got a mm2124, time for amp- is 500w too much?

coolfishy101

I finally got a mm2124 for my '95 bmw 325i. I am going to build my own box to recomended specs except I'm using 1/2" mdf because weight is an issue in drift/drag racing. For the amp I want to go with hifonics. I have about 300 to spend on both the amp and wiring kit, I was going to get a 500w rms amp so I have plenty of head room, but would I have to worry about overpowering the sub? I don't know too much about setting gains either. If someone could point me to a how to do page that would be awsome. Also is 8ga or 4 ga practical, I'm only running 500w and my battery is in the trunk.

I will definately post pics of the project, but I'm getting the amp for my b-day so i have until march. thanks.

vawakemonster

run 4 GA and for the gain waht you do is turn your stereo to 75 percent volume OR what ever you notmally listen at for me its 45 out of 60 and then you slowly turn the gain up till it destorts and then when it does you turn it back till it stops all destortion. after about a month re do this becasue the sub will break in and you may be able to get a smidge more gain in.

also point the sub to the rear it is what is suposed to sound best in a sedan type car.

beardog03

Don`t forget the dynamat...


I have a `94....how much trouble did you have with the speaker install ?
Got any pic`s

MacLeod

If youre going to use 1/2" wood, get birch plywood. MDF is too thin at 1/2" especially for 500+ watts and will flex like a trampoline. Even with birch plywood, Id still recommend slapping at least 1 layer of Dynamat on the outside of the box for added rigidity.

coolfishy101

Thanks guys, good to know about the birch and the gains. I'll defintately post pics before, during, and after the project. Can I just use polyester or cotton instead of dynamat? That stuff's expensive, I might just use a piece for my license plate or small things like that. I have tons of this other stuff laying around, but I'm afraid of the polyester or cotton holding in moisture. And the sub is definately pointing towards the rear.

beardog03

Mac and Cody are the experts...I`ll let them take that one

I take my q`s from them..!!

I would try to use the dynamat, or something similar though

I appreciate the pic`s though as I want to do mine soon also,and anything you learn while doing yours, will help me avoid the same problems..

I have a 10" momo for the trunk, but I also have a couple of 12" momo`s if I decide to go there....(I would only use 1 though)

I think that 8`s are the best choice for what I want to accomplish though, so the 12`s will probably be sold soon to pay for the 8`s

I have a 400.4, a 500.1, and two 300.2`s for amps
I have momo 6x9`s, and the momo 5.25 seperates for the front

I was thing of getting another set of 5.25`s for the rear, and not using the 6x9`s in this install, as I don`t really need , nor want, too much sound in the rear anyway...

The rear deck is useless, as the cross bracing makes it almost impossible to use the 6x9`s

Greg Peters

coolfishy101 wrote:

Thanks guys, good to know about the birch and the gains. I'll defintately post pics before, during, and after the project. Can I just use polyester or cotton instead of dynamat? That stuff's expensive, I might just use a piece for my license plate or small things like that. I have tons of this other stuff laying around, but I'm afraid of the polyester or cotton holding in moisture. And the sub is definately pointing towards the rear.

By all means use polyfill inside the box. It won't strengthen your enclosure any, but it will reduce standing waves inside the enclosure. It's good stuff to use if you build your enclosure on the small side of recommended enclosure volume- it will trick your sub into acting like it's in a larger box by damping internal pressure (much like a larger box would), giving you a bit more low-end extension than an undamped one.

As for the dynamat on the outside- it certainly can't hurt anything.

Consider 5/8" MDF as a compromise...not much heavier than 1/2" but is definitely stronger. If you go this route, you can compensate by countersinking a nice drywall screw every two inches or so on all seams and use some internal bracing. Seal every seem inside with silicone, a heavy bead of HD wood glue, or better yet- fiberglass resin. Add up all of the above and you'll have a rock-solid enclosure.

MacLeod

coolfishy101 wrote:

Can I just use polyester or cotton instead of dynamat? That stuff's expensive, I might just use a piece for my license plate or small things like that.

Youre not using the Dynamat to reduce standing waves like you use polyfill. The Dynamat will go on the OUTSIDE of the box.

The reason youll want to Dynamat the outside of the box is to add mass to it and by doing that, itll make it a lot less likely that it will flex under pressure from the sub.

coolfishy101

Youre not using the Dynamat to reduce standing waves like you use polyfill. The Dynamat will go on the OUTSIDE of the box.

The reason youll want to Dynamat the outside of the box is to add mass to it and by doing that, itll make it a lot less likely that it will flex under pressure from the sub.

Oh, I was thinking it was the same use. Thanks. When you guys say the box flexes, is that actualy wood or the seals, I was going to seal the crap out of it using screws, wood glue, and fiberglass. Could I just use some sort of internal bracing with the birch?
I really don't blast the music very often, I stay around 1/4 - 1/2 way most of the time. however my music is bass heavy (rap, rock mostly, pretty much everything but country)

MacLeod

The wood itself will flex from the pressure of the air moving inside the box. Thats not a good thing and makes it sound worse.

Jethro

Greg Peters wrote:

By all means use polyfill inside the box. It won't strengthen your enclosure any, but it will reduce standing waves inside the enclosure. It's good stuff to use if you build your enclosure on the small side of recommended enclosure volume- it will trick your sub into acting like it's in a larger box by damping internal pressure (much like a larger box would), giving you a bit more low-end extension than an undamped one.

As for the dynamat on the outside- it certainly can't hurt anything.

Consider 5/8" MDF as a compromise...not much heavier than 1/2" but is definitely stronger. If you go this route, you can compensate by countersinking a nice drywall screw every two inches or so on all seams and use some internal bracing. Seal every seem inside with silicone, a heavy bead of HD wood glue, or better yet- fiberglass resin. Add up all of the above and you'll have a rock-solid enclosure.

Just to nitpick a little here... while polyfill can help improve the sonics of an undersized sealed enclosure, it will do absolutely nothing to reduce standing waves in a typical car audio subwoofer enclosure... it is pretty much impossible to have them in the first place.

1180 / frq = wavelength in feet (standing wave possible at 1/2 or full wavelength)

If you figure most car subs are low-passed at 100Hz, we get the following...

1180 / 100 = 11.8 ft (standing wave possible at 5.9 or 11.8 ft)

So, if your box has an internal clear-span of more than 5 ft, then you might worry about standing waves... otherwise, it is a non-issue. Home audio cabinets deal with higher frequencies are a different story, of course...

coolfishy101

I know it's been a while, and well I didn't get the amp yet... Something came up, hopefully some time this year. I already have the sub. But you guys have been a lot of help so I'm at least going to post pics of where it's going.

black magic

Props for the 325i.