leap that there is nothing fundamentally wrong with the environment that is going to play havoc? That is really the comfort level that I was looking for since to do anything is going to be an endeavor in labor and equipment. There really is no piecemeal approach.

Thanks all.
 

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Discussion Starter #8
I would not be too concerned about waterfall chart just the SPL chart, however...

The freqs where the decay stops (the SPL levels off) may just be getting at or near the noise floor. You may want to run a sweep without the amp on to see what the measuring system + external noise level is. At these low freqs there is often noise from other sources that influences the charts.
noise floor - sweep with volume at 0.jpg

Quiet Sunday morning in the cab of the truck that has 125.3 cubic feet. Nothing is running in the truck other than possibly the fan on the netbook.

There isn't a "loudness compensation" control turned on in the head amp that would account for the boosted bass is there? It just seems the bass SPL is too hot even with the bass adjustment set to minimum - strange. I presume there is no level control on the bass amp itself.

Just random thoughts.
There is no loudness function on the amp or head unit. The Bass boost is just what they thought would appeal to the masses. (Boom-Boom-Boom must be a great sound system, right?)

Thanks for the random thoughts. I appreciate it.
 

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Discussion Starter #9
A simplification of the waterfall plot:
Since the frequency plot at the top isn't flat. Look at the drop in SPL for a given frequency. You'll see a pretty decent 35db drop at the low frequencies that "don't look great". The higher frequencies "look good" and are dropping 40-45db over the same time period.

Because the starting level is so much lower you see less big solid red, but it's about the drop.
I appreciate the insight. Thanks.
 

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I get the concept that the Spectrograph is sort of like looking at the waterfall from above, but I don't really get the longer tendrils that curve left and right (changing frequency). I do see that by 400ms the level is down about 40dB for pretty much every frequency.
The spectrogram looks "normal" for your current situation. That is, I don't see any concerns regarding impact on sound quality. The slow decay occurs after a reasonable initial drop as eclipse911t pointed out so it's impact should be insignificant.

So, can I make the leap that there is nothing fundamentally wrong with the environment that is going to play havoc? That is really the comfort level that I was looking for since to do anything is going to be an endeavor in labor and equipment.
Yes, my expectation is that EQ correction to a reasonable house curve should improve sound quality greatly.
 

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Am I understanding the concept of the waterfall graph information correctly? This is a visual representation of the "Mud" I hear?
I agree with jtalden’s comment in Post #5: I wouldn’t be too concerned with the waterfall. The “mud” you’re hearing is because of the huge low end boost. A pretty stiff house curve is usually required in automotive environments because of generally close proximity to the main speakers, the tiny acoustical environment, and to overcome road noise, but obviously they went overboard if you think it sounds muddy.

How does it sound with the bass cut 12 dB? The graph you showed in Post #4 looks like it should sound much better with the maximum bass cut.


It may have been brucek, or possibly Wayne Pflughaupt, or maybe it was someone else who pointed out that the waterfall is a room decay characteristic that will only be influenced by changing the room acoustics not the signal characteristics. The peaks or dips in the SPL can make the waterfall decay seem to look better or worse however if they are not taken into consideration. I didn't find the relevant post with quick look however.
I think this may be the post you’re looking for jt, although there may be others who have commented on the subject.

See the waterfall info posted by brucek here .
I wouldn’t put much stock in most of what’s in that thread. At the time, waterfall graphs and signal decay analysis was a new thing to most of the regulars here, and many of the posts are quite frankly in error or at least ill-informed. And I’d include many of my own to be in that category. John M’s posts in that thread are the most relevant.


So, can I make the leap that there is nothing fundamentally wrong with the environment that is going to play havoc?
It’s not like there’s much you can do for the environment – does anyone make treatments for cars or trucks? :D

Regards,
Wayne

 
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