A 2002 Stereo Odyssey

Bought a 2002 Limited Access cab in early June. It had a 6 disc changer and factory amp with factory speakers. This truck will be used for long road trips and so I wanted a comfy ride with good sound. Also, I always was interested in seeing what an acoustic isolation project could do in a vehicle.

The truck when I got it:


The stock HU

So first things was to replace the HU with a Kenwood DMX 706s. I wanted apple carplay. I wasnt sure how much I would use all those features, but now I am very very glad I went in this direction. It is great to pull up Gaia maps on the display or send texts via voice. I also wired in a reverse camera. My other half can use all the help she can get when driving!!!


Along with the HU, I added Rockford fosgate Punch SI speakers up front (components) and a coaxial pair in the back. If I was to do it again, I would put just bass drivers in the rear with a low pass filter. The HU can give them high pass filter and so it would work out to a band pass set from around 100 hz- 500 hz or so. (Would need to think about that further) The rear speakers at this point are highly attenuated to keep the soundstage up front. I would filter out the highs to remove localizable sounds. Ah well. I plan to get a dsp at some point anyway.

No pics of the speakers.

Now, onto acoustic isolation. This means first a layer of CLD tiles (like dynamat or hushmat). This is pretty much what you will get at a local installer. The purpose of these is to damping vibrations in the metal of the frame and also lower the resonance frequency. Turns out you really only need them on large flat surfaces and 25% coverage is plenty. Well, I didnt know that at first and so I went a bit overboard:
Pulling the interior out:



Here is just a test fit to see how much material I have.


I did the floors, the back wall under the rear window, and inside all doors. The front doors were done around the speaker inserts and also on the outer wall of the door.

What it looks like when laid down and flattened to the surface:


At this point the sound was better than stock: cleaner, but absolutely no bass at all. Whole octaves were missing.

I also knew that the sound damping is just the first of three layers. If you want to block out road noise you are going to put down mass loaded vinyl (MLV) which weighs 1 pound per square foot. I ordered 100 sq ft. I figured I would have a bunch left over. (Wrong, my truck is 100 pounds heavier!) But you need to decouple this layer from the frame and the standard technique to put in a layer of closed cell foam (CCF). The CCF is affixed to the vehicle using gorilla tape. It will be covered with MLV so you can be a loose with it at times. The "bible" is here: https://www.sounddeadenershowdown.com/

While I was waiting for the MLV, I had to address the lack of bass. I wasn't interested in loud, around the block bass, rather tight clean bass. I went to Best Buy and bought an 8 inch powered sub that is very slim and fit under the passenger seat.

Here is the only photo from the side.


Needless to say, it is tiny and puts out a good amount of bass for such a small volume.

Cool, this is coming together. MLV arrives. Time to pull out the interior again. I am getting good at this. BTW: I vacuumed and washed the carpet with it out. Lots of dog hair everywhere!



So here is the interior as the CCF is being laid down:



Here is the roll of MLV, 100 pounds!

:

The MLV does not bend very well and when you cut it to form to the curves of the truck, you need to seal the seams with overlaps of MLV. The idea here is to create an envelope within the frame of the truck to isolate outside noises as much as possible. Of course, a vehicle is a difficult environment acoustically, but you do what you can do. The suggested glue to mate the mlv to itself is vinyl contact cement. In the doors, I used gorilla tape to hold the mlv. I put some on the inside of the plastic door panel as well as against the outer metal panel of the door. Make sure you do not interrupt the workings of the window. The front doors are said to yield the most benefit so I doubled up there.



The back of the cab:


With the additional layers on the frame, it is tough to install everything. I purchased longer bolts for the center console and the passenger seat (front only). The carpet as well can be put back nearly to the original layout but a few places it didnt go all the way. Really, I will be the only one to even know. I also decided to drop the headliner and install a product that does some thermal as well as acoustic isolation there. Something like dynamat headliner. Sorry can't remember the product.


Put the interior back together and tested it out. At first, I was not really that impressed with the sound isolation honestly. I did notice the doors feel more solid. When I hit road bumps, the sound was different: deeper. With the stereo on, the acoustic quality was better and I didn't hear anything from outside unless it was very loud. After some drives on the highway, I am glad I did it. I dont think it is for everybody as you can only get a vehicle so quiet and a truck gets a lot of noise from the suspension itself. But at this point, it is so quiet that the loudest thing inside on a a highway cruise is the air blowing out of the vents and if that is off, it is the wind outside whose noise is likely coming in through the windows.

So I thought, this is pretty good. After a road trip (10 hours each way) I began to notice some of the mid bass missing and just overall the bass not really tight. I decided to up the ante. Look, I said to myself, this is a vehicle you plan to have for a long time so make it the way you want it. After some research, I decided to get a 5 channel kenwood amp, q logic sub box that takes the place of the rear passenger storage, and two alpine 8 inch subs. I pulled the interior out again because I also decided I am going to run my own 14 gauge speaker wire from the amp to all speakers, bypassing the stock wiring. Also, I ran two sets of wires to each of the front speakers because I am likely to add a dsp in the future which will give me independent control of every driver's acoustic characteristics. But that requires speaker wire to each driver. (As of now the second set of wire is not functional for the front. It is ready to go though if I move in that direction.)

