streetheatz28

I have 2 mtx thunder series 12 inch subs and a 800 watt pioneer amp and I enjoy the sound but I HATE the rattle. Does dynomat really work? I was also wondering why the bass sounds so much better from outside when the doors are open opposed to the windows down. Thanks for any help/comments.

Jim85IROC

iTrader: (2)

1. Yes, dynamat works. Your car is made out of stamped tin, which resonates very badly within the audio spectrum, and mass-loading that metal lowers the resonant frequency to a much more tolerable (and less audible) level.
2. In an environment as small as a car, the environment has a profound effect on the performace of the sub, just like the sub's enclosure does. By opening your doors, you're drastically changing the parameters of that secondary enclosure. The air inside of the enclosure exurts a tremendous amount of damping force on the cone of the woofer, and as a result, has a substantial effect on the behavior of the sub. That's why changing the airspace in an enclosure changes how the sub sounds. In your car, the sub is also experiencing another similar force on the front of the cone from the car's enclosed airspace. When you open a door or window, you're partially eliminating the effect of that air's pressure on the cone.

lilwill355

what is the effect of making a box out of the range of the recommend airspace for a subwoofer. It said for a sealed box 0.8-1.1. My box ended up 1.4.

Jim85IROC

iTrader: (2)

Generally if a sealed box is too big, your bass will be a bit "thinner" sounding, but since most car sub manufacturers give specs that are too small anyway, I doubt you'd have a problem, especially considering that a tiny car enclosure is going to boost low frequencies pretty drastically anyway.

Here's a pic to illustrate:


The yellow plot is an enclosure with a Qtc of .7, which is considered "ideal" for reasons that I'm not getting into here. The red plot illustrates what happens to the same sub when the Qtc is moved down to .5, which as you can see, requires over 3x as much airspace for this particular driver. The upper bass output is lower, but the deeper bass output improves. This overall result was minor (+/- 1dB difference above 30hz), and represents a more drastic shift than what you'll experience by adding only around 40% to your volume.

The more important issue (which unfortunately I don't have any pretty pictures to illustrate) is how the larger box will effect power handling. Having the sub in a larger box will lower its power handling because there's less spring force on the driver due to the air compliance in the box (in other words, there's less air pressure to control cone motion). Realistically, I wouldn't expect this increase to have a drastic effect, but as always, you'll want to boom carefully and pay attention to any sounds related to the sub reaching maximum excursion (distortion, clunks, bangs)

brians88gta

you can play with tuning your box by adding some kind of stuffing into the box changes the cubic space inside

Jim85IROC

iTrader: (2)

The effects are minimal. You can sometimes gain the equivalent of a 10% increase in volume, which is barely audible.

BanjaminGTA

iTrader: (2)

now for my stupid/dumbed down reason...lol

the reason the bass sounds louder when the doors are open opposed to just the windows being down...


treble travels like light, if there is an obstical in the way, it will have a "shadow" effect. you will still hear the treble behind the obstical (as you will still see light) but it wont be as clear (or bright) as being directly in front of it.

now bass travels like water, if there is an obstical, it will simply go around it (like in a river, water going around a rock or something) so with your doors open, the sound is "pouring" out of your car to be heard better then if it was just comming from out of your windows.


please correct me if im wrong someone, its just a theory...

Jim85IROC

iTrader: (2)

It has nothing to do with the propigation of the sound wave. In fact, if it was based only on the propigation of the sound wave, you'd get louder bass with the doors & windows closed because it would be continuously redirected within the cabin. I already explained why this situation occurs in my first post. Having the doors & windows closed creates a mechanical impedance (air pressure) that damps cone excursion. Open the windows & especially the doors, that mechanical impedance is reduced, allowing the cone to reach higher excursion.

brians88gta

thats how it was explained to me

brians88gta

at 138.5 db a 10%increase would put you atabout 150 thats a big increase over original

si_camaro

Decibels do not increase like that. I think (correct me if I'm wrong) that a 3 dB increase is effectively double the sound power. Therefore a 10% increase (of sound) on 138.5 dB would be 138.8 dB

ringo234

In electronics school I learned that 3db was in fact double the Power. I also learned that if you turn the volume up until you could just notice an increase in volume that was app. 3db.

Jim85IROC

iTrader: (2)

Dude, the 10% increase in volume is the AIRSPACE of the enclosure, not the SPL. What I'm saying is that the polyfill will fool the sub into thinking it's in a 10% larger enclosure, which is a barely audible change.

Of course it won't give you that kind of massive SPL increase that you calculated. It won't give you any SPL increase.

brians88gta

so your sayin that to get a 3db increase id have to go to 4 12s and 1000 watts that just dont sound right

cub and Matt

Actually if you double the number of speakers with the same power you will get a 3 db increase OR double your powr with the same number of speakers to get same 3 db increase. There is a graph somewhere that demonstrates where this peters out with the speaker doubling just as you can only power speakers so much.

Just a side note of appreciation: Jim85Iroc has some of the best responses. His technical knowledge is fantastic and he adds to it with some great graphs.

brians88gta

misunderstood what you were sayin but are you sure you cant get a db incease by stuffin your box made a big difference on mine maybe took some distortion out???

Jim85IROC

iTrader: (2)

It does neither. The only effect that you'll get by stuffing the box is a slight improvement in output below the corner frequency (the -3dB point in the low-end rolloff). That's all. Not lower distortion, and not more overall output. You'll get a little extra real deep stuff and that's it.