# Dynamat Trunk Question



## Rich_Jenkins (Jul 12, 2003)

Hi - I did a STFF on this but have not found anything specific on this, so bear with me if asked previously:

I have an 03 ZHP that is just about perfect but I would prefer to get a little less "droning" in the 2-3K rev band for when I am not driving smartly i.e. when in traffic etc. I realise this is probably what the car is "supposed" to sound like but it gets to me occasionally.

I had the trunk mat out this past weekend and noticed a LOT of bare metal in the (mostly empty) spare wheel well and on the rear seat back.

Since a lot of the drone seems to come from the back seat / lower area, and I can pretty much eliminate by opening either a window or the sunroof, I am presuming this effect is caused by a resonant frequency feature the passenger cabin.

If I were to dynamat the heck out of the trunk, would this be likely to change the audio characteristics enough to eliminate this sound?

Has anyone tried this in their car? If so what were the results...?

Thanks in advance...rj


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## wrwicky (Jan 17, 2003)

I did this in the trunk of my miata, it helped incrementally with a similar drone at about 3K RPM


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## tgravo2 (Dec 7, 2002)

Did you know the car has a dynamat throughout already except for in the trunk so you can get to the spare tire, etc.


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## CaliColin (Jan 10, 2002)

*I Dynamatted my whole trunk*

As you can see, I took out the trunk liner and Dynamatted the heck out of my trunk and spare tire well.  I did this because I installed a subwoofer and wanted to eliminate any possible rattles or "tin can" sounds. Hate to admit it, but I did NOT notice a difference before and after!  There are still a few rattles, mainly from the rear decklid, which I fixed by stuffing three small self-adhesive rubber circle thingies under the plastic piece at the back of the decklid. There is also a rattle from somewhere behind the rear bumper. In terms of road noise, I had driven my car at least 10K miles before Dynamatting and did not notice any difference whatsoever. So FWIW, I would probably not do this again in the future. Too much money and work for little or no return.


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## SergioK (Aug 14, 2002)

Dynamat is designed to reduce rattles and absorb noises. That 'drone' you mention is actually a resonation caused by exhaust. I don't think you'll be able to eliminate it no matter how much dynamat you add to your car.


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## The HACK (Dec 19, 2001)

One possibility is to swap in an OEM 330i exhaust. The ZHP package exhaust eliminates the resonance reducing "flap" inside one of the exhaust pipes. At high way speed under partial throttle the flap closes to eliminate the resonance.


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## Rich_Jenkins (Jul 12, 2003)

The HACK said:


> One possibility is to swap in an OEM 330i exhaust. The ZHP package exhaust eliminates the resonance reducing "flap" inside one of the exhaust pipes. At high way speed under partial throttle the flap closes to eliminate the resonance.


Thanks HACK. Been giving this some thought. It may be me but it does seem like the booming is getting less and less noticeable; I'm guessing maybe as the carbon builds up it changes the resonant frequency of the exhaust. I'll keep going for a while, certainly to end of breakin period, then see how it sounds.

I'll have to see/find out price of a stock exhaust maybe in the future...

rj


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## Rich_Jenkins (Jul 12, 2003)

Thought I would keep this thread updated with ZHP "drone" progress, just to keep in one place.

So: Since I got the car in Sep I've noticed that the booming/drone has decreased. Actually I think its a combination of 1) my getting used to it 2) the car breaking in 3) learning how to drive above 3,000 RPM 4) advancing old age or 5) some combination of the above.

I did pull up the rear seat trim and have a look around. I concluded that it would be pretty easy to insert a piece of sound deadening material there to see if that helped. (I was a bit surprised the other day - I removed both front sheepskin seat covers to condition the leather and was REALLY surprised I could tell the difference inside the car with them off the seats.)

I located these guys and ordered an 8 square foot piece of something called Lcomp:

http://www.b-quiet.com/lcomp.html

So when this comes in a few days I'll cut out a section and insert it into / under the seat, then put the seat back.

I am not really stressed about the sound, just would prefer to have the "edge" taken off the noise at 2,000 RPM when tootling around town.

More to follow...


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## Rich_Jenkins (Jul 12, 2003)

Well, the LCOMP arrived in good order about a week ago. I spent an hour this afternoon installing it into the rear seat pan under the rear seat cushion.