To get the wire to the speakers, you need to deal with the door and make it clean. You need to go through here:


I found that using a chopstick and gorilla tape worked to "sew" the speaker wires through the rubber hose. Opening the door, you can not tell that anything has been modified.




Here you can see the blue power wire from the battery. I ran it through a hole in the firewall near the fuse box under the drivers side dash. The RCA cables (output from the HU) are on the other side of the car. This is supposed to reduce noise in the system.


The kenwood puts out 70 W rms to each speaker and 500 W rms to a 2 Ohm load. The Alpine drivers have dual voice coils which allow you to wire them in a number of ways to get the impedance match you are looking for. For me: 2 Ohms.


Here is the amp with cables labelled. The blue RCAs came with the wiring kit from Crutchfield, hence they look different. Turns out that they were picking up noise from the alternator and so I moved them to the rear speakers and put in a line filter. (not a great option honestly but it is just the rear.) Funny as they are twisted and considered higher end, though they are also longer.


The Q logic box required some modification. You will read that many need to bore out the holes to get it to fit. Well I was trying to mount this not to the stock frame, but on top of three acoustic layers! I knew I would need longer bolts so I had those ready. But they simply were not long enough. Back to the hardward store to buy the next size up. That did the trick.

You can see the carpet not perfect here.

Tested it out and WOW oh WOW! Now this was after some tuning. The HU allows you to perform time alignment (since the speakers are different distances from your ear you delay the signal) as well as a simple EQ, and highpass (speakers) and lowpass (sub) capabilities. It is really surprising what time alignment does. Highly recommend. I also pumped in some pink noise and ran an RTA to see what frequencies were reinforced and which were being cancelled at the driver's seat. There was a peak around 4K which dropped rapidly in the direction of higher frequencies, and more slowly towards lower frequencies (logarithmic scale). I tried to match a "house" tune as best as possible.




There is a nice soundstage that is on the dash. I can get localized instruments at various locations across the dash. The bass required some work on the EQ so that it didn't sound as if it was coming from the rear of the cab and it is pretty good at this point. I think I mentioned that I am in the camp of turning down the rear speakers A LOT as they destroy a tight soundstage up front. Many people don't even use them. Think about a home stereo (not surround sound) : do you put speakers behind you? DO you go to a concert where the performers are behind you? Just lowering the output on the rear speakers is free way to improve your stereo sound.

So I drove around really enjoying the sound. But, there is a rattle from the right side. Turns out it was the door panel, which being stuffed with mlv, was not completely flush against the metal frame and so I had to secure that. Done! Go for a ride. Yes! But what is that distortion from only the ride side? I can't seem to localize it and the wife doesnt even hear it. I pull the front passenger door off again (it has been on and off maybe 12 times) and find nothing is loose. SO I leave the door panel off and have the wife drive me around and find that the geared motor for the window, which is inside the door panel, is ever so slightly rattling. So I pull the bolts for the motor, put some damping underneath them and around the assembly and go to bolt it back on but the holes will not line up to get the bolts in. Stumped! I can't not budge the assembly at all. I tried making little levers, etc. but nothing.

Ah ha! I bet if I lower the window, it might allow me to move the assembly. It worked. I got it back together and as of July 20, no rattle and the sound is excellent.

This was a lot of work. The acoustic isolation was about 40 hours alone. And I did it in a carport in S. AZ when the temps were in the low 100s in the afternoon. So I often would start at 4 am or so. hey, you gotta do what you gotta do.

The only thing that could be added imho is a digital sound processor (dsp) which would give more control over the acoustic characteristics of each driver.

But for now. I am going to enjoy.

Hope you did as well.

PS: here is the truck now:

 

Wow dude that's a tone of work. Good job!!

 

Much better than my build thread. Cheers!

One day when I finally decide what heas unit I want to use I'll be poking around your inbox with questions. Lol

 

My pleasure. HUs these days have a lot of capabilities. If you really want to understand great sound in an auto, check out:

diymobilaudio.com

 

Might as well add this here as it is my build thread:

I got a minidsp 6 x 8 with UMIK 1.

It took my most of the day to install as I had to pull out the interior again. (Hey might as well vacuum again too.) Re-routing wires, soldering, checking in with work though the day...

Tomorrow I plan to take some measurements to get a driver's side tune done. Basically I place the mic in the location of the drivers head and average over a few where the mic is moved around a few inches on each side of the head. Run a pink noise sweep on each side individually and then use filters (parametric eq's) to hit my target curve. I am using REW which is nice in that it downloads the filters used to hit my target house curve right into the minidsp. There is a wired remote that am setting up to control one channel's volume, which will be my sub channel. There is also the option to save various tunes so that when I am solo, I get the best sound and when there are others, I can hit a button and change the tune to a passenger tune or up front tune etc.