FJF

iTrader: (18)

Rattling is caused by a sympathetic resonance, meaning, the sub is hitting the frequency rage that causes the rattle in the car, with the trunk effectively acting as a transducer. The effect is similar to having two drivers in one box, with one one hooked-up to an amplifier. If you run sweeps at 1Hz intervals, you can find the exact resonant frequency and effectively tune it out.

For the advanced approach, one can also minimize the effect of the above by building an enclose that limits the sub's exposure to that frequency. Of course, you'd have to test beforehand and find the resonant frequency of the trunk. Then, you can model the enclosure with WinISD (as an example), while keeping in mind the car's room gain, as well as its nodes.

biggie5252

iTrader: (47)

I don't think most trunk rattle is caused by resonance or you'd be rattling with a single 8" or maybe even smaller at that frequency. My vehicles in the past have rattled pretty much through the entire sub range also.

How do you tune out specific frequencies with an enclosure without using an eq?

FJF

iTrader: (18)

Any sub, regardless of size, will cause a rattle at a frequency that's sympathetic with the car's body. I'm assuming that one is playing music and not simply pressurizing the trunk for the hell of it. If, OTOH, pressure for the sake of pressure the goal, then this is mostly irrelevant. I have no doubt that such an exercise would cause all kinds of rattles, at least until the pressure is released.

I should also mention that sound deadening, at least the kind seen in the automotive industry, changes the resonant frequency of a panel by adding mass to its surface. More advanced forms of sound deadening, like Sorbothane, can also dissipate the energy stored in a panel.

BTW, when you talk about the sub rage, which sub/enclosure/location are you referring to? I ask, because it's very common to see automotive subwoofer installations, especially using ported enclosures, that are tuned to a frequency that falls into an area where room gain meets a node, in turn resulting in a massive spike in FR. This makes for the loudest install. A sealed enclosure can provide a similar effect, albeit more gradual in its scope. If such a spike falls into an area of sympathetic resonance, it's no surprise that your whole cabin was rattling, regardless of the source material. It's because you were essentially playing a single note throughout the whole time. Of course, I'm only taking an educated guess, as I haven't heard the system. Notice how, in this thread, some subs cause rattles and some don't? Aside from playing/listening habits, it's dependant on the alignment of the woofer/enclosure/location.

Did you model the sub before it was built and calculate its effects? As I'm about to reply to the comment below, it doesn't seem like you have.

I answered that in the post to which you responded. You'll have to model the enclosure with respect to room gain and its nodes. Unless you have a full comprehension of the constraints, and it seems like you have no idea what I'm talking about, you'll have to look for luck. An EQ would most likely be necessary, anyway, if only to knock down the couple of peaks in FR that would be driven by the nodes in the cabin. If the sub was designed and tuned well, there may only be one node to consider or maybe none at all. Feeding power into node-driven dips in FR is pointless due to the nature of the beast. Again, I'm saying this with the assumption that the individual wants to listen to music and he's looking for the most well-defined, articulated, delineated bass response instead of a fart cannon.

Edit - I remember you now. You're the one who's building an enclosure into a spare tire well with a pair of ID10s. Those are very nice drivers. I'm using a pair of ID8s. I also have an IDQ12 in another car. I recall asking you about the volume of the enclosure, but you didn't answer. Do you know its exact volume?

Tnnrx7

iTrader: (3)

FJF,

What about keeping the sub box from sliding around? Any tips?

FJF

iTrader: (18)

Please keep in mind that I'm not a car audio guy, as you may have gathered by my comments. As such, other folks may have better ideas. Depending on the width of the enclosure, you may be able to use muffler (U-bolt) clamps to secure the box to the strut towers, or perhaps to the rear of the trunk. In my case, as I have a trunk cage, I used pipe strap that I covered in black heatshrink to attach the sub to the upper stress bar. You can get pipe strap in any DIY store, like Home Depot. I posted a pic above.

Tnnrx7

iTrader: (3)

Take some quick pics of your setup when you get a chance and post it up.

biggie5252

iTrader: (47)

I do understand cabin/room gain. I don't recall hearing the term node, but it may be referred to something else in the car audio world. I tried to google it real quick, but didn't come up with anything. It's also been a while since I've looked into it as I'm not much into car audio anymore. Actually, the enclosure you mentioned is more than likely not going to be finished, due to the money required to finish the system, I'd like to spend elsewhere in the car and get back to why I really bought an Evo. I'll actually probably get rid of the system completely and just run a head unit and maybe a small amp for my components.

Sorry I didn't answer your post about volume. I remember seeing it. I thought i answered, but I guess not. No I don't know the exact volume. After it was finished I was going to fill it with something to try to measure the volume and then polyfill it to taste. I was shooting for about 1.75^3 before displacement.

The system I was referring to above was 2 JL 12w6v2s with a 500/1 on each one in a sealed enclosure with seperate chambers. The car was a Dodge Avenger. I was talking about the trunk specifically, not the cabin. I had next to nothing rattling in the cabin. I am talking about rattling due to pressure in the trunk. Nothing I did could stop that trunk/rear bumper from rattling. No I never modeled the enclosure. I just built it to recommendations per JL. I've never had the money for a system/car to justify the effort, or to pay someone to figure cabin gain. Nor have I really cared to do so. I also understand that most people don't care to do it either, especially in an evo. I've always just tuned it with an eq by ear until I felt it was balanced, clean, and blended with the components up front.

After rereading your post I understand now what you're saying kind of. It may be due to the fact that I've never done it, but I don't understand how you can take, say a sealed enclosure, and tune out a peak, due to cabin gain, say at 60hz, simply with construction (not considering placement, etc.). I do understand how sealed/ported/bandpass enclosures work and how varying sizes affects roll-offs, and how port sizes affect tuning freqs, etc.

I was actually pretty well educated, believe it or not, about enclosure theory, wave theory, and acoustics back in the day, but I long quit studying it and have forgotten alot of it. Not many people seem to care about sq anymore. The general market sure doesn't, and the industry has followed suit.

While I've never had a sub system that fired into the trunk in the Evo yet, I imagine that due to the extreme light weight of the body panels and trunk lid that rattling due to pressure will take precedence over rattles due to resonance.

Usually, when I try to help on this forum, I don't make this assumption, unless the OP specifically states he's looking for an sqish type setup. Not that I think they just want a fart cannon, but I don't think that they care to put in the effort or money and weight to justify it. Maybe that attitude, and therefore the lack of exposure/awareness is why no one cares about hardcore sq anymore.
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