First, the pictures (bear in mind I'm not a photographer then I will describe what I did.


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## Rich_Jenkins (Jul 12, 2003)

Ok, picture one shows the basic place I started.

First I put the front seats all the way forward and removed the rear floor mats. I then unpacked the roll-up LCOMP material. It weights about 8 pounds, and comes as a 2 foot x 4 foot sheet. Its basically a very thin sheet of lead with a minimal thickness of foam on either side. There is a charcoal colored side and a black shiny side. The black side is meant to go away from the noise.

I then removed the rear seat cushion. First I pulled up smartly on the front right side of the rear seat, then the front left. This releases the catch on both side. Then I lifted the seat out and set aside. I then attached all the seat belts to keep them out of the way.

I then cut up a carboard box to make a 2' x 4' pattern out of. Working with a pair of scissors and razor knife (only cut myself once) I gradually nibbled away at the cardboard until if fit into the seat pan, more or less flat i.e. avoiding the cut-outs I gradually made. 

I found the the carpet on the floor rising from rear foot well to rear seat cushion was loose and lifted off the front area. 

I then placed the cardboard on top of the LCOMP material and cut it out according to the pattern. 

This is when I took the first picture and second pictures, with the first one showing the pattern (box) over the LCOMP, the second picture showing "before" the installation.

I then placed the LCOMP into the "slot" between the front of the rear seat and the carpet, tucking it down as far as it would go (about 3"). I then laid down the LCOMP flat as best it would go, creasing and folding the material into the seat pan.

I found out that I probably could have just cut out the transmission tunnel notch, then lay the LCOMP down and cut it out in place i.e skip the pattern. But doing the pattern I think helped at least a little bit.

I had a slight struggle in getting the carpet to lay back down and over the metal male "receivers" for the seat catch after the LCOMP was in place, but basically all I did was to eye-ball the location and cut it out with a razor knife (I did not cut myself that time.)

The third picture shows the LCOMP in place on the back seat pan.

After manoeuvreing the seat bottom back in place, I had to get all the seat belt bitties in just exactly the right place, but eventually the seat thumped into place and both catches "took".

The result? 

You cannot tell its there by looking, and I can remove it with no side effects. After driving the car, I would say it is incrementally quieter. The sound is pretty much the same frequency and timbre, but I believe it is "just" a bit less "droning" than before. It seems to just take the "edge" off the noise a bit. Certainly this mod is a lot cheaper (total price for LCOMP was $65, plus $8 shipping from Canada) than a new exhaust, retains the factory spec, does not change power, can be easily removed, and seems to help.

I would recommend this to anyone with a ZHP who wants to have a bit quieter sound, but not dramatically affect the spec of the car. The folks at BQUIET were very good, answering a question I had very quickly, and the package came from them in about 8 days which being near Christmas I thought was pretty good.

Right now I am thinking of getting more sheets, and placing another layer on the trunk/rear seat firewall from the rear, and in lining the spare tire well.

Hope this helps.

Rich


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## Rich_Jenkins (Jul 12, 2003)

This mod is working out very well. After a week's driving I think its really taken the edge off the exhaust sound in the car and made it much more enjoyable to drive.

I also noticed today that it seems like I can hear the engine more than the exhaust now.

I think I'll order some of the VCOMP material for the trunk and rear seatback and see what happens after that's installed.

More to come.

rich


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## Rich_Jenkins (Jul 12, 2003)

I received the VCOMP material from B-quiet today and installed it in the trunk.

Well, "install" might be a bit over stated, I lay the 3' x 4' piece of material on the trunk floor and trimmed the piece off the end then flopped that piece over the top of the remainder. 

I don't think I like this as much as the LCOMP, but its cheaper at 64.99 for 3x4 piece vs. 64.99 for a 2x4 piece of LCOMP.

Composition is more like a thick mat covered with foam.

On a test drive the ZHP seems to, again, be incremenatlly quieter in the back end with the engine noise being perceptably louder. So the ZHP drone is pretty much addressed, for me anyway, by the combination of the LCOMP on the back seat bottom and the VCOMP in the trunk.

I think I'll stop now; I've reached that limit of car expenditure for the month above which I would register on the Wife's financial radar :eeps:

rich


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